Uninterruptible power supply method and system based on emergency energy storage power supply vehicle

Abstract

The invention discloses an uninterruptible power supply method and system based on an emergency energy storage power van, and relates to the technical field of emergency power supplies, and the method comprises the steps: controlling the emergency energy storage power van to supply power to a target load through a built-in inverter in response to a fault signal of a main power grid; monitoring the state of the main power grid in real time to detect a recovery signal of the main power grid; in response to the detected recovery signal of the main power grid, controlling the output of the inverter to perform phase locking synchronization with the main power grid; after phase locking synchronization is completed, the inverter is controlled to be connected with the main power grid in parallel; in the parallel connection state, electric energy quality parameters of the main power grid are obtained in real time, and whether the main power grid meets power grid stability conditions or not is determined according to the electric energy quality parameters; and under the condition that the main power grid meets the power grid stability condition, executing load back-switching operation, and smoothly transferring the target load from power supply by the inverter to power supply by the main power grid. According to the invention, safe load back-switching can be realized, so that the economic loss risk of a user is effectively reduced.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of emergency power supply technology, and in particular to an uninterruptible power supply method and system based on an emergency energy storage power supply vehicle. Background Art

[0002] As a specialized vehicle integrating a large-capacity battery pack, inverter, battery management system, energy management system, and mobile carrier, the emergency energy storage power supply vehicle's core function is to provide uninterrupted power. Its goal is to seamlessly take over when the main grid fails or requires planned maintenance, providing a continuous and stable power supply to critical loads such as hospitals, data centers, communication base stations, and important event venues.

[0003] However, during the recovery process of a major power grid failure (such as a line trip or substation outage), its stability is often difficult to guarantee. The grid may experience a brief recovery followed by another outage, or experience significant voltage and frequency fluctuations during the initial recovery phase, leading to "false recovery" or "unstable recovery."

[0004] Traditional emergency power supply systems typically initiate load shedding immediately or after a brief delay upon detecting a positive power signal from the grid. If critical loads, such as power-quality-sensitive servers and precision medical equipment, are switched directly back to the unstable main grid at this point, it can easily lead to device reboots, logical errors, or even physical damage, resulting in significant financial losses for users. Summary of the Invention

[0005] The embodiments of the present application provide an uninterruptible power supply method and system based on an emergency energy storage power supply vehicle, which is used to achieve safe load shedding, thereby effectively reducing the economic losses of users.

[0006] To achieve the above objectives, the embodiments of the present application adopt the following technical solutions: In a first aspect, a method for uninterruptible power supply based on an emergency energy storage power supply vehicle is provided, the method comprising: In response to a fault signal from the main power grid, the emergency energy storage power supply vehicle is controlled to supply power to the target load through the built-in inverter; Monitor the status of the main power grid in real time to detect the restoration signal of the main power grid; In response to detecting a restoration signal of the main power grid, controlling the output of the inverter to be phase-locked and synchronized with the main power grid; After the phase-locked synchronization is completed, the inverter is controlled to be connected in parallel with the main power grid. In the parallel connection state, the emergency energy storage power supply vehicle continues to independently supply power to the target load through the inverter; In the parallel connection state, the power quality parameters of the main grid are obtained in real time, and whether the main grid meets the grid stability conditions is determined based on the power quality parameters; In a case where the main power grid meets the grid stability condition, a load switching back operation is performed to smoothly transfer the target load from being powered by the inverter to being powered by the main power grid.

[0007] In a possible implementation manner of the first aspect, the determination of whether the main power grid meets the grid stability condition according to the power quality parameter comprises: In a case where the power quality parameter meets the corresponding stability parameter threshold in a preset duration window, it is determined that the main power grid meets the grid stability condition, wherein the power quality parameter comprises a voltage fluctuation amplitude, a frequency fluctuation amplitude, and a total harmonic distortion rate.

[0008] In another possible implementation manner of the first aspect, in a case where the main power grid does not meet the grid stability condition, the method further comprises: controlling the emergency energy storage power supply vehicle to enter a buffer power supply mode, wherein in the buffer power supply mode, the inverter is controlled to draw power from the main power grid to charge the battery pack of the emergency energy storage power supply vehicle, and the inverter continues to provide isolated stable power supply to the target load.

[0009] In another possible implementation manner of the first aspect, the control of the inverter to draw power from the main power grid to charge the battery pack of the emergency energy storage power supply vehicle comprises: obtaining a current charging state of the battery pack; determining a current charging phase in a preset charging strategy according to the current charging state, wherein the charging strategy at least comprises a constant current charging phase and a constant voltage charging phase; generating a corresponding charging power instruction according to the current charging phase, so that the charging power drawn from the main power grid by the inverter is equal to a set value of the charging power instruction.

[0010] In another possible implementation manner of the first aspect, in a case where the main power grid meets the grid stability condition, the load switching back operation comprises: starting a flexible load transfer program, and reducing the output power of the inverter within a preset transfer time; compensating for the power required by the target load by the input current of the main power grid during the reduction of the output power of the inverter; monitoring a feedback current value flowing through the output side of the inverter in real time; in a case where the feedback current value is less than a preset zero current threshold, determining that the load has been completely taken over by the main power grid, and controlling a load switching switch to act to disconnect the target load from the inverter, so as to complete zero current switching.

[0011] In another possible implementation manner of the first aspect, after the load switching back operation is performed, the method further comprises: disconnecting the parallel connection of the inverter and the main power grid; Control the emergency energy storage power supply vehicle to enter standby charging mode or departure mode according to preset instructions.

[0012] In another possible implementation of the first aspect, controlling the output of the inverter to perform phase-locked synchronization with the main power grid includes: Through the phase-locked loop circuit, the voltage, frequency and phase of the inverter output are controlled to align with the voltage, frequency and phase of the main grid.

[0013] In another possible implementation of the first aspect, controlling the voltage, frequency, and phase output by the inverter to align with the voltage, frequency, and phase of the main grid through a phase-locked loop circuit includes: Collect the grid voltage of the main grid as the input signal of the phase-locked loop circuit; The phase detector compares the phase of the input signal with the output signal generated by the voltage-controlled oscillator inside the inverter to obtain a phase difference signal; The phase difference signal obtained by comparison is filtered through a low-pass filter; The output frequency of the voltage controlled oscillator is controlled by using the filtered phase difference signal; When the filtered phase difference signal approaches zero, it is determined that phase-locked synchronization has been achieved and the output of the voltage-controlled oscillator is locked, wherein phase-locked synchronization means that the voltage, frequency and phase output of the inverter are aligned with the voltage, frequency and phase of the main grid.

[0014] In another possible implementation of the first aspect, in the parallel connection state, the method further includes: Control the inverter to inject a periodic frequency disturbance signal into its output current; Real-time monitoring of the AC voltage frequency at the grid connection point to obtain a real-time frequency value including a disturbance signal response; Through positive feedback gain, the deviation between the real-time frequency value and the preset grid nominal frequency is amplified, and the output frequency instruction of the inverter is adjusted according to the amplified deviation; Continuously determine whether the real-time frequency value exceeds the preset frequency protection threshold due to the positive feedback gain; When the real-time frequency value exceeds the frequency protection threshold, it is determined that an islanding effect has occurred, and the inverter is immediately controlled to stop output to disconnect the inverter from the main grid.

[0015] In a second aspect, the present application provides an uninterruptible power supply system, comprising: a memory configured to store instructions; and The processor is configured to call the instructions from the memory and implement the above-mentioned uninterruptible power supply method based on the emergency energy storage power supply vehicle when executing the instructions.

[0016] Through the technical solution, the fast response mechanism based on the fault signal ensures that the power supply takeover can be realized within milliseconds when the main power grid fails, avoids the power supply interruption of the key load, and guarantees the continuous operation of important facilities such as medical equipment and data centers. Secondly, through real-time monitoring and phase-locked synchronization technology, accurate synchronization of the inverter output and the main power grid is realized, creating necessary conditions for safe parallel connection, effectively avoiding equipment damage and system instability problems caused by inaccurate synchronization. Thirdly, the independent power supply mode in the parallel connection state not only guarantees the power supply quality of the load, but also provides a technical basis for subsequent smooth transfer, fully embodying the advancement of the system design. In addition, the stability judgment mechanism based on multi-dimensional power quality parameters can accurately identify the real recovery state of the main power grid, avoiding the risk of equipment damage caused by false recovery, and significantly improving the safety and reliability of the system. Finally, the flexible load transfer and zero-current switching technology realizes the smooth reclosing of the load, ensuring zero impact on the load equipment during the entire process, effectively protecting the important equipment and data safety of the user. Compared with the traditional emergency power supply system, this technical solution not only provides higher power supply reliability, but also significantly reduces the reclosing risk, realizes safe load reclosing, and provides a safer and more stable emergency power supply solution for users.

[0017] Other features and advantages of the embodiments of the present application will be described in detail in the subsequent specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 A flowchart of an uninterrupted power supply method based on an emergency energy storage power supply vehicle provided by the embodiments of the present application is shown. Figure 2 A schematic diagram of the connection relationship between the main power grid and the emergency energy storage power supply vehicle provided by the embodiments of the present application is shown. Figure 3 A block diagram of an inverter three-loop control strategy provided by the embodiments of the present application is shown. Figure 4 A schematic diagram of the internal structure of a phase-locked loop provided by the embodiments of the present application is shown. DETAILED DESCRIPTION

[0019] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to illustrate and explain the embodiments of the present application, and are not used to limit the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application.

[0020] It should be noted that if the embodiments of the present application involve directionality indication (such as up, down, left, right, front, back, …), the directionality indication is only used to explain the relative position relationship, motion condition, etc. between components in a certain posture (as shown in the drawings), and if the certain posture changes, the directionality indication also changes accordingly.

[0021] In addition, if the embodiments of the present application involve descriptions such as "first", "second", etc., the descriptions of "first", "second", etc. are only for description purposes and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of a person skilled in the art, and when the combination of technical solutions is contradictory or cannot be realized, it should be considered that the combination of technical solutions does not exist and is not within the protection scope required by the present application.

[0022] Figure 1 The flowchart of the uninterrupted power supply method based on the emergency energy storage power supply vehicle according to the embodiments of the present application is schematically shown. As shown in Figure 1 The embodiments of the present application provide an uninterrupted power supply method based on an emergency energy storage power supply vehicle, which can include the following steps.

[0023] S110, in response to the failure signal of the main power grid, controlling the emergency energy storage power supply vehicle to supply power to the target load through the built-in inverter; S120, monitoring the state of the main power grid in real time to detect the recovery signal of the main power grid; S130, in response to detecting the recovery signal of the main power grid, controlling the output of the inverter to be phase-locked synchronized with the main power grid; S140, after the phase-locked synchronization is completed, controlling the inverter to be connected in parallel with the main power grid, wherein in the parallel connection state, the emergency energy storage power supply vehicle continues to supply power to the target load independently through the inverter; S150, in the parallel connection state, acquiring the power quality parameter of the main power grid in real time, and determining whether the main power grid meets the power grid stability condition according to the power quality parameter; S160, in the case that the main power grid meets the power grid stability condition, performing a load back-switching operation to smoothly transfer the target load from being powered by the inverter to being powered by the main power grid.

