An uninterrupted power supply method and system based on an emergency energy storage power supply vehicle

Abstract

The application discloses an uninterrupted power supply method and system based on an emergency energy storage power supply vehicle, and relates to the technical field of emergency power supplies.The method comprises the following steps: in response to a fault signal of a main power grid, controlling the emergency energy storage power supply vehicle to supply power to a target load through a built-in inverter; 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 detection of the recovery 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, controlling the inverter to be connected in parallel with the main power grid; in the parallel connection state, acquiring the power quality parameters 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 parameters; in the case where 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. The application can realize safe load back-switching, thereby effectively reducing the risk of economic loss of users.

Description

Technical Field

[0001] This application relates to the field of emergency power technology, and in particular to an uninterrupted power supply method and system based on an emergency energy storage power vehicle. Background Technology

[0002] Emergency energy storage vehicles, as special vehicles integrating large-capacity battery packs, inverters, battery management systems, energy management systems, and mobile platforms, have the core function of providing uninterrupted power supply. Their goal is to seamlessly take over the power grid 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 after a major fault (such as line tripping or substation failure) in the main power grid, its stability is often difficult to guarantee. The power grid may experience "pseudo-recovery" or "unstable recovery" phenomena, such as a brief recovery followed by another interruption or sustained large fluctuations in voltage and frequency during the initial recovery phase.

[0004] Traditional emergency power supply systems typically perform load switching operations immediately or after a short delay upon detecting a power signal from the grid. If critical loads such as power quality-sensitive servers and precision medical equipment are directly switched back to the unstable main grid at this time, it can easily lead to equipment restarts, logic errors, or even physical damage, resulting in significant economic losses for users. Summary of the Invention

[0005] This application provides an uninterrupted power supply method and system based on an emergency energy storage power vehicle, which enables safe load switching and effectively reduces the economic losses of users.

[0006] To achieve the above objectives, the embodiments of this application adopt the following technical solutions:

[0007] Firstly, an uninterrupted power supply method based on an emergency energy storage vehicle is provided, the method comprising:

[0008] In response to a fault signal from the main power grid, the emergency energy storage vehicle is controlled to supply power to the target load through its built-in inverter.

[0009] Real-time monitoring of the main power grid status to detect recovery signals from the main power grid;

[0010] In response to the detection of a recovery signal from the main grid, the inverter output is controlled to be phase-locked and synchronized with the main grid.

[0011] After phase-locked synchronization is completed, the control inverter is connected in parallel with the main grid. In the parallel connection state, the emergency energy storage power vehicle continuously supplies power to the target load independently through the inverter.

[0012] In parallel connection mode, the power quality parameters of the main power grid are acquired in real time, and the main power grid is determined to meet the grid stability conditions based on the power quality parameters.

[0013] When the main grid meets the grid stability conditions, a load shedding operation is performed to smoothly transfer the target load from being powered by the inverter to being powered by the main grid.

[0014] In one possible implementation of the first aspect, determining whether the main power grid meets the grid stability conditions based on power quality parameters includes:

[0015] When the power quality parameters all meet the corresponding stability parameter thresholds within a preset duration window, the main power grid is determined to meet the grid stability conditions. The power quality parameters include voltage fluctuation amplitude, frequency fluctuation amplitude, and total harmonic distortion rate.

[0016] In another possible implementation of the first aspect, when the main power grid does not meet the grid stability conditions, the method further includes:

[0017] The emergency energy storage vehicle is controlled to enter a buffer power supply mode. In the buffer power supply mode, the inverter is controlled to draw power from the main grid to charge the battery pack of the emergency energy storage vehicle. At the same time, the inverter continuously provides isolated and stable power supply to the target load.

[0018] In another possible implementation of the first aspect, controlling the inverter to draw electrical energy from the main grid to charge the battery pack of the emergency energy storage vehicle includes:

[0019] Get the current charging status of the battery pack;

[0020] Based on the current charging status, the current charging stage is determined in the preset charging strategy, wherein the charging strategy includes at least a constant current charging stage and a constant voltage charging stage.

[0021] Based on the current charging stage, a corresponding charging power command is generated to control the inverter to draw charging power from the main grid to be equal to the set value of the charging power command.

[0022] In another possible implementation of the first aspect, under the condition that the main grid meets the grid stability conditions, a load shedding operation is performed to smoothly transfer the target load from inverter power supply to main grid power supply, including:

[0023] Initiate the flexible load transfer program to reduce the inverter's output power within a preset transfer time.

[0024] During the process of inverter output power reduction, the power required by the target load is compensated by the input current of the main grid;

[0025] Real-time monitoring of the feedback current value flowing through the inverter output side;

[0026] When the feedback current value is less than the preset zero current threshold, it is determined that the load has been fully 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.

[0027] In another possible implementation of the first aspect, after performing the load rollback operation, the method further includes:

[0028] Disconnect the inverter from the main power grid;

[0029] The emergency energy storage vehicle can be controlled to enter standby charging mode or departure mode according to preset instructions.

[0030] In another possible implementation of the first aspect, the output of the control inverter is phase-locked synchronized with the main grid, including:

[0031] The phase-locked loop circuit is used to align the voltage, frequency, and phase of the inverter output with the voltage, frequency, and phase of the main grid.

[0032] In another possible implementation of the first aspect, the voltage, frequency, and phase of the inverter output are aligned with the voltage, frequency, and phase of the main grid via a phase-locked loop circuit, including:

[0033] The main grid voltage is collected as the input signal for the phase-locked loop circuit;

[0034] The phase difference signal is obtained by comparing the phase of the input signal with the phase of the output signal generated by the voltage-controlled oscillator inside the inverter using a phase detector.

[0035] The phase difference signal obtained from the comparison is filtered through a low-pass filter;

[0036] The output frequency of the voltage-controlled oscillator is controlled by using the filtered phase difference signal.

[0037] 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. Phase-locked synchronization means that the voltage, frequency, and phase of the inverter output are aligned with the voltage, frequency, and phase of the main grid.

[0038] In another possible implementation of the first aspect, in the parallel connection state, the method further includes:

[0039] The inverter is controlled to inject a periodic frequency disturbance signal into its output current;

[0040] Real-time monitoring of the AC voltage frequency at the grid connection point is used to obtain a real-time frequency value that includes the response to disturbance signals.

[0041] By using positive feedback gain, the deviation between the real-time frequency value and the preset grid nominal frequency is amplified, and the inverter's output frequency command is adjusted according to the amplified deviation.

[0042] Continuously determine whether the real-time frequency value exceeds the preset frequency protection threshold due to positive feedback gain;

[0043] When the real-time frequency value exceeds the frequency protection threshold, it is determined that an islanding effect has been formed, and the inverter is immediately controlled to stop output in order to disconnect the inverter from the main grid.

[0044] Secondly, this application provides an uninterruptible power supply system, comprising:

[0045] The memory is configured to store instructions; and

[0046] The processor is configured to retrieve the instructions from the memory and, when executing the instructions, to implement the aforementioned uninterrupted power supply method based on an emergency energy storage vehicle.

[0047] Through the aforementioned technical solutions, the rapid response mechanism based on fault signals ensures power takeover within milliseconds when a main grid fault occurs, preventing power outages for critical loads and guaranteeing the continuous operation of important facilities such as medical equipment and data centers. Secondly, real-time monitoring and phase-locked loop (PLL) synchronization technology achieve precise synchronization between the inverter output and the main grid, creating the necessary conditions for safe parallel operation and effectively preventing equipment damage and system instability caused by inaccurate synchronization. Thirdly, the independent power supply mode in parallel connection not only ensures the power quality of the load but also provides a technical foundation for subsequent smooth transfer, fully demonstrating the advanced nature of the system design. Furthermore, the stability judgment mechanism based on multi-dimensional power quality parameters accurately identifies the true recovery status of the main grid, avoiding the risk of equipment damage due to false recovery phenomena and significantly improving system safety and reliability. Finally, the use of flexible load transfer and zero-current switching technology achieves smooth load shedding, ensuring zero impact on the load equipment throughout the process and effectively protecting the user's important equipment and data security. Compared with traditional emergency power supply systems, this technical solution not only provides higher power supply reliability, but also significantly reduces the risk of load shedding, achieving safe load shedding and providing users with a safer and more stable emergency power supply solution.

[0048] Other features and advantages of the embodiments of this application will be described in detail in the following detailed description section. Attached Figure Description

[0049] Figure 1 A flowchart illustrating an uninterrupted power supply method based on an emergency energy storage vehicle, provided for an embodiment of this application;

[0050] Figure 2 A schematic diagram illustrating the connection relationship between the main power grid and an emergency energy storage vehicle is provided for an embodiment of this application.

[0051] Figure 3 A block diagram of a three-loop control strategy for an inverter provided in this application embodiment;

[0052] Figure 4 This is a schematic diagram of the internal structure of a phase-locked loop provided in an embodiment of this application. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for illustration and explanation of the embodiments of this application and are not intended to limit the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0054] It should be noted that if the embodiments of this application involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0055] Furthermore, if the embodiments of this application involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, features defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed in this application.

[0056] Figure 1 The illustration schematically shows a flow chart of an uninterrupted power supply method based on an emergency energy storage vehicle according to an embodiment of this application. Figure 1 As shown in the figure, this application provides an uninterrupted power supply method based on an emergency energy storage power vehicle, which may include the following steps.

[0057] S110, In response to a fault signal from the main power grid, control the emergency energy storage power vehicle to supply power to the target load through its built-in inverter;

[0058] S120. Monitor the status of the main power grid in real time to detect recovery signals from the main power grid;

[0059] S130. In response to the detection of a recovery signal from the main grid, control the inverter output to perform phase-locked synchronization with the main grid;

[0060] S140. After phase-locked synchronization is completed, the inverter is controlled to be connected in parallel with the main grid. In the parallel connection state, the emergency energy storage power vehicle continuously supplies power to the target load independently through the inverter.

[0061] S150. In parallel connection mode, the power quality parameters of the main power grid are acquired in real time, and the main power grid is determined to meet the grid stability conditions based on the power quality parameters.

