A method for energy management of a marine direct current hybrid power system

Abstract

The present application relates to the technical field of energy management, especially to the energy management technology of the marine DC hybrid power system, in particular to a kind of energy management method for the marine DC hybrid power system composed of multiple groups of fuel cells, multiple groups of lithium batteries and super capacitor.The present application controls each power supply DC / DC converter in the marine DC hybrid power system by monitoring bus voltage, each power supply residual power and other information, so that the hybrid power system switches between 11 kinds of working modes, timely allocates the flow of energy in hybrid power supply, ensures the stability of DC bus at the same time, makes the hybrid power supply system quickly track load change, and realizes the stable and reliable operation of the entire DC hybrid power system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy management, especially to the energy management technology of a ship DC hybrid power system, in particular to an energy management method for a ship DC hybrid power system composed of multiple groups of fuel cells, lithium batteries and super capacitors. BACKGROUND

[0002] Compared with hybrid electric vehicles, all-electric DC ships contain multiple energy sources, and the number of each energy source may not be one. Fuel cells have high energy density, cleanliness, and high energy conversion efficiency, and are widely used. However, a power generation system composed of only fuel cells does not have good load following characteristics, so energy storage devices need to be introduced. Lithium batteries are widely used in energy storage devices, and have a large energy density, but a small power density. When the load power suddenly changes, it cannot quickly absorb or release the target power, and it is difficult to meet the dynamic requirements of the system. The internal physical change occurs when the super capacitor charges and discharges, and it has a large power density, which can provide a large power in a short time to provide a buffer for other devices. Therefore, lithium batteries and super capacitors have strong complementarity in performance. New energy ships usually choose lithium batteries and super capacitors as energy storage devices. The energy management method of the ship DC hybrid power system needs to determine the output of the energy source according to the load change of the ship under different working conditions and the number of grid energy sources, and needs to consider the state of charge (SOC value) and working environment of the energy storage device. The power distribution between different power sources is controlled, and the voltage stability of the entire system is ensured to provide reliable power for the ship at all times.

[0003] In the prior art, there are many studies on the energy management method of a hybrid power system composed of fuel cells and single energy storage devices, such as fuel cells and super capacitors, or fuel cells and lithium batteries, but there is a lack of research on the energy management method of a DC hybrid power system containing fuel cells, lithium batteries and super capacitors, especially the energy management method of a ship DC hybrid power system composed of multiple groups of fuel cells, multiple groups of lithium batteries and super capacitors in parallel. SUMMARY

[0004] The present application provides a ship DC hybrid power system composed of multiple groups of fuel cells, multiple groups of lithium batteries and one group of super capacitors in parallel, and an energy management method for the system. By giving parameter control instructions of the corresponding DC / DC converter of each power source, the output order and power output size of the three types of power sources are controlled, the hybrid power system quickly tracks the load change while ensuring the stability of the DC bus, and the stable and reliable operation of the entire DC system is realized.

[0005] The technical scheme adopted by the present application to achieve the above-mentioned purpose is:

[0006] A marine direct current hybrid power system, comprising: a fuel cell system, a lithium battery system, a super capacitor system, a motor load, a direct current bus, an energy management controller, wherein:

[0007] The fuel cell system is composed of a plurality of fuel cells and a plurality of unidirectional DC / DC converters, one fuel cell and one unidirectional DC / DC converter form a group, and a plurality of groups are connected in parallel to the direct current bus, for providing power to the direct current hybrid power system;

[0008] The lithium battery system is composed of a plurality of lithium batteries and a plurality of bidirectional DC / DC converters, one lithium battery and one bidirectional DC / DC converter form a group, and a plurality of groups are connected in parallel to the direct current bus, for providing power to the direct current hybrid power system and charging the lithium battery;

[0009] The super capacitor system is composed of a super capacitor and a bidirectional DC / DC converter, the super capacitor is connected to the direct current bus through the bidirectional DC / DC converter, for providing power to the direct current hybrid power system and charging the super capacitor;

[0010] The motor load is connected to the direct current bus, for consuming power and feeding back power;

[0011] The energy management controller is used to collect the state information of the fuel cell, the lithium battery and the super capacitor, and send instruction information to each power supply and the DC / DC controller connected thereto.

[0012] The plurality of lithium batteries and a super capacitor are connected in parallel to form an energy storage power supply, and the energy storage power supply and the bidirectional DC / DC converter connected thereto adopt a distributed droop control mode.

[0013] The state information includes current information, voltage information, power information, working mode, and speed information; the instruction information includes instruction current, droop coefficient, and hysteresis bandwidth.

