Ship hybrid energy storage support method and system based on dc bus voltage droop

Abstract

The application discloses a ship hybrid energy storage support method and system based on DC bus voltage droop, and particularly relates to the technical field of energy storage control of a ship power system, and is used for solving the problem of voltage secondary drop and reverse power impact caused by inaccurate identification of actual load bearing state of a standby generator set in the existing anti-power-loss support after the energy storage exits the stage. The product of a modulation ratio instruction value and a DC bus voltage value in a discharging process is calculated, a normalized residual error of an actual output active power value is taken as a decoupling deviation, the standby generator set starts to bear the load is determined, the power gap of the power grid is calculated based on a voltage recovery deviation and a frequency change rate from the determination, a second droop coefficient is used to dynamically adjust the discharging power of the energy storage so that the discharging power decreases with the reduction of the power gap of the power grid, in the decreasing process, the increment ratio of the voltage and the power is taken as a dynamic impedance value to predict the risk of reverse energy flow and suspend the adjustment of the droop coefficient, and the discharging of the energy storage is stopped until the voltage and the frequency are restored to the steady state.

Description

Technical Field

[0001] This invention relates to the field of energy storage control technology for ship power systems, and more specifically, to a method and system for supporting hybrid energy storage in ships based on DC bus voltage droop. Background Technology

[0002] In existing technologies, marine hybrid energy storage systems form a DC grid through a shaft-driven generator, lithium battery pack, and frequency converter. An energy management system controls the power-frequency droop of the energy storage units and grid-side inverters. When the generator or shaft-driven generator fails and disconnects from the grid, the energy storage system detects the DC bus voltage drop and discharges to the grid, providing power loss protection. Once the standby generator starts and completes voltage establishment and grid connection, the energy storage system exits the discharge state, and the grid returns to normal power supply mode.

[0003] However, in the aforementioned control process, the timing of the energy storage system's discharge termination depends on the assessment of the grid's recovery status. Since the process from generator startup and voltage establishment to grid synchronization inherently involves a non-negligible time delay, and the recovery of grid voltage and frequency during this process is not instantaneous, if the energy storage system terminates too early, a power gap will occur in the grid during the gap between the loss of energy storage support and the generator's failure to actually bear the load, leading to a secondary voltage drop. If the energy storage termination is delayed to avoid the aforementioned risks, power distribution conflicts may occur between the grid-connected energy storage system and the generator after the generator has stabilized its output, potentially triggering reverse power or overvoltage surges. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the present invention provides a ship hybrid energy storage support method and system based on DC bus voltage droop to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A shipboard hybrid energy storage support method based on DC bus voltage droop includes the following steps: S1: Obtain the DC bus voltage value, grid-side inverter output frequency value, modulation ratio command value, and actual output active power value; S2: When the DC bus voltage value drops below the preset drop threshold, control the energy storage system to discharge with the first droop coefficient and record the steady-state voltage value of the DC bus before the drop. S3: During the discharge process, the normalized residual of the product of the modulation ratio command value and the DC bus voltage value and the actual output active power value is calculated as the decoupling deviation. When the decoupling deviation jumps from the low value range to the high value range and remains there for more than the preset time, it is determined that the standby generator set begins to bear the load. S4: From the moment the load is determined, the grid power gap is calculated based on the difference between the DC bus voltage and the steady-state voltage and the rate of change of the grid-side inverter output frequency. The energy storage discharge power is adjusted with the second droop coefficient so that it decreases as the grid power gap shrinks. S5: During the decreasing process, the incremental ratio of the DC bus voltage value to the actual output active power value is calculated as the dynamic impedance value; when the dynamic impedance value changes from positive to negative and its absolute value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive. S6: When the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range, stop the energy storage system from discharging.

[0006] Furthermore, S1 includes: The DC bus voltage value is acquired from the DC bus voltage sensor; Obtain the output frequency value and modulation ratio command value of the grid-side inverter from the grid-side inverter controller; The actual output active power value is obtained from the power calculation unit at the output end of the grid-side inverter.

[0007] Furthermore, S2 includes: The acquired DC bus voltage value is continuously compared with the preset drop threshold at multiple points. When the DC bus voltage value is lower than the preset drop threshold at multiple points, it is confirmed that the DC bus voltage value has fallen below the preset drop threshold. After confirming the drop, the first droop coefficient is determined from the droop coefficient interval mapping table based on the rate of change of the DC bus voltage value before the drop, and the energy storage system discharge is controlled by the first droop coefficient. When a voltage drop is confirmed, the average value of the stable sampled values ​​of the DC bus voltage within the preset time period before the drop is recorded as the steady-state voltage value of the DC bus.

[0008] Furthermore, S3 includes: Multiply the modulation ratio command value by the DC bus voltage value to obtain the theoretical value of active power output; Calculate the difference between the actual output active power value and the theoretical active power output value, and divide the difference by the actual output active power value to obtain the decoupling deviation. The decoupling deviation is compared with the upper limit of the preset low value range and the lower limit of the preset high value range. When the decoupling deviation changes from being lower than the upper limit of the preset low value range to being higher than the lower limit of the preset high value range, and remains in this state for more than a preset time, it is determined that the standby generator set begins to bear the load.

[0009] Further, the decoupling deviation is obtained by dividing the difference by the actual output active power value, including: applying a sliding window mean filter to the actual output active power value; calculating the difference between the filtered actual output active power value and the theoretical active power output value to obtain the filtered difference; and dividing the filtered difference by the filtered actual output active power value to obtain the decoupling deviation.

[0010] Furthermore, S4 includes: From the moment when the standby generator set is determined to start assuming load, the difference between the DC bus voltage value and the steady-state voltage value is calculated as the voltage recovery deviation; Calculate the change in the deviation between the grid-side inverter output frequency value and the rated frequency value per unit time, and use it as the rate of change of the grid-side inverter output frequency value. The grid power gap is obtained by multiplying the voltage recovery deviation with the rate of change of the grid-side inverter output frequency. The second droop coefficient is determined from the preset droop coefficient mapping table based on the power gap in the power grid, and the discharge power of the energy storage system is controlled by the second droop coefficient so that the discharge power of the energy storage system decreases as the power gap in the power grid shrinks.

