Ship AC / DC hybrid power system control method and system based on hybrid margin

Abstract

The invention discloses a control method and system of a ship alternating current and direct current hybrid power system based on a hybrid margin. The method comprises the following steps: collecting a direct current voltage of a direct current sub micro-grid and an alternating current frequency of an alternating current sub micro-grid in real time; for each energy storage unit in the DC sub-microgrid, adjusting the input and output power of the energy storage unit in different modes based on the operation margin corresponding to the state of charge; for each power supply in the AC sub-microgrid, adjusting the power supply output active power in different modes based on the power supply operation margin corresponding to the operation parameter; carrying out normalization processing on the direct-current voltage and the alternating-current frequency and calculating deviation values of the direct-current voltage and the alternating-current frequency; if the two deviation values are both in the margin range, the standby state of the interconnection converter is maintained, and the energy storage unit and the power supply autonomously complete power balance through a self droop control strategy; and if one of the two deviation values exceeds the margin range, power mutual assistance and distribution are performed on the DC sub-microgrid and the AC sub-microgrid through the interconnection converter based on a double-droop control strategy.

Description

Control Method and System for Ship AC / DC Hybrid Electric System Based on Hybrid Margin Technical Field

[0001] This invention relates to the field of ship power system control technology, and in particular to a control method and system for a ship AC / DC hybrid power system based on hybrid margin. Background Technology

[0002] In 2014, the International Maritime Organization (IMO) established strict guidelines to limit greenhouse gas emissions from ships. Ship electrification is one of the main ways to improve ship operating efficiency and reduce carbon emissions. Although AC-based electric propulsion systems for ships are widely used and technologically mature, they still have certain limitations: they require additional electrical equipment such as generators, switchboards, rectifier transformers, frequency converters, and propulsion motors. This not only increases the size and weight of the equipment and makes installation more difficult, but also requires additional cooling and ventilation equipment, thus affecting the utilization rate of ship cabin space and operational economy, while also increasing the difficulty of design and retrofitting.

[0003] In recent years, with the continuous improvement of ship maneuverability requirements, all-electric ships, with their advantages of high reliability, good economy, and strong maneuverability, have become an important development direction in my country's shipbuilding industry. Compared with existing all-electric ships using medium-voltage AC power systems, all-electric ships using AC / DC hybrid power systems, relying on advanced power electronic conversion technology, can eliminate a large number of traditional low-frequency transformers, effectively saving deck space and increasing the effective cabin capacity of the hull; at the same time, they can introduce new energy storage systems to efficiently recover the regenerative braking energy of the propulsion motor, further optimizing the system's operational economy. Therefore, all-electric ships equipped with AC / DC hybrid power systems have become an important development direction in my country's shipbuilding industry. Compared with medium-voltage AC power systems, the technological advantages of AC / DC hybrid power systems are mainly reflected in the following aspects:

[0004] (1) Voltage transformation of DC power grids is mainly based on power electronic converters, which have high power density and simple structure. Compared with the design of AC power grids with transformers as the core power devices, the size and weight of traditional switchboards and other electrical equipment are greatly reduced, which reduces ship costs and equipment noise and vibration.

[0005] (2) After adopting the AC / DC hybrid power distribution mode, the diesel generator set in the ship power generation system does not need to operate at a fixed speed. It can adjust the output power in real time according to the load change, so that the system operates in the optimal energy consumption range and improves energy utilization efficiency.

[0006] (3) In the AC / DC hybrid power grid structure, distributed micro-sources such as photovoltaics and fuel cells can be flexibly connected to provide clean energy for ships and further save fuel; and the integration process of each distributed unit is simple and efficient.

[0007] However, as independent active systems, shipboard power systems operate under complex and variable conditions, experiencing strong load fluctuations, which places higher demands on stability, reliability, and intelligent control. Existing AC / DC hybrid power system control strategies largely rely on reliable communication networks to achieve centralized or distributed coordination and optimization. However, the harsh electromagnetic and environmental interference on ships poses a severe challenge to communication reliability. Once communication is interrupted, the control strategy is prone to failure, leading to decreased system stability or damage to critical equipment. Therefore, there is an urgent need for an intelligent control strategy for AC / DC hybrid power systems that is independent of communication, capable of autonomous coordination, and maximizes system stability while ensuring equipment safety. Summary of the Invention

[0008] To address the problems of insufficient power distribution accuracy, stability limitations due to communication reliability, and difficulties in the coordinated regulation of multiple distributed power sources and loads in traditional ship AC / DC hybrid power systems under complex and variable operating conditions, this invention proposes a control method for ship AC / DC hybrid power systems based on hybrid margins. This method utilizes a hierarchical droop control strategy based on hybrid margins (energy storage unit state-of-charge margin, power supply margin, DC voltage margin, and AC frequency margin) and normalization processing to achieve autonomous coordination and power distribution between AC and DC subgrids under communication-free conditions. This improves system stability, economy, and renewable energy absorption capacity. While ensuring system stability, it effectively protects energy storage devices from damage, preventing them from entering dangerous overcharge or over-discharge conditions due to continuous power regulation, thus ensuring the safe and reliable operation of the ship under specific operating conditions. This invention also relates to a control system for ship AC / DC hybrid power systems based on hybrid margins.

[0009] The technical solution of the present invention is as follows:

[0010] A control method for a ship's AC / DC hybrid electric system based on hybrid margin includes the following steps:

[0011] S1: Real-time acquisition of DC voltage of DC bus and AC frequency of AC bus in DC sub-microgrid of ship AC / DC hybrid power system;

[0012] S2: For each energy storage unit in the DC sub-microgrid, the state of charge (SOC) of the energy storage unit is acquired in real time. Based on the operating margin corresponding to the SOC, the input and output power of the energy storage unit is adjusted in different modes: When the SOC is within the normal operating margin range, the system switches to droop control mode. Using the VP droop control strategy, combined with the DC voltage and the rated DC voltage, the input and output power of the energy storage unit is adjusted to participate in the power balance of the DC sub-microgrid; when the SOC is lower than the lower limit of the normal operating margin, the system switches to limited discharge mode, stops the energy storage unit from outputting power to the DC bus, and uses the VP droop control strategy, combined with the DC voltage and the rated DC voltage, to adjust the input power of the energy storage unit to participate in the power balance of the DC sub-microgrid; when the SOC is higher than the upper limit of the normal operating margin, the system switches to limited charging mode, limits the input power of the energy storage unit, and uses the VP droop control strategy, combined with the DC voltage and the rated DC voltage, to adjust the output power of the energy storage unit to participate in the power balance of the DC sub-microgrid.

[0013] S3: For each power supply in the AC sub-microgrid, the operating parameters of the power supply are acquired in real time. Based on the operating margin of the power supply corresponding to the operating parameters, the output active power of the power supply is adjusted in different modes: when the operating parameters are within the preset margin range of the power supply, the Pf droop control strategy is used, combined with the AC frequency, rated AC frequency, the power supply's active power reference value and droop coefficient, to adjust the output active power of the power supply and participate in the AC sub-microgrid power balance; when the operating parameters exceed the preset margin range of the power supply, the output active power of the power supply is limited, and participation in the AC sub-microgrid power balance is suspended to ensure the safe operation of the power supply.

[0014] S4: Normalize the DC voltage and AC frequency respectively to obtain normalized DC voltage and normalized AC frequency; calculate the deviation of the normalized DC voltage from its corresponding reference value and the deviation of the normalized AC frequency from its corresponding reference value; if the deviation of the normalized DC voltage is within the voltage margin range and the deviation of the normalized AC frequency is within the frequency margin range, then maintain the standby state of the interconnecting converter connecting the DC sub-microgrid and the AC sub-microgrid, and the power regulation unit within each sub-microgrid will use its own droop control strategy. The system autonomously completes power balancing. If the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, the interconnect converter, based on a dual droop control strategy of the DC voltage and the AC frequency, performs power sharing and allocation between the DC sub-microgrid and the AC sub-microgrid. When an energy storage unit or power supply limits its power due to exceeding the corresponding margin range, the power balancing task it originally participated in is naturally shared by the interconnect converter and other units that have not exceeded the margin range through their own droop control strategies.