[0062] S160. When the main power grid meets the grid stability conditions, perform a load switching operation to smoothly transfer the target load from being powered by the inverter to being powered by the main power grid.

[0063] The emergency energy storage vehicle in this embodiment is a special vehicle that integrates a large-capacity battery pack, inverter, intelligent battery management system, and energy management system. Figure 2 This application provides an embodiment of an emergency energy storage power vehicle system architecture diagram, which is shown below. Figure 2 The emergency energy storage 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.

[0064] When the main power grid experiences a power outage due to line tripping, substation failure, or other reasons, the monitoring module of the emergency energy storage vehicle immediately detects a grid fault signal. This fault signal may manifest as a sharp drop in voltage to zero, abnormal frequency, or voltage waveform distortion. In practice, the monitoring module uses multiple sensors to collect real-time parameters such as voltage, current, and frequency from the main power grid. When these parameters exceed preset normal ranges, a fault signal is identified. For example, fault detection is triggered when the grid voltage is lower than 85% of the rated voltage or higher than 115% of the rated voltage. Once a fault signal is detected, the control module initiates the emergency power supply program, controlling the inverter to switch from standby to operating mode. The inverter uses PWM (Pulse Width Modulation) technology to convert the DC power from the battery pack into AC power that meets the load requirements. The inverter's output voltage, frequency, and phase are matched to the load's rated parameters. For a 380V three-phase load, the inverter outputs 380V ± 2% three-phase AC power with a stable frequency within the range of 50Hz ± 0.1Hz. By implementing this step, the emergency energy storage vehicle can seamlessly switch over after a main grid failure, ensuring that critical loads such as medical equipment and servers will not shut down due to power outages, effectively avoiding problems such as data loss and equipment damage, and providing users with reliable power protection.

[0065] While the emergency energy storage vehicle takes over the power supply to the load, the monitoring module continuously monitors the status of the main power grid in real time to detect signs of grid recovery in a timely manner. Real-time monitoring is achieved through multiple voltage sensors, current sensors, and frequency detectors, which are installed at different access points to the grid to ensure the accuracy and reliability of the monitoring data. Monitoring parameters include key indicators such as three-phase voltage amplitude, frequency, phase angle, voltage imbalance, and harmonic content.

[0066] As the main power grid begins to recover, these parameters gradually transition from abnormal to normal states. For example, the voltage gradually rises from 0V to near the rated voltage, and the frequency gradually stabilizes from 0Hz or an abnormal value to around 50Hz. The monitoring module uses a sliding window algorithm to process the collected data, determining the stability of the power grid by calculating the mean and variance of parameters within a 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 consecutive milliseconds, it is preliminarily determined to be a power grid recovery signal. To prevent false judgments, the monitoring module also checks the integrity of the voltage waveform to ensure the correct phase relationship of the three-phase voltages, i.e., a phase difference of 120°±2°. Through precise real-time monitoring, a response can be made immediately upon main power grid recovery, providing accurate timing judgments for subsequent synchronization and parallel operations, avoiding the problem of missing the optimal switching opportunity due to monitoring delays.

[0067] When the monitoring module detects a recovery signal from the main grid, the control module immediately initiates the phase-locked loop (PLL) synchronization procedure to ensure that the inverter's output is fully synchronized with the main grid in terms of voltage, frequency, and phase. The core technology of PLL synchronization is the phase-locked loop (PLL) circuit, which includes three main components: a phase detector, a low-pass filter, and a voltage-controlled oscillator (VCO). In practice, the phase detector first acquires the voltage signal from the main grid as a reference signal, and simultaneously obtains the output signal generated by the VCO inside the inverter. The phase detector calculates the phase difference between the two signals using a phase comparison algorithm. This phase difference is output as a voltage, and its 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 remove high-frequency noise and interference signals, resulting in a smooth control voltage. The cutoff frequency of the low-pass filter is typically set to 1 / 10 of the grid's fundamental frequency, i.e., 5Hz, to ensure effective filtering of harmonic components. The filtered control voltage is fed into a voltage-controlled oscillator (VCO) to regulate its output frequency. The VCO's frequency control characteristic is linear, meaning the output frequency is directly proportional to the control voltage. When the phase difference signal approaches zero, it indicates that the inverter output is synchronized with the main grid. At this point, the control module locks the VCO's output frequency, completing the phase-locked synchronization process. Phase-locked synchronization creates the necessary conditions for subsequent parallel connections, avoiding problems such as circulating current and inrush current caused by inaccurate synchronization.

[0068] After phase-locked synchronization is complete, the control module controls the parallel contactor to connect the inverter to the main grid in parallel, forming a dual-power supply architecture. During the parallel connection process, the auxiliary contacts of the parallel contactor are first pre-charged through a pre-charging circuit to avoid arcing and inrush current during direct closing. The pre-charging process lasts approximately 50 milliseconds, reducing the voltage difference across the contactor to below 5V. Then, the main contacts close to complete the parallel connection. In the parallel connection state, the inverter and the main grid form a parallel system, but the inverter still independently supplies power to the target load. The core of this design lies in achieving the inverter's independent power supply function through a power control strategy. That is, the inverter adjusts its output power to meet the load demand, while the main grid mainly serves as a reference and backup.

[0069] In practice, the inverter employs a constant power control mode, adjusting 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 precisely match the 50kW output power. At this point, although the main grid is connected in parallel with the inverter, its output current is close to zero. This parallel architecture with independent power supply has the following advantages: Firstly, the inverter continues to provide high-quality power to the load, avoiding the impact of potential instability in the main grid on the load. Secondly, the presence of the main grid provides a voltage and frequency reference for the system, ensuring the stability of the inverter's operation. Furthermore, the parallel connection provides the technical basis for subsequent smooth load transfer, allowing the load to be smoothly transferred from the inverter to the main grid without interrupting power supply.

[0070] In parallel connection mode, the monitoring module acquires multiple power quality parameters of the main power grid in real time. By comprehensively analyzing these parameters, it determines whether the main power grid meets the conditions for stable power supply. Key power quality parameters include voltage fluctuation amplitude, frequency fluctuation amplitude, total harmonic distortion (THD), voltage imbalance, and power factor. Voltage fluctuation amplitude is calculated by continuously monitoring changes in grid voltage. Specifically, 1000 voltage samples are collected within a 1-second time window, and their standard deviation is calculated as the fluctuation amplitude indicator. Under normal circumstances, this value should be less than 2% of the rated voltage. Frequency fluctuation amplitude is calculated using a similar method, requiring frequency changes not to exceed ±0.2Hz. The THD is calculated using a Fast Fourier Transform algorithm, analyzing the content of each harmonic in the voltage waveform, requiring the THD to be less than 5%. Voltage imbalance is determined by calculating the ratio of the negative-sequence component to the positive-sequence component of the three-phase voltage, and under normal circumstances, it should be less than 2%. When assessing the stability of the main power grid, the following mechanism is employed: First, all power quality parameters must simultaneously meet their corresponding stability thresholds. Second, this satisfaction must be maintained continuously within a preset duration window, typically a 5-10 minute observation period. For example, if voltage fluctuations remain below 1.5% for 10 consecutive minutes, frequency fluctuations remain within ±0.1Hz, and total harmonic distortion (THD) remains below 3%, the main power grid is deemed to meet stability conditions. To improve the reliability of the assessment, future stability can be predicted by analyzing the changing trends of grid parameters, thereby accurately determining the true stable state of the main power grid, avoiding misjudgments caused by short-term parameter fluctuations, and ensuring that load shedding operations are only performed when the main power grid is truly stable.

[0071] Once the main grid meets stability requirements, the control module initiates a load shedding procedure, smoothly transferring the load from inverter power to main grid power. The load shedding operation employs flexible transfer technology to ensure zero impact on the load throughout the process. The implementation involves several precisely controlled stages: First, the flexible load transfer procedure is initiated, gradually reducing the inverter's output power within a preset transfer time (typically 2-5 seconds). The power reduction uses a linear or exponential decline curve to ensure smooth and continuous power change. For example, when the load power is 50kW, the inverter linearly reduces its output power from 50kW to 0kW within 3 seconds, at a rate of approximately 16.7kW / s. Simultaneously with the inverter power reduction, the main grid automatically compensates for the power difference required by the load, ensuring the load always receives sufficient power. This power compensation is achieved through the natural characteristics of parallel systems: when the inverter output power decreases, the power difference between the load and the main grid drives the main grid to increase its output current. Throughout the process, the monitoring module continuously monitors the feedback current flowing through the inverter output side, which directly reflects the degree of power supplied by the inverter to the load. When the feedback current value drops to a preset zero-current threshold (typically below 1% of the rated current), it indicates that the load has been fully taken over by the main grid. At this point, the control module immediately controls the load transfer switch to operate, completely disconnecting the target load from the inverter. The zero-current transfer technology in this embodiment avoids arcing and impacts during switch operation, protecting the switching equipment and ensuring the continuity of power supply to the load. The transfer switch uses a vacuum contactor or solid-state relay, further ensuring the speed and reliability of the transfer process. Through flexible transfer technology, the load can be smoothly transferred from emergency power supply to main grid power supply without any noticeable impact, ensuring the continuity and stability of power supply.

[0072] This embodiment achieves seamless emergency power supply during main grid failures and safe back-off during recovery, effectively solving the back-off risk problem existing in traditional emergency power supply systems. First, the rapid response mechanism based on fault signals ensures power takeover within milliseconds when a main grid failure occurs, avoiding power interruptions to 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 loop (PLL) synchronization technology, precise synchronization between the inverter output and the main grid is achieved, creating the necessary conditions for safe parallel operation and effectively avoiding equipment damage and system instability caused by inaccurate synchronization. Third, the independent power supply mode in parallel connection not only ensures the power quality of the load but also provides a technical foundation for subsequent smooth transfer, fully demonstrating the advanced nature of the system design. Furthermore, the stability judgment mechanism based on multi-dimensional power quality parameters can accurately identify the true recovery status of the main grid, avoiding the risk of equipment damage due to 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 achieves smooth load back-off, ensuring zero impact on the load equipment throughout the process and effectively protecting the user's important equipment and data security. Compared with traditional emergency power supply systems, this technical solution not only provides higher power supply reliability, but also significantly reduces the risk of load shedding, achieving safe load shedding and providing users with a safer and more stable emergency power supply solution.