[0024] The emergency energy storage power supply vehicle in the embodiments is a special vehicle integrating a large-capacity battery pack, an inverter, an intelligent battery management system and an energy management system. Figure 2 The system architecture diagram of the emergency energy storage power supply vehicle provided by the embodiments of the present application is shown, and the system architecture diagram is described with reference to Figure 2The emergency energy storage power supply vehicle includes a battery pack, an inverter, a battery management system, an energy management system, a monitoring module, and a control module. The monitoring module is used to process steps S110 and S120, and the control module is used to process steps S130 to S160.

[0025] When the main power grid experiences a power supply interruption due to line tripping, substation failure, or other reasons, the monitoring module of the emergency energy storage power supply vehicle immediately detects a power grid failure signal. The failure signal can be characterized by a sharp drop in voltage to zero, abnormal frequency, or voltage waveform distortion. In actual implementation, the monitoring module collects parameters such as voltage, current, and frequency of the main power grid in real time through multiple sensors. When these parameters exceed the pre-set normal range, it is determined as a failure signal. For example, when the grid voltage is lower than 85% of the rated voltage or higher than 115% of the rated voltage, the failure detection is triggered. Once the failure signal is detected, the control module starts the emergency power supply program and controls the inverter to switch from standby state to working state. The inverter converts the DC power of the battery pack into AC power that meets the load requirements through PWM (Pulse Width Modulation) technology. The output voltage, frequency, and phase of the inverter match the rated parameters of the load. For a 380V three-phase load, the inverter outputs 380V±2% three-phase AC power with a frequency stabilized within 50Hz±0.1Hz. Through the implementation of this step, the emergency energy storage power supply vehicle can achieve seamless switching after the main power grid failure, ensuring that critical loads such as medical equipment, servers, etc. will not be shut down due to power interruption, effectively avoiding data loss, equipment damage, etc. and providing reliable power protection for users.

[0026] While the emergency energy storage power supply vehicle takes over the load power supply, the monitoring module continuously monitors the status of the main power grid in real time to timely detect signs of power grid recovery. Real-time monitoring is achieved through multiple voltage sensors, current sensors, and frequency detectors installed at different access points of the power grid, ensuring the accuracy and reliability of the monitoring data. The monitoring parameters include three-phase voltage amplitude, frequency, phase angle, voltage unbalance degree, and harmonic content, etc. key indicators.

[0027] When the main grid begins to recover, these parameters will gradually transition from abnormal to normal state, for example, the voltage gradually rises from 0V to near the rated voltage, and the frequency gradually stabilizes near 50Hz from 0Hz or abnormal value. The monitoring module uses a sliding window algorithm to process the collected data, and determines the stability of the grid state by calculating the mean and variance of the parameters in the continuous time window. Specifically, when the voltage amplitude remains within 90% to 110% of the rated voltage and the frequency remains within 49.5Hz to 50.5Hz for 100 milliseconds, it is preliminarily determined that the grid recovery signal. To prevent misjudgment, the monitoring module also checks the integrity of the voltage waveform to ensure that the phase relationship of the three-phase voltage is correct, i.e. the phase difference is 120°±2°. Through accurate real-time monitoring, the response to the main grid recovery can be made at the first time, providing accurate timing judgment for subsequent synchronization and parallel operation, avoiding the problem of missing the best switching opportunity due to monitoring delay.

[0028] When the monitoring module detects the recovery signal of the main grid, the control module immediately starts the phase-locked synchronization program to ensure that the output of the inverter is completely synchronized with the main grid in terms of voltage, frequency and phase. The core technology of phase-locked synchronization is the phase-locked loop (PLL) circuit, which includes a phase detector, a low-pass filter and a voltage-controlled oscillator. In specific implementation, the phase detector first acquires the voltage signal of the main grid as the reference signal, and simultaneously obtains the output signal generated by the voltage-controlled oscillator inside the inverter. The phase detector calculates the phase difference between the two signals through a phase comparison algorithm, and the phase difference is output in the form of voltage, whose amplitude is proportional to the phase difference. For example, when the phase difference is 0°, the phase detector outputs 0V; when the phase difference is 90°, it outputs half of the peak voltage. The phase difference signal is then filtered by a low-pass filter to filter out high-frequency noise and interference signals, resulting in a smooth control voltage. The cutoff frequency of the low-pass filter is usually set to 1 / 10 of the grid fundamental frequency, i.e. 5Hz, to ensure that harmonic components can be effectively filtered out. The filtered control voltage is sent to the voltage-controlled oscillator to adjust its output frequency. The frequency control characteristic of the voltage-controlled oscillator is linear, i.e. the output frequency is proportional to the control voltage. When the phase difference signal approaches zero, it indicates that the output of the inverter has achieved synchronization with the main grid, at which point the control module locks the output frequency of the voltage-controlled oscillator, completing the phase-locked synchronization process. Through phase-locked synchronization, necessary conditions are created for subsequent parallel connection, avoiding problems such as circulating current and impact current caused by inaccurate synchronization.

[0029] After the phase-locked synchronization is completed, the control module controls the parallel contactor to act, connects the inverter with the main power grid in parallel, and forms a dual-power supply architecture. During the parallel connection process, the auxiliary contact of the parallel contactor is pre-charged through the pre-charging circuit first to avoid the arc and impact current generated when the contactor is directly closed. The pre-charging process lasts about 50 milliseconds, and then the main contact is closed to complete the parallel connection. In the parallel connection state, the inverter and the main power grid form a parallel system, but the inverter still maintains the state of independent power supply to the target load. The core of this design is to realize the independent power supply function of the inverter through the power control strategy, that is, the inverter adjusts its output power to meet the load demand, and the main power grid mainly plays a reference and backup role at this time.

[0030] In a specific implementation, the inverter adopts a constant power control mode, and adjusts its output current according to the actual power demand of the load. For example, when the load power is 50kW, the inverter adjusts its output current to make its output power accurately match 50kW, and at this time the output current of the main power grid is close to zero. This independent power supply parallel architecture has the following advantages: on the one hand, the inverter continues to provide high-quality power to the load, avoiding the influence of possible unstable factors of the main power grid on the load; on the other hand, the existence of the main power grid provides a reference benchmark for the voltage and frequency of the system, ensuring the stability of the inverter operation. In addition, the parallel connection provides a technical basis for subsequent load smooth transfer, so that the load can be smoothly transferred from the inverter to the main power grid without interruption of power supply.

[0031] In parallel connection state, the monitoring module will obtain a plurality of power quality parameters of the main power grid in real time, and judge whether the main power grid meets the stable power supply condition by comprehensive analysis of these parameters. The power quality parameters mainly include voltage fluctuation amplitude, frequency fluctuation amplitude, total harmonic distortion rate, voltage unbalance degree and power factor and other key indicators. The voltage fluctuation amplitude is calculated by continuously monitoring the change of the grid voltage. The specific method is to collect 1000 voltage samples in a 1 second time window, and calculate the standard deviation as the fluctuation amplitude index. Under normal circumstances, the value should be less than 2% of the rated voltage. The frequency fluctuation amplitude is calculated by a similar method, which requires that the frequency change should not exceed ±0.2Hz. The total harmonic distortion rate is calculated by the fast Fourier transform algorithm, which analyzes the content of each harmonic in the voltage waveform, and requires that the total harmonic distortion rate should be less than 5%. The voltage unbalance degree is determined by calculating the ratio of the negative sequence component to the positive sequence component of the three-phase voltage. Under normal circumstances, it should be less than 2%. In the judgment of the stability of the main power grid, the following judgment mechanism is adopted: first, all power quality parameters must meet the corresponding stable parameter threshold at the same time; second, this meeting state must be maintained continuously in the preset duration window, usually set to an observation period of 5-10 minutes. For example, when the voltage fluctuation amplitude is continuously maintained below 1.5%, the frequency fluctuation amplitude is maintained within ±0.1Hz, and the total harmonic distortion rate is maintained below 3%, it is determined that the main power grid meets the stable condition. In order to improve the reliability of the judgment, the trend of the change of the grid parameters can also be analyzed to predict its future stability, so as to accurately judge the true stability state of the main power grid, avoid misjudgment caused by temporary parameter fluctuation, and ensure that the load reclosing operation is only performed when the main power grid is truly stable.

[0032] When the main grid meets the stability condition, the control module will start the load back-switching program to achieve the smooth transition of the load from inverter power supply to main grid power supply. The load back-switching operation adopts flexible transfer technology to ensure zero impact on the load throughout the process. The specific implementation process is divided into several precisely controlled stages: first, start the flexible load transfer program, gradually reduce the output power of the inverter within the preset transfer time (usually 2-5 seconds). The power reduction adopts linear or exponential decline curve to ensure smooth and continuous power change. For example, when the load power is 50kW, the inverter will linearly reduce the output power from 50kW to 0kW within 3 seconds, with a reduction rate of about 16.7kW / s. At the same time of inverter power reduction, the main grid will automatically compensate for the power difference required by the load to ensure that the load always obtains sufficient power supply. This power compensation is achieved through the natural characteristics of the parallel system: when the inverter output power decreases, the power difference between the load and the main grid will drive the main grid to increase the output current. Throughout the process, the monitoring module will monitor the feedback current value flowing through the output side of the inverter in real time, which directly reflects the degree of inverter power supply to the load. When the feedback current value drops to the preset zero current threshold (usually below 1% of the rated current), it indicates that the load has been completely taken over by the main grid, at which point the control module immediately controls the load switching switch to act, completely disconnecting the target load from the inverter. The zero-current switching technology of this embodiment can avoid the electric arc and impact generated by the switching action, protecting the switching device and ensuring the continuity of load power supply. The switching switch uses vacuum contactor or solid-state relay, further ensuring the rapidity and reliability of the switching process. Through the flexible transfer technology, the load can be smoothly transferred from emergency power supply to main grid power supply without any awareness, ensuring the continuity and stability of power supply.

[0033] The embodiment realizes seamless emergency power supply in the event of main grid failure and safe back-switching in the recovery process, effectively solving the back-switching risk problem existing in traditional emergency power supply systems. First, the fast response mechanism based on fault signals ensures that power supply takeover can be realized within milliseconds when the main grid fails, avoiding power supply interruption of critical loads and ensuring the continuous operation of important facilities such as medical equipment and data centers. Second, through real-time monitoring and phase-locked synchronization technology, accurate synchronization of the inverter output with the main grid is achieved, creating the necessary conditions for safe parallel connection and effectively avoiding equipment damage and system instability problems caused by inaccurate synchronization. Third, the independent power supply mode in the parallel connection state not only guarantees the power supply quality of the load, but also provides a technical basis for subsequent smooth transfer, fully embodying the advancement of the system design. In addition, the stability determination mechanism based on multi-dimensional power quality parameters can accurately identify the true recovery state of the main grid, avoiding the risk of equipment damage caused by false recovery phenomena and significantly improving the safety and reliability of the system. Finally, the use of flexible load transfer and zero-current switching technology realizes the smooth back-switching of the load, ensuring zero impact on the load equipment throughout the process and effectively protecting the important equipment and data security of the user. Compared with traditional emergency power supply systems, this technical solution not only provides higher power supply reliability, but also significantly reduces the back-switching risk, realizes safe load back-switching, and provides users with a more secure and stable emergency power supply solution.

