A range-extending power system for small fishing vessels and an energy management method thereof

Abstract

This invention discloses a range-extended propulsion system for small fishing boats and its energy management method, belonging to the technical field of marine power devices. It is applicable to small and medium-sized fishing boats with a length of less than 12 meters and a main engine power of less than 44.1 kW (60 horsepower). The system includes a range extender, a lithium iron phosphate battery pack, a motor controller, a drive motor, and an energy management system. The range extender consists of a small marine diesel engine and a permanent magnet synchronous generator. The battery pack is a 400V high-voltage DC lithium iron phosphate battery, equipped with a full-function battery management system and a liquid cooling device. The drive motor uses a water-cooled permanent magnet synchronous motor to directly drive the propeller, eliminating the need for a gearbox and a long drive shaft. The energy management system automatically switches between pure electric mode, range-extended mode, and hybrid mode based on the battery's state of charge and navigation conditions, ensuring that the range extender diesel engine always operates within the optimal fuel consumption range of 70%~80% load, with peak shaving and valley filling by the battery pack. This invention enables zero-emission, quiet navigation when entering and leaving port, reduces overall fuel consumption by 30%~40%, provides ample low-speed torque, significantly reduces failure rate and maintenance costs, and balances port environmental protection with energy conservation.

Description

Technical Field

[0002] This invention belongs to the field of marine propulsion technology, specifically relating to a range-extended propulsion system suitable for small and medium-sized fishing vessels with a length of less than 12 meters and a main engine power of less than 44.1 kW (60 horsepower), as well as the energy management method of the system. Background Technology

[0003] There are a large number of small and medium-sized fishing vessels in my country's coastal and inland waters. Among them, fishing vessels with a length of less than 12 meters generally use a propulsion system in which the marine diesel engine directly drives the propeller through a gearbox and drive shaft. According to relevant regulations on the inspection of fishing vessels, the main engine power of such fishing vessels is mostly below 60 horsepower (44.1 kW).

[0004] The existing direct-drive propulsion system for diesel engines has the following drawbacks: (1) When fishing boats enter and leave the port, they frequently accelerate and decelerate and cruise at low speeds. The diesel engines operate in the low load range of 20% to 40% for a long time, resulting in incomplete combustion, low fuel efficiency, high fuel consumption, and a significant increase in carbon soot and harmful emissions, which seriously pollutes the fishing port waters and the atmospheric environment of the port area. (2) The diesel engine has insufficient output torque at low speed. In order to meet the requirements of starting, headwind, trawling and other working conditions, it is necessary to configure a multi-speed gearbox and a long drive shaft to achieve speed reduction and torque increase. The structure is complex, occupies cabin space, has a high failure rate and high maintenance cost. (3) The direct drive system of diesel engine has a slow torque response, poor maneuverability in fishing boats with frequent speed changes and headwind operation, and limited torque reserve under heavy load conditions. (4) Although the pure battery power solution can achieve zero emissions, it is limited by the energy density of the battery and cannot meet the endurance requirements of fishing boats for all-weather and deep-sea operations. Moreover, the initial cost is high and it is difficult for existing small fishing boats to adopt it directly.

[0005] Therefore, it is necessary to provide a small fishing boat power system that meets the environmental protection requirements of fishing ports while also taking into account range, fuel economy, and maintenance economy. Summary of the Invention

[0006] In view of the shortcomings of the existing technology, the technical problem to be solved by the present invention is to overcome the defects of the existing small fishing boat diesel engine direct drive system, such as serious pollution when entering and leaving the port, high fuel consumption under low load conditions, complex transmission structure and high maintenance cost, and to provide a range-extended fishing boat power system to achieve environmentally friendly navigation and energy saving in fishing ports.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a range-extended power system for small fishing boats, including a range extender, an energy storage battery pack, a motor controller, a drive motor, and an energy management system.

[0008] The range extender includes a small marine diesel engine and a permanent magnet synchronous generator that is driven (preferably coaxially directly connected) to the diesel engine. The AC output of the generator is connected to the high-voltage DC bus via an AC / DC converter. The energy storage battery pack is a lithium iron phosphate (LFP) battery pack, which is connected to the high-voltage DC bus via a battery management system. The input terminal of the motor controller is connected to the high-voltage DC bus, and the output terminal is connected to the drive motor. The drive motor is a permanent magnet synchronous motor, and its output terminal is driven by a propeller. The energy management system is communicatively connected to the AC / DC converter, the battery management system, and the motor controller.