[0011] Furthermore, S5 includes: As the discharge power of the energy storage system decreases with the shrinking power gap in the grid, the first difference between the DC bus voltage value at the current sampling time and the previous sampling time is calculated, and the second difference between the actual output active power value at the current sampling time and the previous sampling time is calculated. The ratio of the first difference to the second difference is used as the dynamic impedance value. When the dynamic impedance value changes from positive to negative and the absolute value of the dynamic impedance value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused, and the energy storage system continues to discharge with the droop coefficient at the pause time. During the pause, the dynamic impedance value is continuously calculated. When the dynamic impedance value returns to a positive value, the discharge power of the energy storage system is adjusted by the second droop coefficient.

[0012] Furthermore, the ratio of the first difference to the second difference is used as the dynamic impedance value, including: performing a ratio calculation on the first difference of the DC bus voltage value and the second difference of the actual output active power value at multiple consecutive sampling times, performing exponential smoothing filtering on the ratio results at multiple consecutive sampling times, and using the filtered ratio results as the dynamic impedance value; the preset impedance change threshold is determined according to the percentage of the initial dynamic impedance value when the energy storage system discharges with the first droop coefficient.

[0013] Furthermore, S6 includes: The DC bus voltage value is continuously compared with the steady-state voltage value at multiple points. When the DC bus voltage value falls within the preset recovery range centered on the steady-state voltage value at multiple consecutive sampling times, it is confirmed that the DC bus voltage value has recovered to the steady-state voltage value. The grid-side inverter output frequency value is continuously compared with the rated frequency range at multiple points. When the grid-side inverter output frequency value falls within the rated frequency range at multiple consecutive sampling times, it is confirmed that the grid-side inverter output frequency value is stable within the rated frequency range. The energy storage system stops discharging when both the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range.

[0014] On the other hand, the present invention provides a shipboard hybrid energy storage support system based on DC bus voltage droop, comprising the following modules: The parameter acquisition module is used to acquire the DC bus voltage value, the grid-side inverter output frequency value, the modulation ratio command value, and the actual output active power value. The drop control module is used to control the energy storage system to discharge with a first droop coefficient when the DC bus voltage value drops below the preset drop threshold, and to record the steady-state voltage value of the DC bus before the drop. The decoupling determination module is used to calculate the normalized residual of the product of the modulation ratio command value and the DC bus voltage value and the actual output active power value during the discharge process as the decoupling deviation degree; when the decoupling deviation degree jumps from the low value range to the high value range and remains for more than the preset time, it is determined that the standby generator set begins to bear the load. The power regulation module is used to calculate the grid power gap based on the difference between the DC bus voltage and the steady-state voltage and the rate of change of the grid-side inverter output frequency, starting from the time the load is determined. It then adjusts the energy storage discharge power with a second droop coefficient so that it decreases as the grid power gap shrinks. The impedance monitoring module is used to calculate the incremental ratio of the DC bus voltage value to the actual output active power value as the dynamic impedance value during the decreasing process; when the dynamic impedance value changes from positive to negative and its absolute value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive. The recovery stop module is used to stop the energy storage system from discharging when the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. By introducing decoupling deviation as the criterion for determining the load borne by the standby generator set, the timing of the energy storage system's discharge termination no longer depends on the passive waiting for the voltage or frequency to recover to a fixed threshold. Instead, it directly captures the physical moment when the coupling relationship between the grid-side inverter's modulation ratio command value and output power is broken. This allows for accurate identification of the generator set's active power injection into the grid even when the generator set's speed and voltage are still fluctuating. This precisely aligns the starting point of the energy storage support's decline with the actual output time of the generator set, fundamentally avoiding the dilemma in existing technologies where premature energy storage termination due to judgment lag leads to a secondary voltage drop, or premature energy storage termination due to judgment lag leads to a power conflict.

[0016] 2. During the energy storage discharge power reduction process, the grid power gap is calculated by comprehensively considering the voltage recovery deviation and the rate of change of the grid-side inverter output frequency. This gap is then dynamically mapped to a second droop coefficient, enabling the energy storage exit rate to adaptively match the actual loading capacity of the generator set. This avoids the problem of incoordination between the exit rate and the generator set response under a fixed slope exit method. At the end of the reduction period, a dynamic impedance value is introduced as a predictive indicator of reverse energy flow risk. By detecting the polarity reversal of the ratio of the DC bus voltage value to the actual output active power value increment, the reduction adjustment of the energy storage discharge power is suspended before the power flow actually reverses. This shifts the response timing of reverse power suppression from post-event protection to pre-event intervention, ensuring a smooth transition during grid recovery and safe operation of equipment. Attached Figure Description

[0017] Figure 1 This is a flowchart of the ship hybrid energy storage support method based on DC bus voltage droop according to the present invention; Figure 2 This is a schematic diagram of the ship hybrid energy storage support system based on DC bus voltage droop according to the present invention. Detailed Implementation

[0018] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] Example 1: Figure 1 The present invention provides a ship hybrid energy storage support method based on DC bus voltage droop, which includes the following steps: S1: Obtain the DC bus voltage value, grid-side inverter output frequency value, modulation ratio command value, and actual output active power value; S2: When the DC bus voltage value drops below the preset drop threshold, control the energy storage system to discharge with the first droop coefficient and record the steady-state voltage value of the DC bus before the drop. S3: During the discharge process, the normalized residual of the product of the modulation ratio command value and the DC bus voltage value and the actual output active power value is calculated as the decoupling deviation. When the decoupling deviation jumps from the low value range to the high value range and remains there for more than the preset time, it is determined that the standby generator set begins to bear the load. S4: From the moment the load is determined, the grid power gap is calculated based on the difference between the DC bus voltage and the steady-state voltage and the rate of change of the grid-side inverter output frequency. The energy storage discharge power is adjusted with the second droop coefficient so that it decreases as the grid power gap shrinks. S5: During the decreasing process, the incremental ratio of the DC bus voltage value to the actual output active power value is calculated as the dynamic impedance value; when the dynamic impedance value changes from positive to negative and its absolute value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive. S6: When the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range, stop the energy storage system from discharging.