[0015] Preferably, step S2 further includes: using maximum power point tracking technology to adjust the output power of each photovoltaic unit in the DC sub-microgrid, and outputting power to the DC bus in a constant power mode, without directly participating in the voltage regulation of the DC bus;

[0016] When the DC voltage is lower than a preset safety threshold, the secondary loads in the DC sub-microgrid are disconnected to reduce the power consumption of the DC bus.

[0017] Preferably, in step S2, for each energy storage unit in the DC sub-microgrid, when switching to the droop control mode, the deviation value between the DC voltage and the rated DC voltage, and the preset VP droop characteristic curve corresponding to the energy storage unit are determined. Based on the deviation value and the preset VP droop characteristic curve, the target input / output power corresponding to the energy storage unit is calculated, and the actual input / output power of the energy storage unit is adjusted according to the target input / output power.

[0018] When switching to the limited discharge mode, the deviation between the DC voltage and the rated DC voltage is determined, as well as the preset VP droop characteristic curve corresponding to the energy storage unit. Based on the deviation and the preset VP droop characteristic curve, the target input / output power corresponding to the energy storage unit is calculated. If the target input power of the energy storage unit is calculated, the actual input power of the energy storage unit is adjusted according to the target input power. If the target output power of the energy storage unit is calculated, the output power from the energy storage unit to the DC bus is stopped.

[0019] When switching to the limited charging mode, the deviation between the DC voltage and the rated DC voltage is determined, as well as the preset VP droop characteristic curve corresponding to the energy storage unit. Based on the deviation and the preset VP droop characteristic curve, the target input / output power corresponding to the energy storage unit is calculated. If the target input power of the energy storage unit is calculated, the input power of the energy storage unit is limited. If the target output power of the energy storage unit is calculated, the actual output power of the energy storage unit is adjusted according to the target output power.

[0020] Preferably, in step S2, the droop coefficient of the preset VP droop characteristic curve corresponding to each energy storage unit is set based on the ratio of the per-unit value of the maximum available capacity of each energy storage unit.

[0021] Preferably, in step S3, the target output active power of the power supply is calculated using the Pf droop control formula in the Pf droop control strategy, and the actual output active power of the power supply is adjusted based on the target output active power; the Pf droop control formula is as follows:

[0022] ,

[0023] Wherein, P is the output active power of the power supply. This refers to the reference value of the active power of the power supply. The droop coefficient is... The rated AC frequency of the AC bus is [missing information]. The AC frequency is collected in real time;

[0024] Based on the ratio of the per-unit values ​​of the maximum output power of each power supply, a droop coefficient is set for each power supply. ;

[0025] The power supply includes a diesel generator, and the operating parameters include the fuel level and temperature of the power supply. The preset margin range of the power supply includes a fuel level margin range and a temperature margin range.

[0026] Preferably, in step S4, the DC voltage and the AC frequency are normalized based on normalized expressions, as shown below:

[0027] ,

[0028] ,

[0029] in, The normalized AC frequency, The normalized DC voltage, The AC frequency is... The maximum frequency of the AC bus. The minimum frequency of the AC bus. The DC voltage is... The maximum voltage of the DC bus. This is the minimum voltage of the DC bus.

[0030] Preferably, in step S4, if the deviation of the normalized DC voltage exceeds the voltage margin range and / or the deviation of the normalized AC frequency exceeds the frequency margin range, the following steps are performed:

[0031] If the deviation value of the normalized AC frequency is negative and the deviation value of the normalized DC voltage is positive, then the power on the DC bus is absorbed by the interconnect converter and transmitted to the AC bus.

[0032] If the deviation value of the normalized DC voltage is negative and the deviation value of the normalized AC frequency is positive, then the power absorbed from the AC bus is transmitted to the DC bus through the interconnect converter.

[0033] If both the normalized AC frequency deviation and the normalized DC voltage deviation are negative, the direction of power transmission through the interconnect converter is determined based on the absolute values ​​of their deviations: if the absolute value of the normalized AC frequency deviation is greater than the absolute value of the normalized DC voltage deviation, power is absorbed from the DC bus and transmitted to the AC bus through the interconnect converter; if the absolute value of the normalized AC frequency deviation is less than the absolute value of the normalized DC voltage deviation, power is absorbed from the AC bus and transmitted to the DC bus through the interconnect converter; if the absolute value of the normalized AC frequency deviation is equal to the absolute value of the normalized DC voltage deviation, power is not transmitted through the interconnect converter.

[0034] If the deviation of the normalized AC frequency is positive and the deviation of the normalized DC voltage is positive, then power transmission will not be performed through the interconnect converter.

[0035] Preferably, in step S4, the first response power that the interconnect converter needs to absorb from the DC bus is determined based on the normalized DC voltage and the preset DC-side VP droop characteristic curve of the interconnect converter.

[0036] Based on the normalized AC frequency and the preset AC-side Pf droop characteristic curve of the interconnect converter, the second response power that the interconnect converter needs to deliver to the AC bus is determined.

[0037] The difference between the first response power and the second response power is the actual transmission power of the interconnect converter.

[0038] A control system for a ship's AC / DC hybrid electric system based on hybrid margin includes a data acquisition module, a DC sub-microgrid internal power autonomy module, an AC sub-microgrid internal power autonomy module, and an AC / DC sub-microgrid inter-power interaction control module connected in sequence.

[0039] The data acquisition module: collects in real time the DC voltage of the DC bus in the DC sub-microgrid and the AC frequency of the AC bus in the AC sub-microgrid of the ship's AC / DC hybrid power system;

[0040] The power autonomy module within the DC sub-microgrid: For each energy storage unit in the DC sub-microgrid, it acquires the state of charge (SOC) of the energy storage unit in real time. Based on the operating margin corresponding to the SOC, it adjusts the input and output power of the energy storage unit in different modes: When the SOC is within the normal operating margin range, it switches to droop control mode, using the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the input and output power of the energy storage unit and participate in the power balance of the DC sub-microgrid; When the SOC is lower than the lower limit of the normal operating margin, it switches to limited discharge mode, stops the energy storage unit from outputting power to the DC bus, and uses the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the input power of the energy storage unit and participate in the power balance of the DC sub-microgrid; When the SOC is higher than the upper limit of the normal operating margin, it switches to limited charging mode, limits the input power of the energy storage unit, and uses the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the output power of the energy storage unit and participate in the power balance of the DC sub-microgrid.

[0041] The internal power autonomy module of the AC sub-microgrid: For each power supply in the AC sub-microgrid, it acquires the operating parameters of the power supply in real time, and adjusts the output active power of the power supply according to the operating margin corresponding to the operating parameters in different modes: When the operating parameters are within the preset margin range of the power supply, the output active power of the power supply is adjusted by using the Pf droop control strategy, combined with the AC frequency, rated AC frequency, the power supply's active power reference value and droop coefficient, to participate in the AC sub-microgrid power balance; When the operating parameters exceed the preset margin range of the power supply, the output active power of the power supply is limited, and participation in the AC sub-microgrid power balance is suspended to ensure the safe operation of the power supply.

[0042] The AC / DC sub-microgrid power interaction control module: normalizes the DC voltage and the AC frequency respectively to obtain normalized DC voltage and normalized AC frequency; calculates the deviation values ​​of the normalized DC voltage and its corresponding reference value, and the deviation values ​​of the normalized AC frequency and its corresponding reference value; if the deviation value of the normalized DC voltage is within the voltage margin range, and the deviation value of the normalized AC frequency is within the frequency margin range, then the interconnecting converter connecting the DC sub-microgrid and the AC sub-microgrid is maintained in standby state, and the power regulation unit within each sub-microgrid is responsible for power regulation through self-regulation. The droop control strategy autonomously completes power balancing. If the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, the interconnect converter, based on the dual droop control strategy of the DC voltage and the AC frequency, performs power mutual assistance and distribution on the DC sub-microgrid and the AC sub-microgrid. When the energy storage unit or power supply limits its power due to exceeding the corresponding margin range, the power balancing task it originally participated in is naturally shared by the interconnect converter and other units that have not exceeded the margin range through their own droop control strategies.