[0014] An energy management method of a marine direct current hybrid power system, according to different operating conditions of the ship, the energy management controller controls the working mode of the fuel cell system, the lithium battery system and the super capacitor system respectively, thereby controlling the flow of energy in the direct current hybrid power system, and stabilizing the direct current bus voltage, wherein the different operating conditions of the ship are: ship running at constant speed, ship accelerating, and ship decelerating.

[0015] When the ship runs at constant speed, the energy management method is specifically:

[0016] The energy management controller predicts the demand power Pd_constant according to the motor speed of the ship running at constant speed.

[0017] The fuel cell outputs current according to the required power Pd_constant value, sets the minimum power Pfc_min allowed to work of the fuel cell, if the required power Pd_constant is greater than Pfc_min, the fuel cell outputs constant current according to the required power value, otherwise, the fuel cell outputs constant current according to the minimum power Pfc_min allowed to work;

[0018] By setting the super capacitor DC / DC voltage hysteresis bandwidth greater than the lithium battery DC / DC voltage hysteresis bandwidth, the super capacitor is on standby, and the lithium battery is charged and discharged to make up the difference power after the required power Pd_constant minus the fuel cell output power Pfc;

[0019] If the bus voltage value Udc is higher than the upper limit value U H1_bat of the lithium battery DC / DC voltage hysteresis, the fuel cell discharges according to the required power, the lithium battery automatically droops charging, and the super capacitor is on standby; if the bus voltage value Udc is lower than the lower limit value U L1_bat of the lithium battery DC / DC voltage hysteresis, the fuel cell discharges according to the required power, the lithium battery automatically droops discharging, and the super capacitor is on standby; if the bus voltage value is within the lithium battery DC / DC voltage hysteresis, the fuel cell discharges according to the required power, the super capacitor is on standby, and the lithium battery is on standby.

[0020] When the ship runs in the acceleration working condition, the energy management method is specifically:

[0021] After the energy management controller receives the acceleration instruction, the fuel cell outputs constant current according to the current corresponding to the steady-state speed of the motor load before acceleration, and reads the SOC state of charge value SOCsc of the super capacitor. If the SOCsc is lower than the minimum SOC value SOCsc_min allowed to discharge of the super capacitor, the super capacitor is on standby, the lithium battery droops discharging, and the lithium battery provides the power difference required for acceleration; if the SOC value of the super capacitor is greater than or equal to the minimum SOC value SOCsc_min allowed to discharge of the super capacitor, the power value Pd_new corresponding to the speed of the motor load after acceleration is obtained, and the power difference Pd between the power Pd_new corresponding to the speed of the motor load after acceleration and the required power Pd_old of the original motor load is calculated, Pd=Pd_new-Pd_old;

[0022] The Pd is compared with the maximum discharging power Psc_max of the super capacitor, if the Pd is less than the maximum discharging power Psc_max of the super capacitor, the lithium battery is on standby, and the power difference is provided by the super capacitor, otherwise the super capacitor and the lithium battery are both discharged through the corresponding bidirectional DC / DC converter; when the super capacitor and the lithium battery are discharged at the same time, the droop coefficient of the bidirectional DC / DC converter corresponding to the super capacitor is adjusted to be greater than the droop coefficient of the bidirectional DC / DC converter corresponding to the lithium battery, so that the discharging current of the super capacitor is greater than the discharging current of the lithium battery;

[0023] In the discharging process, the energy management controller reads the super capacitor SOC value SOCsc in real time, judges whether it reaches the minimum SOC value SOCsc_min allowed to be discharged, if it reaches, the super capacitor is on standby by increasing the super capacitor DC / DC voltage hysteresis width, and the lithium battery is discharged by droop, otherwise the super capacitor is always discharged until the motor load reaches the stable target speed and enters the uniform speed working condition.

[0024] When the ship runs in the deceleration working condition, the energy management method is specifically:

[0025] The energy management controller obtains the speed corresponding power value Pd_new' of the motor load after deceleration according to the received deceleration command, if the speed corresponding power Pd_new' of the motor load after deceleration is greater than the minimum power Pfc_min allowed to work of the fuel cell, the fuel cell outputs constant current according to Pd_new', otherwise the fuel cell outputs constant current according to Pfc_min;