[0073] In one embodiment of this invention, determining whether the main power grid meets the grid stability conditions based on power quality parameters includes the following steps:

[0074] S210. When the power quality parameters all meet the corresponding stability parameter thresholds within the preset duration window, the main power grid is determined to meet the grid stability conditions. The power quality parameters include voltage fluctuation amplitude, frequency fluctuation amplitude, and total harmonic distortion rate.

[0075] In this embodiment, voltage fluctuation amplitude is monitored using a voltage sensor. The voltage fluctuation amplitude is calculated using statistical methods, specifically by calculating the standard deviation of the effective voltage value within a preset time window (typically 1 second or 5 seconds). The calculation formula is as follows:

[0076] ;

[0077] Among them U i U is the effective voltage value at the i-th sampling point. avg Let n be the average voltage within the time window, and n be the number of sampling points. For example, when the rated voltage is 380V, if the standard deviation of 1000 voltage samples collected in 1 second is 3V, then the voltage fluctuation amplitude is 3 / 380×100%=0.79%.

[0078] Frequency fluctuation amplitude is monitored using zero-point detection or phase-locked loop (PLL) technology, calculating the frequency by detecting the zero-crossing points of the voltage waveform. Specifically, the instantaneous frequency is determined by calculating the time interval between two adjacent positive zero-crossing points, and the frequency fluctuation amplitude is calculated using the standard deviation method. Total harmonic distortion (THD) is calculated using a Fast Fourier Transform (FFT) algorithm, converting the time-domain voltage signal into a frequency-domain signal to analyze the amplitude of each harmonic. The formula for calculating THD is:

[0079] ;

[0080] Where THD is the total harmonic distortion, U1 is the fundamental effective value, and U2, U3, ..., U... n These represent the effective values ​​of each harmonic. In practical applications, calculating up to the 50th harmonic is usually sufficient to meet accuracy requirements. This multi-parameter integrated monitoring method can comprehensively assess the power quality of the main power grid, providing an accurate data foundation for subsequent stability assessments.

[0081] The stability parameter thresholds are set based on international power system standards and practical application needs, combined with the specific power quality requirements of emergency power supply systems. For voltage fluctuation amplitude, the stability parameter threshold is typically set at ±2% of the rated voltage. That is, in a 380V system, the voltage fluctuation amplitude should not exceed 7.6V; voltage fluctuations within this range will not adversely affect the load equipment. For frequency fluctuation amplitude, since the grid frequency should be maintained within 50Hz ±0.2Hz, the stability parameter threshold for frequency fluctuation amplitude is set at ±0.1Hz to ensure the high reliability of the emergency power supply system. The stability parameter threshold for total harmonic distortion (THD) is set at 5%, meeting the operating requirements of most precision equipment. In actual implementation, these thresholds can be adjusted according to the specific load type and application scenario.

[0082] The preset duration window is a key parameter for ensuring the accuracy of main grid stability assessment. Its setting needs to comprehensively consider the time characteristics of grid recovery, load sensitivity, and system response speed requirements. In practice, the duration window is typically set to 5-15 minutes. This time length effectively identifies the true stable state of the grid without excessively prolonging emergency power supply time. The time window is implemented using a sliding window algorithm, which can update monitoring data in real time and perform continuous evaluation. The sliding window works by establishing a fixed-length data buffer. Newly collected data is added from the tail of the queue, while the oldest data is removed from the head, maintaining a constant buffer length. For example, when the duration window is set to 10 minutes and the sampling frequency is 1Hz, the buffer length is 600 data points. Each time new data arrives, the algorithm calculates whether all data in the current buffer meets the stability parameter threshold requirements. The specific judgment logic is as follows: iterate through all voltage fluctuation amplitude data in the buffer, checking if they are all less than the set threshold; iterate through all frequency fluctuation amplitude data, checking if they are all within the allowable range; iterate through all total harmonic distortion rate data, checking if they are all below the limit value. The main power grid is considered to meet stability conditions only when all three parameters consistently meet their respective threshold requirements throughout the entire time window. When parameter anomalies are detected, the time window automatically resets and restarts timing, ensuring that stability is only determined when the parameters remain consistently stable.

[0083] The comprehensive judgment logic employs a multi-level verification mechanism to ensure the accuracy and reliability of the main power grid stability assessment. In the first level of judgment, three core power quality parameters are monitored in real time, and voltage fluctuation amplitude, frequency fluctuation amplitude, and total harmonic distortion (THD) are calculated simultaneously using parallel processing. Each parameter calculation has an independent processing thread to ensure the real-time performance and accuracy of data processing. The second level of judgment uses a logical AND operation, meaning that all three parameters must simultaneously meet their respective stability threshold requirements; failure to meet the condition for any parameter will result in an unstable overall judgment. The third level of judgment introduces time persistence verification, using a sliding window algorithm to ensure the persistence of the stable state.

[0084] This implementation method establishes a comprehensive evaluation system for main grid stability based on multi-dimensional power quality parameters, enabling accurate judgment of grid recovery status and effectively solving the load shedding risk problem caused by false grid recovery in traditional emergency power supply systems. First, real-time monitoring of three core parameters—voltage fluctuation amplitude, frequency fluctuation amplitude, and total harmonic distortion (THD)—comprehensively reflects the power quality status of the main grid, significantly improving the accuracy and reliability of grid status assessment compared to traditional methods that only monitor voltage presence. Second, by setting strict stability parameter thresholds and combining them with duration window constraints, load shedding is ensured only when the grid is truly and continuously stable, effectively avoiding equipment damage risks caused by brief grid fluctuations. Compared to traditional simple voltage detection methods, this provides users with a safer and more reliable emergency power supply guarantee, significantly reducing economic losses and safety risks caused by improper shedding.

[0085] In one embodiment of this invention, when the main power grid does not meet the grid stability conditions, the method further includes the following steps:

[0086] S310. Control the emergency energy storage power vehicle to enter the buffer power supply mode. In the buffer power supply mode, control the inverter to draw power from the main grid to charge the battery pack of the emergency energy storage power vehicle. At the same time, the inverter continuously provides isolated and stable power supply to the target load.

[0087] When the main grid does not meet stability requirements, the control module immediately activates the buffer power supply mode. This buffer power supply mode is a bidirectional energy management strategy that utilizes the restored but unstable main grid to supplement the battery pack while continuously providing high-quality isolated power to the load. The core technology of the buffer power supply mode is based on the bidirectional energy flow control of a bidirectional inverter, which has both rectification and inversion functions. In implementation, the bidirectional inverter adopts a three-phase bridge structure, containing six power switching devices (usually IGBTs), each equipped with an anti-parallel diode. When operating in rectification mode, the inverter converts AC power from the main grid to DC power to charge the battery pack by controlling the switching devices; when operating in inversion mode, it converts the DC power from the battery pack to AC power to supply power to the load. The key to the buffer power supply mode is achieving simultaneous operation of these two modes, which is achieved through time-division multiplexing and power distribution strategies. Specifically, within each switching cycle (typically 20kHz, i.e., 50 microseconds per cycle), the inverter performs rectification and inversion operations according to a preset time ratio. For example, within a switching cycle, the first 30 microseconds are used for inverter power supply to the load, and the last 20 microseconds are used for rectification to draw power from the main grid for charging. This high-frequency switching time-division multiplexing method is transparent to both the load and the grid because the switching frequency is much higher than the power frequency of 50Hz. The power distribution controller dynamically adjusts the time ratio of the two modes according to the load power demand and battery charging demand, ensuring priority for load power supply while effectively charging the battery. Through this precise bidirectional energy control, the buffered power supply mode solves the problem of battery power consumption while ensuring the continuity and stability of load power supply.

[0088] The inverter draws power from the main grid using controlled rectification technology. This technology precisely controls the power and current waveform drawn from the grid, ensuring no additional impact or interference to the already unstable grid. Controlled rectification employs a PWM (Pulse Width Modulation) rectifier structure, controlling the magnitude and waveform of the rectified current by adjusting the on-time of the switching devices. In practice, the rectifier uses a closed-loop current control strategy, monitoring the charging current flowing into the battery in real time and comparing it with a set charging current command. A PI (Proportional-Integral) controller generates the PWM control signal. The mathematical model for current control is as follows:

[0089] ;

[0090] Where I ref As the reference current, I set To set the charging current, I f K represents the actual feedback current. p and K i These are the proportional and integral coefficients, respectively.

[0091] To minimize the impact on the main power grid, the rectifier also employs power factor correction (PFC) technology, ensuring that the current drawn from the main grid remains in phase with the grid voltage, resulting in a power factor close to 1. Specifically, 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, with the current waveform as close to a sine wave as possible. For example, when the main grid voltage is 380V and 50Hz, the rectifier controls the frequency of the drawn current to also be 50Hz, with the phase difference controlled within ±2°. Furthermore, to prevent impact on an unstable main grid, a soft-start strategy is used for the rectified power, gradually increasing it from zero power to the set value, typically at a rate of 10-20% of the rated power per second. This precise and controllable rectification technology allows for safe energy extraction even when the main grid is unstable, achieving battery charging while avoiding further deterioration of grid stability.

[0092] The battery pack employs an intelligent charging management strategy to ensure safe and efficient charging even under unstable main grid conditions. Charging management is based on real-time battery status monitoring and dynamic charging strategy adjustment. Core components include a battery management system, a charging controller, and a temperature monitoring system. The battery management system monitors the voltage, current, temperature, and internal resistance of each individual battery cell in real time, exchanging data with the charging controller via a CAN bus. The charging strategy uses a multi-stage charging algorithm, including four stages: pre-charging, constant current charging, constant voltage charging, and float charging maintenance. In the pre-charging stage, when the battery voltage is too low (e.g., below 80% of the nominal voltage), a small current (typically 0.1C) is used for pre-charging to avoid damage to deeply discharged batteries. In the constant current charging stage, a set charging current (typically 0.3-0.5C) is used, with the current dynamically adjusted based on the available power and stability of the main grid. When the voltage of any individual battery cell reaches the charging cutoff voltage, the system switches to the constant voltage charging stage, where the charging voltage remains constant while the charging current gradually decreases.