[0034] In one embodiment of the present embodiment, determining whether the main grid meets the grid stability condition according to the power quality parameters includes the following steps: S210, when the power quality parameters all meet the corresponding stability parameter threshold value within the preset duration window, it is determined that the main grid meets the grid stability condition, wherein the power quality parameters include voltage fluctuation amplitude, frequency fluctuation amplitude, and total harmonic distortion rate.

[0035] In the present embodiment, the monitoring of voltage fluctuation amplitude is realized by a voltage sensor. The calculation of voltage fluctuation amplitude uses a statistical method to calculate the standard deviation of voltage effective value within a preset time window (usually 1 second or 5 seconds). The calculation formula is: ; where U i is the voltage effective value of the i-th sampling point, U avg is the average voltage within the time window, and n is the number of sampling points. For example, when the rated voltage is 380V, if the standard deviation of 1000 voltage samples collected within 1 second is 3V, then the voltage fluctuation amplitude is 3 / 380x100%=0.79%.

[0036] The monitoring of frequency fluctuation amplitude adopts zero-crossing detection method or phase-locked loop technology to calculate the frequency by detecting the zero-crossing point of voltage waveform. In specific implementation, the instantaneous frequency is determined by calculating the time interval between two adjacent positive zero-crossing points, and the frequency fluctuation amplitude is also calculated by standard deviation method. The calculation of total harmonic distortion rate adopts fast Fourier transform algorithm to convert time-domain voltage signal into frequency-domain signal and analyze the amplitude of each harmonic. The calculation formula of total harmonic distortion rate is: ; where THD is the total harmonic distortion rate, U1 is the fundamental effective value, U2, U3, …, U n are the effective values of each harmonic. In practical application, calculating up to 50th harmonic can meet the accuracy requirement. Through this multi-parameter comprehensive monitoring method, the power quality status of the main power grid can be comprehensively evaluated, and accurate data basis is provided for subsequent stability judgment.

[0037] The setting of stability parameter threshold is based on international standards of power system and actual application requirements, combined with the special requirements of emergency power supply system on power quality. For voltage fluctuation amplitude, the stability parameter threshold is usually set to ±2% of the rated voltage, that is, in 380V system, the voltage fluctuation amplitude should not exceed 7.6V, and the voltage fluctuation within this range will not cause adverse effects on load devices. For frequency fluctuation amplitude, since the grid frequency should be maintained within 50Hz±0.2Hz range, the stability parameter threshold of frequency fluctuation amplitude is set to ±0.1Hz to ensure the high reliability of emergency power supply system. The stability parameter threshold of total harmonic distortion rate is set to 5% to meet the operation requirements of most precision devices. In actual implementation, these thresholds can be adjusted according to specific load type and application scenario.

[0038] The preset duration window is a key parameter to ensure the accuracy of the main grid stability judgment, and its setting needs to consider the time characteristics of grid recovery, the sensitivity of load and the response speed requirements of the system. In specific implementation, the duration window is usually set to 5-15 minutes, which can effectively identify the real stable state of the grid and will not excessively prolong the emergency power supply time. The time window is implemented by using a sliding window algorithm, which can update the monitoring data in real time and perform continuous evaluation. The working principle of the sliding window is to establish a fixed-length data buffer, new data is added from the tail, and the oldest data is removed from the head to keep the buffer length constant. For example, when the duration window is set to 10 minutes and the sampling frequency is 1 Hz, the length of the buffer is 600 data points. Each time new data arrives, the algorithm calculates whether all data in the current buffer meet the requirements of the stability parameter threshold. The specific judgment logic is: traverse all voltage fluctuation amplitude data in the buffer, check whether they are all less than the set threshold; traverse all frequency fluctuation amplitude data, check whether they are all within the allowed range; traverse all total harmonic distortion rate data, check whether they are all below the limit value. Only when all three parameters continuously meet their respective threshold requirements within the entire time window, the main grid is determined to meet the stability condition. When parameter abnormalities are detected, the time window is automatically reset and the timing is restarted to ensure that only in the case of continuous parameter stability can the stability condition be determined.

[0039] The implementation of the comprehensive judgment logic adopts a multi-level verification mechanism to ensure the accuracy and reliability of the main grid stability evaluation. In the first layer of judgment, three core power quality parameters are monitored in real time, and voltage fluctuation amplitude, frequency fluctuation amplitude and total harmonic distortion rate are calculated simultaneously using parallel processing. Each parameter has an independent processing thread to ensure real-time and accuracy of data processing. The second layer of judgment uses logical AND operation, i.e. all three parameters must simultaneously meet their respective stability parameter threshold requirements, and any parameter not meeting the conditions will result in an overall unstable judgment. The third layer of judgment introduces time persistence verification to ensure the stability of the state through a sliding window algorithm.

[0040] The embodiment realizes accurate judgment of the power grid recovery state by establishing a comprehensive evaluation system of the main power grid stability based on multi-dimensional power quality parameters, and effectively solves the load back-feeding risk problem caused by false recovery of the power grid in the traditional emergency power supply system. Firstly, real-time monitoring of three core parameters of voltage fluctuation amplitude, frequency fluctuation amplitude and total harmonic distortion rate can comprehensively reflect the power quality condition of the main power grid, and compared with the traditional method of only monitoring whether the voltage exists, the accuracy and reliability of the power grid state evaluation are significantly improved. Secondly, by setting strict stable parameter threshold and combining with the constraint condition of the duration window, it is ensured that the load back-feeding operation is only performed when the power grid is truly stable and continuously stable, and the risk of equipment damage caused by temporary power grid fluctuation is effectively avoided. Compared with the traditional simple voltage detection method, more safe and reliable emergency power supply guarantee is provided for users, and the economic loss and safety risk caused by improper back-feeding are significantly reduced.

[0041] In one of the embodiments of the present embodiment, in the case that the main power grid does not meet the power grid stability condition, the method further comprises the following steps: S310, control the emergency energy storage power supply vehicle to enter the buffer power supply mode, wherein in the buffer power supply mode, the inverter is controlled to draw power from the main power grid to charge the battery pack of the emergency energy storage power supply vehicle, and at the same time the inverter continuously provides isolated stable power supply to the target load.

[0042] When the main grid does not meet the stability condition, the control module will immediately start the buffer power supply mode, which is a bidirectional energy management strategy that can both supplement the charging of the battery pack using the already restored but unstable main grid and continuously provide high-quality isolated power supply for the load. The core technology of the buffer power supply mode is based on the bidirectional energy flow control of the bidirectional inverter, which has the dual functions of rectification and inversion. In specific implementation, the bidirectional inverter adopts a three-phase bridge structure, including six power switching devices (usually IGBT), each of which is equipped with an anti-parallel diode. When working in rectification mode, the inverter converts the AC power of the main grid into DC power to charge the battery pack by controlling the on-off of the switching devices; when working in inversion mode, it converts the DC power of the battery pack into AC power to supply power to the load. The key to the buffer power supply mode is to achieve the simultaneous operation of the two working modes, which is achieved through time division multiplexing and power distribution strategy. Specifically, the inverter performs rectification and inversion operations according to the preset time ratio in each switching cycle (usually 20 kHz, i.e. 50 microseconds per cycle). For example, in a switching cycle, the first 30 microseconds are used for inversion to supply power to the load, and the last 20 microseconds are used for rectification to charge from the main grid. This time division multiplexing method of high-frequency switching is transparent to the load and the grid, because the switching frequency is much higher than the power frequency of 50 Hz. The power distribution controller dynamically adjusts the time ratio of the two modes according to the load power demand and the battery charging demand, ensuring that the load power supply is prioritized while effectively charging the battery. Through this precise bidirectional energy control, the buffer power supply mode not only solves the problem of battery power consumption, but also ensures the continuity and stability of the load power supply.

[0043] The process of the inverter drawing power from the main grid is achieved through controllable rectification technology, which can accurately control the size of the power drawn from the main grid and the current waveform, ensuring that it will not cause additional impact and interference to the already unstable main grid. Controllable rectification adopts a PWM (Pulse Width Modulation) rectifier structure, which controls the size and waveform of the rectified current by adjusting the on-time of the switching device. In specific implementation, the rectifier adopts a current closed-loop control strategy, which monitors the charging current flowing into the battery in real time and compares it with the set charging current command to generate a PWM control signal through a PI (Proportional-Integral) controller. The mathematical model of current control is: ; where I ref is the reference current, I set is the set charging current, I f is the actual feedback current, K p and K i are the proportional and integral coefficients, respectively.

[0044] To minimize the impact on the main grid, the rectifier also employs power factor correction (PFC) technology, making the current drawn from the main grid in phase with the grid voltage, with a power factor close to 1. In specific implementation, by detecting the phase information of the main grid voltage, the phase of the rectified current is controlled to be consistent with the voltage phase, and the current waveform is as close to a sine wave as possible. For example, when the main grid voltage is 380V, 50Hz, the rectifier controls the frequency of the current drawn to be 50Hz as well, with a phase difference controlled within ±2°. In addition, to prevent impacting the unstable main grid, the rectified power adopts a soft start strategy, starting from zero power and gradually increasing to the set value, with an increase rate usually controlled at 10-20% of the rated power per second. Through this precise controllable rectification technology, it is possible to safely draw power from the main grid even in unstable conditions, achieving the purpose of battery charging while avoiding further deterioration of grid stability.

[0045] The charging process of the battery pack adopts intelligent charging management strategy to ensure safe and efficient charging under unstable conditions of the main grid. The charging management is based on real-time state monitoring of the battery and dynamic charging strategy adjustment, with core components including the battery management system, the charging controller, and the temperature monitoring system. The battery management system monitors the voltage, current, temperature, and internal resistance of each battery cell in real time, and exchanges data with the charging controller through the CAN bus. The charging strategy adopts a multi-stage charging algorithm, including pre-charging, constant current charging, constant voltage charging, and floating maintenance. In the pre-charging stage, when the battery voltage is too low (e.g., below 80% of the nominal voltage), a small current (usually 0.1C) is used for pre-charging to avoid damage to deeply discharged batteries. In the constant current charging stage, a set charging current (usually 0.3-0.5C) is used for charging, with the current size dynamically adjusted according to the available power and stability of the main grid. When the voltage of any battery cell reaches the charging cutoff voltage, it enters the constant voltage charging stage, where the charging voltage is kept constant and the charging current gradually decreases.

[0046] The formula for calculating the charging power is: P = U x I x η, where P is the charging power, U is the charging voltage, I is the charging current, and η is the charging efficiency (usually 90-95%). Considering the instability of the main grid, the charging controller also has the ability to quickly adjust the power, which can reduce the charging power or suspend charging within 10 milliseconds when detecting that the main grid voltage or frequency fluctuation exceeds the preset range, avoiding exacerbating the grid burden when the main grid is unstable. The temperature protection function ensures that the battery works within a safe temperature range, automatically reduces the charging current when the battery temperature exceeds 45°C, and stops charging when it exceeds 55°C. Through this intelligent charging management, both the safety of the battery charging and the flexible adjustment of the charging strategy according to the actual conditions of the main grid are guaranteed.