[0020] In S1, the DC bus voltage, grid-side inverter output frequency, modulation ratio command, and actual output active power are acquired. The DC bus voltage is collected in real time from a voltage divider-type voltage detection device connected between the positive and negative terminals of the DC bus. This device uses a precision resistor network to convert the high-voltage DC bus voltage into a low-voltage signal matching the input range of the analog-to-digital converter (ADC). The ADC converts this low-voltage signal into a digital quantity at a sampling rate of at least kilohertz. The converted digital quantity is then linearly calibrated to obtain the DC bus voltage value in volts. The DC bus voltage directly reflects the energy supply and demand balance on the DC side for the energy storage system, grid-side inverter, and any generator sets that may be connected.

[0021] The output frequency of the grid-side inverter is read in real time from the main control loop of the grid-side inverter. The main control loop calculates the frequency of the current output AC voltage by detecting the zero-crossing point of the output voltage of the grid-side inverter and tracking the phase change using a phase-locked loop. The output frequency of the grid-side inverter is in Hertz, reflecting the frequency at which the grid-side inverter transmits AC power to the ship's power grid. The modulation ratio command value is also obtained from the main control loop of the grid-side inverter. The modulation ratio command value is the ratio of the amplitude of the reference signal to the amplitude of the carrier signal, which is generated in real time by the voltage amplitude closed-loop regulation algorithm when the grid-side inverter is performing sinusoidal pulse width modulation. The modulation ratio command value determines the proportional relationship between the fundamental amplitude of the inverter's output AC voltage and the current DC bus voltage value. The modulation ratio command value is dimensionless and can continuously vary between zero and the maximum linear modulation ratio.

[0022] The actual output active power value is obtained by acquiring instantaneous current and voltage signals from current and voltage detection devices installed at the output of the grid-side inverter. First, the instantaneous power is obtained by multiplying in the analog domain. Then, the average active power component is extracted by an analog low-pass filter with a cutoff frequency lower than the output fundamental frequency. Finally, it is converted into a digital form of the actual output active power value in watts by an analog-to-digital converter. The actual output active power value reflects the active power currently being delivered by the grid-side inverter to the ship's power grid.

[0023] The DC bus voltage, grid-side inverter output frequency, modulation ratio command, and actual output active power are all periodically transmitted to the control device executing this method via a real-time data bus. The transmission period is no longer than one fundamental frequency cycle corresponding to the grid-side inverter output frequency to ensure the real-time performance and accuracy of calculations in subsequent steps. The acquisition of these values ​​does not depend on a specific communication protocol and can utilize conventional industrial fieldbuses such as Controller Area Networks (CLAN) or Ethernet. The acquisition of the DC bus voltage is not affected by the connection of the DC bus insulation monitoring device. The reading of the grid-side inverter output frequency and modulation ratio command values ​​shares the same processor with the control tasks for normal grid-side inverter operation, eliminating the need for additional dedicated detection circuits. The measurement of the actual output active power utilizes the voltage and current detection channels built into the grid-side inverter, eliminating the need for independent sensors in the power circuit. This step, with relatively low hardware complexity, obtains four key parameters characterizing the DC-side voltage state, AC-side frequency state, inverter control strength, and actual output power, providing basic data for subsequent steps to identify grid power gaps and adjust energy storage discharge power.

[0024] In S2, when the DC bus voltage value drops below the preset drop threshold, the energy storage system is controlled to discharge with the first droop coefficient, and the steady-state voltage value of the DC bus before the drop is recorded.

[0025] The preset dropout threshold is set as a percentage of the rated operating voltage of the DC bus under the rated voltage of the ship's power grid. The setting method is to multiply the rated operating voltage of the DC bus by a proportional coefficient less than 1. For example, when the rated operating voltage of the DC bus is 1000 volts, the preset dropout threshold is set to a value within the range of 85% to 95% of this rated value. A value below this threshold indicates a severe energy supply-demand imbalance on the DC bus side, with a high probability of generator or shaft generator disconnection from the grid. The specific value of the preset dropout threshold is determined during the system commissioning phase based on the minimum allowable input voltage of the grid-side inverter. This ensures that the grid-side inverter can maintain normal sinusoidal pulse width modulation output above the preset dropout threshold, preventing the grid-side inverter from entering the overmodulation zone due to excessively low DC bus voltage, which could lead to output waveform distortion or shutdown protection.

[0026] The DC bus voltage value obtained in S1 is continuously compared with a preset drop threshold at multiple points. Continuous multi-point comparison means comparing the DC bus voltage value with the preset drop threshold one by one at multiple consecutive sampling times, with the number of sampling times being a preset number of consecutive points. Only when the DC bus voltage value at each of these consecutive sampling times is lower than the preset drop threshold is the DC bus voltage value confirmed to have fallen below the preset drop threshold confirmed. For example, if the preset number of consecutive points is 5, then the DC bus voltage value at 5 consecutive sampling points must be lower than the preset drop threshold to confirm a drop. Using continuous multi-point comparison avoids misjudging a voltage drop due to instantaneous sensor noise or occasional spikes in the DC bus voltage, ensuring that the power loss protection function is only triggered when a substantial and sustained voltage drop is confirmed, thereby preventing unnecessary discharge of the energy storage system due to false triggering.

[0027] After confirming that the DC bus voltage value has fallen below the preset drop threshold, the first droop coefficient is determined from the droop coefficient interval mapping table based on the rate of change of the DC bus voltage value before the drop. The rate of change of the DC bus voltage value before the drop is obtained by dividing the difference between the DC bus voltage values ​​obtained from two adjacent samples before the drop time by the time interval between the two samples, in volts per second. The droop coefficient interval mapping table is a table that maps the absolute value range of the rate of change of the DC bus voltage value before the drop to the droop coefficient value. This table is pre-established based on the maximum discharge power limit of the energy storage system and the dynamic response characteristics of the DC bus voltage. The larger the absolute value of the rate of change of the DC bus voltage value before the drop, the more severe the DC bus voltage drop caused by the fault, and the larger the corresponding droop coefficient value, resulting in a stronger discharge power response of the energy storage system. Each segment of the droop coefficient range mapping table and its corresponding droop coefficient value are determined through offline simulation and on-site debugging. This ensures that the energy storage system can support the DC bus voltage with appropriate discharge power under various fault severity levels, preventing the system from triggering internal protection due to excessive discharge power or causing a continuous drop in DC bus voltage due to insufficient discharge power, thus ensuring the normal operation of the grid-side inverter. After the first droop coefficient is determined, the energy storage system is controlled to discharge at the first droop coefficient, which is calculated by multiplying the first droop coefficient by the difference between the current DC bus voltage value and the preset drop threshold. The product is used as the discharge power command value for the energy storage system.