[0093] The formula for calculating charging power 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 (typically 90-95%). Considering the instability of the main power grid, the charging controller also has a rapid power regulation capability. When it detects that the main power grid voltage or frequency fluctuation exceeds a preset range, it can reduce the charging power or suspend charging within 10 milliseconds to avoid increasing the burden on the grid when it is unstable. The temperature protection function ensures that the battery operates within a safe temperature range. When the battery temperature exceeds 45°C, it automatically reduces the charging current and stops charging when it exceeds 55°C. Through this intelligent charging management, both safe battery charging and flexible adjustment of the charging strategy based on the actual conditions of the main power grid are ensured.

[0094] Providing isolated and stable power to the target load is the core function of the buffered power supply mode. Electrical isolation and power filtering technologies ensure a high-quality power supply to the load, completely unaffected by instability in 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 inverter output, and the secondary side is connected to the load; there is no electrical connection between the two sides, thus achieving complete electrical isolation. The isolation transformer is designed with a toroidal core structure and uses high-permeability silicon steel sheets to ensure low loss and high transmission efficiency under high-frequency operating conditions. The transformer's turns ratio is designed according to voltage requirements; for example, when the battery pack voltage is 600V and the load requires 380V, the turns ratio is designed to be 600:380. Power filtering uses a combination of LC filters and active filters. The LC filter, composed of inductors and capacitors, is used to filter out high-frequency components of the inverter's switching frequency, while the active filter is used to compensate for harmonic components in the load current. To further improve power quality, the inverter employs a multi-level topology and space vector PWM modulation technology, resulting in an output voltage waveform closer to an ideal sine wave, with total harmonic distortion controlled below 3%. The inverter is also equipped with comprehensive protection functions, including overvoltage protection, undervoltage protection, overcurrent protection, overtemperature protection, and short-circuit protection, ensuring the safety of the load equipment under various abnormal conditions. Output voltage and frequency stability are achieved through closed-loop control, maintaining voltage stability within ±1% and frequency stability within ±0.05Hz. Through isolated power supply technology, the load receives a stable power supply completely independent of the main grid conditions, effectively avoiding the adverse effects of main grid instability on the load equipment.

[0095] The buffer power supply mode's operational status monitoring and intelligent switching control ensure that the mode can automatically adjust operating parameters according to the actual conditions of the main grid and load, achieving optimal energy management. Operational status monitoring includes comprehensive monitoring of main grid parameters, battery status, load conditions, and inverter operating status. Main grid parameter monitoring primarily focuses on the real-time trends of power quality changes, analyzing voltage, frequency, and harmonic fluctuations through a sliding window algorithm to predict the direction of grid stability changes. Battery status monitoring includes key indicators such as remaining capacity, charging status, health, and expected availability time, which are updated in real-time through the BMS system. Load condition monitoring includes parameters such as power demand, power factor, and harmonic content, providing a basis for power allocation. Inverter operating status monitoring includes information such as switching device temperature, output current, efficiency, and fault status. Intelligent switching control, based on fuzzy logic and expert systems, makes optimal control decisions based on the monitored multi-dimensional parameter information. For example, when the main grid quality continuously improves and approaches a stable threshold, the control algorithm gradually increases charging power to prepare for subsequent load shedding; when the main grid quality further deteriorates, it reduces or even stops charging, focusing on load power supply.

[0096] This implementation method effectively solves the technical challenges faced by traditional emergency power supply systems during the main grid instability recovery phase by implementing a buffered power supply mode, achieving intelligent coordination between emergency power supply and grid recovery. Firstly, the application of bidirectional energy management technology enables the emergency energy storage vehicle to fully utilize the restored but unstable main grid for battery recharging while ensuring the quality of power supply to the load. This significantly extends the duration of emergency power supply and avoids the risk of power outages due to insufficient battery power. Secondly, the combination of electrical isolation and power filtering technologies ensures that the power quality obtained by the load is completely unaffected by the instability of the main grid. The load equipment can operate normally in a stable and clean power environment, effectively preventing equipment failures or data loss due to grid quality issues. The intelligent charging management strategy dynamically adjusts charging parameters based on the real-time status of the main grid and battery status, ensuring both charging safety and efficiency while avoiding additional impacts on the unstable grid, reflecting a grid-friendly design philosophy. Furthermore, the application of controllable rectification technology and power factor correction ensures that the current drawn from the main grid has good waveform quality and power factor, reducing harmonic pollution and reactive power impacts on the grid, thus contributing to the stable recovery of the main grid. Finally, intelligent operation control and fault self-recovery capabilities ensure the reliable operation of the buffer power supply mode under various complex working conditions, providing users with a more flexible and intelligent emergency power supply solution. Compared with the traditional simple mode that either relies entirely on battery power or directly switches back to the grid, the buffer power supply mode achieves flexible coupling between the emergency power supply system and the main grid, ensuring both the power supply safety of the load and the efficient use of energy.

[0097] In one embodiment of this invention, controlling the inverter to draw power from the main grid to charge the battery pack of the emergency energy storage vehicle includes the following steps:

[0098] S410: Obtain the current charging status of the battery pack;

[0099] S420. Based on the current charging state, determine the current charging stage in the preset charging strategy, wherein the charging strategy includes at least a constant current charging stage and a constant voltage charging stage.

[0100] S430: Based on the current charging stage, generate a corresponding charging power command to control the inverter to draw charging power from the main grid to equal the set value of the charging power command.

[0101] Reference Figure 2 The current state of charge of the battery pack is obtained through various sensors and monitoring circuits integrated into the battery management system (BMS). This process involves real-time acquisition and analysis of multiple key parameters such as battery voltage, current, temperature, and internal resistance. In specific implementation, Figure 3This illustration shows a schematic diagram of the connection between a battery management system and a battery pack according to an embodiment of this application. Figure 3 As shown, the battery pack consists of multiple lithium-ion battery cells connected in series and parallel. Each battery cell is equipped with an independent voltage monitoring circuit, using an analog-to-digital converter to monitor changes in cell voltage. Current monitoring is achieved through a Hall effect current sensor. Temperature monitoring uses a multi-point arrangement of thermistors or infrared temperature sensors to monitor the temperature distribution at different locations within the battery pack, ensuring timely detection of hot spots and temperature anomalies. Internal resistance monitoring is achieved through AC impedance testing technology. Small-amplitude AC test signals are periodically injected into the battery, and the internal resistance is calculated by measuring the phase relationship between voltage and current. Changes in internal resistance reflect the battery's health and aging level. The state of charge (SOC) is calculated using a combination of the ampere-hour integration method and the open-circuit voltage method. The ampere-hour integration method calculates the change in charge by integrating the charging and discharging current over time; the formula is:

[0102] ;

[0103] 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 battery's terminal voltage in a resting state and comparing it to a pre-established SOC-OCV (open-circuit voltage) characteristic curve. State of health (SOH) is assessed by comparing the current available capacity to the nominal capacity; periodic capacity calibration tests are performed to update the SOH value. Through this multi-parameter integrated monitoring and intelligent algorithm processing, the real-time charging status of the battery pack can be accurately grasped, providing a reliable data foundation for subsequent charging strategy selection.

[0104] The determination of charging stages is based on battery chemical characteristics and charging safety requirements. The most suitable charging strategy is selected by analyzing the current charging state to ensure the safety and efficiency of the charging process. The preset charging strategy employs a multi-stage charging algorithm, mainly including four different charging stages: pre-charging stage, constant current charging stage, constant voltage charging stage, and float charging maintenance stage. The pre-charging stage is suitable for situations where the battery voltage is too low. This stage is typically initiated when the individual cell voltage is below 2.5V or the SOC is below 10%, using a small current of 0.05C-0.1C to avoid damaging deeply discharged batteries. The constant current charging stage is the main charging stage. It begins when the battery voltage recovers to a safe range and the temperature is normal. The charging current remains constant, typically set at 0.3C-0.5C, and this stage can quickly replenish the battery's charge. The constant voltage charging stage is initiated when any individual cell voltage reaches the charging cutoff voltage (usually 4.2V). At this point, the charging voltage remains constant, and the charging current gradually decreases as the battery charge increases until the current drops to the set cutoff current value. The float charging maintenance phase is used for maintenance after the battery is fully charged, employing a very small current to compensate for the battery's self-discharge losses. The phase determination logic adopts a state machine design approach, comparing real-time values ​​of parameters such as battery voltage, current, temperature, and SOC with preset thresholds to determine the current charging phase. For example, when the SOC is less than 10% and the lowest single-cell voltage is less than 2.8V, it is determined to be in the pre-charging phase; when the SOC is between 10% and 90% and the highest single-cell voltage is less than 4.15V, it is determined to be in the constant current charging phase; when any single-cell voltage reaches 4.2V, it switches to the constant voltage charging phase. Phase switching uses a smooth transition to avoid sudden changes in charging parameters impacting the battery. Furthermore, the charging strategy also considers the influence of ambient temperature, adjusting charging parameters accordingly under low or high temperature conditions. At low temperatures, the charging current is reduced and the charging time is extended; at high temperatures, charging is paused or cooling measures are activated. This intelligent charging phase determination based on battery state ensures that the battery is charged under the most suitable conditions, guaranteeing both charging safety and optimized charging efficiency.

[0105] By translating the strategy requirements of the charging phase into specific power control commands, the inverter is driven to draw corresponding electrical energy from the main grid. Power command generation employs a multi-level control architecture, comprising three layers: a strategy layer, a calculation layer, and an execution layer. The strategy layer determines the basic charging parameter requirements based on the current charging phase, such as constant current for the constant current phase and constant voltage for the constant voltage phase. The calculation layer calculates the specific power command value based on the strategy layer's requirements and the battery's real-time status. 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. During the constant current charging phase, the charging current I remains constant, while the charging voltage U gradually increases with the increase of the state of charge (SOC), thus the power command shows a slow upward trend. For example, when the charging current is set to 100A, as the battery voltage increases from 350V to 420V, the charging power increases from 35kW to 42kW.