[0009] The energy management system automatically switches between pure electric mode, range-extending mode, and hybrid mode based on the state of charge (SOC) of the energy storage battery pack and the navigation conditions. In range-extending mode and hybrid mode, the diesel engine is controlled to operate stably at the optimal fuel consumption point of 70% to 80% load. When the navigation power demand is lower than the output power at this operating point, the excess electrical energy is used to charge the energy storage battery pack. When the output power is higher than the output power at this operating point, the power gap is supplemented by the discharge of the energy storage battery pack, i.e., "peak shaving and valley filling".

[0010] Furthermore, the rated power of the drive motor is 40~45kW, the peak power is 60~70kW, the protection level is not lower than IP67, the insulation level is F or H, and water cooling is adopted to adapt to marine salt spray, humid environment and high temperature environment of cabin.

[0011] Furthermore, the rated power of the permanent magnet synchronous generator is 25~35kW, which is about 60%~70% of the rated power of the drive motor. It only needs to cover the average cruise power, and the peak power is undertaken by the battery pack. Therefore, a diesel engine with smaller power and lighter weight can be selected to reduce the system weight and cost.

[0012] Furthermore, the total capacity of the energy storage battery pack is 40~60kWh, and the system voltage is 320~400V high voltage DC; the battery management system has overcharge, over-discharge, overcurrent, short circuit, high temperature, low temperature protection, cell balancing and thermal management functions; the battery pack adopts liquid cooling, with a cycle life of not less than 3000 cycles (80% DOD) and a service life of 5~8 years.

[0013] Furthermore, the energy storage battery pack is located in an independent battery compartment, which is equipped with a combustible gas detection device, a fire extinguishing device, and a forced ventilation device; the battery pack should be a marine product certified by a classification society (such as CCS), and should not be a modified industrial energy storage or vehicle battery, nor should it use pouch cells.

[0014] Furthermore, the output shaft of the drive motor is directly connected to the propeller via a coupling, and the system does not have a gearbox or a long drive shaft.

[0015] The present invention also provides an energy management method for the above system: real-time acquisition of SOC, propeller power demand and operating condition commands; when SOC is not lower than a first threshold (e.g., 80%), it enters pure electric mode and the range extender stops; when SOC is not higher than a second threshold (e.g., 30%), it enters forced range extender mode, the range extender generates electricity at the maximum sustainable power and limits the drive power; during this period, it enters range extender / hybrid mode, the diesel engine load rate is maintained at 70%~80%, and the battery peaks and valleys are filled.

[0016] Compared with the prior art, the beneficial effects of the present invention are: (1) The diesel engine always operates in the optimal fuel consumption range of 70%~80% load, avoiding the low-efficiency low-load area, reducing the overall fuel consumption by 30%~40%, and saving energy significantly; (2) The port entry and exit and the no-discharge zone adopt pure electric mode, with zero emissions and low noise, which fundamentally solves the problem of environmental pollution in fishing ports; (3) The low-speed and high-torque characteristics of the permanent magnet synchronous motor, combined with its peak power capability, are suitable for frequent speed changes, headwind and heavy-load operations of fishing boats, and have a fast operating response. (4) Eliminating the gearbox and long drive shaft reduces the number of system components, significantly lowers the failure rate and maintenance costs, and improves the utilization rate of cabin space; (5) The range extender only needs to cover the average cruising power. The diesel engine displacement is smaller than the original direct drive solution. With the help of the battery to smooth out peaks and valleys, the weight and cost of the whole machine can be controlled. (6) Lithium iron phosphate batteries have good thermal stability, long cycle life and high safety. Combined with an independent battery compartment safety subsystem, they meet marine safety requirements. Attached Figure Description

[0017] Figure 1 This is a block diagram of the overall system structure according to an embodiment of the present invention; Figure 2 This is a flowchart of the energy management mode switching process of the present invention; Figure 3 This is a schematic diagram of power distribution (peak shaving and valley filling) in range-extended mode.