[0043] Preferably, the power autonomy module inside the DC sub-microgrid further includes: using maximum power point tracking technology to adjust the output power of each photovoltaic unit in the DC sub-microgrid, and outputting power to the DC bus in a constant power mode, without directly participating in the voltage regulation of the DC bus;

[0044] When the DC voltage is lower than a preset safety threshold, the secondary loads in the DC sub-microgrid are disconnected to reduce the power consumption of the DC bus.

[0045] The beneficial effects of this invention are as follows:

[0046] This invention provides a control method for a ship AC / DC hybrid power system based on hybrid margin, also known as a comprehensive operation control strategy for a ship AC / DC hybrid power system based on hybrid margin. This method acquires in real time the DC voltage of the DC bus of the DC sub-microgrid (the DC voltage of the DC bus is a core indicator for measuring the power balance state of the DC bus) and the AC frequency of the AC bus of the AC sub-microgrid (the AC frequency of the AC bus is a key indicator for measuring the power balance state of the AC bus). This ensures that the subsequent adjustment actions of energy storage units, power supplies, and the modal decisions of interconnecting converters are based on real operating conditions, laying a data foundation for stable control of the entire system. Based on the operating margin corresponding to the state of charge (SOC) of the energy storage units, the input and output power are adjusted in different modes. The adaptive switching of the three modes enables each energy storage unit to... The unit can balance equipment safety and system regulation needs under different SOC states. When the SOC is normal (within the normal operating margin range), it actively participates in the power balancing of the DC sub-microgrid. When the SOC is critical, it prioritizes its own safety (avoiding the risk of over-discharge of energy storage units through limited discharge mode and the risk of over-charge of energy storage units through limited charging mode), effectively extending the service life of energy storage equipment and ensuring equipment safety. At the same time, the application of VP droop control strategy ensures that the regulation action and DC voltage deviation are accurately matched under no communication conditions, and the utilization rate of each energy storage unit is balanced, avoiding overload of a single energy storage unit and maintaining the DC sub-microgrid power balance. The microgrid voltage is stable, improving the reliability of DC power supply. For each power source in the AC sub-microgrid, when the operating parameters (such as fuel level and temperature) are within the preset margin range, a Pf droop control strategy is adopted. This strategy can quickly respond to frequency deviations caused by AC load fluctuations, pushing the AC frequency back to the rated range and ensuring the normal operation of AC equipment. Simultaneously, by combining the design of the active power reference value and droop coefficient for each power source, multiple power sources can share the load power according to their capacity (maximum generating power), avoiding overload of a single power source and improving the efficiency of the AC sub-microgrid. The power distribution balance and power supply stability are adapted to the dynamic changes of the ship's AC load. When the operating parameters of the power supply exceed the preset margin range (such as low fuel level or high temperature), the output active power is limited and participation in the AC sub-microgrid power balancing is suspended, which can effectively avoid the failure and damage caused by the power supply exceeding the safe operating boundary and extend the service life of the equipment. By normalizing the DC voltage and AC frequency, the difference in units and magnitude between the two is eliminated, providing a unified analysis benchmark for the dual droop control of the interconnected converter and ensuring the accuracy of the power distribution judgment between sub-microgrids.Modal decision-making based on margin thresholds enables the interconnected converter to maintain a standby state when the fluctuations in the two sub-microgrids are small (the deviations of the normalized DC voltage and its corresponding reference value, and the deviations of the normalized AC frequency and its corresponding reference value are all within the margin range). The power balance within each sub-microgrid is autonomously completed by the distributed power sources (such as energy storage units and power supplies) within each sub-microgrid through local droop control, reducing unnecessary power transmission losses and solving the problem of high switching losses and low operating efficiency caused by the interconnected converter's immediate response to any small power fluctuations between sub-microgrids in traditional droop control. When the fluctuation of any sub-microgrid exceeds the margin range, the dual droop control strategy can accurately identify the power demand priority of the sub-microgrids and realize power mutual assistance and distribution between sub-microgrids through the interconnected converter, making up for the deficiency of insufficient internal regulation capability of a single sub-microgrid. The dual sub-microgrids can achieve coordinated stability without additional communication equipment, which not only improves the anti-interference capability of the entire system, but also enhances the operational reliability and flexibility of the ship's AC / DC hybrid power system. This invention utilizes the concept of per-unit control to unify AC droop control and DC droop control, thereby regulating the power transmission of interconnected converters and achieving coordinated control of a ship's AC / DC hybrid power system without communication. Simultaneously, it defines operating margins for distributed power sources (such as energy storage units and power supplies) in the ship's AC / DC hybrid power system based on their own states (such as State of Charge, fuel level, and temperature). Based on these margin thresholds, it intelligently switches between "participating in system regulation" and "self-protection" modes without communication, achieving maximum self-consistent and stable operation of the ship's AC / DC hybrid power system while ensuring equipment safety.

[0047] This invention utilizes Maximum Power Point Tracking (MPPT) technology to regulate the output power of photovoltaic (PV) units, maximizing the potential of PV energy and supplying power to the DC bus in a constant power mode. This improves the efficiency of new energy utilization and operational economy on ships. Furthermore, since PV typically does not directly participate in DC bus voltage regulation (although it can enter power-limiting mode when necessary), it avoids the interference of power fluctuations on voltage stability. This clear division of labor and coordinated operation with the voltage regulation function of the energy storage unit ensures the stability of the DC sub-microgrid power supply. When the DC voltage falls below a preset safety threshold, disconnecting secondary loads (such as unnecessary lighting and other household equipment loads) quickly reduces the power consumption of the DC bus. As a passive power balancing method, this effectively alleviates the continuous voltage drop caused by severe power shortages.

[0048] This invention uses a unified calculation core of "the deviation between DC voltage and rated DC voltage + a preset VP droop characteristic curve" as the core for calculating the power of energy storage units in each mode. This ensures the consistency and accuracy of the energy storage regulation logic, making the power regulation highly matched with the DC bus voltage deviation. This avoids problems such as regulation disconnection or response disorder when switching between different modes, and improves the reliability of DC sub-microgrid voltage stability control. In droop control mode, the accurate calculation based on the VP droop characteristic curve enables smooth adjustment of energy storage charging / discharging power, rapid response to voltage fluctuations, and efficient balance of DC sub-microgrid power. In limited discharge mode, only the calculated target input power (charging) is allowed, and output power (discharging) is prohibited. This ensures equipment safety when the energy storage SOC is below the lower limit of normal operating margin, while not wasting charging opportunities with surplus power on the DC side. In limited charging mode, the input power (charging) is limited, and the calculated target output power (discharging) is executed. This effectively avoids the risk of overcharging energy storage, while ensuring that energy storage can still participate in energy replenishment when there is a power gap in the DC sub-microgrid. The overall design not only adheres to the safe operation boundaries of energy storage equipment, but also maximizes its power support capability for DC sub-microgrids under different conditions. It is adapted to the operating conditions of frequent fluctuations in the load of ship DC sub-microgrids and the output of new energy sources, achieving a deep balance between "equipment safety protection" and "system regulation efficiency".

[0049] This invention sets the droop coefficient of the VP droop characteristic curve based on the ratio of the per-unit maximum available capacity of each energy storage unit. This ensures that when there is a voltage deviation on the DC bus, the power regulation of each energy storage unit is proportional to its own maximum available capacity. This avoids small-capacity energy storage units from bearing excessive regulation load due to excessively large coefficients, leading to overload, or large-capacity energy storage units from failing to fully utilize their regulation potential due to excessively small coefficients. It enables multiple energy storage units to share the power regulation task proportionally according to their own capacity. At the same time, it ensures that the DC bus voltage returns to the rated range quickly and smoothly, improves the stability and regulation efficiency of the DC sub-microgrid power balance, and adapts to the dynamic fluctuation characteristics of the DC side load of ships.

[0050] This invention, based on normalized expressions, normalizes both the DC voltage and the AC frequency. This normalization process controls the range of both DC voltage and AC frequency to between -1 and 1, thus resolving the issue of their inability to be analyzed and compared within the same range due to their different units and magnitudes. Simultaneously, it provides a unified quantitative benchmark for subsequent droop control of interconnected converters and determination of power transmission direction between subnets, ensuring the accuracy and rationality of power mutual assistance decisions and meeting the core requirement of shipboard AC / DC subnets lacking communication coordination.