[0106] During the constant-voltage charging phase, the charging voltage U remains constant, while the charging current I gradually decreases with increasing SOC, resulting in a decreasing power command. The execution layer is responsible for converting the power command into control signals for the inverter, adjusting the inverter's switching duty cycle via the PWM controller to achieve power regulation. The power command also needs to consider the actual conditions and constraints of the main grid. When the main grid power is limited, the charging power needs to be restricted to avoid exceeding the grid's capacity. Power limiting employs a dynamic adjustment algorithm, monitoring parameters such as voltage and frequency of the main grid in real time. When a decline in grid quality is detected, the charging power is automatically reduced, and when the grid condition improves, the charging power is gradually restored. Command output uses digital communication, transmitting the power command to the inverter controller via CAN bus or Ethernet to ensure accurate and real-time command transmission. This precise power command generation and control mechanism enables precise control of the charging process, ensuring that the charging power strictly adheres to the preset strategy.

[0107] In this embodiment, the inverter adopts a bidirectional AC-DC converter topology, enabling bidirectional power flow. It can convert DC to AC to supply power to the load, and AC to DC to charge the battery. In charging mode, the inverter operates in rectification mode, regulating the power drawn from the main grid by controlling the switching of power switching devices. Power control employs a three-loop control strategy, including an outer power loop, an inner current loop, and a voltage loop. The outer power loop compares the power command with the actual power drawn to generate a current reference signal; the inner current 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 uses a PI controller, with the PI parameters for the power loop set to Kpp=0.1, Kip=10; and the PI parameters for the current loop set to Kpi=5, Kii=500.

[0108] Power measurement employs a true RMS method, simultaneously sampling voltage and current signals to calculate instantaneous power and then averaging the results to obtain the actual power drawn. To minimize harmonic pollution to the main grid, the inverter utilizes power factor correction (PFC) and active filtering technologies to ensure the input current waveform is as close to a sine wave as possible and in phase with the voltage. Specifically, by detecting the phase information of the main grid voltage, the phase of the input current is controlled to maintain consistency with the voltage phase, while current waveform control technology minimizes the harmonic content of the input current. In this way, the inverter can accurately draw power from the main grid according to power commands, achieving precise and controllable charging.

[0109] This implementation method effectively solves the technical problems of low charging efficiency, poor safety, and significant impact on the power grid in traditional charging systems by implementing an intelligent charging control strategy based on charging state recognition and phased management, achieving safe, efficient, and intelligent battery charging management. The multi-stage charging strategy based on battery chemical characteristics ensures both charging safety and optimizes charging efficiency. Smooth switching between different charging stages avoids the impact of sudden changes in charging parameters on the battery, extending battery life and improving the reliability of the entire energy storage system. The combination of power command generation and three-loop control technology enables precise control of charging power, ensuring that the power drawn by the inverter from the main grid strictly follows the preset strategy, meeting the battery's charging needs while avoiding unnecessary impact on the main grid. Furthermore, the application of power factor correction and active filtering technology significantly improves the quality of the current drawn from the main grid, reducing harmonic pollution and reactive power impact, contributing to the stable operation of the power grid. When fluctuations occur in the main grid or equipment malfunctions, timely protective measures can be taken to prevent equipment damage and safety accidents. Compared with traditional constant current or constant voltage single charging modes, this intelligent charging control strategy has higher adaptability and safety, and can dynamically adjust charging parameters according to the actual conditions of the battery and the power grid, providing a more reliable and efficient charging solution for emergency energy storage vehicles.

[0110] In one embodiment of this invention, when the main grid meets the grid stability conditions, a load shedding operation is performed to smoothly transfer the target load from inverter power supply to main grid power supply, including the following steps:

[0111] S510: Start the flexible load transfer program and reduce the inverter's output power within the preset transfer time.

[0112] S520. During the process of reducing the output power of the inverter, the input current of the main grid compensates for the power required by the target load.

[0113] S530: Real-time monitoring of the feedback current value flowing through the inverter output side;

[0114] S540: When the feedback current value is less than the preset zero current threshold, it is determined that the load has been fully 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.

[0115] The initiation of the flexible load transfer procedure marks the official start of the load shedding operation. This procedure employs a gradual power regulation strategy to ensure a smooth decrease in inverter output power, avoiding any impact or interference to the load. The core of the flexible transfer procedure is the power ramp control algorithm, which calculates the power decrease slope based on the preset transfer time and current output power, ensuring the linearity and continuity of the power change process.

[0116] In practical implementation, power ramp control employs piecewise linear or exponential curve control. Piecewise linear control divides the entire transition process into multiple time periods, within which the power decreases at a constant slope. A smooth transition algorithm is used between segments to avoid abrupt changes in the slope. Exponential curve control uses an exponential function to describe the power decrease process, with the power change formula as follows:

[0117] Where P(t) is the output power at time t, P0 is the initial power, and τ is the time constant. Adjusting the time constant controls the rate of power decrease. The preset transfer time is typically determined based on the load type and power level. For capacitive loads, the transfer time can be relatively short, usually set to 2-3 seconds; for inductive loads, due to 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 paused and protective measures activated, thus ensuring a smooth decrease in inverter output power and creating ideal conditions for seamless load transfer.

[0118] Power compensation of the main grid input current is used to achieve seamless load transfer. This process is achieved through a combination of the natural power balance characteristics of the parallel system and active power regulation technology. In parallel power supply mode, the inverter and the main grid jointly supply power to the load, and the total power required by the load is equal to the sum of the inverter output power and the main grid output power. When the inverter output power begins to decrease, in order to maintain a constant load power, the main grid must correspondingly increase its output power to compensate for this difference. The realization of power compensation is based on the basic principle of parallel voltage sources. When two voltage sources are connected in parallel, the distribution of output current depends on their respective internal resistances and control strategies. In specific implementation, the inverter adopts a droop control strategy, which reduces the output current by artificially increasing the output internal resistance. 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 inverter's output current will decrease accordingly, thereby achieving a decrease in output power. At the same time, due to its low internal resistance characteristics, the main grid will automatically bear more load current, achieving natural power compensation. To improve the accuracy and stability of compensation, active power regulation technology is employed. This technology calculates the power that the main grid should handle by monitoring load power and inverter power in real time, and actively adjusts the grid's output power using grid-side power regulation devices (such as static synchronous compensators). The power compensation process also considers power factor matching, ensuring that the main grid can compensate for inverter power drops not only in active power but also maintain a stable system power factor in reactive power. The compensation control uses a fast-response algorithm to ensure timely adaptation to inverter power changes. Through this precise power compensation mechanism, the load consistently receives a stable power supply, experiencing no power fluctuations or interruptions throughout the transfer process.

[0119] The feedback current flowing through the inverter output side is monitored by at least one sensor. Specifically, a Hall effect current sensor can be used to determine the feedback current value. Based on the Hall effect principle, when a current-carrying conductor passes through the sensor, the resulting magnetic field generates a corresponding voltage signal in the Hall element, which is proportional to the current flowing through it.

[0120] Zero-current switching judgment and switching action control are the final steps in achieving safe load transfer. Accurate current threshold judgment and fast, reliable switching operations complete the final transfer of the load from the inverter to the main grid. Setting the zero-current threshold requires consideration of multiple factors, including the accuracy of current measurement, load characteristics, and the switching capacity. It is typically set at 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 uses a continuous judgment mechanism, meaning 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 misjudgments caused by transient interference or measurement noise.

[0121] The switching device employs either a vacuum contactor or a solid-state relay. Vacuum contactors are suitable for high-power applications, while solid-state relays are suitable for applications requiring frequent switching. In practice, a dual-switching structure is typically used, with a vacuum contactor as the main switching switch and a solid-state relay as the pre-switching switch. The solid-state relay quickly disconnects the circuit first, followed by final isolation by the vacuum contactor. Switching operation control utilizes pre-charging and soft-switching technologies. Before switching, the voltage across the switch is equalized via a pre-charging circuit to minimize the voltage difference, and then the switch is controlled to operate. Precise timing control employs a precise timing program. The inverter-side switch is disconnected first, followed by a delay (typically 1-5 milliseconds) before disconnecting the load-side switch, ensuring the reliability of the switching process. Switch status monitoring is achieved through auxiliary contacts and arc detection devices, ensuring the accuracy and integrity of the switching operation. If a switch malfunction is detected, a backup switching circuit is activated or a fault alarm is issued. After switching is completed, the switching result is verified by measuring the voltage and current at various key points to confirm that the load has been fully transferred to the main grid. This precise and reliable zero-current switching technology enables the load to be 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.

[0122] This implementation method successfully solves the technical challenges of large impacts, poor reliability, and harmful effects on load equipment during load switching in traditional emergency power supply systems by implementing load switching operations based on flexible transfer and zero-current switching. It achieves a smooth, safe, and seamless transfer of load power. First, the flexible load transfer program employs a progressive power regulation strategy and a precise ramp control algorithm to ensure a smooth decrease in inverter output power, avoiding the impact of sudden power changes on the load. Compared to traditional hard switching methods, this 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 main grid power compensation mechanism, through a combination of droop control and active power regulation technology, achieves precise compensation from the main grid for the inverter power decrease, ensuring a stable power supply to the load throughout the transfer process and effectively avoiding voltage fluctuations or frequency deviations 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. It can accurately capture minute changes in inverter output current, providing a reliable data basis for zero-current switching judgment and avoiding inappropriate switching timing due to monitoring errors. Furthermore, zero-current switching technology, combined with precise threshold judgment and reliable switch control, enables the switch to operate at its minimum current, minimizing switch arcing and contact wear, extending the lifespan of the switching equipment, and improving system reliability and maintainability. Finally, the dual-switch structure and sophisticated timing control ensure absolute reliability of the switching process, enabling safe switching even in the event of a single switch failure. Compared to traditional load-bearing switching or simple time-delay switching methods, this flexible back-cutting technology achieves shock-free load transfer, providing emergency energy storage vehicles with a more advanced and reliable load management solution, significantly enhancing the technical level and practical value of emergency power supply systems.