[0018] Explanation of reference numerals in the attached diagram: 1-Diesel engine; 2-Permanent magnet synchronous generator; 3-AC / DC converter; 4-High voltage DC bus; 5-Lithium iron phosphate energy storage battery pack; 6-Battery management system; 7-Motor controller; 8-Drive motor; 9-Propeller; 10-Energy management system; 11-Battery compartment safety subsystem. Detailed Implementation

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the following embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention.

[0020] like Figure 1As shown, the range-extended propulsion system for a small fishing boat in this embodiment includes: a range extender (composed of a diesel engine 1 and a permanent magnet synchronous generator 2), an AC / DC converter 3, a high-voltage DC bus 4, a lithium iron phosphate energy storage battery pack 5, a battery management system 6, a motor controller 7, a drive motor 8, a propeller 9, an energy management system 10, and a battery compartment safety subsystem 11. The diesel engine 1 drives the permanent magnet synchronous generator 2 to generate electricity, which is then rectified and regulated by the AC / DC converter 3 and connected to the 320~400V high-voltage DC bus 4. The energy storage battery pack 5 is connected to the bus 4 via the battery management system 6. The motor controller 7 draws power from the bus 4 to drive the permanent magnet synchronous drive motor 8, which directly drives the propeller 9 via a coupling. The energy management system 10 is communicatively connected to the AC / DC converter 3, the battery management system 6, and the motor controller 7, and uniformly manages the system power flow.

[0021] For fishing vessels under 12 meters with a power rating of 44.1kW (60 horsepower), a 400V high-voltage DC bus is recommended: at this power level, the bus current is approximately 100A, and cable loss is controllable; the 48V low-voltage platform has excessive current and high line loss, and is only suitable for small vessels under 10kW; platforms above 600V are too expensive and are used for large vessels above 100kW.

[0022] Drive Motor 8: A permanent magnet synchronous motor (PMSM) is selected, with an efficiency of over 95%, small size, and high torque, making it the mainstream choice for marine applications. The rated power is 40~45kW, equivalent to the thrust of the original 60 horsepower diesel engine (the motor has high efficiency, and the equivalent thrust of a 40kW motor is approximately equal to that of a 60 horsepower diesel engine); the peak power is 60~70kW, capable of handling short-term high-load conditions such as start-up, headwinds, and heavy loads; the protection level is not lower than IP67, waterproof and salt spray resistant; the insulation class is F or H; water cooling is preferred, providing good sealing and corrosion resistance.

[0023] Range extender: Generator 2's function is to "supplement" power rather than provide full-power supply. Its rated power only needs to cover the average cruising power (approximately 60%~70% of the drive motor's rated power), so it is selected as 25~35kW, with the battery pack responsible for peak shaving and valley filling. Diesel engine 1 is a small marine high-speed diesel engine, compatible with the fishing boat's existing fuel system, and its marine safety is higher than that of gasoline engines; water cooling is preferred to adapt to long-term continuous operation. Generator is preferably a permanent magnet synchronous generator, which is small in size, light in weight, and highly efficient; a rated speed of 1500rpm is quieter and longer-lasting, while 3000rpm is more compact, depending on the cabin space layout.

[0024] Energy storage battery pack 5: Uses lithium iron phosphate (LFP) cells with a cycle life of over 3000 cycles, good thermal stability, and high safety; total capacity of 40~60kWh, meeting the power buffer requirements for 2~4 hours of pure electric navigation and all-day operation; system voltage of 320~400V; energy density of 130~160Wh / kg; protection level of not less than IP67; equipped with a full-function battery management system 6 (overcharge / over-discharge / overcurrent / short circuit / high temperature / low temperature protection, cell balancing, thermal management), with liquid cooling as the preferred cooling method, a cycle life of not less than 3000 cycles (80% DOD), and a service life of 5~8 years.

