A full-electric ship braking energy recovery and utilization system and method

Abstract

The present invention discloses a system for recovering and utilizing the braking energy of an all-electric ship. The system of the present invention includes a composite energy storage system, a propulsion system, a bidirectional inverter system, and a signal acquisition and control system. The method for recovering and utilizing energy includes: receiving a braking instruction and obtaining the state parameters of relevant devices; calculating the target electromagnetic torque of the propulsion motor according to the water flow velocity to match the propeller load, so that the generator operates at the maximum power point; configuring the charging power according to the rotational speed of the propulsion motor, the maximum charging power of the battery, and the capacity of the supercapacitor; feeding back the actual braking torque instruction according to the SOC value of the battery and the state of the supercapacitor; and feeding back the real-time target torque of the propulsion motor according to the change in the water flow velocity to adjust the rotational speed and blade pitch of the propeller, so as to keep the water energy utilization rate at the maximum. The present invention can effectively exert the potential of the power system of a pure electric ship and improve the energy utilization efficiency and endurance of the all-electric ship.

Description

Technical Field

[0001] The present invention relates to the field of new energy ship electric propulsion, and particularly to a full-electric ship braking energy recovery and utilization system and method adopting a maximum power point tracking strategy. Background Art

[0002] As the core system of a ship, the ship power system is directly related to the main performance of the ship. Therefore, seeking an optimized design method for the ship power system is a hot topic in ship design. The adoption of an electric propulsion system for a ship can achieve flexible arrangement of power devices, make full use of the engine room space, improve fuel consumption, and enhance the energy efficiency of the ship. In addition to using an electric motor to replace the diesel engine to drive the propeller, a full-electric ship also replaces the power generation diesel engine of a traditional electric propulsion ship with new energy equipment such as fuel cells or adopts various energy storage devices to achieve zero carbon emissions of the ship.

[0003] The ship braking process is a process of stopping the hull from sailing, which has the characteristic of large energy feedback. Currently, the commonly adopted method is to dissipate this part of the feedback energy through a resistor, that is, a braking resistor is connected during the braking process, and the braking energy during the braking process is converted into heat energy and consumed. The advantage of this form is simple structure and low cost, but at the same time, there is also the problem of low braking efficiency. A larger braking resistor needs to be configured under frequent braking conditions, resulting in a large amount of energy waste; while adopting the energy storage method can also effectively solve the problem of feedback energy during the ship braking process. According to the classification of energy storage devices, there are mainly supercapacitor energy storage, flywheel energy storage, battery energy storage, and superconducting magnetic energy storage. Among them, the control of flywheel energy storage is relatively complex, and problems such as friction loss affect the service life; the cost of superconducting energy storage devices is relatively high, and the energy density per unit volume is low, making it difficult to apply in practice. Battery energy storage has been relatively maturely developed and has been successfully applied in the fields of wind power generation, rail transit, and aerospace; supercapacitors have the characteristics of high energy density, long cycle service life, fast charge and discharge, etc., and are more adaptable to the complex working environment of the ship electric propulsion system.

[0004] The ship braking energy recovery and utilization system of the present invention combines the characteristics of the power device of the full-electric ship itself, flexibly configures the charging power of the battery and the supercapacitor, and adopts a maximum power point tracking strategy to realize the energy recovery during the full-electric ship braking process, improving the energy recovery efficiency of the system; this system gives full play to the advantages of the energy storage system of the full-electric ship, can solve the problems of poor battery cycle life and supercapacitor capacity configuration, and plays an important role in improving the energy efficiency level of the ship. Summary of the Invention

[0005] The present invention provides a full-electric ship braking energy recovery and utilization system and method adopting a maximum power point tracking strategy to achieve efficient energy recovery during the full-electric ship braking process.

[0006] The present invention adopts the following technical solutions:

[0007] The full-electric ship braking energy recovery and utilization system provided by the present invention mainly consists of a composite energy storage system, a propulsion system, a bidirectional inverter system, and a signal acquisition and control system. The composite energy storage system is connected to the propulsion system through a DC bus, and data monitoring of the power grid and various devices is carried out through the signal acquisition and control system. The bidirectional inverter system is connected to the DC bus and the propulsion motor, and is used to convert the AC electric energy converted by the propulsion motor into DC electric energy and transmit it to the DC bus during the process of ship braking energy recovery.

[0008] The composite energy storage system includes a power battery pack and a series-connected supercapacitor bank. The power battery pack serves as the energy source of the full-electric ship, is connected to the DC bus through a DC / DC converter, and is used to store the energy during the ship braking process and provide electric energy to the load on the DC power grid.