[0028] When the DC bus voltage value is confirmed to have fallen below the preset drop threshold, the steady-state voltage value of the DC bus is simultaneously recorded. The steady-state voltage value of the DC bus is obtained by averaging the stable sampled values ​​of the DC bus voltage value within a preset time period before the drop time. The preset time period is set according to the time constant of the ship's power grid load change, and is between several hundred milliseconds and several seconds, for example, sampling data within 500 milliseconds before the fault occurs. The stable sampled value refers to the DC bus voltage sampled value within the preset time period after removing instantaneous spikes caused by switching noise and load changes. Removing instantaneous spikes can be achieved through median filtering or other smoothing algorithms. The steady-state voltage value of the DC bus reflects the actual operating voltage level of the DC bus under normal grid-connected operation before the fault occurs, and will serve as the benchmark reference value for calculating the voltage recovery deviation in S4 and judging the recovery status of the DC bus voltage value in S6.

[0029] S2 activates energy storage discharge support when a voltage drop fault is confirmed, and simultaneously retains the steady-state voltage reference before the drop at the moment of discharge initiation. This avoids the loss of the steady-state reference due to continuous fluctuations in the DC bus voltage after the fault, and provides conditions for correctly assessing the grid recovery process and determining the timing of stopping the discharge in subsequent steps.

[0030] In S3, during the process of discharging the energy storage system with the first droop coefficient under the control of S2, the normalized residual of the product of the modulation ratio command value obtained in S1 and the DC bus voltage value obtained in S1 and the actual output active power value obtained in S1 is calculated as the decoupling deviation. When the decoupling deviation jumps from the low value range to the high value range and remains for more than the preset time, it is determined that the standby generator set begins to bear the load.

[0031] The calculation of decoupling deviation is based on the following physical principle. When the grid-side inverter independently supplies power to the ship's power grid, the fundamental amplitude of the output AC voltage of the grid-side inverter is approximately equal to the product of the modulation ratio command value and the DC bus voltage value. Under the condition that the load power factor is relatively stable, there is a definite proportional relationship between the active power actually delivered to the grid by the grid-side inverter and the fundamental amplitude of the output AC voltage. Therefore, the product of the modulation ratio command value and the DC bus voltage value can be used as a theoretical estimate of the active power output of the grid-side inverter in independent power supply mode, i.e., the theoretical value of active power output. When the standby generator set completes voltage establishment and synchronizes with the ship's power grid and begins to inject active power into the grid, the voltage amplitude and phase of the ship's power grid will be jointly determined by the generator set and the grid-side inverter. The voltage at the output of the grid-side inverter is no longer completely determined by the product of its own modulation ratio command value and the DC bus voltage value, but is constrained by the grid voltage established by the generator set. At this point, the actual output active power of the grid-side inverter will deviate from the theoretical active power output value. The degree of deviation reflects the extent to which the generator set bears the load. The greater the deviation, the more load the generator set has taken over from the grid-side inverter.

[0032] The calculation steps for decoupling deviation are as follows. First, multiply the modulation ratio command value by the DC bus voltage value to obtain the theoretical active power output value. The formula for calculating the theoretical active power output value is: Ptheory = m × Udc; where Ptheory represents the theoretical active power output value in watts, m represents the modulation ratio command value (dimensionless), and Udc represents the DC bus voltage value in volts.

[0033] Next, a sliding window mean filter is applied to the actual output active power value obtained in S1. The sliding window mean filter takes the arithmetic mean of the actual output active power values ​​at the current sampling time and several consecutive previous sampling times as the filtered actual output active power value. The width of the sliding window is set according to the fluctuation frequency of the ship's power grid load; for example, it takes the number of sampling points equivalent to 10 fundamental cycles corresponding to the output frequency of the grid-side inverter. By applying the sliding window mean filter to the actual output active power value, high-frequency power disturbance components introduced by short-term load fluctuations and sensor noise in the ship's power grid can be filtered out. This makes the filtered actual output active power value more accurately reflect the average active power level currently supplied to the grid by the grid-side inverter, thereby improving the stability of the decoupling deviation calculation. The difference between the filtered actual output active power value and the theoretical active power output value is calculated to obtain the filtering difference. Then, the filtering difference is divided by the filtered actual output active power value to obtain the decoupling deviation. The formula for calculating the decoupling deviation is: D=(Prealfiltered-Ptheory) / Prealfiltered; where D represents the decoupling deviation, which is dimensionless, Prealfiltered represents the actual output active power value after filtering, in watts, and Ptheory represents the theoretical value of active power output.

[0034] When the grid-side inverter supplies power independently, the filtered actual output active power value is close to the theoretical active power output value, and the decoupling deviation is close to zero and remains within the preset low value range. When the standby generator sets start injecting active power into the grid, the filtered actual output active power value is significantly lower than the theoretical active power output value, and the decoupling deviation will increase and jump into the preset high value range.

[0035] The preset lower limit and preset higher limit are set based on the typical distribution range of decoupling deviation of the grid-side inverter in independent power supply mode and generator parallel power supply mode. The preset lower limit is set by collecting decoupling deviation samples over a steady-state period when the generator is not connected to the grid, calculating the mean and standard deviation of the samples, and adding three times the standard deviation to the mean as the preset lower limit. The preset higher limit is set by collecting decoupling deviation samples over a steady-state period when the generator is connected to the grid and bears part of the load, calculating the mean and standard deviation of the samples, and subtracting three times the standard deviation from the mean as the preset higher limit.

[0036] The decoupling deviation is compared with the upper limit of a preset low range and the lower limit of a preset high range. When the decoupling deviation changes from below the upper limit of the preset low range to above the lower limit of the preset high range, and remains above the lower limit for a preset duration, the standby generator set is determined to begin assuming load. The preset duration is set based on the response time of the generator set speed control system and the power ramp-up rate after grid connection, and is between several hundred milliseconds and several seconds, for example, a preset duration of 500 milliseconds. By maintaining the condition for exceeding the preset duration, interference from brief jumps in the decoupling deviation caused by instantaneous load impacts on the ship's power grid can be eliminated, ensuring that the determination result corresponds to the state where the generator set continuously and stably injects active power into the grid.