[0047] The core function of the buffer power supply mode is to provide isolated and stable power supply to the target load. Through electrical isolation and power filtering technology, the load can obtain high-quality power supply, completely unaffected by the instability of the main power grid. Electrical isolation is achieved using a high-frequency isolation transformer. The primary side of the isolation transformer is connected to the output of the inverter, and the secondary side is connected to the load. There is no electrical connection between the two sides, thus achieving complete electrical isolation. The design of the isolation transformer uses a toroidal core structure and high magnetic permeability silicon steel material to ensure low loss and high transmission efficiency under high-frequency working conditions. The turns ratio of the transformer is designed according to the voltage requirement, for example, when the battery pack voltage is 600V and the load requires 380V, the turns ratio is designed as 600:380. Power filtering uses a combination of LC filter and active filter. The LC filter is composed of inductance and capacitance, used to filter out the high-frequency components of the inverter switching frequency, and the active filter is used to compensate for the harmonic components in the load current. To further improve the power supply quality, the inverter uses a multi-level topology and space vector PWM modulation technology, the output voltage waveform is closer to the ideal sine wave, and the total harmonic distortion rate is controlled below 3%. The inverter is also equipped with perfect protection functions, including over-voltage protection, under-voltage protection, over-current protection, over-temperature protection and short-circuit protection, to ensure the safety of the load equipment under various abnormal conditions. The stability of output voltage and frequency is achieved through closed-loop control, with voltage stability within ±1% and frequency stability within ±0.05Hz. Through isolation power supply technology, the load can obtain stable power supply completely independent of the main power grid state, effectively avoiding the adverse effects of main power grid instability on load equipment.

[0048] The running state monitoring and intelligent switching control of the buffer power supply mode ensure that the mode can automatically adjust the working parameters according to the actual situation of the main power grid and the load, achieving the optimal energy management effect. Running state monitoring includes comprehensive monitoring of main power grid parameters, battery status, load condition and inverter working state. Main power grid parameter monitoring mainly focuses on the real-time change trend of its power quality, analyzes the voltage, frequency and harmonic fluctuation through sliding window algorithm, and predicts the change direction of power grid stability. Battery state monitoring includes key indicators such as remaining capacity, state of charge, health degree and expected available time, which are updated in real time through the BMS system. Load condition monitoring includes power demand, power factor and harmonic content, etc., providing basis for power distribution. Inverter working state monitoring includes switch device temperature, output current, efficiency and fault state information. Intelligent switching control is based on fuzzy logic and expert system, making optimal control decisions based on multi-dimensional parameter information. For example, when the quality of the main power grid improves continuously and approaches the stability threshold, the control algorithm will gradually increase the charging power to prepare for subsequent load back switching; when the quality of the main power grid deteriorates further, it will reduce or even stop charging, focusing on load power supply.

[0049] The present embodiment effectively solves the technical problems faced by traditional emergency power supply systems during the unstable recovery stage of the main power grid by implementing the buffer power supply mode, realizing the intelligent coordination of emergency power supply and power grid recovery. First, the application of bidirectional energy management technology enables the emergency energy storage power supply vehicle to fully utilize the restored but unstable main power grid for battery charging under the premise of ensuring the power supply quality of the load, significantly extending the duration of emergency power supply and avoiding the risk of power supply interruption due to insufficient battery power. Second, the combination of electrical isolation and power filtering technology ensures that the power quality obtained by the load is completely unaffected by the unstable factors of the main power grid, and the load equipment can work normally in a stable and pure power environment, effectively preventing equipment failure or data loss caused by power grid quality problems. The intelligent charging management strategy dynamically adjusts the charging parameters according to the real-time status of the main power grid and the battery state, ensuring the safety and efficiency of charging, and avoiding additional impact on the unstable power grid, embodying the design concept of being friendly to the power grid. In addition, the application of controllable rectification technology and power factor correction makes the current drawn from the main power grid have good waveform quality and power factor, reducing harmonic pollution and reactive impact on the power grid, which helps the stable recovery of the main power grid. Finally, intelligent operation control and fault self-recovery capability ensure the reliable operation of the buffer power supply mode under various complex conditions, providing a more flexible and intelligent emergency power supply solution for users. Compared with the traditional simple mode of either completely relying on battery power supply or directly switching back to the power grid, the buffer power supply mode realizes the flexible coupling between the emergency power supply system and the main power grid, ensuring the power supply safety of the load and realizing the efficient use of energy.

[0050] In one embodiment of the present embodiment, controlling the inverter to draw power from the main power grid to charge the battery pack of the emergency energy storage power supply vehicle includes the following steps: S410, obtaining the current charging state of the battery pack; S420, determining the current charging phase in the preset charging strategy according to the current charging state, wherein the charging strategy at least includes constant current charging phase and constant voltage charging phase; S430, generating a corresponding charging power instruction according to the current charging phase to control the charging power drawn by the inverter from the main power grid to equal the set value of the charging power instruction.

[0051] Reference Figure 2 The acquisition of the current charging state of the battery pack is realized by a variety of sensors and monitoring circuits integrated in the battery management system (BMS), which involves real-time collection and calculation analysis of multiple key parameters such as battery voltage, current, temperature, internal resistance, etc. In specific implementation, Figure 3 A battery management system and a battery pack connection schematic diagram provided by an embodiment of the present application is shown inFigure 3 As shown, the battery pack is composed of multiple lithium-ion battery cells connected in series and parallel, each of which is equipped with an independent voltage monitoring circuit that uses an analog-to-digital converter to monitor the voltage changes of the individual cells. Current monitoring is achieved through a Hall effect current sensor. Temperature monitoring uses multiple-point arranged thermistors or infrared temperature sensors to monitor the temperature distribution at different positions inside the battery pack, ensuring that hot spots and temperature abnormalities can be detected in a timely manner. Internal resistance monitoring is achieved through alternating current impedance testing technology, which periodically injects a small amplitude alternating current test signal into the battery, and calculates the internal resistance value of the battery by measuring the phase relationship between voltage and current. Changes in internal resistance can reflect the health status and aging degree of the battery. The calculation of the state of charge (SOC) uses a combination of ampere-hour integration method and open-circuit voltage method. The ampere-hour integration method calculates the change in electric quantity by integrating the charging and discharging current over time, and the calculation formula is: ; where SOC(t) is the state of charge at time t, SOC(t0) is the initial state of charge, I(τ) is the current at time τ, and C is the battery capacity. The open-circuit voltage method determines the state of charge by measuring the terminal voltage of the battery in a stationary state and comparing it with the pre-established SOC-OCV (open-circuit voltage) characteristic curve. The health status (SOH) is evaluated by comparing the ratio of the current available capacity to the nominal capacity, and regular capacity calibration tests are performed to update the SOH value. Through this multi-parameter comprehensive monitoring and intelligent algorithm processing, the real-time charging status of the battery pack can be accurately mastered, providing a reliable data foundation for subsequent charging strategy selection.

[0052] The charging stage is determined based on battery chemistry and charging safety requirements. The most appropriate charging strategy is selected by analyzing the current charging state to ensure safe and efficient charging. The preset charging strategy utilizes a multi-stage charging algorithm, consisting of four distinct charging phases: pre-charge, constant current, constant voltage, and float maintenance. The pre-charge phase is designed for low battery voltage conditions. Typically initiated when the cell voltage falls below 2.5V or the SOC falls below 10%, this phase uses a low charging current of 0.05C-0.1C to avoid damaging deeply discharged batteries. The constant current charging phase is the primary charging phase, initiated when the battery voltage returns to a safe range and the temperature is normal. The charging current remains constant, typically set at 0.3C-0.5C, enabling rapid battery replenishment. The constant voltage charging phase initiates when any cell voltage reaches the charge cutoff voltage (typically 4.2V). During this phase, the charge voltage is maintained constant, and the charge current gradually decreases as the battery charge increases until it reaches the set cutoff current value. The float charge maintenance phase is used for maintenance after the battery is fully charged, using a very low current to compensate for self-discharge losses. The phase determination logic utilizes a state machine design approach, monitoring real-time values ​​of battery parameters such as voltage, current, temperature, and SOC, and comparing them with preset thresholds to determine the current charging phase. For example, when the SOC is less than 10% and the lowest cell voltage is less than 2.8V, the pre-charge phase is determined; when the SOC is between 10% and 90% and the highest cell voltage is less than 4.15V, the constant current charging phase is determined; and when any cell voltage reaches 4.2V, the battery switches to the constant voltage charging phase. Phase transitions are performed smoothly to avoid sudden changes in charging parameters that could impact the battery. Furthermore, the charging strategy considers the impact of ambient temperature, adjusting charging parameters accordingly for low or high temperatures. In low temperatures, the charging current is reduced and the charging time is extended; in high temperatures, charging is suspended or cooling measures are initiated. This intelligent charging phase determination based on battery status ensures that the battery is charged under optimal conditions, ensuring both safe charging and optimized charging efficiency.

[0053] The strategy requirements of the charging phase are converted into specific power control instructions to drive the inverter to draw corresponding power from the main power grid. The power instruction generation adopts a multi-level control architecture, including a strategy layer, a calculation layer, and an execution layer. The strategy layer determines the basic parameter requirements of charging according to the current charging phase, such as constant current in the constant current phase and constant voltage in the constant voltage phase. The calculation layer calculates the specific power instruction value according to the requirements of the strategy layer combined with the real-time state of the battery. The power calculation formula is: P = U × I × η, where P is the charging power, U is the charging voltage, I is the charging current, and η is the charging efficiency. In the constant current charging phase, the charging current I remains constant, and the charging voltage U gradually rises as the SOC increases, so the power instruction shows a slow upward trend. For example, when the charging current is set to 100 A and the battery voltage rises from 350 V to 420 V, the charging power increases from 35 kW to 42 kW.

[0054] In the constant voltage charging phase, the charging voltage U remains constant, the charging current I gradually decreases as the SOC increases, and the power instruction shows a downward trend. The execution layer is responsible for converting the power instruction into the control signal of the inverter, and adjusting the switching duty cycle of the inverter through the PWM controller to realize power regulation. The power instruction also needs to consider the actual situation and constraints of the main power grid. When the main power grid power is limited, the charging power needs to be limited to avoid exceeding the bearing capacity of the main power grid. The power limit adopts a dynamic adjustment algorithm, which monitors the voltage, frequency and other parameters of the main power grid in real time, and automatically reduces the charging power when the grid quality decreases, and gradually restores the charging power when the grid condition improves. The instruction output adopts digital communication mode, and the power instruction is transmitted to the inverter controller through CAN bus or Ethernet to ensure the accuracy and real-time performance of the instruction transmission. Through this accurate power instruction generation and control mechanism, accurate control of the charging process can be realized, and the charging power can be strictly executed according to the preset strategy.