[0051] This invention, by subdividing the power transmission decision scenarios of interconnected converters according to the positive and negative attributes and magnitude relationships of normalized DC voltage deviation and normalized AC frequency deviation, achieves precise, scenario-based, and redundancy-free control of power mutual assistance between sub-microgrids, maximizing both system stability and operational efficiency. First, for the "one negative, one positive" deviation scenario (one side with a deficit, the other with a surplus), it directly determines the power flow from the surplus sub-microgrid to the deficit sub-microgrid. This allows for rapid bidirectional adaptation of surplus absorption and deficit replenishment without complex calculations, avoiding misjudgments of power transmission direction, improving adjustment response speed, and efficiently utilizing surplus power in sub-microgrids to reduce energy waste. Second, for the "double negative deviation" scenario (both sub-microgrids have power deficits), it determines the transmission direction based on the absolute value of the deviations, prioritizing support for the sub-microgrid with the more severe imbalance, quickly alleviating the main system contradiction. Furthermore, for the "double positive deviation" scenario (both microgrids have power surplus), power transmission is explicitly prohibited. This avoids switching losses and energy losses caused by ineffective power flow at the source, while also preventing transmission from exacerbating the overvoltage / overfrequency risk on one side, thus ensuring equipment safety and system economy. The overall detailed rules can be executed locally autonomously without additional communication coordination, adapting to the core needs of ships without communication control.

[0052] This invention determines the first response power that the interconnect converter needs to absorb from the DC bus based on the normalized DC voltage and the preset DC-side droop characteristic curve of the interconnect converter. It also determines the second response power that the interconnect converter needs to deliver to the AC bus based on the normalized AC frequency and the preset AC-side droop characteristic curve of the interconnect converter. The calculation process strictly relies on the preset droop characteristic curve of the interconnect converter, improving the accuracy of the power transmitted through the interconnect converter and ensuring precise matching between the transmitted power and the imbalance of the twin microgrid, thus promoting a rapid return of voltage and frequency to a stable range. Furthermore, the entire calculation relies only on locally acquired normalized parameters and relevant droop characteristic curves, requiring no additional communication interaction. This fully meets the core requirements of ships without communication control, ensuring the real-time performance and reliability of power transmission decisions under extreme operating conditions.

[0053] This invention also relates to a control system for a ship AC / DC hybrid power system based on hybrid margin. This control system corresponds to the aforementioned control method for a ship AC / DC hybrid power system based on hybrid margin, and can be understood as a system that implements the aforementioned control method for a ship AC / DC hybrid power system based on hybrid margin. It includes a data acquisition module, a DC sub-microgrid internal power autonomy module, an AC sub-microgrid internal power autonomy module, and an AC / DC sub-microgrid inter-power interaction control module. The data acquisition module provides real-time electrical quantities and equipment status data for the entire system control, laying the data foundation for precise control. The DC sub-microgrid internal power autonomy module and the AC sub-microgrid internal power autonomy module are based on the state-of-charge margin of the energy storage unit and the power supply, respectively. The system provides operational margins to achieve autonomous power balancing within subgrids and ensure the safety of critical equipment. The AC / DC inter-subgrid power interaction control module, based on coordinated judgment of voltage and frequency margins, drives the interconnecting converter to complete power mutual assistance between subgrids. Each module works collaboratively. This control system, through hierarchical linkage between the power transmission margins (voltage and frequency margins) of the interconnecting converters and the state margins (operational margins corresponding to the state of charge and power supply operating margins) of critical equipment, collectively constitutes a highly efficient and reliable hierarchical AC / DC hybrid power system for ships, forming a communication-free coordination control system for AC / DC hybrid microgrids. This system ensures the stability of the ship's AC / DC hybrid power system while significantly improving operational economy and equipment lifespan, achieving the optimal balance between stability and efficiency. Attached Figure Description

[0054] Figure 1 shows the architecture of a ship's AC / DC hybrid power system.

[0055] Figure 2 is a flowchart of the control method for a ship AC / DC hybrid electric system based on hybrid margin according to the present invention.

[0056] Figure 3 is an example waveform diagram of the active power output of the fuel cell in the AC sub-microgrid of the present invention.

[0057] Figure 4 is an example waveform diagram of the active power output of the diesel generator in the AC sub-microgrid of the present invention.

[0058] Figure 5 is an example diagram of the AC frequency waveform of the AC sub-microgrid of the present invention.

[0059] Figure 6 is an example waveform diagram of the active power output of the energy storage unit in the DC sub-microgrid of the present invention.

[0060] Figure 7 is an example waveform diagram of the DC voltage of the DC bus of the present invention.

[0061] Figure 8 is an example waveform diagram of the SOC variation curve of the energy storage unit of the present invention.

[0062] Figure 9 is an example waveform diagram of the active power transmitted by the interconnect converter of the present invention.

[0063] Figure 10 is a structural block diagram of the control system of the ship AC / DC hybrid power system based on hybrid margin of the present invention. Detailed Implementation

[0064] The present invention will now be described with reference to the accompanying drawings.

[0065] This invention discloses a control method for a ship AC / DC hybrid power system based on hybrid margin. The method is applied to a ship AC / DC hybrid power system, as shown in Figure 1, which is a partial architecture diagram of such a system. The system includes an AC sub-microgrid, a DC sub-microgrid, and interconnecting converters. The AC sub-microgrid includes an AC bus and power supplies connected to it (such as diesel generators), AC loads (such as shaft-driven generator converters, scrubber seawater pump power cabinets, scrubber process water pump power cabinets, main air compressors, auxiliary fans, ballast pumps, and main engine reducing agent pipeline heat tracing). The DC sub-microgrid includes a DC bus and various energy storage units (also called energy storage systems) connected to the DC bus, DC loads (divided into primary DC loads and secondary DC loads according to importance: primary DC loads such as propulsion motors, and secondary DC loads such as auxiliary ship lighting equipment corresponding to DC load 1 and DC load 2), photovoltaic units, etc.; the interconnecting converter is a cross-grid component independent of the AC sub-microgrid and DC sub-microgrid, used to connect the AC bus and the DC bus, transfer power in the AC sub-microgrid and DC sub-microgrid, and realize power mutual assistance and distribution between the two sub-microgrids. The control method of the present invention, as shown in Figure 2, includes the following steps:

[0066] S1: Real-time acquisition of DC voltage of DC bus in DC sub-microgrid and AC frequency of AC bus in AC sub-microgrid of ship AC / DC hybrid power system.

[0067] Since the DC bus voltage is a core indicator for measuring its power balance (the DC voltage drops when the power on the DC bus is insufficient, and rises when the power is excessive), and the AC bus frequency is a core indicator for measuring its power balance (the AC frequency drops when the power on the AC bus is insufficient, and rises when the power is excessive), this embodiment of the invention collects the DC voltage of the DC bus in the DC sub-microgrid and the AC frequency of the AC bus in the AC sub-microgrid in real time to detect the power balance between the DC and AC sub-microgrids. Each energy storage unit and power supply (such as a diesel generator) connected to each bus is equipped with a data acquisition module, which can obtain voltage / current data on the bus without relying on communication.

[0068] S2: For each energy storage unit in the DC sub-microgrid, the state of charge (SOC) of the energy storage unit is acquired in real time. Based on the operating margin corresponding to the SOC, the input and output power of the energy storage unit is adjusted in different modes: When the SOC is within the normal operating margin range (e.g., 20% to 90%), the droop control mode is switched to, and the input and output power of the energy storage unit is adjusted using the VP droop control strategy, combined with the DC voltage and the rated DC voltage, to actively participate in the power balance of the DC sub-microgrid; when the SOC is below the lower limit of the normal operating margin (e.g., less than 20%), the discharge-limited mode is switched to (discharge is stopped to protect the battery). When the battery is in a state of charge higher than the normal operating margin (e.g., greater than 90%), the system switches to a limited charging mode (limiting charging power to prevent battery overcharging), limiting the input power of the energy storage unit and adjusting its output power using the VP droop control strategy in conjunction with the DC voltage and rated DC voltage to participate in the power balance of the DC sub-microgrid.