[0026] If the bus voltage value Udc exceeds the upper and lower limit values of the lithium battery DC / DC voltage hysteresis, if the bus voltage value Udc is within the bandwidth of the lithium battery DC / DC voltage hysteresis, the lithium battery and the super capacitor are both in standby state; if the bus voltage value Udc is higher than the upper limit value of the lithium battery hysteresis, the super capacitor and the lithium battery are charged, at this time, if the super capacitor SOC value does not reach the upper limit value, the lithium battery DC / DC voltage hysteresis bandwidth is increased, so that the lithium battery is on standby and the super capacitor is charged; if the super capacitor SOC reaches the upper limit value, the super capacitor DC / DC voltage hysteresis bandwidth is kept greater than the lithium battery DC / DC voltage hysteresis bandwidth, so that the super capacitor is on standby and the lithium battery is charged; if the bus voltage Udc is lower than the lower limit value of the lithium battery DC / DC voltage hysteresis, the lithium battery DC / DC voltage hysteresis bandwidth is set to be greater than the super capacitor DC / DC voltage hysteresis bandwidth, so that the lithium battery is on standby and the super capacitor is discharged;

[0027] In this process, if the super capacitor SOC reaches the discharging lower limit, the lithium battery is discharged, otherwise, the super capacitor is always discharged to supplement the power difference until the motor load reaches the stable target speed and enters the uniform speed working condition.

[0028] The present application has the following advantages and benefits:

[0029] 1. The marine DC hybrid power system proposed by the present application is composed of multiple groups of fuel cells, multiple groups of lithium batteries and a single group of super capacitors in parallel, and the energy management method proposed thereby realizes energy coordination between different power sources and between power sources and loads, thereby stabilizing the bus voltage and balancing the system power.

[0030] 2. The energy management method of the marine DC hybrid power system proposed by the present application can solve the problems of automatic voltage stabilization and power distribution of multiple groups of energy storage power sources in parallel, does not require mutual communication between each power source, reduces the control complexity, enhances the reliability and modularity of the system, and enables the marine DC hybrid power system to have the feature of power source plug-and-play.

[0031] 3. The energy management method of the marine DC hybrid power system of the present application can make full use of the different performances of each device, so that the fuel cells and lithium batteries with poor dynamic performance are exempted from bearing frequent changes in power demand, while ensuring that the super capacitor energy storage power source will not appear overcharging or overdischarging, ensuring the safety of the power source and prolonging the service life and maintenance cost of the system. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a structure diagram of a marine DC hybrid power system composed of n groups of fuel cells, n groups of lithium batteries and one group of super capacitors;

[0033] Figure 2 is a constant current control mode principle diagram of a fuel cell DC / DC converter;

[0034] Figure 3 is a droop characteristic curve of an energy storage power source (super capacitor and lithium battery) DC / DC converter;

[0035] Figure 4 is a droop characteristic curve of an energy storage power source when the super capacitor is on standby and the lithium battery is charging / discharging;

[0036] Figure 5 is a droop characteristic curve of an energy storage power source when the lithium battery is on standby and the super capacitor is charging / discharging;

[0037] Figure 6 is a droop characteristic curve of an energy storage power source when the lithium battery and the super capacitor are simultaneously charging / discharging;

[0038] Figure 7 is an energy management control flowchart of a marine DC hybrid power system in a ship uniform speed working condition;

[0039] Figure 8 is an energy management control flowchart of a marine DC hybrid power system in a ship acceleration working condition;

[0040] Figure 9 is the energy management control flow chart of the marine DC hybrid power system in the ship deceleration working condition. DETAILED DESCRIPTION

[0041] The application will be further described in detail below with reference to the accompanying drawings and examples.

[0042] The composition of a marine DC hybrid power system is shown in Figure 1 which 1 is a fuel cell system, internally containing n groups of parallel fuel cell units, each group of fuel cell units being composed of a 1-1 fuel cell and a 4-1 unidirectional DC / DC converter used in cooperation; 2 is a lithium battery system, internally containing n groups of parallel lithium battery units, each group of lithium battery units being composed of a 2-1 lithium battery and a 5-1 bidirectional DC / DC converter used in cooperation; 3 is a super capacitor system, internally containing a 3-1 super capacitor and a 6-1 bidirectional DC / DC converter used in cooperation, 7 is a motor load, 8 is a system DC bus, and 9 is an energy management controller.