[0055] In this embodiment, the inverter adopts a bidirectional AC-DC converter topology structure, which can realize the bidirectional flow of electric energy, that is, it can convert DC power into AC power to supply power to the load, and also can convert AC power into DC power to charge the battery. In the charging mode, the inverter works in the rectification state, and adjusts the power drawn from the main power grid by controlling the on-off of the power switching device. The power control adopts a three-loop control strategy, including a power outer loop, a current inner loop, and a voltage loop. The power outer loop compares the power instruction with the actual drawn power to generate a current reference signal; the current inner loop compares the current reference signal with the actual charging current to generate a voltage modulation signal; and the voltage loop is responsible for maintaining the stability of the DC bus voltage. The control algorithm adopts a PI controller, and the PI parameters of the power loop are set as: Kpp=0.1, Kip=10; the PI parameters of the current loop are set as: Kpi=5, Kii=500.

[0056] The power measurement adopts a true effective value measurement method, calculates the instantaneous power by simultaneously sampling the voltage and current signals, and obtains the actual power consumption by taking the average value. In order to reduce the harmonic pollution to the main power grid, the inverter adopts power factor correction (PFC) technology and active filtering technology, so that the input current waveform is as close to a sine wave as possible and is in phase with the voltage. In the specific implementation, by detecting the phase information of the main power grid voltage, the phase of the input current is controlled to be consistent with the voltage phase, and the current waveform control technology is used to minimize the harmonic content of the input current. In this way, the inverter can accurately draw power from the main power grid according to the power instruction, and realizes accurate and controllable charging process.

[0057] The embodiment effectively solves the technical problems of low charging efficiency, poor safety and large impact on the power grid in traditional charging systems by implementing an intelligent charging control strategy based on state-of-charge identification and phased management, and realizes safe, efficient and intelligent battery charging management. The multi-stage charging strategy based on the chemical properties of the battery not only ensures the safety of charging, but also optimizes the charging efficiency. The smooth switching between different charging stages avoids the impact of sudden changes in charging parameters on the battery, prolongs the service life of the battery and improves the reliability of the entire energy storage system. The combination of power instruction generation and three-loop control technology realizes precise control of charging power, ensures that the power drawn from the main power grid by the inverter strictly follows the preset strategy, meets the charging needs of the battery, and avoids unnecessary impact on the main power grid. In addition, the application of power factor correction and active filtering technology significantly improves the quality of the current drawn from the main power grid, reduces harmonic pollution and reactive impact, and helps maintain the stable operation of the power grid. When the main power grid fluctuates or the equipment fails, protective measures can be taken in time to avoid equipment damage and safety accidents. Compared with the traditional constant current or constant voltage single charging mode, the intelligent charging control strategy has higher adaptability and safety, can dynamically adjust the charging parameters according to the actual status of the battery and the power grid, and provides a more reliable and efficient charging solution for emergency energy storage power supply vehicles.

[0058] In one of the embodiments of the present embodiment, under the condition that the main power grid meets the power grid stability condition, a load back-switching operation is performed to smoothly transfer the target load from being powered by the inverter to being powered by the main power grid, including the following steps: S510, starting a flexible load transfer program, reducing the output power of the inverter within a preset transfer time; S520, during the output power reduction process of the inverter, compensating the power required by the target load by the input current of the main power grid; S530, real-time monitoring of the feedback current value flowing through the output side of the inverter; S540: When the feedback current value is less than the preset zero current threshold, it is determined that the load has been completely taken over by the main grid, and the load switching switch is controlled to disconnect the target load from the inverter to complete the zero current switching.

[0059] The initiation of the flexible load transfer program marks the official start of load shedding. This program employs a progressive power regulation strategy to ensure a smooth decrease in inverter output power, avoiding any impact or disruption to the load. The core of the flexible transfer program is the power ramp control algorithm, which calculates the power reduction slope based on the preset transfer time and current output power, ensuring a linear and continuous power change.

[0060] In specific implementations, power ramp control uses piecewise linear or exponential curve control. Piecewise linear control divides the entire transfer process into multiple time periods. Within each time period, the power decreases at a constant slope. A smooth transition algorithm is used between segments to avoid sudden changes in slope. Exponential curve control uses an exponential function to describe the power reduction process. The power change formula is: , where P(t) is the output power at time t, P0 is the initial power, and τ is the time constant. By adjusting the time constant, the speed of power decline can be controlled. The preset transfer time is usually determined according to the load type and power size. For capacitive loads, the transfer time can be relatively short, usually set to 2-3 seconds; for inductive loads, due to the presence of inductive energy storage, the transfer time needs to be appropriately extended, usually set to 3-5 seconds; for resistive loads, the transfer time can be set at a medium level, usually 2-4 seconds. The transfer program also has anomaly detection and protection functions. When a sudden load change or grid anomaly is detected, the transfer process can be suspended and protection measures can be initiated, thereby ensuring a smooth decline in the inverter output power and creating ideal conditions for seamless load transfer.

[0061] The power compensation of the main grid input current is used to realize the seamless transfer of the load, which is realized by combining the natural power balance characteristics of the parallel system and the active power regulation technology. In the parallel power supply state, the inverter and the main grid supply power to the load together, and the total power required by the load is equal to the sum of the output power of the inverter and the output power of the main grid. When the output power of the inverter begins to decrease, in order to maintain the constant of the load power, the main grid must increase the output power to compensate for the difference. The realization of power compensation is based on the basic principle of voltage source parallel, when two voltage sources are parallel, the distribution of output current depends on the respective internal resistance and control strategy. In the specific implementation, the inverter adopts droop control strategy, reduces the output current by artificially increasing the output internal resistance, and the mathematical model of droop control is: U=U0-R×I, where U is the output voltage, U0 is the rated output voltage, R is the droop coefficient, and I is the output current. By gradually increasing the droop coefficient R, the output current of the inverter will decrease accordingly, so as to realize the decrease of the output power. At the same time, the main grid will automatically bear more load current due to its low internal resistance characteristic, and realize the natural compensation of power. In order to improve the accuracy and stability of compensation, active power regulation technology is also used, which calculates the power that the main grid should bear by monitoring the load power and inverter power in real time, and actively adjusts the output power of the grid through the grid side power regulation device (such as static synchronous compensator). The matching problem of power factor needs to be considered in the process of power compensation, to ensure that the main grid can not only compensate the power decrease of the inverter in active power, but also maintain the stability of the power factor of the system in reactive power. The compensation control adopts a fast response algorithm to ensure that it can keep up with the changes of inverter power in time. Through this accurate power compensation mechanism, the load can always obtain stable power supply and will not feel any power fluctuation or interruption during the whole transfer process.

[0062] The feedback current value flowing through the output side of the inverter is realized by monitoring at least one sensor, and specifically, the feedback current value can be determined by a Hall effect current sensor. The Hall effect current sensor is based on the principle of Hall effect, when the current-carrying conductor passes through the sensor, the magnetic field generated will generate a corresponding voltage signal in the Hall element, which is proportional to the current passing through.

[0063] Zero-current switching judgment and switch action control is the last step to realize safe load transfer. The final switching of the load from the inverter to the main grid is completed through accurate current threshold judgment and fast and reliable switch operation. The setting of the zero-current threshold needs to consider multiple factors such as the accuracy of current measurement, the characteristics of the load, and the capacity of the switching switch. The threshold is usually set to 1%-2% of the rated current, for example, when the rated current is 100A, the zero-current threshold is set to 1-2A. The threshold judgment adopts a continuous judgment mechanism, that is, the feedback current value must be less than the threshold for several consecutive sampling periods to be considered to meet the zero-current condition, preventing false positives caused by transient interference or measurement noise.

[0064] The switching switch uses a vacuum contactor or a solid-state relay. The vacuum contactor is suitable for high-power applications, and the solid-state relay is suitable for frequent switching applications. In actual implementation, a vacuum contactor is usually used as the main switching switch, and a solid-state relay is used as the pre-switching switch in a double-switch structure. The circuit is first disconnected by the solid-state relay, and then the final isolation is performed by the vacuum contactor. The control of switch action uses pre-charge and soft switching technology. Before switching, the pre-charge circuit is used to balance the voltage across the switch, and the voltage difference is minimized, and then the switch action is controlled. The switching timing control uses an accurate time program. First, the switch on the inverter side is disconnected, then a certain time delay (usually 1-5 milliseconds) is applied before the switch on the load side is disconnected, ensuring the reliability of the switching process. Switch state monitoring is achieved through auxiliary contacts and arc detection devices, ensuring the accuracy and integrity of switch action. When the switch fails to operate normally, a backup switching circuit or a fault alarm is activated. After switching is completed, the switching result is verified by measuring the voltage and current at each key point to confirm that the load has been completely transferred to the main grid for power supply. Through this accurate and reliable zero-current switching technology, the load is transferred from inverter power supply to main grid power supply without any impact or interruption, ensuring the safety of the load equipment and the continuity of power supply.

[0065] The embodiment successfully solves the technical problems of large impact, poor reliability, and harm to load equipment during load switching in traditional emergency power supply systems by implementing load return switching operation based on flexible transfer and zero-current switching. The embodiment realizes smooth, safe, and seamless transfer of load power supply. First, the gradual power regulation strategy and precise slope control algorithm used in the flexible load transfer program ensure smooth reduction of inverter output power, avoiding the impact of power mutation on the load. Compared with the traditional hard switching mode, the embodiment significantly improves the smoothness of the switching process and the safety of the load equipment. Second, based on the power balance characteristics of the parallel system, the embodiment realizes accurate compensation of the main grid for the inverter power reduction through the combination of droop control and active power regulation technology, ensuring stable power supply for the load during the entire transfer process and effectively avoiding voltage fluctuations or frequency deviation caused by power mismatch. Third, the application of multi-sensor redundancy design and high-precision data processing technology makes real-time monitoring of feedback current more accurate and reliable, accurately capturing small changes in inverter output current and providing a reliable data basis for zero-current switching judgment, avoiding improper switching timing due to monitoring errors. In addition, the zero-current switching technology combined with precise threshold judgment and reliable switch control realizes the action of the switch at the minimum current, maximally reduces switch arc and contact wear, prolongs the service life of the switch equipment, and improves the reliability and maintainability of the system. Finally, the double switch structure and perfect timing control ensure the absolute reliability of the switching process, and even in the case of single switch failure, safe switching can be completed. Compared with the traditional load switching or simple delay switching mode, the flexible return switching technology realizes impact-free load transfer and provides a more advanced and reliable load management solution for emergency energy storage power supply vehicles, significantly improving the technical level and practical value of the emergency power supply system.

[0066] In one embodiment of the present embodiment, after performing the load return switching operation, the method further comprises the following steps: S610, disconnecting the parallel connection of the inverter and the main grid; S620, controlling the emergency energy storage power supply vehicle to enter standby charging mode or off-site mode according to the preset instructions.