[0009] The propulsion system includes a propulsion motor and a controllable pitch propeller (CPP). The propulsion motor acts as a generator to transmit electric energy to the power grid during the ship braking process. The controllable pitch propeller adjusts the blade pitch to maximize the water energy utilization rate during the ship braking process.

[0010] For the bidirectional inverter system, the main circuit topology adopts a diode neutral point clamped three-level inverter structure, and the main switch device selects IGBT, which can work in the inverter state to generate AC output, or work in the active rectification state to feed back energy to the power grid.

[0011] The signal acquisition and control system consists of a host computer, a PLC signal acquisition and control unit, and sensors. The sensors collect data of relevant devices, the host computer receives the data collected by the PLC controller, and the PLC and the host computer conduct data communication through the industrial Ethernet TCP / IP method. The PLC signal acquisition and control unit mainly completes the control function through hardware wiring and serial communication.

[0012] The full-electric ship braking energy recovery and utilization method provided by the present invention specifically includes the following steps:

[0013] S1 Receive the braking command and obtain the state parameters of relevant devices;

[0014] S2 Calculate the target electromagnetic torque of the propulsion motor according to the water flow velocity to match the propeller load, so that the generator operates at the maximum power point;

[0015] S3 Configure the charging power according to the propulsion motor speed, the maximum charging power of the battery, and the capacity of the supercapacitor;

[0016] S4 Feedback the actual braking torque command according to the SOC value of the battery and the supercapacitor state;

[0017] S5 adjusts the real-time target torque of the propulsion motor according to the change in water flow velocity to regulate the propeller speed so as to keep the water energy utilization rate maximized.

[0018] In the step S1, receiving the braking instruction and obtaining the status parameters of relevant devices includes the braking signal, water flow velocity V, propulsion motor speed n, propulsion power, ship speed Vs, SOC value of the battery and the maximum charging power Pch-max, and SOC value of the supercapacitor.

[0019] The braking signal in the step S1 is the telegraph order issued by the ship's bridge.

[0020] The SOC value of the battery and the SOC value of the supercapacitor are determined by sampling through the controller, reflecting the actual remaining power of the battery and the actual remaining capacity of the supercapacitor; the maximum charging power Pch-max of the battery is the rated voltage U of the battery × the maximum charging current Imax of the battery.

[0021] The target torque command of the propulsion motor is calculated from the kinetic energy of the water flow and the propeller energy recovery coefficient to obtain the motor energy recovery power, which is used as the maximum power point for the operation of the propulsion motor.

[0022] The process of the step S3 is as follows:

[0023] S31 calculates the propulsion motor energy recovery power Ph according to the propulsion motor speed and the propeller energy recovery coefficient;

[0024] S32 according to the relationship between the maximum charging power Pch-max of the battery and the propulsion motor energy recovery power Ph, if Ph > Pch-max and SOC < 1, the battery works at the maximum charging power, and the remaining part of the power is borne by the supercapacitor; if Ph < Pch-max and SOC < 1, the battery works at the maximum energy recovery power; at any energy recovery power, if the battery SOC = 1, the supercapacitor bears the energy recovery power.

[0025] In the step S4, the target braking torque command is corrected according to the SOC value of the battery and the remaining capacity of the supercapacitor to obtain the real-time braking torque command.

[0026] In the step S5, according to the change in water flow velocity, that is, the change in the kinetic energy of the water flow, the energy recovery power is recalibrated and used as the basis for adjusting the real-time target torque to adjust the propeller blade pitch to keep the water energy utilization rate maximized.

[0027] Advantages compared with the prior art:

[0028] The present invention realizes the following functions through the composite energy storage system, propulsion system, bidirectional inverter system and signal acquisition and control system:

[0029] First, it realizes the recovery and utilization of the braking energy of the ship. Compared with the existing flywheel energy storage control mode, it has a long service life and low friction energy consumption.

[0030] Compared with the existing battery energy storage mode, the ship power grid of the present invention adopts a DC networking technology, reducing the distribution boards and transformers required by the system and having better compatibility with the composite energy storage system.

[0031] Second, it combines the characteristics of the power plant of the all-electric ship itself to flexibly configure the charging power of the battery and the supercapacitor, thereby realizing the maximum power point tracking strategy to recover the energy during the braking process of the all-electric ship and improving the energy recovery efficiency.