[0123] In one embodiment of this example, after performing the load shedding operation, the method further includes the following steps:

[0124] S610, Disconnect the inverter from the main power grid in parallel;

[0125] S620 controls the emergency energy storage vehicle to enter standby charging mode or departure mode according to preset instructions.

[0126] Disconnecting the inverter from the main grid in parallel is a crucial safety measure after load shedding. Disconnecting the parallel connection involves the coordinated operation of multiple electrical devices, including key equipment such as parallel contactors, synchronization devices, and protective relays. In practice, the disconnection operation employs a step-by-step strategy. First, the inverter control system issues a disconnection command, which is simultaneously transmitted to all relevant control units. Disconnection timing control uses preset program logic to ensure that each device operates in the correct sequence, avoiding arcing, overcurrent, or equipment damage due to improper operation. The first step is to gradually reduce the circulating current between the inverter and the main grid. This is achieved by fine-tuning the inverter's output voltage and phase, gradually reducing the current flowing through the parallel branch to near zero. Circulating current control uses a precise current detection and feedback control algorithm to monitor the magnitude and direction of the current in the parallel branch in real time, actively controlling the circulating current by adjusting the inverter's output parameters. When the circulating current decreases to a preset safe level (typically below 1% of the rated current), the second step of the disconnection procedure is initiated. The second step involves controlling the parallel contactor to disconnect the physical connection between the inverter and the main grid. The contactors selected are either vacuum contactors or SF6 gas contactors, which have interrupting capacity and electrical life. Before the contactors operate, a pre-opening operation is performed, where an auxiliary contactor first disconnects the small current circuit, and then the main contactor operates to disconnect the main circuit. During the disconnection process, the contactor status is monitored in real time, including contact position, arc detection, and insulation condition, to ensure thorough and safe disconnection. The third step is system status verification and confirmation, using voltage detection, insulation testing, and other methods to confirm that the inverter is completely isolated from the main grid. After disconnection, the inverter automatically switches to standby mode, shuts down all outputs, and enters a safe non-operating state. This step-by-step, multi-protection disconnection operation ensures the safe isolation of the inverter from the main grid, creating safe conditions for subsequent mode switching.

[0127] The emergency energy storage vehicle enters the corresponding working mode according to preset instructions. The generation of these preset instructions is based on a comprehensive consideration of multiple factors, including remaining battery power, main grid stability, future load demand forecasts, and vehicle dispatch arrangements. Instruction generation employs a decision-making algorithm combining expert systems and fuzzy logic, establishing a detailed decision tree and rule base. The standby charging mode is suitable for situations where the main grid has stabilized and is expected to remain stable for an extended period. In this mode, the emergency energy storage vehicle remains in its original position, the inverter operates in charging mode, and uses the main grid to supplement the battery pack's charge. The implementation of the standby charging mode involves the coordinated operation of multiple subsystems: the charging system adopts an appropriate charging strategy based on the battery status, typically using a constant current-constant voltage charging method, with the charging current dynamically adjusted according to battery temperature and remaining capacity; the monitoring system continuously monitors the main grid and battery status, immediately switching to emergency response mode upon detecting any anomalies; and the communication system maintains contact with the dispatch center, reporting equipment status and location information. The off-site mode is suitable for situations where the emergency has ended, the main grid has returned to normal, and there is an emergency power supply demand at other locations. In off-site mode, the emergency energy storage vehicle performs pre-departure checks and preparations, including equipment status monitoring, battery charge assessment, and vehicle system checks. The off-site preparation process employs automated detection procedures, using sensors and diagnostic systems to comprehensively check key equipment, ensuring the vehicle is capable of safe operation and providing power for future emergencies. The mode selection logic is based on preset priority rules: when the battery charge is below a certain threshold, standby charging mode is prioritized; when a new emergency task instruction is received, off-site mode is prioritized; when the main power grid is unstable, standby mode is maintained without charging. The instruction execution process also includes a manual intervention function, allowing operators to manually select the operating mode based on the actual situation, overriding the automated decision-making results. Through this intelligent mode control, the emergency energy storage vehicle can flexibly adjust its operating status according to actual conditions, achieving optimal resource allocation and utilization.

[0128] After the standby charging mode is activated, system initialization is performed first, including device status checks, parameter settings, and communication link establishment. The charging subsystem formulates a detailed charging plan based on battery status information provided by the battery management system, taking into account factors such as the battery's current state of charge, health condition, temperature distribution, and charging history. The charging strategy employs an intelligent optimization algorithm to maximize charging efficiency while ensuring charging safety. In practice, the charging process is divided into several stages: the evaluation stage involves comprehensive battery testing, including key parameters such as individual cell voltage balance, internal resistance consistency, and temperature distribution; the pre-charging stage uses a small current to activate the battery, especially for batteries that have been stored for extended periods; the main charging stage uses the optimal charging curve based on battery characteristics, typically an improved constant current / constant voltage charging method; the equalization charging stage balances the individual cells within the battery pack to ensure voltage consistency; and the maintenance charging stage uses float charging to compensate for battery self-discharge. Temperature management during the charging process is achieved through an active thermal management system, including air cooling, liquid cooling, or phase change material cooling, to ensure the battery temperature remains within the optimal range. The safety monitoring system continuously monitors various parameters during the charging process, including current, voltage, temperature, and insulation resistance, and takes immediate protective measures upon detecting any abnormalities. The communication system regularly reports equipment status to the dispatch center, including charging progress, equipment health status, and estimated completion time. The standby charging mode also includes preventative maintenance functions, utilizing standby time to perform self-checks and calibrations on critical equipment, ensuring that the equipment is always in optimal working condition. Through this comprehensive standby charging management, efficient charging and equipment maintenance of the emergency energy storage vehicle are ensured during standby periods.

[0129] The departure mode is initiated based on dispatch instructions or preset departure conditions, including confirmation of emergency mission completion, good equipment condition, and restoration of main grid stability. The departure preparation process employs a standardized inspection procedure. First, the battery system is checked to assess remaining battery power, health status, and estimated usable time, ensuring it can meet the needs of the transfer process and subsequent emergency power supply. If battery power is insufficient, rapid charging is prioritized, using high-power charging to quickly raise battery power to a safe level. Equipment system checks include functional testing and performance verification of key equipment such as inverters, chargers, protection systems, and monitoring systems. Automated testing programs comprehensively inspect each subsystem to ensure all equipment is functioning correctly. Vehicle system checks involve testing basic vehicle functions such as the chassis, powertrain, braking system, and steering system to ensure safe driving capability. The communication system receives final confirmation from the dispatch center, receiving detailed transfer instructions including target location, route planning, and time requirements. Data backup and transmission before departure ensure that all operational data and event records during this emergency power supply process are completely preserved, providing data support for subsequent analysis and improvement. The safety protection system automatically activates the transportation protection mode, including measures such as physical securing of the equipment, electrical isolation, and vibration protection, to ensure the safety of the equipment during transportation. The departure status monitoring and reporting function ensures that the dispatch center can understand the vehicle's location, status, and estimated arrival time in real time, providing accurate information for the unified dispatch of emergency resources. Through this systematic departure management, the emergency energy storage power vehicle can quickly and safely complete task transitions and relocations.

[0130] This implementation method improves the overall technical solution for uninterrupted power supply to emergency energy storage vehicles by implementing subsequent management operations such as disconnecting parallel connections and intelligent mode switching, achieving intelligent management of the entire process from emergency power supply to mission completion. First, the step-by-step, multi-protection parallel disconnection operation ensures the safe isolation of the inverter from the main grid. Through precise circulating current control and timing management, dangerous situations such as arcing and inrush currents that may occur during the disconnection process are avoided, protecting equipment safety and extending equipment lifespan. Compared with the traditional simple disconnection method, this significantly improves the safety and reliability of the operation. Second, the intelligent mode selection mechanism based on expert systems and fuzzy logic can automatically select the most suitable subsequent working mode according to the actual situation, considering both equipment status and grid conditions, as well as the unified scheduling needs of emergency resources, achieving optimal allocation and efficient utilization of emergency power supply resources. Third, the precise management of the standby charging mode not only achieves efficient battery replenishment and charging, but also ensures the continuous availability of the equipment through preventive maintenance and equipment self-checking functions, making full preparations for the next emergency mission, reflecting the forward-looking and systematic nature of emergency equipment management. Furthermore, the systematic management of the off-site mode ensures that emergency energy storage vehicles can quickly and safely complete mission transitions. Comprehensive equipment checks and status verification guarantee vehicle safety during transfer and immediate availability upon arrival at the new mission location. Finally, comprehensive status monitoring and communication reporting functions enable transparent management of emergency resources, providing accurate information support for unified command and optimized resource allocation at the dispatch center. Compared to the traditional method of simply disconnecting emergency power supply equipment after a mission, this intelligent post-operation management technology significantly improves the management level and utilization efficiency of the emergency power supply system.

[0131] In one embodiment of this invention, controlling the inverter output to synchronize with the main power grid via phase-locked loop includes the following steps:

[0132] S710 uses a phase-locked loop circuit to align the voltage, frequency, and phase of the inverter output with the voltage, frequency, and phase of the main grid.