[0067] The disconnection operation of the parallel connection of the inverter and the main grid is an important safety measure after the completion of load switching. The disconnection of parallel connection involves the coordinated action of multiple electrical devices, including parallel contactors, synchronization devices, protection relays and other key devices. In specific implementation, the disconnection operation adopts a step-by-step execution strategy, first sending a disconnection instruction through the inverter control system, which will be transmitted to all relevant control units at the same time. The disconnection timing control uses preset program logic to ensure that each device acts in the correct order, avoiding arcs, overcurrents or device damage due to improper operation. The first step is to gradually reduce the circulating current between the inverter and the main grid by fine-tuning the output voltage and phase of the inverter, so that the current flowing through the parallel branch gradually decreases to a level close to zero. The circulating current control uses precise current detection and feedback control algorithms to monitor the current size and direction of the parallel branch in real time, and actively controls the size of the circulating current by adjusting the output parameters of the inverter. When the circulating current is reduced to a preset safety level (usually below 1% of the rated current), the second step disconnection program is started. The second step is to control the action of the parallel contactor to disconnect the physical connection between the inverter and the main grid. The selection of the contactor uses a vacuum contactor or an SF6 gas contactor with current breaking capacity and electrical life. The contactor will perform a pre-trip operation before action, disconnecting the small current circuit through the auxiliary contactor, and then the main contactor will act to disconnect the main circuit. The state of the contactor will be monitored in real time during the disconnection process, including contact position, arc detection and insulation condition, to ensure the thoroughness and safety of the disconnection. The third step is to verify and confirm the system state, confirming that the inverter and the main grid have been completely isolated through voltage detection, insulation test and other means. After the disconnection is completed, the inverter will automatically switch to standby state, turn off all outputs and enter a safe non-working state. Through this step-by-step, multi-protection disconnection operation, the inverter and the main grid are safely isolated, creating safe conditions for subsequent mode switching.

[0068] The emergency energy storage power vehicle enters the corresponding working mode according to the preset instruction. The generation of the preset instruction is based on the comprehensive consideration of multiple factors, including the remaining battery capacity, the main power grid stability, the future demand forecast of the load, the vehicle dispatching arrangement and other key information. The instruction generation adopts a decision-making algorithm combining expert systems and fuzzy logic, and establishes a detailed decision tree and rule base. The standby charging mode is suitable for the case where the main power grid has been restored to stability and is expected to remain stable for a long time. In this mode, the emergency energy storage power vehicle remains in the original position, and the inverter works in the charging mode, using the main power grid to supplement the charging of the battery pack. The implementation of the standby charging mode includes the coordinated work of multiple subsystems: the charging system adopts appropriate charging strategies according to the battery state, usually using constant current-constant voltage charging, and the charging current is dynamically adjusted according to the battery temperature and remaining capacity; the monitoring system continuously monitors the main power grid state and battery state, and switches to the emergency response state immediately upon finding an abnormality; the communication system maintains contact with the dispatch center and reports the device state and location information. The off-site mode is suitable for the case where the emergency event has ended, the main power grid has been restored to normal, and there is an emergency power supply demand at other locations. In the off-site mode, the emergency energy storage power vehicle will perform pre-off-site inspection and preparation work, including device state detection, battery capacity evaluation, vehicle system inspection, etc. The off-site preparation process adopts an automated detection program, which conducts a comprehensive inspection of key equipment through sensors and diagnostic systems to ensure that the vehicle has the ability to safely travel and provide emergency power next time. The judgment logic of mode selection is based on preset priority rules: when the battery capacity is below a certain threshold, the standby charging mode is selected first; when a new emergency task instruction is received, the off-site mode is selected first; when the main power grid is unstable, the standby state is maintained but no charging is performed. During the instruction execution process, there is also a manual intervention function, and the operator can manually select the working mode according to the actual situation on site, overriding the automatic decision result. Through this intelligent mode control, the emergency energy storage power vehicle can flexibly adjust the working state according to the actual situation, realizing the optimal configuration and utilization of resources.

[0069] After the standby charging mode is started, system initialization is first performed, including device state checking, parameter setting, communication link establishment and other preparation work. The charging subsystem formulates a detailed charging plan according to the battery state information provided by the battery management system, which takes into account the current state of charge, health status, temperature distribution and charging history of the battery. The charging strategy uses an intelligent optimization algorithm to maximize charging efficiency while ensuring safety. In specific implementation, the charging process is divided into multiple stages: the evaluation stage conducts comprehensive detection of the battery, including key parameters such as cell voltage uniformity, internal resistance consistency, temperature distribution, etc.; the pre-charging stage uses a small current to activate the battery, especially for long-term stored batteries; the main charging stage uses the optimal charging curve according to the battery characteristics, usually an improved constant current and constant voltage charging method; the equalization charging stage balances the individual cells in the battery pack to ensure consistency of individual cell voltages; the maintenance charging stage uses a floating charging method to compensate for the self-discharge of the battery. Temperature management during the charging process is achieved through active thermal management systems, including air cooling, liquid cooling or phase change material cooling, to ensure that the battery temperature remains within the optimal range. The safety monitoring system continuously monitors various parameters during the charging process, including current, voltage, temperature, insulation resistance, etc., and takes protective measures immediately upon detecting abnormalities. The communication system regularly reports device status to the dispatch center, including charging progress, device health status, estimated completion time and other information. The standby charging mode also includes preventive maintenance functions for the device, which uses standby time to perform self-checking and calibration on key devices to ensure that the device is always in optimal working condition. Through this comprehensive standby charging management, efficient charging and device maintenance of the emergency energy storage power supply vehicle during standby period are ensured.

[0070] Departure mode is initiated based on dispatch instructions or pre-set departure conditions, including confirmation of the emergency mission's completion, equipment in good condition, and restoration of the main power grid's stability. Departure preparation utilizes a standardized inspection process, beginning with a battery system inspection to assess the remaining charge, health status, and estimated lifespan to ensure it can meet the needs of the transfer process and the next emergency power supply. If the battery is low, rapid recharging is prioritized, using high-power charging to quickly restore the battery to a safe level. Equipment system inspections include functional testing and performance verification of key equipment such as the inverter, charger, protection system, and monitoring system. Automated testing procedures thoroughly inspect each subsystem to ensure proper operation. Vehicle system inspections examine fundamental vehicle functions, including the chassis, powertrain, braking system, and steering system, to ensure the vehicle's safe operation. The communications system conducts final confirmation with the dispatch center and receives detailed transfer instructions, including the target location, route plan, and time requirements. Pre-departure data backup and transmission ensures the complete preservation of all operational data and event records during the emergency power supply process, providing data support for subsequent analysis and improvements. The safety protection system automatically activates transport protection mode, including physical securing, electrical isolation, and anti-vibration protection, to ensure equipment safety during transport. Departure status monitoring and reporting ensures the dispatch center has real-time information on the vehicle's location, status, and estimated arrival time, providing accurate information for the unified dispatch of emergency resources. This systematic departure management ensures that emergency energy storage power supply vehicles can quickly and safely complete mission transitions and relocations.

[0071] The embodiment improves the overall technical solution of the uninterrupted power supply method of the emergency energy storage power supply vehicle by implementing the subsequent management operation of disconnecting parallel connection and intelligent mode switching, and realizes intelligent management of the whole process from emergency power supply to task completion. First, the step-by-step and multi-protected parallel disconnection operation ensures the safe isolation of the inverter and the main power grid, avoids dangerous situations such as electric arc and impact current that may occur during the disconnection process through precise circulating current control and timing management, protects the safety of the equipment and prolongs the service life of the equipment, and significantly improves the safety and reliability of the operation compared with the traditional simple disconnection method. Second, the intelligent mode selection mechanism based on expert system and fuzzy logic can automatically select the most suitable subsequent working mode according to the actual situation, taking into account the device state and power grid conditions, and also considering the unified scheduling needs of emergency resources, realizing the optimal configuration and efficient use of emergency power supply resources. Third, the precise management of standby charging mode not only realizes efficient supplementary charging of the battery, but also ensures the continuous availability of the equipment through preventive maintenance and equipment self-checking function, fully prepares for the next emergency task, and reflects the foresight and systematicness of emergency equipment management. In addition, the systematic management of the off-site mode ensures that the emergency energy storage power supply vehicle can quickly and safely complete the task conversion, and through comprehensive equipment inspection and state verification, the safety of the vehicle in the transfer process and the instant availability after arriving at the new task site are guaranteed. Finally, the perfect state monitoring and communication reporting function realizes the transparent management of emergency resources, and provides accurate information support for the unified command of the dispatch center and the optimal configuration of resources. Compared with the traditional emergency power supply equipment which simply disconnects and leaves the site after the task is completed, the intelligent subsequent management technology greatly improves the management level and use efficiency of the emergency power supply system.

[0072] In one embodiment of the present embodiment, the output of the inverter is controlled to be phase-locked synchronized with the main power grid, including the following steps: S710, the voltage, frequency and phase of the output of the inverter are controlled to be aligned with the voltage, frequency and phase of the main power grid through a phase-locked loop circuit.

[0073] Reference Figure 4, the precise synchronization of the inverter output and the main grid through the phase-locked loop circuit can ensure safe parallel operation. This technology is based on the principle of phase locking, and through a closed-loop control system, the voltage, frequency, and phase of the inverter output are made completely consistent with the main grid parameters. The phase-locked loop circuit is mainly composed of three core components: a phase detector, a loop filter, and a voltage-controlled oscillator. The phase detector, as the comparison unit of the system, is responsible for detecting the phase difference between the main grid voltage signal and the internal reference signal of the inverter. In specific implementation, a digital phase detector is used to achieve high-precision phase comparison. The phase detector takes the three-phase voltage signal of the main grid as the reference input, and after sampling and digital processing, it compares it with the reference signal generated internally by the inverter. The phase difference is calculated using the arctangent function method, which calculates the instantaneous phase angle by simultaneously sampling the sine and cosine components of the voltage signal. The formula is: θ = arctan(Vsin / Vcos), where θ is the phase angle, and Vsin and Vcos are the sine and cosine components of the voltage signal, respectively. The loop filter receives the phase difference signal output by the phase detector and generates a control voltage through low-pass filtering and integration processing. The design parameters of the filter directly affect the dynamic performance and stability of the phase-locked loop. The voltage-controlled oscillator adjusts the output frequency according to the control voltage output by the filter, achieving automatic tracking of frequency and phase. When the phase difference is zero, it indicates that the inverter output is completely synchronized with the main grid, at which point the phase-locked loop enters the locked state. Through this precise phase-locked control, the inverter can achieve millisecond-level fast synchronization with the main grid.

[0074] This embodiment effectively solves the synchronization problem of the inverter and the main grid in parallel operation by implementing the precise synchronization control technology based on the phase-locked loop, achieving high-precision alignment of voltage, frequency, and phase, and creating necessary conditions for safe parallel operation. The fast dynamic response capability enables the inverter to quickly track and adjust when the main grid parameters change, maintaining the stability of the synchronization state. The digital phase-locked loop design improves the system's anti-interference ability and long-term stability, and has higher precision and reliability compared to traditional analog phase-locked loops. This synchronization technology provides a solid technical foundation for the safe parallel operation and flexible switching of emergency energy storage power supply vehicles.