[0069] For each photovoltaic unit in the DC sub-microgrid, maximum power point tracking technology is used to adjust the output power of each photovoltaic unit in the DC sub-microgrid, and output power to the DC bus in a constant power mode, without directly participating in the voltage regulation of the DC bus; when necessary (such as when there is insufficient sunlight or the DC bus does not need more power), the operation mode of the photovoltaic unit is switched to power limiting mode, and no more power is transmitted to the DC bus.

[0070] For each DC load in the DC sub-microgrid, when the DC voltage is lower than a preset safety threshold, the secondary DC loads in the DC sub-microgrid are disconnected to reduce the power consumption of the DC bus, while the main DC loads are not disconnected to ensure the normal operation of the ship.

[0071] For each energy storage unit in the DC sub-microgrid, when switching to the droop control mode, the deviation between the DC voltage and the rated DC voltage, and the preset VP droop characteristic curve corresponding to the energy storage unit are determined. Based on the deviation and the preset VP droop characteristic curve, the target input / output power corresponding to the energy storage unit is calculated. According to the target input / output power, the actual input / output power of the energy storage unit is adjusted (if it is the target input power, power is absorbed from the DC bus to replenish the energy storage unit's energy; if it is the target output power, power is supplied to the DC bus to replenish the DC bus's power). In the droop control mode, both discharging and charging of the energy storage unit are allowed.

[0072] When switching to the limited discharge mode, the deviation between the DC voltage and the rated DC voltage is determined, along with the preset VP droop characteristic curve corresponding to the energy storage unit. Based on this deviation and the preset VP droop characteristic curve, the target input / output power of the energy storage unit is calculated. If the target input power of the energy storage unit is calculated, the actual input power of the energy storage unit is adjusted to absorb power from the DC bus and replenish the energy of the energy storage unit. If the target output power of the energy storage unit is calculated, the energy storage unit stops outputting power to the DC bus to protect the energy storage unit and prevent over-discharge. In the limited discharge mode, only charging of the energy storage unit is allowed; discharging is not permitted.

[0073] When switching to the limited charging mode, the deviation between the DC voltage and the rated DC voltage is determined, along with the preset VP droop characteristic curve corresponding to the energy storage unit. Based on this deviation and the preset VP droop characteristic curve, the target input / output power of the energy storage unit is calculated. If the target input power of the energy storage unit is calculated, the input power of the energy storage unit is limited to prevent overshoot. If the target output power of the energy storage unit is calculated, the actual output power of the energy storage unit is adjusted according to the target output power to deliver power to the DC bus. In the limited charging mode, only discharging of the energy storage unit is allowed, while charging is limited (e.g., by reducing the charging power).

[0074] Furthermore, in this embodiment of the invention, the droop coefficient of the preset VP droop characteristic curve corresponding to each energy storage unit is set based on the ratio of the per-unit value of the maximum available capacity of each energy storage unit. For example, if the active power reference value of energy storage unit 1 is set to 5kW and the active power reference value of energy storage unit 2 is set to 10kW, the active capacity ratio between the two is 1:2, and the ratio of the droop coefficient of the preset VP droop characteristic curve corresponding to energy storage unit 1 to the droop coefficient of the preset VP droop characteristic curve corresponding to energy storage unit 2 is 1:2.

[0075] S3: For each power supply in the AC sub-microgrid (such as a diesel generator as the main power supply), the operating parameters of the power supply (including fuel level, temperature, etc.) are acquired in real time. Based on the operating margin of the power supply corresponding to the operating parameters (including fuel level margin range, temperature margin range, etc.), the output active power of the power supply is adjusted in different modes: When the operating parameters are within the preset margin range of the power supply, the Pf droop control strategy is used, combined with the AC frequency, rated AC frequency, the power supply's active power reference value and droop coefficient, to adjust the output active power of the power supply and participate in the AC sub-microgrid power balance; when the operating parameters exceed the preset margin range of the power supply, the output active power of the power supply is limited, and participation in the AC sub-microgrid power balance is suspended to ensure the safe operation of the power supply.

[0076] This invention utilizes the Pf droop control formula in the Pf droop control strategy to calculate the target output active power of the power supply, and adjusts the actual output active power of the power supply based on the target output active power; the Pf droop control formula is as follows:

[0077] ,

[0078] Wherein, P is the output active power of the power supply; The active power reference value of the power supply; The droop factor is set based on the ratio of the per-unit values ​​of the maximum output power of each power supply, so as to realize the power distribution of multiple power supplies according to the capacity ratio. The rated AC frequency of the AC bus; The AC frequency is collected in real time.

[0079] Furthermore, in this embodiment of the invention, the diesel generator, as a rotating synchronous generator, essentially achieves "active power-frequency droop control" through its droop control. This is an inherent electromechanical regulation process of the synchronous generator or implemented through a speed governor system, which is physically different from the droop control implemented by a power electronic converter, the latter being implemented through controller software. The droop control of the diesel generator is a closed-loop system, the core components of which are: the synchronous generator generating electricity, its speed strictly locked to the AC frequency on the AC bus; the speed governor, a key mechanism controlling the fuel injection quantity of the diesel engine set, which is the physical device that executes "droop control"; and the excitation system, responsible for controlling the output voltage and maintaining voltage stability. Through the speed governor, the frequency deviation is converted into fuel commands and mechanical power inputs, thereby automatically adjusting the generator's output active power.

[0080] S4: Normalize the DC voltage and the AC frequency respectively to obtain normalized DC voltage and normalized AC frequency; calculate the deviation of the normalized DC voltage from its corresponding reference value (in this embodiment, the reference value can be any value between -1 and 1, but for ease of calculation, it is usually taken as 0) and the deviation of the normalized AC frequency from its corresponding reference value; if the deviation of the normalized DC voltage is within the voltage margin range and the deviation of the normalized AC frequency is within the frequency margin range, then maintain the standby state of the interconnecting converter connecting the DC sub-microgrid and the AC sub-microgrid, and the internal... The units participating in power regulation autonomously complete power balancing through their own droop control strategies. If the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, the interconnect converter, based on the dual droop control strategy of the DC voltage and the AC frequency, performs power mutual assistance and distribution on the DC sub-microgrid and the AC sub-microgrid. When the energy storage unit or power supply limits its power due to exceeding the corresponding margin range, the power balancing task it originally participated in is naturally shared by the interconnect converter and other units that have not exceeded the margin range through their own droop control strategies.

[0081] This invention embodiment normalizes the DC voltage and the AC frequency based on normalized expressions, as shown below:

[0082] ,

[0083] ,

[0084] in, The normalized AC frequency, The normalized DC voltage, The AC frequency is... The maximum frequency of the AC bus. The minimum frequency of the AC bus. The DC voltage is... The maximum voltage of the DC bus. This is the minimum voltage of the DC bus. Since voltage and frequency have different order of magnitude, they cannot be directly compared. Therefore, normalization is required. After normalization, the values ​​of DC voltage and AC frequency are controlled between -1 and 1 for easy comparison.

[0085] In this embodiment of the invention, by setting a start-up threshold (voltage margin range and frequency margin range) for the power transmission command of the interconnect converter, the standby state of the interconnect converter is maintained under the condition that the deviation value of the normalized DC voltage is within the voltage margin range and the deviation value of the normalized AC frequency is within the frequency margin range. The power balance of the DC sub-microgrid is autonomously completed by each energy storage unit through local droop control (VP droop control strategy), and the power balance of the AC sub-microgrid is autonomously completed by each power supply through local droop control (Pf droop control strategy).

[0086] If the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, the following steps are performed:

[0087] If the deviation value of the normalized AC frequency is negative (indicating that the AC bus is short of power) and the deviation value of the normalized DC voltage is positive (indicating that the DC bus has a power surplus), then the power on the DC bus is absorbed by the interconnect converter and transmitted to the AC bus.

[0088] If the deviation value of the normalized DC voltage is negative and the deviation value of the normalized AC frequency is positive, then the power absorbed from the AC bus is transmitted to the DC bus through the interconnect converter.