[0032] Third, according to the change in the water flow velocity, i.e., the change in the kinetic energy of the water flow, the energy recovery power is recalibrated and used as the basis for adjusting the real-time target torque to adjust the pitch of the propeller blades, maintaining the maximum water energy utilization rate and further improving the energy recovery efficiency and endurance in cooperation with the second aspect. Brief Description of the Drawings

[0033] Figure 1 It is a schematic structural diagram of the all-electric ship braking energy recovery and utilization system according to Embodiment 1 of the present invention;

[0034] Figure 2 It is a structural diagram of the all-electric ship power system according to Embodiment 1 of the present invention;

[0035] Figure 3 It is a topological structural diagram of the bidirectional inverter system according to Embodiment 1 of the present invention;

[0036] Figure 4 It is a signal acquisition and control flow chart according to Embodiment 1 of the present invention;

[0037] Figure 5 It is a flow chart according to Embodiment 2 of the present invention. Detailed Embodiments

[0038] The following further elaborates in detail the specific embodiments of the all-electric ship braking energy recovery and utilization method of the present invention in conjunction with the drawings.

[0039] Embodiment 1, an all-electric ship braking energy recovery and utilization system, as Figure 1As shown in the figure, the braking energy recovery and utilization system of the all-electric ship mainly consists of a composite energy storage system, a propulsion system, a bidirectional inverter system, and a signal acquisition and control system. Among them, electric energy is transmitted through the DC power grid; the composite energy storage system is connected to the propulsion system through the DC bus and the bidirectional inverter system, and is used for the recovery and storage of braking energy; the energy flow between the composite energy storage system, the ship power grid, and the propulsion system is bidirectional. In the braking energy recovery state, energy is transmitted from the propeller to the propulsion motor, the ship power grid, and the energy storage device; the signal acquisition and control system is respectively connected to the ship power grid, the propulsion motor, and the controllable pitch propeller, and is used to monitor the operating status of each device; the DC side and the AC side of the bidirectional inverter system are respectively connected to the ship power grid and the propulsion motor, and are used to supply power to the propulsion motor and convert the alternating current generated by the propulsion motor into direct current during braking.

[0040] As Figure 2 As shown in the figure is the structural diagram of the all-electric ship power system. The composite energy storage system includes a power battery pack and a supercapacitor bank. The battery used in the power battery pack is a lithium iron phosphate battery, which is connected to the DC power grid in series with a bidirectional DC / DC converter. The power battery pack, as the energy source of the all-electric ship, is connected to the DC bus through the bidirectional DC / DC converter, and is used to store the energy during the ship braking process and supply electric energy to the loads on the DC power grid; the supercapacitor bank can be composed of multiple supercapacitors connected in series and parallel according to the power demand of the all-electric ship. In this way, the equivalent capacitance value of a single supercapacitor can be reduced under the same capacity requirement, the inertial time constant can be reduced, the charge and discharge process can be accelerated, and the system cost can be reduced; the composite energy storage system combines the characteristics of high energy density of the battery and the advantages of fast charge and discharge speed and long life of the supercapacitor. For the all-electric ship, after adding the supercapacitor energy storage unit, it can effectively absorb the feedback energy during the ship braking process and reduce the impact of frequent high-power charge and discharge on the battery life. In the ship braking energy recovery state, the energy flow of the braking energy recovery is as follows: the water flow drives the propeller to rotate, that is, the propeller absorbs the kinetic energy of the water flow and converts it into mechanical energy; and drives the rotor of the propulsion motor to rotate. The propulsion motor acts as a generator during this process and converts mechanical energy into electric energy; the electric energy generated by the propulsion motor is rectified by the inverter system and then input into the ship DC power grid, and the charging power of each energy storage device and the energy consumption of the power grid load device are allocated according to the aforementioned charging strategy, and finally the conversion, utilization, and energy storage of the energy during the ship braking process are completed.

[0041] The propulsion system includes a propulsion motor and a controllable pitch propeller (CPP). During the ship braking process, the propulsion motor acts as a generator to transmit electrical energy to the power grid. The controllable pitch propeller adjusts the blade pitch to maximize the utilization rate of water energy during the ship braking process. During the ship braking process, the controllable pitch propeller can adjust the blade pitch according to the water flow speed and make real-time adjustments following the change of the water flow speed, enabling the propeller to maximize the utilization of the kinetic energy of the water flow. The propulsion motor is connected to the propeller. During the braking process, the propulsion motor operates in the power generation mode, and the propeller drives the propulsion motor to generate electricity to achieve energy recovery during the ship braking process.