[0075] In one embodiment of the present embodiment, the voltage, frequency, and phase of the inverter output are aligned with the voltage, frequency, and phase of the main grid through a phase-locked loop circuit, including the following steps: S810, collect the grid voltage of the main grid as the input signal of the phase-locked loop circuit; S820, compare the phase of the input signal and the output signal generated by the voltage-controlled oscillator inside the inverter through the phase detector to obtain a phase difference signal; S830, filter the phase difference signal obtained by comparison through a low-pass filter; S840, control the output frequency of the voltage-controlled oscillator using the filtered phase difference signal; S850, when the filtered phase difference signal approaches zero, determine that phase-locked synchronization has been achieved, and lock the output of the voltage-controlled oscillator, wherein the phase-locked synchronization aligns the voltage, frequency and phase of the inverter output with the voltage, frequency and phase of the main power grid.

[0076] The collection of the main power grid voltage signal is a basic link for the normal operation of the phase-locked loop circuit, and the real-time acquisition and preprocessing of the grid voltage are realized through the voltage sensor and the signal conditioning circuit. The grid voltage collection adopts a precision voltage transformer or a Hall effect voltage sensor, which can accurately measure the three-phase voltage signal of the grid.

[0077] The signal conditioning circuit includes an amplifier, a filter and a level converter, which adjusts the collected voltage signal to an amplitude and format suitable for digital processing. The amplifier adopts an instrument amplifier structure, which has high input impedance, low noise and high common mode rejection ratio. The amplification factor is usually set to 1-10 times, which is adjusted according to the input range of the subsequent ADC. The anti-aliasing filter adopts a 4th order Butterworth low-pass filter, with a cutoff frequency of 1 kHz, effectively filtering out high-frequency interference and noise. The analog-to-digital converter (ADC) adopts a 16-bit high-precision ADC, with a sampling frequency of 10 kHz, ensuring accurate capture of the waveform details of the grid voltage.

[0078] The phase comparison function of the phase detector is the core technical link for the phase-locked loop circuit to achieve accurate phase locking, which generates a control signal by detecting the phase difference between the input signal and the internal reference signal. The phase detector adopts a digital phase detector structure, which realizes high-precision phase detection and comparison based on digital signal processing technology. The digital phase detector first synchronously samples the input grid voltage signal and the voltage-controlled oscillator output signal, with a sampling frequency usually set to more than 200 times the fundamental frequency, i.e. for a 50Hz power frequency signal, the sampling frequency is at least 10kHz. The phase detection adopts the discrete Fourier transform method, which determines the instantaneous phase angle by calculating the real part and the imaginary part of the signal. In the specific calculation process, the voltage signal obtained by sampling is correlated with the sine and cosine reference signals of the same frequency to obtain the quadrature components of the signal. The calculation formula of the phase angle is: φ = arctan(Im / Re), where φ is the phase angle, Im is the imaginary component, and Re is the real component. The phase difference between the two signals is obtained by subtracting the phase angles: Δφ = φ1-φ2.

[0079] To improve the accuracy of phase detection, interpolation algorithm and window function technology are also adopted. Interpolation algorithm improves the time resolution by interpolating between sampling points, and window function technology reduces the influence of spectral leakage by selecting appropriate window functions. The phase detector also has a phase unwrapping function. When the phase difference exceeds ±π, it automatically performs 2π addition and subtraction operation to ensure that the phase difference is always within a reasonable range. The output of the phase difference signal is linearized to convert the phase difference into a voltage signal proportional to it. The conversion coefficient is usually set to 1V / π, which means that the output voltage is 1V when the phase difference is π. The dynamic range of the phase detector is designed to be ±2π, which can handle larger initial phase differences and ensure that the phase-locked loop can capture and lock from any initial state. Through this high-precision digital phase detection technology, phase difference detection accuracy of micro-radian level can be achieved, providing accurate error signals for subsequent frequency control.

[0080] Low-pass filter processing of phase difference signal, by filtering out high-frequency noise and interference signals to obtain smooth control signal. The filter uses an active low-pass filter structure based on operational amplifier and RC network. The transfer function of the filter is designed as a second-order Butterworth characteristic, and the transfer function is: ; Where ωn is the natural frequency, set to about 1 / 10 of the system bandwidth, usually in the range of 5-50Hz. The quality factor Q is set to 0.707 to ensure that the filter has flat passband characteristics and moderate transition band steepness. The cutoff frequency of the filter is determined according to the expected bandwidth and noise characteristics of the phase-locked loop. A lower cutoff frequency can provide better noise suppression capability, but will reduce the dynamic response speed of the system; a higher cutoff frequency can provide faster response speed, but may introduce more high-frequency noise. In actual design, the cutoff frequency is usually set to 1 / 5-1 / 10 of the desired phase-locked bandwidth. The filter also has a gain adjustment function, which changes the DC gain of the filter by adjusting the size of the feedback resistor. The gain range is usually set to 0.1-10 times. To improve the phase characteristics of the filter, a phase lead or lag compensation network can also be added to the filter to compensate for the phase delay introduced by other components in the loop. The output of the filter is impedance matched through a buffer amplifier to ensure that it can drive the subsequent voltage-controlled oscillator circuit. The filter is also equipped with a saturation limiting circuit to prevent saturation distortion when a large signal is input. Through low-pass filtering, both the smoothness and stability of the control signal are ensured, and the necessary dynamic response capability of the system is maintained.

[0081] The voltage-controlled oscillator adjusts the output frequency according to the filtered phase difference signal, and realizes precise adjustment of the oscillation frequency through voltage control. The voltage-controlled oscillator adopts an LC oscillator or a crystal oscillator structure. The LC oscillator is based on a resonance loop composed of an inductor and a varactor diode, and the equivalent capacitance is adjusted by changing the reverse bias voltage of the varactor diode, thereby changing the resonance frequency. The calculation formula of the oscillation frequency is: ; where L is the inductance value and C is the equivalent capacitance value. The relationship between the capacitance of the varactor diode and the control voltage is generally: C(V)=C0 / (1+V / V j ) n , where C0 is the zero-bias capacitance, V is the control voltage, V j is the junction potential, and n is the varactor index. The frequency control sensitivity (Kv) of the voltage-controlled oscillator is defined as the ratio of the frequency change to the control voltage change, with the unit of Hz / V. In order to improve the frequency stability, the oscillator adopts temperature compensation technology, detects the environmental temperature through a temperature sensor, and performs corresponding compensation on the oscillation frequency. Frequency calibration is realized by comparison with a high-precision frequency reference, and automatic calibration is performed regularly to ensure long-term frequency stability. The output of the oscillator is isolated and amplified through a buffer amplifier, and the output waveform is shaped into a standard square wave signal, with the amplitude usually set to 5V CMOS level. Through the voltage-controlled oscillator, precise control and rapid adjustment of the frequency are realized, providing a reliable frequency source for stable locking of the phase-locked loop.

[0082] Finally, the synchronization state is determined by monitoring the size and stability of the phase difference signal, and corresponding locking measures are taken. The synchronization determination adopts a combination of multiple criteria to ensure the accuracy and reliability of the determination result. The main determination conditions include phase difference amplitude criterion, phase difference stability criterion and frequency deviation criterion. The phase difference amplitude criterion requires the absolute value of the filtered phase difference signal to be less than the preset threshold, which is usually set to ±0.1V, and the corresponding phase error is about ±5.7°. The phase difference stability criterion requires the phase difference signal to remain stable within a continuous time window, which is usually set to 10-50 power frequency cycles, i.e. 0.2-1 seconds. The stability is evaluated by calculating the standard deviation of the phase difference signal, and the signal is considered stable when the standard deviation is less than the set threshold. The frequency deviation criterion requires the output frequency of the voltage-controlled oscillator to be less than ±0.01Hz from the grid frequency, and this criterion is realized by a frequency counter for real-time monitoring. When all criteria are met at the same time, the phase-locked loop enters the locked state. The locking control adopts a hierarchical locking strategy, including coarse locking and fine locking stages. The coarse locking stage allows larger phase error and frequency deviation, and the main purpose is to make the frequency of the voltage-controlled oscillator quickly approach the grid frequency; the fine locking stage requires more stringent synchronization accuracy to ensure the final locking quality. The maintenance of the locked state is realized by the lock detector and the holding circuit, the lock detector continuously monitors the synchronization state, and when the lock is detected, the phase-locked process is restarted immediately. The holding circuit adjusts the control voltage of the voltage-controlled oscillator in the locked state, compensating for the frequency drift caused by factors such as temperature change and device aging. The locking indication is realized by the LED indicator and the digital signal output, providing intuitive state information for the operator and the control system. The measurement and recording function of the locking time provides data support for system performance evaluation and optimization, and the typical locking time is in the range of 0.5-2 seconds. Through synchronization determination and reliable locking control, the high-precision synchronization of the inverter output with the main grid is ensured, creating ideal conditions for safe parallel operation.

[0083] The present embodiment successfully realizes high-precision alignment of the inverter output with the voltage, frequency and phase of the main power grid by implementing a precision synchronization control technology based on a phase-locked loop circuit, effectively solving the synchronization problem of power electronic equipment when connected in parallel with the power grid. First, high-precision power grid voltage acquisition and signal conditioning technology ensures that the phase-locked loop obtains accurate and stable reference signals, and multiple filtering and calibration measures effectively suppress the influence of noise and interference on synchronization accuracy, laying a solid foundation for the entire phase-locked process. Second, the phase detection technology based on digital signal processing achieves a phase difference detection accuracy of micro-radians, which has higher precision and stronger anti-interference ability than traditional analog phase detectors, ensuring the accuracy and reliability of phase comparison. Third, the carefully designed low-pass filter maintains the dynamic response capability of the system while ensuring the smoothness of the control signal, and through reasonable parameter selection, the best balance between noise suppression and fast response is achieved. In addition, the linear control characteristics and temperature compensation function of the high-performance voltage-controlled oscillator ensure the accuracy and long-term stability of frequency regulation, providing a high-quality frequency source for the reliable operation of the phase-locked loop. Finally, the multi-criteria synchronization determination and hierarchical locking control strategy ensures the accuracy and reliability of the phase-locked process, and the typical synchronization accuracy reaches ±0.1° phase error and ±0.01Hz frequency deviation range. Compared with the traditional simple synchronization method, this phase-locked loop synchronization technology significantly improves the synchronization accuracy and reliability, providing key technical support for the safe parallel connection and smooth switching of emergency energy storage power supply vehicles, and effectively ensuring the safe operation and high-quality service of uninterrupted power supply systems.

[0084] In one embodiment of the present embodiment, in the parallel connection state, the method further comprises the following steps: S910, controlling the inverter to inject a periodic frequency disturbance signal into its output current; S920, real-time monitoring the AC voltage frequency of the grid connection point to obtain a real-time frequency value containing the response of the disturbance signal; S930, amplifying the deviation of the real-time frequency value from the preset grid nominal frequency by a positive feedback gain, and adjusting the output frequency command of the inverter according to the amplified deviation; S940, continuously judging whether the real-time frequency value exceeds the preset frequency protection threshold due to the positive feedback gain; S950, when the real-time frequency value exceeds the frequency protection threshold, determining that an islanding effect has been formed, and immediately controlling the inverter to stop outputting to achieve disconnection of the inverter from the main power grid.