[0037] Compared with the passive criteria of simply waiting for frequency or voltage recovery in existing technologies, S3 captures the physical nature of the broken coupling relationship between grid-side inverter control and output by decoupling deviation. It can identify the moment when the standby generator set actually begins to bear the load earlier and more reliably, even when the generator set speed has not yet fully stabilized and voltage and frequency are still fluctuating. This provides an accurate time starting point for the safe reduction of energy storage discharge power in subsequent steps.

[0038] In S4, starting from the moment when the standby generator set is determined to start bearing the load in S3, the power grid gap is calculated based on the difference between the DC bus voltage value obtained in S1 and the steady-state voltage value of the DC bus recorded in S2, and the rate of change of the grid-side inverter output frequency value obtained in S1. The discharge power of the energy storage system is adjusted with the second droop coefficient so that the discharge power of the energy storage system decreases as the power grid gap shrinks.

[0039] S3 determines that the moment the standby generator begins to bear the load signifies that the generator has completed voltage establishment and grid synchronization, and has begun injecting active power into the ship's power grid. However, at this time, the generator has not yet fully taken over the entire load, and there is still a power gap in the grid, which is filled by the grid-side inverter and the energy storage system. If the energy storage system immediately stops discharging at this moment, the generator may not be able to respond instantly due to the load rate limitation, resulting in insufficient power in the grid again and causing a secondary voltage drop on the DC bus. Therefore, S4 adjusts the discharge power of the energy storage system according to the real-time dynamic changes in the grid power gap, so that it gradually withdraws as the generator output increases.

[0040] The voltage recovery deviation is calculated by subtracting the DC bus voltage value obtained in S1 from the steady-state DC bus voltage value recorded in S2. The formula for voltage recovery deviation is: ΔU = Udc - Usteady; where ΔU represents the voltage recovery deviation in volts, Udc represents the DC bus voltage value, and Usteady represents the steady-state DC bus voltage value. After the generator unit injects power into the grid, the DC bus voltage value will recover from its low value after the drop to the steady-state voltage value. The larger the voltage recovery deviation, the closer the DC bus voltage is to the normal operating level before the fault, and the more significant the support effect of the generator unit's output on the grid.

[0041] The rate of change of the grid-side inverter output frequency is calculated as follows: First, the frequency deviation between the grid-side inverter output frequency obtained in S1 and the rated frequency is calculated. Then, the change in this frequency deviation per unit time is taken as the rate of change of the grid-side inverter output frequency. The rated frequency is preset and stored in the control device according to the design operating frequency of the ship's power grid. For example, if the rated frequency of the ship's power grid is 60 Hz, the rated frequency is set to 60 Hz. The change in frequency deviation per unit time is obtained by dividing the difference between the frequency deviation at the current sampling moment and the frequency deviation at the previous sampling moment by the time interval between the two samplings. The formula for the rate of change of the grid-side inverter output frequency is: df / dt=(Δfcurrent-Δfprevious) / Ts; where df / dt represents the rate of change of the grid-side inverter output frequency in Hertz per second, Δfcurrent represents the frequency deviation at the current sampling moment, Δfprevious represents the frequency deviation at the previous sampling moment, and Ts represents the time interval between the two samplings in seconds. As the output of the generator sets gradually increases and the active power of the power grid tends to be balanced, the rate of change of the output frequency value of the grid-side inverter will gradually level off from large fluctuations until it stabilizes near zero, indicating that the frequency has returned to stability.

[0042] The grid power gap is obtained by multiplying the voltage recovery deviation by the rate of change of the grid-side inverter output frequency. The formula for the grid power gap is: Pgap = ΔU × |df / dt|; where Pgap represents the grid power gap in volts per second, ΔU represents the voltage recovery deviation, and df / dt represents the rate of change of the grid-side inverter output frequency. The voltage recovery deviation reflects the absolute degree of voltage recovery, and the rate of change of the grid-side inverter output frequency reflects the recovery trend of the system's active power balance. The product of the two comprehensively characterizes the size of the remaining power gap that the generator units have not yet filled. The more incomplete the voltage recovery and the more drastic the frequency change, the larger the grid power gap, indicating that the energy storage system still needs to provide greater discharge support. As the generator output increases, both the voltage recovery deviation and the rate of change of frequency decrease, and the grid power gap shrinks accordingly.

[0043] The second droop coefficient is determined from a preset droop coefficient mapping table based on the grid power gap. The preset droop coefficient mapping table divides the grid power gap value range into several intervals, with each interval corresponding to a second droop coefficient value. This table is established offline based on parameters such as the maximum continuous discharge capacity of the energy storage system and the generator loading rate. The larger the grid power gap, the larger the corresponding second droop coefficient value in the mapping table; when the grid power gap approaches zero, the second droop coefficient value also approaches zero. The preset droop coefficient mapping table is established by recording the measured grid power gap values ​​corresponding to different loading stages under generator loading test conditions, as well as the discharge power required by the energy storage system to maintain DC bus voltage stability under that gap. The ratio of the discharge power to the difference between the current DC bus voltage value and the preset droop threshold is used as the expected droop coefficient. This expected droop coefficient is then mapped to the measured grid power gap value, establishing a correspondence between the expected droop coefficient and the measured grid power gap value.

[0044] Once the second droop coefficient is determined, it is used to control the discharge power of the energy storage system. The discharge power command of the energy storage system is the product of the second droop coefficient and the difference between the current DC bus voltage value and the preset droop threshold. As the power gap in the grid narrows, the second droop coefficient decreases. Even if the difference between the DC bus voltage value and the preset droop threshold has not fully recovered, the discharge power of the energy storage system is forcibly reduced, thereby achieving the control objective of actively withdrawing the energy storage discharge power as the generator output increases.

[0045] S4 comprehensively assesses the power gap in the grid by combining voltage recovery deviation and frequency change rate, and maps the gap to a second droop coefficient to dynamically adjust the energy storage discharge power. Compared with the exit method that relies solely on voltage amplitude or frequency as a single criterion, it can more accurately match the actual load capacity of the generator set, avoiding both premature energy storage exit leading to a secondary voltage drop and slow energy storage exit causing energy waste and reverse power risk.