[0025] drive motor Permanent magnet synchronous, rated 40kW / peak 60kW, water-cooled Approximately 80 kg generator + diesel engine 25kW permanent magnet generator + small diesel engine (approximately 30 horsepower) Approximately 180 kg battery pack Lithium iron phosphate, 40kWh, 400V, IP67 Approximately 350 kg motor controller Compatible with 40kW motors, water-cooled Approximately 20 kg Energy Management System Vehicle-level EMS, automatic start-stop range extender Approximately 5 kg total — Approximately 635 kg Pure electric range is about 2-3 hours (at economic speed); extended range depends on the fuel tank, adding 50L of diesel can extend the range by about 4-6 hours; suitable for fishing boats that mainly operate in coastal waters and for daily short-distance trips.

[0026] drive motor Permanent magnet synchronous, rated 45kW / peak 70kW, water-cooled Approximately 90 kg generator + diesel engine 30kW permanent magnet generator + marine diesel engine (approximately 40 horsepower) Approximately 220 kg battery pack Lithium iron phosphate, 55kWh, 400V, liquid cooling Approximately 450 kg motor controller Compatible with 45kW motor, water-cooled Approximately 25 kg Energy Management System Intelligent EMS, multi-mode switching Approximately 5 kg total — Approximately 790 kg With a pure electric range of approximately 3-4 hours and an extended range, it is suitable for most 10-12 meter fishing and aquaculture vessels.

[0027] drive motor Permanent magnet synchronous, rated 45kW / peak 70kW, water-cooled Approximately 90 kg generator + diesel engine 35kW permanent magnet generator + marine diesel engine (approximately 50 horsepower) Approximately 260 kg battery pack Lithium iron phosphate, 80kWh, 400V, liquid cooling Approximately 650 kg motor controller Compatible with 45kW motor, water-cooled Approximately 25 kg Energy Management System Intelligent EMS, multi-mode switching Approximately 5 kg total — Approximately 1030 kg With a pure electric range of approximately 5-6 hours, it is suitable for fishing vessels operating in the open sea and requiring high endurance.

[0028] like Figure 2 As shown, the energy management system 10 executes the following strategies: Step S1: Real-time collection of battery pack state of charge (SOC), propeller power requirements, speed, and operating commands (port entry / exit / cruising / operation). Step S2: When the SOC is not lower than the first threshold (e.g., 80%), the system enters pure electric mode, the range extender stops, and the battery pack provides power independently, achieving zero-emission and quiet navigation when entering and leaving ports and in restricted areas. Step S3: When the SOC is not higher than the second threshold (e.g., 30%), enter the forced range extender mode, start the range extender and generate electricity at its maximum sustainable power, while appropriately limiting the output power of the drive motor to prevent the battery from being over-discharged; Step S4: When the SOC is between the first threshold and the second threshold, enter the range extender / hybrid mode, and set the range extender power generation to stabilize the diesel engine load rate in the optimal fuel consumption range of 70%~80%. Step S5: As Figure 3As shown, comparing the propeller power demand with the range extender's power generation—when demand is low (such as light-load cruising), excess electrical energy is charged into the battery pack (valley charging); when demand is high (such as starting, headwind, trawling), the power gap is supplemented by the instantaneous discharge of the battery pack (peak-shaving discharge), and the diesel engine always maintains operation at the economic operating point, avoiding inefficient combustion caused by frequent acceleration and deceleration.

[0029] In addition, the fishing boat can charge the battery packs via shore power when it is moored; if the power demand is low when anchoring at night, the battery packs can directly supply power to the boat's electrical loads, further reducing the diesel engine's idling time.

[0030] Battery pack 5 must use marine lithium iron phosphate batteries certified by a classification society (such as CCS), and the use of industrial energy storage or decommissioned vehicle batteries is strictly prohibited; the use of pouch cells is also strictly prohibited (relevant ship inspection rules explicitly exclude this). The battery compartment is independently set up and equipped with combustible gas detection, fire extinguishing and forced ventilation devices, constituting the battery compartment safety subsystem 11. All high-voltage components of the system meet IP67 or higher protection standards, are resistant to salt spray corrosion, and insulation monitoring is installed in the high-voltage circuit.