[0089] If both the normalized AC frequency deviation and the normalized DC voltage deviation are negative, the direction of power transmission through the interconnect converter is determined based on the absolute values ​​of their deviations: if the absolute value of the normalized AC frequency deviation is greater than the absolute value of the normalized DC voltage deviation, power is absorbed from the DC bus and transmitted to the AC bus through the interconnect converter; if the absolute value of the normalized AC frequency deviation is less than the absolute value of the normalized DC voltage deviation, power is absorbed from the AC bus and transmitted to the DC bus through the interconnect converter; if the absolute value of the normalized AC frequency deviation is equal to the absolute value of the normalized DC voltage deviation, power is not transmitted through the interconnect converter.

[0090] If the deviation of the normalized AC frequency is positive and the deviation of the normalized DC voltage is positive, then power transmission will not be performed through the interconnect converter.

[0091] The power (magnitude) transmitted by the interconnect converter is calculated in the following way:

[0092] Based on the normalized DC voltage and the preset DC-side VP droop characteristic curve of the interconnect converter, the first response power that the interconnect converter needs to absorb from the DC bus is determined.

[0093] Based on the normalized AC frequency and the preset AC-side Pf droop characteristic curve of the interconnect converter, the second response power that the interconnect converter needs to deliver to the AC bus is determined.

[0094] The difference between the first response power and the second response power is the actual transmission power of the interconnect converter.

[0095] For example, to demonstrate the effectiveness of the above-mentioned overall operation control method for ship AC / DC hybrid power systems based on hybrid margin, this embodiment of the invention uses MATLAB / Simulink simulation tools, combined with specific simulation examples, to further illustrate and verify the above method. The total load on the AC bus is initially set to 20kW (light load), switches to 40kW (heavy load) after 7 seconds, and switches to 30kW (heavy load) after 10 seconds; the total load on the DC bus is initially set to 5kW (light load), switches to 10kW after 10 seconds, and so on for simulation.

[0096] The AC sub-microgrid in this simulation consists of two micro-source systems (fuel cell 1 and fuel cell 2) and a diesel generator. The active power reference value of fuel cell 1 is set to 5kW, and the reactive power reference value is set to 0.5kW; the active power reference value of fuel cell 2 is set to 10kW, and the reactive power reference value is set to 1kW; the active power reference value of the diesel generator is set to 20kW, and the active power capacity ratio of the three is 1:2:4. The DC sub-microgrid consists of two energy storage units (energy storage unit 1 and energy storage unit 2) and a photovoltaic unit. The active power reference value of energy storage unit 1 is set to 5kW, and the active power reference value of energy storage unit 2 is set to 10kW, and the active power capacity ratio of the two is 1:2.

[0097] The simulation results are as follows:

[0098] Simulation data for fuel cell 1 is shown as Source1 in Figure 3, and simulation data for fuel cell 2 is shown as Source2 in Figure 3. The horizontal axis represents time (in seconds), and the vertical axis represents active power (in W). Simulation data for the diesel generator is shown in Figure 4 (where "diesel generator" refers to a diesel generator). The horizontal axis represents time (in seconds), and the vertical axis represents active power (in 10 W). 4In the initial stage, as shown in Figure 3, fuel cell 1 outputs an active power of 2.5kW, fuel cell 2 outputs an active power of 5kW, and the diesel generator outputs an active power of 10kW, with a power ratio of 1:2:4. After 7 seconds, as the total load increases to 40kW, as shown in Figure 3, the active power output of fuel cell 1 changes to 4.5kW, the active power output of fuel cell 2 changes to 9kW, and the active power output of the diesel generator changes to 18kW, maintaining the power ratio of 1:2:4. After 10 seconds, as the total load decreases to 30kW, as shown in Figure 3, the active power output of fuel cell 1 changes to 4kW, the active power output of fuel cell 2 changes to 8kW, and the active power output of the diesel generator changes to 16kW, maintaining the power ratio of 1:2:4. Therefore, it can be concluded that the output power ratio of fuel cell 1, fuel cell 2, and the diesel generator is approximately 1:2:4, consistent with the simulation results of the control method of this invention. The voltage at the point of common coupling (PCC) where fuel cells 1, 2, and the diesel generator connect to the AC bus (i.e., the AC bus voltage) decreases slightly with increasing load. Figure 5 shows the AC frequency waveform of the AC bus, with the horizontal axis representing time (in seconds) and the vertical axis representing AC frequency (in Hz). The frequencies of fuel cells 1 and 2 (i.e., the AC frequency of the AC bus) also decrease slightly with increasing load, fluctuating around 50Hz by 0.5. As shown in Figure 5, there are significant fluctuations at 7s and 10s due to changes in the total load. Subsequently, this invention uses a Pf droop control strategy, employing the Pf droop control formula to calculate the target output active power of the power supply and adjust its actual output power, achieving dynamic adaptation and allocation of active power. Ultimately, this allows the AC frequency to quickly stabilize, verifying the effectiveness of the control method in improving system frequency stability.

[0099] Figure 6 shows the waveforms of the output active power of energy storage unit 1 and energy storage unit 2 as time increases (horizontal axis is time, unit: s; vertical axis is active power, unit: W). The simulation data of energy storage unit 1 is shown as ESS1 in Figure 6, and the simulation data of energy storage unit 2 is shown as ESS2 in Figure 6. In the initial stage, the output active power of energy storage unit 1 is 2.65kW, and the output active power of energy storage unit 2 is 5.3kW, with a power ratio of approximately 1:2. After 7 seconds, as the AC sub-microgrid side becomes overloaded, more power is transmitted from the DC sub-microgrid side to the AC sub-microgrid side. The output active power of energy storage unit 1 changes to 4.5kW, and the output active power of energy storage unit 2 changes to 9.1kW, with the power ratio still maintaining 1:2. After 10 seconds, as the total load on the DC side increases to 10kW and the total load on the AC side decreases, the output active power of energy storage unit 1 changes to 4.1kW, and the output active power of energy storage unit 2 changes to 8.15kW, with the power ratio remaining at 1:2. It can be concluded that the output power ratio of energy storage unit 1 to energy storage unit 2 is approximately 1:2, and the simulation results are consistent with the control method of this invention. As shown in Figure 7, the DC bus voltage versus time waveform, with the horizontal axis representing time (s) and the vertical axis representing DC bus voltage (V), shows that at 7s and 10s in Figure 7, the DC bus voltage decreases slightly with increasing total load. Subsequently, by adjusting the output power of the energy storage unit through the VP droop control strategy of this invention, the DC bus voltage quickly stabilizes, verifying the stability of the DC side voltage. As shown in Figure 8 (horizontal axis representing time (s); vertical axis representing SOC (%)), the SOC of energy storage unit 1 changes over time. The SOC is neither greater than 90% nor less than 20%, remaining within the normal operating margin range during the simulation. No overcharging or over-discharging risk was observed, and the energy storage unit maintained normal operation, demonstrating the equipment protection effect of this invention based on hybrid margin.

[0100] As shown in Figure 9, the horizontal axis represents time (seconds), and the vertical axis represents transmitted active power (watts). Initially, the interconnect converter absorbs 2.7 kW of power from the DC sub-microgrid to the AC sub-microgrid. After 7 seconds, the interconnect converter absorbs 8.55 kW of power from the DC sub-microgrid to the AC sub-microgrid, quickly alleviating the power shortage on the AC side. After 10 seconds, the interconnect converter absorbs 2 kW of power from the DC sub-microgrid to the AC sub-microgrid, dynamically adapting to the load / power demand. The simulation results are consistent with the control method of this invention.

[0101] Simulation results demonstrate that the control method for the ship's AC / DC hybrid power system based on hybrid margin, as proposed in this invention, can not only achieve reasonable power allocation within the ship's AC / DC sub-microgrids, but also realize power mutual assistance and coordinated operation between AC / DC sub-microgrids through interconnecting converters. Furthermore, the simulation shows that the output power of each micro-source is proportional to its own capacity, indicating the correctness of the proposed solution.