[0046] In S5, during the process of adjusting the discharge power of the energy storage system with the second droop coefficient in S4 so that the discharge power of the energy storage system decreases as the power gap of the grid shrinks, the incremental ratio of the DC bus voltage value obtained in S1 to the actual output active power value obtained in S1 is calculated as the dynamic impedance value. When the dynamic impedance value changes from positive to negative and the absolute value of the dynamic impedance value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive.

[0047] During the decrement of S4, the discharge power of the energy storage system gradually decreases, while the output of the standby generator gradually increases to support the load. The power balance between the energy storage system and the standby generator approaches a critical point. When the output of the standby generator exceeds the load demand of the ship's power grid, the excess power will flow back from the AC side to the DC bus side via the grid-side inverter, forming a reverse energy flow. This can cause an abnormal rise in the DC bus voltage and potentially trigger overvoltage protection or reverse power protection. If protection is triggered by detecting the direction of the actual output active power of the grid-side inverter or the over-limit of the DC bus voltage, the power direction detection has a response lag, and it can only act after the power sign has reversed. S5 uses dynamic impedance values ​​to detect the impending reversal of the power flow in advance, identifying the risk and intervening while the power sign is still positive, thereby preventing the actual occurrence of reverse energy flow.

[0048] The calculation steps for the dynamic impedance value are as follows. Between the current sampling time and the previous sampling time, calculate the first difference in the DC bus voltage value and the second difference in the actual output active power value. The formula for calculating the first difference in the DC bus voltage value is: ΔUs = Udc(k) - Udc(k-1); where ΔUs represents the first difference in the DC bus voltage value in volts, Udc(k) represents the DC bus voltage value at the current sampling time, and Udc(k-1) represents the DC bus voltage value at the previous sampling time.

[0049] The formula for calculating the second difference of the actual output active power value is: ΔPs=Preal(k)-Preal(k-1); where ΔPs represents the second difference of the actual output active power value in watts, Preal(k) represents the actual output active power value at the current sampling time, and Preal(k-1) represents the actual output active power value at the previous sampling time.

[0050] The instantaneous ratios of the first difference between the DC bus voltage and the second difference between the actual output active power are calculated at multiple consecutive sampling times to obtain an instantaneous ratio sequence. An exponential smoothing filter is applied to this instantaneous ratio sequence, and the filtered result is used as the dynamic impedance value. The formula for calculating the exponential smoothing filter is: Rdyn(k) = α × (ΔUs / ΔPs) + (1-α) × Rdyn(k-1); where Rdyn(k) represents the filtered dynamic impedance value at the current sampling time, in volts per watt; ΔUs / ΔPs represents the instantaneous ratio at the current sampling time; Rdyn(k-1) represents the filtered dynamic impedance value at the previous sampling time; and α is the smoothing coefficient, with a value between 0 and 1, for example, α = 0.2. The smoothing coefficient α is set by acquiring the instantaneous ratio sequence under steady-state conditions during offline debugging, calculating the variance of the instantaneous ratios, and selecting an α value that reduces the variance of the filtered dynamic impedance value to below 10% of the instantaneous ratio variance. Exponential smoothing filtering can suppress instantaneous ratio jumps caused by sampling noise or instantaneous load fluctuations, making the change in dynamic impedance value smooth and stable in reflecting the dynamic relationship trend between DC bus voltage value and actual output active power value.

[0051] The physical meaning of dynamic impedance is that during the discharge process of an energy storage system, the DC bus voltage and the actual output active power of the grid-side inverter typically exhibit the same direction of change. That is, a decrease in the discharge power of the energy storage system leads to a decrease in the DC bus voltage, and consequently, a decrease in the actual output active power. At this time, the first difference between the DC bus voltage and the second difference between the actual output active power have the same sign, and the dynamic impedance is positive. When the output of the standby generator unit approaches or even exceeds the load demand of the ship's power grid, and the discharge power of the energy storage system continues to decrease while the standby generator unit further increases its output, the DC bus voltage is forcibly raised by the standby generator unit. However, the actual output active power of the grid-side inverter continues to decrease due to the standby generator unit's contribution. At this time, the DC bus voltage rises while the actual output active power decreases. The first difference between the DC bus voltage and the second difference between the actual output active power are positive, and the dynamic impedance changes from positive to negative, indicating a reverse energy flow trend from the AC side to the DC side. The larger the absolute value of the dynamic impedance, the more intense the reverse energy flow trend.

[0052] The preset impedance mutation threshold is determined as a percentage of the initial dynamic impedance value of the energy storage system when it discharges with the first droop coefficient in S2. The initial dynamic impedance value refers to the average of the dynamic impedance values ​​continuously calculated according to the aforementioned dynamic impedance value calculation method within a steady-state period after the energy storage system begins discharging with the first droop coefficient in S2. The arithmetic mean of the dynamic impedance values ​​within a preset delay to a preset time interval after the start of discharge is taken as the initial dynamic impedance value. The preset impedance mutation threshold is set as a predetermined percentage of the initial dynamic impedance value, for example, 50% of the initial dynamic impedance value. Using a percentage of the initial dynamic impedance value to set the preset impedance mutation threshold takes into account the differences in initial dynamic impedance values ​​under different fault conditions. This allows for automatic adjustment of the discrimination sensitivity based on the system's current actual operating point, avoiding oversensitivity or undersensitivity issues that may arise from a fixed threshold value under different operating conditions.

[0053] When the dynamic impedance value changes from positive to negative, and the absolute value of the dynamic impedance value exceeds the preset impedance mutation threshold, it indicates that the reverse energy flow trend has become clear and has reached a level requiring intervention. At this time, the adjustment of the second droop coefficient is suspended, and the energy storage system continues to discharge with the droop coefficient at the time of suspension. During the suspension period, the dynamic impedance value is continuously calculated. When the dynamic impedance value returns to a positive value, it means that the power distribution between the standby generator and the energy storage system has stabilized again, and the risk of reverse energy flow has been eliminated. At this time, the discharge power of the energy storage system is adjusted with the second droop coefficient, and the process of decreasing the discharge power of the energy storage system as the power gap in the grid decreases in S4 continues.

[0054] S5 introduces a dynamic impedance value—a criterion based on the incremental ratio of the DC bus voltage to the actual output active power—to identify the risk of reverse energy flow before the power flow actually reverses. This allows for the early suspension of the energy storage system's power reduction adjustment, effectively preventing reverse power surges. Compared to reactive protection methods that rely solely on power direction or voltage amplitude, S5's predictive intervention mechanism improves the smoothness of the recovery process and equipment safety.