Claims

1. A range-extended propulsion system for small fishing boats, characterized in that, The system includes a range extender, an energy storage battery pack, a motor controller, a drive motor, and an energy management system. The range extender comprises a small marine diesel engine and a permanent magnet synchronous generator (PMSG) connected to the diesel engine. The AC output of the PMSG is connected to a high-voltage DC bus via an AC / DC converter. The energy storage battery pack is a lithium iron phosphate battery pack, connected to the PMSG via the battery management system. The input terminal of the motor controller is connected to the PMSG, and the output terminal is connected to the drive motor. The drive motor is a PMSG, and its output terminal is connected to a propeller. The energy management system... It is communicatively connected to the AC / DC converter, the battery management system, and the motor controller, respectively. The energy management system is configured to automatically switch between pure electric mode, range-extending mode, and hybrid mode based on the state of charge of the energy storage battery pack and the navigation conditions. In the range-extending mode and the hybrid mode, the diesel engine is controlled to operate stably at the optimal fuel consumption point of 70%~80% load. When the navigation power demand is lower than the output power of the operating point, excess electrical energy is used to charge the energy storage battery pack. When the output power is higher than the output power of the operating point, the power gap is supplemented by the discharge of the energy storage battery pack.

2. The range-extended propulsion system for small fishing boats according to claim 1, characterized in that, The drive motor has a rated power of 40~45kW, a peak power of 60~70kW, a protection level of not less than IP67, an insulation class of F or H, and a water cooling method.

3. The range-extended propulsion system for small fishing boats according to claim 1, characterized in that, The rated power of the permanent magnet synchronous generator is 25~35kW, which is 60%~70% of the rated power of the drive motor, and it is coaxially and directly connected to the diesel engine; the diesel engine is a small marine diesel engine.

4. The range-extended propulsion system for small fishing boats according to claim 1, characterized in that, The total capacity of the energy storage battery pack is 40~60kWh, and the system voltage is 320~400V high voltage DC.

5. The range-extended propulsion system for small fishing boats according to claim 4, characterized in that, The battery management system has overcharge protection, over-discharge protection, overcurrent protection, short circuit protection, high temperature protection, low temperature protection, cell balancing and thermal management functions; the energy storage battery pack is cooled by liquid cooling and has a cycle life of not less than 3000 cycles (80% DOD).

6. The range-extended propulsion system for small fishing boats according to claim 1, characterized in that, The energy storage battery pack is located in an independent battery compartment, which is equipped with a combustible gas detection device, a fire extinguishing device, and a forced ventilation device; the energy storage battery pack is a marine lithium iron phosphate battery pack certified by a classification society.

7. The range-extended propulsion system for small fishing boats according to claim 1, characterized in that, The energy management system is configured to: enter pure electric mode and shut down the range extender when the state of charge is not lower than a first threshold; enter forced range extender mode when the state of charge is not higher than a second threshold, start the range extender and generate electricity at its maximum sustainable power while limiting the output power of the drive motor; and enter the range extender mode or the hybrid mode when the state of charge is between the first threshold and the second threshold.

8. The range-extended propulsion system for small fishing boats according to claim 7, characterized in that, The pure electric mode is used for fishing vessels to enter and leave ports and navigate in prohibited areas, achieving zero emissions and low noise navigation; the first threshold is 80%, and the second threshold is 30%.

9. The range-extended propulsion system for small fishing vessels according to any one of claims 1 to 8, characterized in that, The output shaft of the drive motor is directly connected to the propeller via a coupling, and the system does not have a gearbox or a long drive shaft.

10. An energy management method for a range-extended propulsion system of a small fishing vessel, characterized in that, The small fishing boat range-extended propulsion system according to any one of claims 1 to 9 includes the following steps: S1, real-time acquisition of the state of charge of the energy storage battery pack, propeller power demand, and navigation condition commands; S2, when the state of charge is not lower than a first threshold, controlling the range extender to stop, and the energy storage battery pack provides power independently, entering pure electric mode; S3, when the state of charge is not higher than a second threshold, starting the range extender and generating electricity at its maximum sustainable power, while limiting the output power of the drive motor, entering forced range-extending mode; S4, when the state of charge is between the first and second thresholds, controlling the range extender to operate, and setting the range extender's power generation to maintain the diesel engine's load rate within the optimal fuel consumption range of 70% to 80%; S5, comparing the propeller power demand with the range extender's power generation, charging excess energy into the energy storage battery pack when the demand is low, and discharging the energy storage battery pack to supplement the power gap when the demand is high, thus achieving peak shaving and valley filling.

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