[0102] Based on the same inventive concept, one or more embodiments of this specification also provide a control system for a ship AC / DC hybrid electric system based on hybrid margin. Since the working principle of the control system for the ship AC / DC hybrid electric system based on hybrid margin is the same as the aforementioned control method for the ship AC / DC hybrid electric system based on hybrid margin, the implementation of the control system for the ship AC / DC hybrid electric system based on hybrid margin can refer to the aforementioned implementation of the control method for the ship AC / DC hybrid electric system based on hybrid margin, and the repeated parts will not be described again.

[0103] Figure 10 is a block diagram of a control system structure for a shipboard AC / DC hybrid electric system based on hybrid margin, provided in one or more embodiments of this specification. As shown in Figure 10, the control system includes a data acquisition module 101, a DC sub-microgrid internal power autonomy module 102, an AC sub-microgrid internal power autonomy module 103, and an AC / DC sub-microgrid power interaction control module 104, connected in sequence.

[0104] Data acquisition module 101 collects in real time the DC voltage of the DC bus in the DC sub-microgrid and the AC frequency of the AC bus in the AC sub-microgrid of the ship's AC / DC hybrid power system;

[0105] The DC sub-microgrid internal power autonomy module 102 acquires the state of charge (SOC) of each energy storage unit in real time. Based on the operating margin corresponding to the SOC, it adjusts the input and output power of the energy storage units in different modes: when the SOC is within the normal operating margin range, it switches to droop control mode, using the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the input and output power of the energy storage units and participate in the DC sub-microgrid power balance; when the SOC is lower than the lower limit of the normal operating margin, it switches to limited discharge mode, stops the energy storage units from outputting power to the DC bus, and uses the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the input power of the energy storage units and participate in the DC sub-microgrid power balance; when the SOC is higher than the upper limit of the normal operating margin, it switches to limited charging mode, limits the input power of the energy storage units, and uses the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the output power of the energy storage units and participate in the DC sub-microgrid power balance.

[0106] The internal power autonomy module 103 of the AC sub-microgrid acquires the operating parameters of each power supply in real time. Based on the operating margin corresponding to the operating parameters, it adjusts the output active power of the power supply in different modes: when the operating parameters are within the preset margin range of the power supply, it uses a Pf droop control strategy, combined with the AC frequency, rated AC frequency, power supply active power reference value and droop coefficient, to adjust the output active power of the power supply and participate in the power balance of the AC sub-microgrid; when the operating parameters exceed the preset margin range of the power supply, it limits the output active power of the power supply, suspends participation in the power balance of the AC sub-microgrid, and ensures the safe operation of the power supply.

[0107] The AC / DC sub-microgrid power interaction control module 104 normalizes the DC voltage and the AC frequency to obtain normalized DC voltage and normalized AC frequency; it calculates the deviations of the normalized DC voltage from its corresponding reference value and the deviations of the normalized AC frequency from its corresponding reference value; if the deviation of the normalized DC voltage is within the voltage margin range and the deviation of the normalized AC frequency is within the frequency margin range, then the standby state of the interconnecting converter connecting the DC sub-microgrid and the AC sub-microgrid is maintained, and the power regulation is controlled by the units within each sub-microgrid. The self-droop control strategy autonomously completes power balancing; if the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, then the interconnect converter, based on the dual droop control strategy of the DC voltage and the AC frequency, performs power mutual assistance and distribution on the DC sub-microgrid and the AC sub-microgrid; when the energy storage unit or power supply limits its power due to exceeding the corresponding margin range, the power balancing task it originally participated in is naturally shared by the interconnect converter and other units that have not exceeded the margin range through the self-droop control strategy.

[0108] Furthermore, the DC sub-microgrid internal power autonomy module 102 also includes: using maximum power point tracking technology to adjust the output power of each photovoltaic unit in the DC sub-microgrid, outputting power to the DC bus in a constant power mode, and not directly participating in the voltage regulation of the DC bus; when the DC voltage is lower than a preset safety threshold, disconnecting the secondary loads in the DC sub-microgrid to reduce the power consumption of the DC bus, without disconnecting the main loads in the DC sub-microgrid, so as not to affect the normal operation of the ship.

[0109] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product implemented 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. The solutions in the embodiments of the present invention can be implemented using various computer languages, such as the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0110] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and 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 means for implementing the functions specified in one or more blocks of the flowchart illustrations and / or one or more blocks of the block diagrams.

[0111] 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 that implement the functions specified in one or more flowcharts and / or one or more block diagrams.

[0112] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, such that the instructions, which execute on the computer or other programmable apparatus, provide steps for implementing the functions specified in one or more flowcharts and / or one or more block diagrams.

[0113] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although preferred embodiments of the present invention have been described, those skilled in the art can make other modifications or equivalent substitutions to these embodiments once they understand the basic inventive concept. In short, all technical solutions and improvements that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the present invention patent.

Claims

1. A control method for a ship's AC / DC hybrid electric system based on hybrid margin, characterized in that, Includes the following steps: S1: Real-time acquisition of the DC voltage of the DC bus in the DC sub-microgrid and the AC frequency of the AC bus in the AC sub-microgrid of the ship's AC / DC hybrid power system; S2: For each energy storage unit in the DC sub-microgrid, real-time acquisition of the state of charge (SCC) of the energy storage unit, and based on the operating margin corresponding to the SCC, adjusting the input and output power of the energy storage unit in different modes: When the SCC is within the normal operating margin range, switch to droop control mode, and use the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the input and output power of the energy storage unit to participate in the power balance of the DC sub-microgrid; When the SCC is lower than the lower limit of the normal operating margin, switch to limited discharge mode, stop the energy storage unit from outputting power to the DC bus, and use the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the input power of the energy storage unit to participate in the power balance of the DC sub-microgrid; When the SCC is higher than ... When the operating margin reaches the upper limit, switch to the limited charging mode to limit the input power of the energy storage unit. Utilize the VP droop control strategy, combined with the DC voltage and rated DC voltage, to adjust the output power of the energy storage unit and participate in the DC sub-microgrid power balance. S3: For each power supply in the AC sub-microgrid, obtain the operating parameters of the power supply in real time. Based on the operating margin corresponding to the operating parameters, adjust the output active power of the power supply in different modes: When the operating parameters are within the preset margin range of the power supply, use the Pf droop control strategy, combined with the AC frequency, rated AC frequency, the power supply's active power reference value, and the droop coefficient, to adjust the output active power of the power supply and participate in the AC sub-microgrid power balance; when the operating parameters exceed the preset margin range of the power supply, limit the output active power of the power supply, suspend participation in the AC sub-microgrid power balance, and ensure the safe operation of the power supply. S4: Normalize the DC voltage and the AC frequency respectively to obtain normalized DC voltage and normalized AC frequency; The deviations of the normalized DC voltage and its corresponding reference value, and the deviations of the normalized AC frequency and its corresponding reference value are calculated. If the deviation of the normalized DC voltage is within the voltage margin range and the deviation of the normalized AC frequency is within the frequency margin range, the interconnect converter connecting the DC sub-microgrid and the AC sub-microgrid remains in standby mode, and the power balance is autonomously achieved by the units participating in power regulation within each sub-microgrid through their own droop control strategies. If the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, the interconnect converter performs power mutual assistance and distribution on the DC sub-microgrid and the AC sub-microgrid based on the dual droop control strategy of the DC voltage and the AC frequency. When the energy storage unit or power supply limits its power due to exceeding the corresponding margin range, the power balancing task it originally participated in is naturally shared by the interconnect converter and other units that have not exceeded the margin range through their own droop control strategies.

2. The method according to claim 1, characterized in that, The S2 step further includes: using maximum power point tracking technology to adjust the output power of each photovoltaic unit in the DC sub-microgrid, outputting power to the DC bus in a constant power mode, and not directly participating in the voltage regulation of the DC bus; when the DC voltage is lower than a preset safety threshold, disconnecting the secondary loads in the DC sub-microgrid to reduce the power consumption of the DC bus.