[0055] In S6, when the DC bus voltage recovers to the steady-state DC bus voltage recorded in S2, and the grid-side inverter output frequency obtained in S1 stabilizes within the rated frequency range, the energy storage system discharge is stopped. S6 is executed after S4 and S5. At this time, the energy storage system discharge power has decreased to a low level as the power gap in the grid narrows, the standby generator set has basically taken over all the load of the ship's power grid, and the energy storage system has completed its power failure prevention support task and enters the final exit determination stage.

[0056] The method for confirming the recovery of the DC bus voltage value to its steady-state voltage value is to continuously compare the DC bus voltage value obtained in S1 with the steady-state voltage value recorded in S2 at multiple points. The preset recovery interval is a voltage range centered on the steady-state voltage value of the DC bus, offset above and below by a preset recovery tolerance value. The preset recovery tolerance value is set based on the peak-to-peak value of the voltage ripple of the DC bus under normal grid-connected operation, for example, taking 3% to 5% of the rated operating voltage of the DC bus as the preset recovery tolerance value. When the DC bus voltage value falls within the preset recovery interval for multiple consecutive sampling moments, it is confirmed that the DC bus voltage value has recovered to the steady-state voltage value of the DC bus. The number of consecutive sampling moments is set according to the fluctuation characteristics of the ship's power grid load and the sensor sampling frequency, for example, the number of consecutive sampling points is equivalent to 5 fundamental cycles corresponding to the output frequency value of the grid-side inverter. Using continuous multi-point comparison can avoid misjudgment caused by the DC bus voltage value briefly falling back to the preset recovery range due to instantaneous load fluctuations or voltage ripples, and ensure that the DC bus voltage is continuously and stably restored to the normal level.

[0057] The method for confirming that the grid-side inverter output frequency value is stable within the rated frequency range is to continuously compare the grid-side inverter output frequency value obtained in S1 with the rated frequency range at multiple points. The rated frequency range is a frequency range centered on the rated frequency value, offset above and below by a preset frequency tolerance value. The rated frequency value is preset and stored in the control device according to the design operating frequency of the ship's power grid, and is the same value as the rated frequency value used in S4. For example, if the rated frequency of the ship's power grid is 60 Hz, the rated frequency value is set to 60 Hz. The preset frequency tolerance value is set according to the allowable range of frequency fluctuation of the ship's power grid under normal grid-connected operation. For example, ±0.5% of the rated frequency value is taken as the preset frequency tolerance value. When the grid-side inverter output frequency value falls within the rated frequency range for multiple consecutive sampling times, it is confirmed that the grid-side inverter output frequency value is stable within the rated frequency range. The number of consecutive sampling times is set to be the same as the number used for continuous point comparison of the DC bus voltage value to ensure the consistency of the two judgment conditions in the time window.

[0058] The recovery of the DC bus voltage to its steady-state value indicates that the DC bus voltage has returned to its normal operating level before the fault, and the energy supply and demand on the DC side have been restored to balance. The stabilization of the grid-side inverter output frequency within its rated frequency range indicates that the active power supply and demand on the AC side have been restored to balance, and the standby generator set has fully assumed the ship's grid load and is operating stably. When both the DC bus voltage recovery to its steady-state value and the grid-side inverter output frequency stabilization within its rated frequency range are met, the energy storage system stops discharging, and the ship's grid is fully powered by the standby generator set, restoring normal power supply mode.

[0059] S6 combines the two conditions of DC bus voltage recovery and frequency stability through continuous multi-point comparison. Compared with a single criterion that relies solely on voltage amplitude recovery or frequency recovery, it can more reliably confirm that the power grid has truly and stably returned to normal, thus avoiding the possibility of another power outage due to premature cessation of energy storage discharge.

[0060] Example 2: Figure 2 A schematic diagram of the ship hybrid energy storage support system based on DC bus voltage droop is provided. The ship hybrid energy storage support system based on DC bus voltage droop includes the following modules: The parameter acquisition module is used to acquire the DC bus voltage value, the grid-side inverter output frequency value, the modulation ratio command value, and the actual output active power value. The drop control module is used to control the energy storage system to discharge with a first droop coefficient when the DC bus voltage value drops below the preset drop threshold, and to record the steady-state voltage value of the DC bus before the drop. The decoupling determination module is used to calculate the normalized residual of the product of the modulation ratio command value and the DC bus voltage value and the actual output active power value during the discharge process as the decoupling deviation degree; when the decoupling deviation degree jumps from the low value range to the high value range and remains for more than the preset time, it is determined that the standby generator set begins to bear the load. The power regulation module is used to calculate the grid power gap based on the difference between the DC bus voltage and the steady-state voltage and the rate of change of the grid-side inverter output frequency, starting from the time the load is determined. It then adjusts the energy storage discharge power with a second droop coefficient so that it decreases as the grid power gap shrinks. The impedance monitoring module is used to calculate the incremental ratio of the DC bus voltage value to the actual output active power value as the dynamic impedance value during the decreasing process; when the dynamic impedance value changes from positive to negative and its absolute value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive. The recovery stop module is used to stop the energy storage system from discharging when the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range.

[0061] The calculations involved in the embodiments are all dimensionless numerical calculations, and the preset parameters and thresholds in the calculations are set by those skilled in the art according to the actual situation.

[0062] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0063] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and inventive constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

Claims

1. A ship hybrid energy storage support method based on DC bus voltage droop, characterized in that, Includes the following steps: S1: Obtain the DC bus voltage value, grid-side inverter output frequency value, modulation ratio command value, and actual output active power value; S2: When the DC bus voltage value drops below the preset drop threshold, control the energy storage system to discharge with the first droop coefficient and record the steady-state voltage value of the DC bus before the drop. S3: During the discharge process, the normalized residual of the product of the modulation ratio command value and the DC bus voltage value and the actual output active power value is calculated as the decoupling deviation. When the decoupling deviation jumps from the low value range to the high value range and remains there for more than the preset time, it is determined that the standby generator set begins to bear the load. S4: From the moment the load is determined, the grid power gap is calculated based on the difference between the DC bus voltage and the steady-state voltage and the rate of change of the grid-side inverter output frequency. The energy storage discharge power is adjusted with the second droop coefficient so that it decreases as the grid power gap shrinks. S5: During the decreasing process, the incremental ratio of the DC bus voltage value to the actual output active power value is calculated as the dynamic impedance value; when the dynamic impedance value changes from positive to negative and its absolute value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive. S6: When the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range, stop the energy storage system from discharging.

2. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 1, characterized in that, S1 includes: The DC bus voltage value is acquired from the DC bus voltage sensor; Obtain the output frequency value and modulation ratio command value of the grid-side inverter from the grid-side inverter controller; The actual output active power value is obtained from the power calculation unit at the output end of the grid-side inverter.

3. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 1, characterized in that, S2 include: The acquired DC bus voltage value is continuously compared with the preset drop threshold at multiple points. When the DC bus voltage value is lower than the preset drop threshold at multiple points, it is confirmed that the DC bus voltage value has fallen below the preset drop threshold. After confirming the drop, the first droop coefficient is determined from the droop coefficient interval mapping table based on the rate of change of the DC bus voltage value before the drop, and the energy storage system discharge is controlled by the first droop coefficient. When a voltage drop is confirmed, the average value of the stable sampled values ​​of the DC bus voltage within the preset time period before the drop is recorded as the steady-state voltage value of the DC bus.

4. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 1, characterized in that, S3 include: Multiply the modulation ratio command value by the DC bus voltage value to obtain the theoretical value of active power output; Calculate the difference between the actual output active power value and the theoretical active power output value, and divide the difference by the actual output active power value to obtain the decoupling deviation. The decoupling deviation is compared with the upper limit of the preset low value range and the lower limit of the preset high value range. When the decoupling deviation changes from being lower than the upper limit of the preset low value range to being higher than the lower limit of the preset high value range, and remains in this state for more than a preset time, it is determined that the standby generator set begins to bear the load.

5. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 4, characterized in that, Dividing the difference by the actual output active power value yields the decoupling deviation, which includes: applying a sliding window mean filter to the actual output active power value; calculating the difference between the filtered actual output active power value and the theoretical active power output value to obtain the filtered difference; and dividing the filtered difference by the filtered actual output active power value to obtain the decoupling deviation.

6. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 1, characterized in that, S4 include: From the moment when the standby generator set is determined to start assuming load, the difference between the DC bus voltage value and the steady-state voltage value is calculated as the voltage recovery deviation; Calculate the change in the deviation between the grid-side inverter output frequency value and the rated frequency value per unit time, and use it as the rate of change of the grid-side inverter output frequency value. The grid power gap is obtained by multiplying the voltage recovery deviation with the rate of change of the grid-side inverter output frequency. The second droop coefficient is determined from the preset droop coefficient mapping table based on the power gap in the power grid, and the discharge power of the energy storage system is controlled by the second droop coefficient so that the discharge power of the energy storage system decreases as the power gap in the power grid shrinks.

7. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 1, characterized in that, S5 include: As the discharge power of the energy storage system decreases with the shrinking power gap in the grid, the first difference between the DC bus voltage value at the current sampling time and the previous sampling time is calculated, and the second difference between the actual output active power value at the current sampling time and the previous sampling time is calculated. The ratio of the first difference to the second difference is used as the dynamic impedance value. When the dynamic impedance value changes from positive to negative and the absolute value of the dynamic impedance value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused, and the energy storage system continues to discharge with the droop coefficient at the pause time. During the pause, the dynamic impedance value is continuously calculated. When the dynamic impedance value returns to a positive value, the discharge power of the energy storage system is adjusted by the second droop coefficient.

8. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 7, characterized in that, The ratio of the first difference to the second difference is used as the dynamic impedance value, including: performing a ratio calculation on the first difference of the DC bus voltage value and the second difference of the actual output active power value at multiple consecutive sampling times, performing exponential smoothing filtering on the ratio results at multiple consecutive sampling times, and using the filtered ratio results as the dynamic impedance value; the preset impedance change threshold is determined according to the percentage of the initial dynamic impedance value when the energy storage system discharges with the first droop coefficient.

9. The ship hybrid energy storage support method based on DC bus voltage droop according to claim 1, characterized in that, S6 include: The DC bus voltage value is continuously compared with the steady-state voltage value at multiple points. When the DC bus voltage value falls within the preset recovery range centered on the steady-state voltage value at multiple consecutive sampling times, it is confirmed that the DC bus voltage value has recovered to the steady-state voltage value. The grid-side inverter output frequency value is continuously compared with the rated frequency range at multiple points. When the grid-side inverter output frequency value falls within the rated frequency range at multiple consecutive sampling times, it is confirmed that the grid-side inverter output frequency value is stable within the rated frequency range. The energy storage system stops discharging when both the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range.

10. A ship hybrid energy storage support system based on DC bus voltage droop, used to implement the ship hybrid energy storage support method based on DC bus voltage droop as described in any one of claims 1-9, characterized in that, Includes the following modules: The parameter acquisition module is used to acquire the DC bus voltage value, the grid-side inverter output frequency value, the modulation ratio command value, and the actual output active power value. The drop control module is used to control the energy storage system to discharge with a first droop coefficient when the DC bus voltage value drops below the preset drop threshold, and to record the steady-state voltage value of the DC bus before the drop. The decoupling determination module is used to calculate the normalized residual of the product of the modulation ratio command value and the DC bus voltage value and the actual output active power value during the discharge process as the decoupling deviation degree; when the decoupling deviation degree jumps from the low value range to the high value range and remains for more than the preset time, it is determined that the standby generator set begins to bear the load. The power regulation module is used to calculate the grid power gap based on the difference between the DC bus voltage and the steady-state voltage and the rate of change of the grid-side inverter output frequency, starting from the time the load is determined. It then adjusts the energy storage discharge power with a second droop coefficient so that it decreases as the grid power gap shrinks. The impedance monitoring module is used to calculate the incremental ratio of the DC bus voltage value to the actual output active power value as the dynamic impedance value during the decreasing process; when the dynamic impedance value changes from positive to negative and its absolute value exceeds the preset impedance change threshold, the adjustment of the second droop coefficient is paused until the dynamic impedance value returns to positive. The recovery stop module is used to stop the energy storage system from discharging when the DC bus voltage value recovers to the steady-state voltage value and the grid-side inverter output frequency value stabilizes within the rated frequency range.

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