[0133] Reference Figure 4Precise synchronization between the inverter output and the main grid via a phase-locked loop (PLL) circuit ensures safe parallel operation. This technology, based on the phase-locked principle, uses a closed-loop control system to ensure that the inverter's output voltage, frequency, and phase are completely consistent with the main grid parameters. The PLL circuit mainly consists of three core components: a phase detector, a loop filter, and a voltage-controlled oscillator (VCO). The phase detector, as the system's comparison unit, is responsible for detecting the phase difference between the main grid voltage signal and the inverter's internal reference signal. In practice, a digital phase detector is used to achieve high-precision phase comparison. The phase detector uses the three-phase voltage signal from the main grid as a reference input, samples and digitizes it, and then compares its phase with the reference signal generated internally by the inverter. The phase difference is calculated using the arctangent function method, by simultaneously sampling the sine and cosine components of the voltage signal to calculate the instantaneous phase angle, with the formula: 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 from the phase detector, and generates a control voltage through low-pass filtering and integration. The design parameters of the filter directly affect the dynamic performance and stability of the phase-locked loop (PLL). The voltage-controlled oscillator (VCO) adjusts its output frequency according to the control voltage output from the filter, achieving automatic frequency and phase tracking. When the phase difference is zero, it indicates that the inverter output is fully synchronized with the main grid, at which point the PLL enters a locked state. This precise phase-locked control ensures that the inverter can achieve millisecond-level rapid synchronization with the main grid.

[0134] This implementation method effectively solves the synchronization problem when the inverter is connected in parallel with the main grid by implementing precise synchronization control technology based on phase-locked loop (PLL). It achieves high-precision alignment of voltage, frequency, and phase, creating the necessary conditions for safe parallel operation. The rapid dynamic response capability allows the inverter to quickly track and adjust when the main grid parameters change, maintaining the stability of the synchronization state. The digital PLL design improves the system's anti-interference capability and long-term stability, offering higher accuracy and reliability compared to traditional analog PLLs. This synchronization technology provides a solid technical foundation for the safe parallel operation and flexible switching of emergency energy storage power vehicles.

[0135] In one embodiment of this invention, 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:

[0136] S810: Collect the main grid voltage as the input signal for the phase-locked loop circuit;

[0137] S820: The phase difference signal is obtained by comparing the phase of the input signal with the phase of the output signal generated by the voltage-controlled oscillator inside the inverter using a phase detector.

[0138] S830. The phase difference signal obtained from the comparison is filtered through a low-pass filter;

[0139] S840: The output frequency of the voltage-controlled oscillator is controlled by the filtered phase difference signal.

[0140] S850: 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. Here, phase-locked synchronization means that the voltage, frequency and phase of the inverter output are aligned with the voltage, frequency and phase of the main grid.

[0141] Acquiring the main grid voltage signal is a fundamental step for the normal operation of a phase-locked loop (PLL) circuit. Real-time acquisition and preprocessing of the grid voltage are achieved through voltage sensors and signal conditioning circuits. The grid voltage acquisition utilizes precision voltage transformers or Hall effect voltage sensors, enabling accurate measurement of the three-phase voltage signals of the grid.

[0142] The signal conditioning circuit includes an amplifier, a filter, and a level shifter, adjusting the acquired voltage signal to an amplitude and format suitable for digital processing. The amplifier employs an instrumentation amplifier architecture, featuring high input impedance, low noise, and a high common-mode rejection ratio. The amplification factor is typically set between 1 and 10, adjusted according to the input range of the subsequent ADC. The anti-aliasing filter uses a 4th-order Butterworth low-pass filter with a cutoff frequency set to 1kHz, effectively filtering out high-frequency interference and noise. The analog-to-digital converter (ADC) uses a 16-bit high-precision ADC with a sampling frequency set to 10kHz, ensuring accurate capture of the waveform details of the mains voltage.

[0143] The phase comparison function of the phase detector is a core technical component for achieving precise phase locking in a phase-locked loop (PLL) circuit. It generates a control signal by detecting the phase difference between the input signal and an internal reference signal. The phase detector employs a digital phase detector structure, utilizing digital signal processing technology to achieve high-precision phase detection and comparison. The digital phase detector first synchronously samples the input mains voltage signal and the voltage-controlled oscillator (VCO) output signal. The sampling frequency is typically set to at least 200 times the fundamental frequency; for a 50Hz power frequency signal, the sampling frequency is at least 10kHz. Phase detection uses the Discrete Fourier Transform (DFT) method, determining the instantaneous phase angle by calculating the real and imaginary parts of the signal. Specifically, the sampled voltage signal is correlated with sine and cosine reference signals of the same frequency to obtain the quadrature components of the signals. The formula for calculating 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.

[0144] To improve phase detection accuracy, interpolation algorithms and window function techniques are employed. Interpolation improves time resolution by interpolating between sampling points, while window function techniques reduce spectral leakage by selecting appropriate window functions. The phase detector also features phase unwrapping functionality; when the phase difference exceeds ±π, it automatically performs addition and subtraction operations of 2π to ensure the phase difference remains within a reasonable range. The phase difference signal output is linearized, converting the phase difference into a proportional voltage signal. The conversion coefficient is typically set to 1V / π, meaning the output voltage is 1V when the phase difference is π. The phase detector's dynamic range is designed to be ±2π, enabling it to handle large initial phase differences and ensuring the phase-locked loop can capture and lock from any initial state. This high-precision digital phase detection technology achieves phase difference detection accuracy at the micro-radian level, providing accurate error signals for subsequent frequency control.

[0145] The low-pass filter processes the phase difference signal, obtaining a smooth control signal by filtering out high-frequency noise and interference. The filter employs an active low-pass filter structure, based on an operational amplifier and an RC network. The filter's transfer function is designed to have second-order Butterworth property, and the transfer function is:

[0146] ;

[0147] Where ωn is the natural frequency, set to approximately 1 / 10 of the system bandwidth, typically within the range of 5-50Hz. The quality factor Q is set to 0.707 to ensure the filter has a flat passband and a moderate transition band steepness. The filter's cutoff frequency is determined based on the expected bandwidth and noise characteristics of the phase-locked loop (PLL). A lower cutoff frequency provides better noise suppression but reduces the system's dynamic response speed; a higher cutoff frequency provides a faster response speed but may introduce more high-frequency noise. In practical designs, the cutoff frequency is typically set to 1 / 5-1 / 10 of the desired PLL bandwidth. The filter also features gain adjustment, allowing the DC gain of the filter to be changed by adjusting the feedback resistor; the gain range is typically set to 0.1-10 times. To improve the filter's phase characteristics, phase lead or lag compensation networks can be added to compensate for phase delays introduced by other components in the loop. The filter's output is impedance matched through a buffer amplifier to ensure it can drive the subsequent voltage-controlled oscillator (VCO) circuit. The filter is also equipped with a saturation limiting circuit to prevent saturation distortion under large signal input conditions. By using low-pass filtering, the smoothness and stability of the control signal are ensured, while maintaining the necessary dynamic response capability of the system.

[0148] A voltage-controlled oscillator (VCO) adjusts its output frequency based on a filtered phase difference signal, achieving precise frequency regulation through voltage control. VCOs employ either an LC oscillator or a crystal oscillator structure. An LC oscillator is based on a resonant circuit composed of an inductor and a varactor diode. The resonant frequency is changed by altering the reverse bias voltage of the varactor diode to adjust the equivalent capacitance. The formula for calculating the oscillation frequency is:

[0149] ;

[0150] Where L is the inductance and C is the equivalent capacitance. The relationship between the capacitance of a varactor diode and the control voltage is usually: C(V) = C0 / (1 + V / V) j ) n Where C0 is the zero-bias capacitor, V is the control voltage, and V j Let n be the junction potential and n be the varactor exponent. The frequency control sensitivity (Kv) of the voltage-controlled oscillator is defined as the ratio of frequency change to control voltage change, in Hz / V. To improve frequency stability, the oscillator employs temperature compensation technology, using a temperature sensor to detect ambient temperature and compensate accordingly for the oscillation frequency. Frequency calibration is achieved by comparison with a high-precision frequency reference, and periodic automatic calibration ensures long-term frequency stability. The oscillator output is isolated and amplified by a buffer amplifier, and the output waveform is shaped into a standard square wave signal, with the amplitude typically set to 5V CMOS level. Through the voltage-controlled oscillator, precise frequency control and rapid adjustment are achieved, providing a reliable frequency source for stable locking of the phase-locked loop.

[0151] Finally, the magnitude and stability of the phase difference signal are monitored to determine whether synchronization has been achieved and appropriate locking measures are taken. Synchronization determination employs a combination of multiple criteria to ensure the accuracy and reliability of the results. The main criteria include phase difference amplitude, phase difference stability, and frequency deviation. The phase difference amplitude criterion requires that the absolute value of the filtered phase difference signal be less than a preset threshold, typically set at ±0.1V, corresponding to a phase error of approximately ±5.7°. The phase difference stability criterion requires that the phase difference signal remain stable within a continuous time window, typically set at 10-50 power frequency cycles, or 0.2-1 seconds. Stability is assessed by calculating the standard deviation of the phase difference signal; a standard deviation less than a set threshold indicates signal stability. The frequency deviation criterion requires that the output frequency of the voltage-controlled oscillator deviate from the grid frequency by less than ±0.01Hz, monitored in real-time by a frequency counter. When all criteria are met simultaneously, the phase-locked loop (PLL) enters a locked state. The locking control employs a hierarchical locking strategy, including coarse locking and fine locking stages. The coarse locking stage allows for larger phase errors and frequency deviations, primarily to quickly bring the voltage-controlled oscillator (VCO) frequency close to the grid frequency. The fine locking stage requires even stricter synchronization accuracy to ensure the final locking quality. Maintaining the locked state is achieved through a lock-in detector and a holding circuit. The lock-in detector continuously monitors the synchronization status and immediately restarts the phase-locking process when a loss of lock is detected. The holding circuit fine-tunes the control voltage of the VCO in the locked state to compensate for frequency drift caused by temperature changes, component aging, and other factors. Lock-in indication is provided via LED indicators and digital signal output, offering intuitive status information to operators and the control system. The lock-in time measurement and recording function provides data support for system performance evaluation and optimization; typical lock-in times are in the range of 0.5-2 seconds. Through synchronization determination and reliable lock-in control, high-precision synchronization between the inverter output and the main grid is ensured, creating ideal conditions for safe parallel operation.