[0085] Periodic frequency disturbance signal can be achieved by superimposing a specific frequency disturbance in the inverter output current for active detection of grid connection state. The disturbance signal adopts sinusoidal modulation, the frequency is usually selected in the range of 1-5Hz, the amplitude is controlled in the range of 1%-3% of the rated current, which ensures that it will not affect the normal power supply. The generation of disturbance signal is realized by digital signal processor, which uses direct digital frequency synthesis technology to generate high-precision sinusoidal waveform. The injection control adopts current superposition method, which vector superimposes the disturbance signal and the basic output current, and modulates it into the output of the inverter through the PWM controller. The phase and amplitude of the disturbance signal can be dynamically adjusted according to the detection needs, which improves the sensitivity and reliability of the detection.

[0086] Real-time monitoring of grid-connected point AC voltage frequency is realized by high-precision frequency detection circuit, which adopts the combination of zero-point detection method and digital phase-locked loop technology. The frequency detection circuit continuously samples the voltage signal of the grid-connected point, and the sampling frequency is set to more than 10kHz to ensure that the small changes in frequency can be accurately captured. The detection algorithm uses the sliding window DFT method to calculate the fundamental frequency of the voltage signal in each detection period. When the inverter injects frequency disturbance, if the grid is normally connected, the disturbance signal will be absorbed by the large grid, and the frequency change is very small; if it forms an island, the disturbance signal will cause a significant frequency deviation. The monitoring system can capture these frequency changes in real time and provide accurate data for island judgment.

[0087] Positive feedback gain amplification technology accelerates the island detection process by amplifying the frequency deviation, improving the detection speed and sensitivity. The deviation between the monitored frequency value and the nominal frequency 50Hz is calculated in real time, and the deviation calculation formula is: Δf=fm-fn. The positive feedback gain K is usually set in the range of 10-50, and the amplified deviation is: Δfa=K×Δf. The amplified deviation signal is used to adjust the output frequency command of the inverter, forming a positive feedback loop. In the normal grid-connected state, the strong support of the large grid makes the frequency deviation remain in a very small range, and the positive feedback effect is not obvious; in the island state, after losing the support of the grid, the positive feedback effect will rapidly amplify the frequency deviation, causing the frequency to quickly deviate from the nominal value.

[0088] The frequency protection threshold is usually set to ±0.5Hz, that is, when the frequency exceeds the range of 49.5Hz-50.5Hz, the protection action is triggered. The judgment logic adopts a continuous judgment mechanism, which requires the frequency to exceed the threshold for several consecutive detection periods to confirm the island state, avoiding false actions caused by transient disturbances. The judgment period is usually set to 10-50 milliseconds, and the detection and protection actions can be completed within 2 seconds after the island is formed.

[0089] Confirmation of islanding and disconnection control are the final execution steps of the protection system. Once an island is confirmed, the inverter is immediately controlled to stop output. Disconnection control employs multiple protection strategies, including software control and hardware protection. Software control shuts down the inverter output by stopping the PWM drive signal, with a response time of less than 10 milliseconds. Hardware protection physically disconnects the output circuit via relays or contactors, ensuring reliable disconnection. The disconnection process also includes fault logging and status indication, providing information support for subsequent fault analysis and recovery operations.

[0090] This embodiment effectively solves the problem of island detection in the grid-connected operation of distributed power sources by implementing island detection technology based on active frequency disturbance, and significantly improves the safety and reliability of grid operation. The injection of periodic frequency disturbance signals and the positive feedback gain amplification technology are combined to achieve rapid and accurate detection of the island state. The detection time is usually within 2 seconds, and the detection accuracy reaches the international advanced level. Real-time frequency monitoring and multi-level protection threshold judgment ensure the high reliability of the detection system and effectively avoid false operations and missed operations. Compared with traditional passive detection methods, this active detection technology has higher detection sensitivity and shorter detection time, and is particularly suitable for situations where the load and power generation are matched. The perfect disconnection control and protection mechanism ensures that the inverter can be disconnected in a timely and reliable manner after the island is detected, avoiding the safety hazards that may be caused by island operation.

[0091] The present invention also provides an uninterruptible power supply system, including: a memory configured to store instructions; and The processor is configured to call instructions from the memory and implement the above-mentioned uninterruptible power supply method based on the emergency energy storage power supply vehicle when executing the instructions.

[0092] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware. Furthermore, the present application may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0093] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or combination thereof. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or combination thereof.

[0094] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or combination thereof. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or combination thereof.

[0095] The computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart block or blocks. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or combination thereof. Figure 1 one or more flowcharts and / or blocks in the flowcharts and / or combination thereof.

[0096] In one typical configuration, the computing device includes one or more processors (CPUs), input / output interfaces, network interfaces, and memory.

[0097] The memory can include non-persistent memory and / or volatile memory, such as a random access memory (RAM) including a cache area for the temporary storage of data. The memory can also include non-volatile memory, such as read only memory (ROM) for storing structural information and / or instruction code to implement the functions of the computing device. The memory can additionally or alternatively include mass storage for persistent storage of information and instructions.

[0098] Computer-readable media includes permanent and non-permanent, movable and non-movable media that can implement information storage by any method or technology. The information can be computer-readable instructions, data structures, program modules or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, compact disc read-only memory (CD-ROM), digital versatile disc (DVD) or other optical storage, magnetic cassette, magnetic tape disk storage or other magnetic storage devices, or any other non-transmission medium that can be used to store information accessible to a computing device. According to the definition herein, computer-readable media does not include transitory media such as modulated data signals and carriers.

[0099] It should also be noted that the terms "comprising", "containing", or any other variant thereof are intended to cover non-exclusive inclusions, so that a process, method, article or apparatus that includes a list of elements does not only include those elements, but also includes other elements not explicitly listed, or further includes elements inherent in such a process, method, article or apparatus. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article or apparatus that includes the element.

[0100] The above is only an embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the present application shall be included in the scope of claims of the present application.

Claims

1. An uninterruptible power supply method based on an emergency energy storage power supply vehicle, characterized in that: The method includes: In response to a fault signal from the main power grid, the emergency energy storage power supply vehicle is controlled to supply power to the target load through the built-in inverter; Monitor the status of the main power grid in real time to detect the restoration signal of the main power grid; In response to detecting a restoration signal of the main power grid, controlling the output of the inverter to be phase-locked and synchronized with the main power grid; After the phase-locked synchronization is completed, the inverter is controlled to be connected in parallel with the main power grid. In the parallel connection state, the emergency energy storage power supply vehicle continues to independently supply power to the target load through the inverter; In the parallel connection state, the power quality parameters of the main grid are obtained in real time, and whether the main grid meets the grid stability conditions is determined based on the power quality parameters; When the main grid meets the grid stability conditions, the load shedding operation is performed to smoothly transfer the target load from being powered by the inverter to being powered by the main grid.

2. The method according to claim 1, characterized in that Determine whether the main grid meets grid stability conditions based on power quality parameters, including: When the power quality parameters all meet the corresponding stability parameter thresholds within a preset duration window, it is determined that the main power grid meets the grid stability condition, where the power quality parameters include voltage fluctuation amplitude, frequency fluctuation amplitude and total harmonic distortion rate.

3. The method according to claim 1, characterized in that When the main power grid does not meet the power grid stability condition, the method further includes: The emergency energy storage power supply vehicle is controlled to enter the buffer power supply mode. In the buffer power supply mode, the inverter is controlled to draw power from the main power grid to charge the battery pack of the emergency energy storage power supply vehicle. At the same time, the inverter continues to provide isolated and stable power supply to the target load.

4. The method according to claim 3, characterized in that Control the inverter to draw power from the main grid to charge the battery pack of the emergency energy storage power supply vehicle, including: Get the current charging status of the battery pack; Determine the current charging stage in a preset charging strategy according to the current charging state, wherein the charging strategy includes at least a constant current charging stage and a constant voltage charging stage; According to the current charging stage, a corresponding charging power instruction is generated to control the charging power drawn by the inverter from the main power grid to be equal to the set value of the charging power instruction.

5. The method according to claim 1, wherein When the main grid meets the grid stability conditions, the load shedding operation is performed to smoothly transfer the target load from the inverter power supply to the main grid power supply, including: Start the flexible load transfer program to reduce the output power of the inverter within the preset transfer time; When the inverter output power is reduced, the power required by the target load is compensated by the input current of the main grid; Real-time monitoring of the feedback current value flowing through the output side of the inverter; When the feedback current value is less than the preset zero current threshold, it is determined that the load has been completely taken over by the main grid, and the load transfer switch is controlled to disconnect the target load from the inverter to complete the zero current switching.

6. The method according to claim 1, characterized in that After performing the load shedding operation, the method further includes: Disconnect the parallel connection between the inverter and the main grid; Control the emergency energy storage power supply vehicle to enter standby charging mode or departure mode according to preset instructions.

7. The method according to claim 1, characterized in that Control the inverter output to phase-lock synchronization with the main grid, including: Through the phase-locked loop circuit, the voltage, frequency and phase of the inverter output are controlled to align with the voltage, frequency and phase of the main grid.

8. The method according to claim 7, characterized in that The voltage, frequency, and phase of the inverter output are controlled to align with the voltage, frequency, and phase of the main grid through a phase-locked loop circuit, including: Collect the grid voltage of the main grid as the input signal of the phase-locked loop circuit; The phase detector compares the phase of the input signal with the output signal generated by the voltage-controlled oscillator inside the inverter to obtain a phase difference signal; The phase difference signal obtained by comparison is filtered through a low-pass filter; The output frequency of the voltage controlled oscillator is controlled by using the filtered phase difference signal; When the filtered phase difference signal approaches zero, it is determined that phase-locked synchronization has been achieved and the output of the voltage-controlled oscillator is locked, wherein phase-locked synchronization means that the voltage, frequency and phase output of the inverter are aligned with the voltage, frequency and phase of the main grid.

9. The method according to claim 1, characterized in that In the parallel connection state, the method further includes: Control the inverter to inject a periodic frequency disturbance signal into its output current; Real-time monitoring of the AC voltage frequency at the grid connection point to obtain a real-time frequency value including a disturbance signal response; Through positive feedback gain, the deviation between the real-time frequency value and the preset grid nominal frequency is amplified, and the output frequency instruction of the inverter is adjusted according to the amplified deviation; Continuously determine whether the real-time frequency value exceeds the preset frequency protection threshold due to the positive feedback gain; When the real-time frequency value exceeds the frequency protection threshold, it is determined that an islanding effect has occurred, and the inverter is immediately controlled to stop output to disconnect the inverter from the main grid.

10. An uninterruptible power supply system, characterized in that: include: a memory configured to store instructions; as well as A processor is configured to call the instructions from the memory and to implement the uninterruptible power supply method based on the emergency energy storage power supply vehicle according to any one of claims 1 to 9 when executing the instructions.

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