[0042] The bidirectional inverter system, as Figure 3 shown, adopts a diode neutral point clamped three-level inverter structure for the main circuit topology. The main switch device selects IGBT, which can not only operate in the inverter state to generate AC output but also operate in the active rectification state to feed back energy to the power grid. The adopted three-level inverter structure can effectively reduce the turn-off voltage borne by the switching components and has little impact on the propulsion motor. A protection circuit is set for the IGBT in the inverter. By setting a current limiting inductor, the current change rate of the inverter is suppressed and the overvoltage during the turn-off of the IGBT is protected. At the AC output end of the bidirectional inverter system, a three-phase LRC filter needs to be connected to reduce the harmonics of the output voltage to protect the propulsion motor from being impacted by impulse voltage.

[0043] The signal acquisition and control system, as Figure 4 is composed of a host computer, a PLC information acquisition and control unit, a transmitter, and sensors. The specific acquisition process is that the sensors collect the rotational speed, voltage, and current information of the propulsion motor, the temperature and voltage data of the battery pack, the current and voltage data of the supercapacitor bank, and the blade displacement data of the controllable pitch propeller, and then the signals are transmitted to the PLC through the transmitter. The PLC communicates with the host computer through the industrial Ethernet TCP / IP method, and the PLC and the device control unit mainly complete the control function through hardware wiring and serial communication.

[0044] Embodiment 2, as Figure 5 shown, is a method for recovering and utilizing the braking energy of an all-electric ship disclosed by the present invention, including the following steps:

[0045] S1. Receive the braking instruction and obtain the state parameters of relevant devices;

[0046] S2. Calculate the target electromagnetic torque of the propulsion motor according to the water flow speed to match the propeller load, so that the generator operates at the maximum power point;

[0047] S3. Configure the charging power according to the rotational speed of the propulsion motor, the maximum charging power of the battery, and the capacity of the supercapacitor;

[0048] S4. Feed back the actual braking torque command according to the SOC value of the storage battery and the status of the super capacitor;

[0049] S5. Feed back the real-time target torque of the motor according to the change of water flow velocity to adjust the propeller speed so that the water energy utilization rate is maximized.

[0050] In the step S1, receiving the braking command and obtaining the status parameters of relevant devices include braking signal, water flow velocity V, propulsion motor speed n, propulsion power, ship speed Vs, SOC value of the storage battery and maximum charging power Pch-max, and SOC value of the super capacitor. Specifically, the operation parameters of the above-mentioned various devices are sampled through the signal acquisition and control system, that is, the SOC value of the storage battery and the SOC value of the super capacitor are determined by sampling through the controller, reflecting the actual remaining power of the storage battery and the actual remaining capacity of the super capacitor; the maximum charging power Pch-max of the storage battery is the rated voltage U of the storage battery × the maximum charging current Imax of the battery; when the controller detects that the telegraph level signal of ship braking is sent from the ship's bridge, that is, the system enters the braking energy recovery mode, and step S2 is executed.

[0051] In the step S2, after the system enters the braking energy recovery mode, the PLC processes the collected device data and calculates the target torque command of the propulsion motor; the target torque command of the propulsion motor is obtained by calculating the propulsion motor energy recovery power from the kinetic energy of water flow and the propeller energy recovery coefficient, and is used as the maximum power point of the propulsion motor; the propeller energy recovery coefficient is a functional relationship between the propeller tip speed ratio and the pitch angle, and is the energy recovery coefficient determined according to the propeller speed at different water flow velocities.

[0052] The specific process of the step S3 is as follows:

[0053] S31. Calculate the propulsion motor energy recovery power Ph according to the propulsion motor speed and the propeller energy recovery coefficient. The propulsion motor energy recovery power is calculated by the following formula:

[0054]

[0055] In the formula, is the propeller energy recovery coefficient, is the water density, is the swept area of the propeller blade, and V is the ship speed.

[0056] S32. According to the relationship between the maximum charging power Pch-max of the storage battery and the motor energy recovery power Ph, if Ph > Pch-max and SOC < 1, the storage battery works at the maximum charging power, and the remaining fluctuating power is borne by the super capacitor; if Ph < Pch-max and SOC < 1, the storage battery works at the maximum energy recovery power; at any energy recovery power, if the SOC of the storage battery = 1, the super capacitor bears the energy recovery power.

[0057] In the step S4, the target braking torque command is corrected according to the SOC value of the battery and the remaining capacity of the super capacitor to obtain a real-time braking torque command; that is, according to the real-time monitoring of the SOC value of the battery and the SOC value of the super capacitor, and according to the power distribution strategy in step S3, the energy recovery mode is adjusted in real time, and the corrected motor braking torque is recalculated.

[0058] In the step S5, according to the change in water flow velocity, that is, the change in the kinetic energy of water flow, the energy recovery power is recorrected and used as the adjustment basis for the real-time target torque to adjust the pitch of the propeller blades to keep the utilization rate of water energy maximized.