[0152] This implementation method successfully achieves high-precision alignment of the inverter output with the main grid voltage, frequency, and phase by implementing precision synchronization control technology based on a phase-locked loop (PLL) circuit, effectively solving the synchronization problem when power electronic equipment is connected in parallel with the grid. First, high-precision grid voltage acquisition and signal conditioning technology ensures that the PLL obtains an accurate and stable reference signal. Multiple filtering and calibration measures effectively suppress the impact of noise and interference on synchronization accuracy, laying a solid foundation for the entire phase-locking process. Second, phase detection technology based on digital signal processing achieves micro-radian-level phase difference detection accuracy, which has higher accuracy and stronger anti-interference capability compared to traditional analog phase detectors, ensuring the accuracy and reliability of phase comparison. Third, a carefully designed low-pass filter maintains the system's dynamic response capability while ensuring the smoothness of the control signal, achieving an optimal balance between noise suppression and fast response through reasonable parameter selection. Furthermore, 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 PLL. Finally, the multi-criteria synchronization determination and hierarchical locking control strategy ensure the accuracy and reliability of the phase-locked loop (PLL) process, with typical synchronization accuracy reaching within ±0.1° phase error and ±0.01Hz frequency deviation. Compared with traditional simple synchronization methods, this PLL synchronization technology significantly improves synchronization accuracy and reliability, providing key technical support for the safe parallel connection and smooth switching of emergency energy storage power vehicles, and effectively guaranteeing the safe operation and high-quality service of uninterruptible power supply systems.

[0153] In one embodiment of this invention, in the parallel connection state, the method further includes the following steps:

[0154] S910, Control the inverter to inject a periodic frequency disturbance signal into its output current;

[0155] S920: Real-time monitoring of the AC voltage frequency at the grid connection point to obtain a real-time frequency value that includes the response to disturbance signals;

[0156] S930: Through positive feedback gain, the deviation between the real-time frequency value and the preset grid nominal frequency is amplified, and the inverter's output frequency command is adjusted according to the amplified deviation.

[0157] S940: Continuously determine whether the real-time frequency value exceeds the preset frequency protection threshold due to positive feedback gain;

[0158] S950: When the real-time frequency value exceeds the frequency protection threshold, it is determined that an islanding effect has been formed, and the inverter is immediately controlled to stop output in order to disconnect the inverter from the main grid.

[0159] Periodic frequency disturbance signals can be generated by superimposing a specific frequency disturbance into the inverter output current for active detection of grid connection status. The disturbance signal employs sinusoidal modulation, with the frequency typically selected within the 1-5Hz range and the amplitude controlled within 1%-3% of the rated current to ensure no impact on normal power supply. The disturbance signal is generated using a digital signal processor, employing direct digital frequency synthesis (DPS) to produce a high-precision sinusoidal waveform. Injection control uses current superposition, vector-superimposing the disturbance signal with the basic output current and modulating it into the inverter output via a PWM controller. The phase and amplitude of the disturbance signal can be dynamically adjusted according to detection needs, improving detection sensitivity and reliability.

[0160] Real-time monitoring of the AC voltage frequency at the grid connection point is achieved through a high-precision frequency detection circuit, employing a combination of zero-point detection and digital phase-locked loop (PLL) technology. The frequency detection circuit continuously samples the voltage signal at the grid connection point, with a sampling frequency set above 10kHz to ensure accurate capture of minute frequency changes. The detection algorithm uses a sliding window DFT method to calculate the fundamental frequency of the voltage signal in each detection cycle. When the inverter injects a frequency disturbance, if the grid connection is normal, the disturbance signal will be absorbed by the large grid, resulting in minimal frequency change; however, if islanding occurs, the disturbance signal will cause a significant frequency shift. The monitoring system can capture these frequency changes in real time, providing accurate data for islanding detection.

[0161] Positive feedback gain amplification technology accelerates the islanding detection process and improves detection speed and sensitivity by amplifying frequency deviation. The deviation between the monitored frequency value and the nominal frequency of 50Hz is calculated in real time using the formula: Δf = fm - fn. The positive feedback gain K is typically set in the range of 10-50, and the amplified deviation is: Δfa = K × Δf. The amplified deviation signal is used to adjust the inverter's output frequency command, forming a positive feedback loop. Under normal grid-connected conditions, the strong support of the large power grid keeps the frequency deviation within a small range, and the positive feedback effect is not significant. However, in islanded conditions, after losing grid support, the positive feedback effect rapidly amplifies the frequency deviation, causing the frequency to deviate rapidly from the nominal value.

[0162] The frequency protection threshold is typically set to ±0.5Hz, meaning protection is triggered when the frequency exceeds the range of 49.5Hz-50.5Hz. The judgment logic employs a continuous judgment mechanism, requiring the frequency to exceed the threshold for multiple consecutive detection cycles before confirming an islanded state, thus avoiding false triggers caused by momentary interference. The judgment period is typically set to 10-50 milliseconds, ensuring detection and protection actions are completed within 2 seconds of islanding formation.

[0163] The confirmation and disconnection control of the islanding effect is the final execution stage of the protection system. Upon confirmation of islanding, the inverter is immediately stopped from outputting. The disconnection control employs a multi-layered protection strategy, including both 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 using relays or contactors, ensuring reliable disconnection. The disconnection process also includes fault logging and status indication functions, providing information support for subsequent fault analysis and recovery operations.

[0164] This implementation method effectively solves the islanding detection problem in distributed power generation grid-connected operation by implementing islanding detection technology based on active frequency disturbance, significantly improving the safety and reliability of grid operation. The combination of periodic frequency disturbance signal injection and positive feedback gain amplification technology enables rapid and accurate detection of islanding conditions, with a detection time typically within 2 seconds and detection accuracy reaching international advanced levels. Real-time frequency monitoring and multi-level protection threshold judgment ensure the high reliability of the detection system, effectively avoiding malfunctions and missed actions. Compared with traditional passive detection methods, this active detection technology has higher detection sensitivity and shorter detection time, making it particularly suitable for load-generation power matching situations. A comprehensive disconnection control and protection mechanism ensures timely and reliable disconnection of the inverter after islanding is detected, avoiding potential safety hazards caused by islanding operation.

[0165] This application also provides an uninterruptible power supply system, including:

[0166] The memory is configured to store instructions; and

[0167] The processor is configured to retrieve instructions from memory and, when executing instructions, to implement the aforementioned uninterrupted power supply method based on an emergency energy storage vehicle.

[0168] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0169] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, as well as combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0170] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0171] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0172] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0173] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, such as read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0174] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, 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, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0175] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.

[0176] The above are merely embodiments of this application and are not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for uninterrupted power supply based on an emergency energy storage vehicle, characterized in that, The method includes: In response to a fault signal from the main power grid, the emergency energy storage vehicle is controlled to supply power to the target load through its built-in inverter. Real-time monitoring of the main power grid status to detect recovery signals from the main power grid; In response to the detection of a recovery signal from the main grid, the inverter output is controlled to be phase-locked and synchronized with the main grid. After phase-locked synchronization is completed, the control inverter is connected in parallel with the main grid. In the parallel connection state, the emergency energy storage power vehicle continuously supplies power to the target load independently through the inverter. In parallel connection mode, the power quality parameters of the main power grid are acquired in real time, and the main power grid is determined to meet the grid stability conditions based on the power quality parameters. When the main power grid meets the grid stability conditions, a flexible load transfer procedure is initiated, and the output power of the inverter is reduced within a preset transfer time. During the process of inverter output power reduction, 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 inverter output side; When the feedback current value is less than the preset zero current threshold, it is determined that the load has been fully 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. When the main power grid does not meet the grid stability conditions, the emergency energy storage power vehicle is controlled to enter the buffer power supply mode. In buffered power supply mode, obtain the current charging status of the battery pack; Based on the current charging status, the current charging stage is determined in the preset charging strategy, wherein the charging strategy includes at least a constant current charging stage and a constant voltage charging stage. Based on the current charging stage, a corresponding charging power command is generated to control the inverter to draw charging power from the main grid to be equal to the set value of the charging power command. At the same time, the inverter continuously provides isolated and stable power supply to the target load through the rectifier, so that the current drawn from the main grid and the grid voltage remain in phase. The rectifier controls the rectified current phase to match the voltage phase by detecting the phase information of the main grid voltage. It also employs a soft-start strategy, gradually increasing the current from zero power to a set value to prevent impact on the unstable main grid. The inverter provides stable power supply through a high-frequency isolation transformer and a power filter circuit. The high-frequency isolation transformer connects to the inverter output on the primary side and to the load on the secondary side for electrical isolation. The power filter circuit includes an LC filter and an active filter. The LC filter removes high-frequency components of the inverter's switching frequency, while the active filter compensates for harmonic components in the load current.

2. The method according to claim 1, characterized in that, Determining whether the main power grid meets the grid stability conditions based on power quality parameters includes: When the power quality parameters all meet the corresponding stability parameter thresholds within a preset duration window, the main power grid is determined to meet the grid stability conditions. 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, After performing the load shedding operation, the method also includes: Disconnect the inverter from the main power grid; The emergency energy storage vehicle can be controlled to enter standby charging mode or departure mode according to preset instructions.

4. The method according to claim 1, characterized in that, The inverter output is synchronized with the main power grid via phase-locking, including: The phase-locked loop circuit is used to align the voltage, frequency, and phase of the inverter output with the voltage, frequency, and phase of the main grid.

5. The method according to claim 4, characterized in that, The inverter's output voltage, frequency, and phase are aligned with those of the main grid using a phase-locked loop (PLL) circuit, including: The main grid voltage is collected as the input signal for the phase-locked loop circuit; The phase difference signal is obtained by comparing the phase of the input signal with the phase of the output signal generated by the voltage-controlled oscillator inside the inverter using a phase detector. The phase difference signal obtained from the 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. Phase-locked synchronization means that the voltage, frequency, and phase of the inverter output are aligned with the voltage, frequency, and phase of the main grid.

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

7. An uninterruptible power supply system, characterized in that, include: The memory is configured to store instructions; as well as The processor is configured to retrieve the instructions from the memory and, when executing the instructions, to implement the uninterrupted power supply method based on an emergency energy storage vehicle according to any one of claims 1 to 6.

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