3. The method according to claim 1 or 2, characterized in that, In step S2, for each energy storage unit in the DC sub-microgrid, when switching to the droop control mode, the deviation value between the DC voltage and the rated DC voltage, and the preset VP droop characteristic curve corresponding to the energy storage unit are determined. Based on the deviation value and the preset VP droop characteristic curve, the target input / output power corresponding to the energy storage unit is calculated, and the actual input / output power of the energy storage unit is adjusted according to the target input / output power. When switching to the limited discharge mode, the deviation between the DC voltage and the rated DC voltage, and the preset VP droop characteristic curve corresponding to the energy storage unit are determined. Based on the deviation and the preset VP droop characteristic curve, the target input / output power of the energy storage unit is calculated. If the target input power of the energy storage unit is obtained, the actual input power of the energy storage unit is adjusted according to the target input power. If the target output power of the energy storage unit is obtained, the output power of the energy storage unit to the DC bus is stopped. When switching to the limited charging mode, the deviation between the DC voltage and the rated DC voltage, and the preset VP droop characteristic curve corresponding to the energy storage unit are determined. Based on the deviation and the preset VP droop characteristic curve, the target input / output power of the energy storage unit is calculated. If the target input power of the energy storage unit is obtained, the input power of the energy storage unit is limited. If the target output power of the energy storage unit is calculated, the actual output power of the energy storage unit is adjusted according to the target output power.

4. The method according to claim 3, characterized in that, In step S2, based on the ratio of the per-unit value of the maximum available capacity of each energy storage unit, the droop coefficient of the preset VP droop characteristic curve corresponding to each energy storage unit is set.

5. The method according to claim 1 or 2, characterized in that, In step S3, the target output active power of the power supply is calculated using the Pf droop control formula in the Pf droop control strategy, and the actual output active power of the power supply is adjusted based on the target output active power; the Pf droop control formula is as follows: Where P is the output active power of the power supply. This refers to the reference value of the active power of the power supply. The droop coefficient is... The rated AC frequency of the AC bus is [missing information]. The AC frequency is collected in real time; based on the ratio of the per-unit values ​​of the maximum output power of each power supply, a droop coefficient is set for each power supply. The power supply includes a diesel generator, and the operating parameters include the fuel level and temperature of the power supply. The preset margin range of the power supply includes a fuel level margin range and a temperature margin range.

6. The method according to claim 1, characterized in that, In step S4, the DC voltage and the AC frequency are normalized based on normalized expressions, as shown below: ， ,in, The normalized AC frequency, The normalized DC voltage, The AC frequency is... The maximum frequency of the AC bus. The minimum frequency of the AC bus. The DC voltage is... The maximum voltage of the DC bus. This is the minimum voltage of the DC bus.

7. The method according to claim 1 or 2, characterized in that, In step S4, if the deviation value of the normalized DC voltage exceeds the voltage margin range, and / or the deviation value of the normalized AC frequency exceeds the frequency margin range, the following steps are performed: If the deviation value of the normalized AC frequency is negative and the deviation value of the normalized DC voltage is positive, then the power on the DC bus is absorbed by the interconnect converter and transmitted to the AC bus; if the deviation value of the normalized DC voltage is negative and the deviation value of the normalized AC frequency is positive, then the power on the AC bus is absorbed by the interconnect converter and transmitted to the DC bus; if the deviation value of the normalized AC frequency is negative and the deviation value of the normalized DC voltage is negative, then the power transmitted through the interconnect converter is determined based on the absolute value of the two deviation values. Direction of power transmission: If the absolute value of the deviation of the normalized AC frequency is greater than the absolute value of the deviation of the normalized DC voltage, then the power on the DC bus is absorbed by the interconnect converter and transmitted to the AC bus; if the absolute value of the deviation of the normalized AC frequency is less than the absolute value of the deviation of the normalized DC voltage, then the power on the AC bus is absorbed by the interconnect converter and transmitted to the DC bus; if the absolute value of the deviation of the normalized AC frequency is equal to the absolute value of the deviation of the normalized DC voltage, then power transmission does not occur through the interconnect converter; if both the deviation of the normalized AC frequency and the deviation of the normalized DC voltage are positive, then power transmission does not occur through the interconnect converter.

8. The method according to claim 7, characterized in that, In step S4, based on the normalized DC voltage and the preset DC-side VP droop characteristic curve of the interconnect converter, the first response power that the interconnect converter needs to absorb from the DC bus is determined; based on the normalized AC frequency and the preset AC-side Pf droop characteristic curve of the interconnect converter, the second response power that the interconnect converter needs to deliver to the AC bus is determined; the difference between the first response power and the second response power is the actual transmission power of the interconnect converter.

9. A control system for a ship's AC / DC hybrid electric system based on hybrid margin, characterized in that, The system includes a data acquisition module, a DC sub-microgrid internal power autonomy module, an AC sub-microgrid internal power autonomy module, and an AC / DC sub-microgrid power interaction control module connected in sequence. The data acquisition module collects in real-time the DC voltage of the DC bus in the DC sub-microgrid and the AC frequency of the AC bus in the AC sub-microgrid of the ship's AC / DC hybrid power system. The DC sub-microgrid internal power autonomy module acquires the state of charge (SOC) of each energy storage unit in the DC sub-microgrid in real-time and adjusts the input and output power of the energy storage units according to the operating margin corresponding to the SOC: when the SOC is within the normal operating margin range, it switches to droop control mode and utilizes VP droop control... The system employs a control strategy that, in conjunction with the DC voltage and rated DC voltage, adjusts the input and output power of the energy storage unit to participate in the power balance of the DC sub-microgrid. When the state of charge (SBC) is lower than the lower limit of the normal operating margin, it switches to a limited discharge mode, stopping the energy storage unit from outputting power to the DC bus. Then, using a VP droop control strategy, in conjunction with the DC voltage and rated DC voltage, it adjusts the input power of the energy storage unit to participate in the power balance of the DC sub-microgrid. When the SBC is higher than the upper limit of the normal operating margin, it switches to a limited charge mode, limiting the input power of the energy storage unit. Then, using a VP droop control strategy, in conjunction with the DC voltage and rated DC voltage, it adjusts the output power of the energy storage unit. The AC sub-microgrid participates in power balancing. The AC sub-microgrid's internal power autonomy module: For each power supply in the AC sub-microgrid, it acquires the operating parameters of the power supply in real time, and adjusts the output active power of the power supply according to the operating margin corresponding to the operating parameters, in different modes: When the operating parameters are within the preset margin range of the power supply, it uses a Pf droop control strategy, combined with the AC frequency, rated AC frequency, the power supply's active power reference value, and the droop coefficient, to adjust the output active power of the power supply and participate in AC sub-microgrid power balancing; when the operating parameters exceed the preset margin range of the power supply, it limits the output active power of the power supply and suspends its participation in AC sub-microgrid power balancing. Microgrid power balancing ensures safe operation of the power supply. The AC / DC sub-microgrid power interaction control module normalizes the DC voltage and AC frequency to obtain normalized DC voltage and normalized AC frequency. It calculates the deviation of the normalized DC voltage from its corresponding reference value and the deviation of the normalized AC frequency from its corresponding reference value. If the deviation of the normalized DC voltage is within the voltage margin range and the deviation of the normalized AC frequency is within the frequency margin range, the interconnecting converter connecting the DC sub-microgrid and the AC sub-microgrid is kept in standby mode, and the power balancing is autonomously completed by the power regulation units within each sub-microgrid through their own droop control strategies.If the deviation of the normalized DC voltage exceeds the voltage margin range, and / or the deviation of the normalized AC frequency exceeds the frequency margin range, then the interconnect converter, based on a dual droop control strategy of the DC voltage and the AC frequency, performs power balancing and distribution between the DC sub-microgrid and the AC sub-microgrid. When an energy storage unit or power supply limits its power due to exceeding the corresponding margin range, the power balancing task it originally participated in is naturally shared by the interconnect converter and other units that have not exceeded the margin range through their own droop control strategies.

10. The system according to claim 9, characterized in that, The internal power autonomy module of the DC sub-microgrid further includes: using maximum power point tracking technology to adjust the output power of each photovoltaic unit in the DC sub-microgrid, outputting power to the DC bus in a constant power mode, and not directly participating in the voltage regulation of the DC bus; when the DC voltage is lower than a preset safety threshold, disconnecting the secondary loads in the DC sub-microgrid to reduce the power consumption of the DC bus.

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