[0059] Through the above steps, the energy recovery and utilization during the braking process of the all-electric ship can be realized, the feedback energy during the ship braking process can be maximally utilized, the potential of the pure electric ship power system can be effectively exerted, the energy utilization efficiency of the all-electric ship is improved, and the endurance of the ship is increased.

[0060] In addition, the above embodiments are not limitations on the present invention. The all-electric ship energy recovery and utilization system and method described in the present invention include but are not limited to the above specific embodiments. Therefore, the protection scope of this invention patent shall be defined by the appended claims.

Claims

1. A method for recovering and utilizing the braking energy of an all-electric ship, characterized in that, For a fully electric ship braking energy recovery and utilization system, the fully electric ship braking energy recovery and utilization system includes a composite energy storage system, a propulsion system, a bidirectional inverter system, and a signal acquisition and control system; the composite energy storage system includes a power battery pack and a series-connected supercapacitor bank. The power battery pack serves as the energy source of the fully electric ship and is connected to the DC bus through a DC / DC converter, used to store the energy during the ship braking process and supply electrical energy to the loads on the DC grid. The propulsion system includes a propulsion motor and an adjustable pitch propeller. The propulsion motor acts as a generator to deliver electrical energy to the grid during the ship braking process. The adjustable pitch propeller adjusts the blade pitch to maximize the water energy utilization rate during the ship braking process. For the bidirectional inverter system, the main circuit topology adopts a diode neutral point clamped three-level inverter structure, and the main switch device is an IGBT, which can work in the inverter state to generate an AC output or in the active rectification state to feed back energy to the grid. The signal acquisition and control system consists of a host computer, a PLC signal acquisition and control unit, and sensors. The sensors collect data of relevant equipment, and the PLC communicates with the host computer through the industrial Ethernet TCP / IP method. The PLC signal acquisition and control unit mainly completes the control function through hardware wiring and serial communication. The method for recovering and utilizing the braking energy of the fully electric ship includes the following steps: S1 Receive a braking command and obtain the state parameters of relevant equipment. S2 Calculate the target electromagnetic torque of the propulsion motor according to the water flow velocity to match the propeller load, so that the generator operates at the maximum power point. S3 Configure the charging power according to the propulsion motor speed, the maximum charging power of the battery, and the capacity of the supercapacitor. S4 Feedback the actual braking torque command according to the SOC value of the battery and the state of the supercapacitor. S5 Feedback the real-time target torque of the motor according to the change in the water flow velocity to adjust the pitch of the propeller blades to maximize the water energy utilization rate. The process of step S3 is as follows: S31 Calculate the energy recovery power Ph of the propulsion motor according to the propulsion motor speed and the propeller energy recovery coefficient. S32 According to the relationship between the maximum charging power Pch-max of the battery and the energy recovery power Ph of the propulsion motor, if Ph > Pch-max and SOC < 1, the battery works at the maximum charging power, and the remaining power is borne by the supercapacitor; if Ph < Pch-max and SOC < 1, the battery works at the maximum energy recovery power; at any energy recovery power, if the battery SOC = 1, the supercapacitor bears the energy recovery power. In step S4, the target braking torque command is corrected according to the SOC value of the battery and the remaining capacity of the supercapacitor to obtain the real-time braking torque command.

2. The method for recovering and utilizing the braking energy of an all-electric ship according to claim 1, characterized in that: In step S1, receiving a braking command and obtaining the state parameters of relevant equipment include a braking signal, water flow velocity V, propulsion motor speed n, propulsion power, ship speed Vs, SOC value and maximum charging power Pch-max of the battery, and SOC value of the supercapacitor.

3. The method for recovering and utilizing the braking energy of an all-electric ship according to claim 2, characterized in that: The braking signal is the telegraph order issued by the ship's bridge.

4. The method for recovering and utilizing the braking energy of an all-electric ship according to claim 2, characterized in that: The SOC values of the storage battery and the super capacitor are determined by sampling through a controller, reflecting the actual remaining power of the storage battery and the actual remaining capacity of the super capacitor; the maximum charging power Pch-max of the storage battery is calculated and determined by multiplying the rated voltage U of the storage battery by the maximum charging current Imax of the battery.

5. The method for recovering and utilizing the braking energy of an all-electric ship according to claim 1, characterized in that: In the step S5, according to the change in the water flow velocity, i.e., the change in the kinetic energy of the water flow, the power recovery is recalibrated and used as the basis for adjusting the real-time target torque to adjust the pitch of the propeller blades to maintain the maximum water energy utilization rate.

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