[0043] The fuel cell can only release electric energy and cannot absorb electric energy, the electric energy flows unidirectionally from the fuel cell to the DC bus, the fuel cell passes through the unidirectional DC / DC converter to realize voltage and current conversion and is connected in parallel to the system DC bus, and Pfc is the output power of the fuel cell, which flows unidirectionally. The fuel cell DC / DC adopts a constant current control mode, a minimum output power value Pfc_min is set, and if the load demand power is lower than Pfc_min, the fuel cell outputs in constant current according to the current command corresponding to Pfc_min. As shown in Figure 2 the fuel cell DC / DC converter constant current control mode schematic diagram. In the diagram, Uin is the input voltage of the DC / DC converter, Uout is the output voltage of the DC / DC converter, Iout is the output current of the DC / DC converter, and Iref is the current command value of the current controller. The main purpose of constant current control is to keep the DC / DC converter output current stable and track the command current. By collecting the actual output current of the DC / DC converter and comparing it with the current command value, an error signal is generated, which is used as a modulation wave after passing through a current comparator, and the PWM trigger pulse signal for driving the switch of the converter to turn on and off is obtained by comparing it with a triangular carrier.

[0044] The lithium battery can release and absorb electric energy as a storage power supply, the electric energy flows bidirectionally between the DC bus and the lithium battery, the lithium battery passes through the bidirectional DC / DC converter to realize voltage and current conversion and is connected in parallel to the DC bus, and Pbat is the output power of the lithium battery, which can flow bidirectionally.

[0045] As an energy storage power source, supercapacitors can both release and absorb electrical energy. The electrical energy flows bidirectionally between the DC bus and the supercapacitor. The supercapacitor undergoes voltage and current conversion through a bidirectional DC / DC converter and is connected to the DC bus. Psc is the output power of the supercapacitor, which can flow bidirectionally.

[0046] n groups of lithium battery cells and 1 group of supercapacitor cells are connected in parallel to form an energy storage power supply. The bidirectional DC / DC converter of the energy storage power supply adopts a distributed droop control mode, that is, each power supply DC / DC converter collects the bus voltage value U. dc Then, each outputs current I according to its own set droop characteristic curve, and power balance can be achieved without communication between them.

[0047] like Figure 3 The diagram shown illustrates the droop characteristic curve of energy storage power sources (lithium batteries and supercapacitors). Wherein, U... dc K represents the bus voltage; I represents the output current of the energy storage power source. A positive I value indicates that the energy storage power source is discharging, while a negative I value indicates that the bus is charging the energy storage power source. m To adjust K, which is the droop factor of the energy storage power source. m It can control the magnitude of the charging / discharging current. L2 U L1 U H1 U H2 These are the critical values ​​for the operation of the energy storage power source, where U... L1 U H1 This forms a DC / DC voltage hysteresis loop, when U dc Between U L1 U H1 During the hysteresis loop, the energy storage power supply is in standby mode with zero output current. The fluctuations in the DC bus voltage within the voltage hysteresis loop are tolerable by the system. When U L2 dc L1 At that time, the energy storage power supply begins to discharge, and when the voltage drops below U... L2 Then, the energy storage power supply operates at its maximum current I. max Constant current discharge; when U H1 dc H2 At that time, the energy storage power supply begins charging, and when the voltage is higher than U... H2 Then, the energy storage power supply operates at its maximum current -I max Constant current charging; by adjusting the U of the lithium battery and the supercapacitor DC / DC converter. L1 U H1 The voltage hysteresis width can be changed to control the order in which energy storage power supplies output power. Energy storage power supplies with a smaller voltage hysteresis width will start first to make up for the power difference and maintain the bus voltage; energy storage power supplies with a larger voltage hysteresis width will first be in standby mode and will not output power until the voltage exceeds the hysteresis before they start to regulate the voltage.​​​​

[0048] When the lithium battery is on standby and the super capacitor is charging / discharging, the DC / DC voltage hysteresis bandwidth of the lithium battery is set to be greater than the DC / DC voltage hysteresis bandwidth of the super capacitor, that is, U L1_bat <U L1_sc , U H1_bat >U H1_sc , as shown in FIG. 2. Figure 4

[0049] When the super capacitor is on standby and the lithium battery is charging / discharging, the DC / DC voltage hysteresis bandwidth of the super capacitor is set to be greater than the DC / DC hysteresis bandwidth of the lithium battery, that is, U L1_sc <U L1_bat , U H1_sc >U H1_bat , as shown in FIG. 3. Figure 5

[0050] When the lithium battery and the super capacitor are simultaneously discharged, the DC / DC voltage hysteresis bandwidth of the lithium battery and the DC / DC hysteresis bandwidth of the super capacitor are set to be the same, and at the same time, the droop coefficient Km_sc of the super capacitor is set to be greater than Km_bat, so that when the super capacitor and the lithium battery are simultaneously discharged, the super capacitor discharge current I sc is greater than the lithium battery discharge current I bat , as shown in FIG. 4. Figure 6

[0051] The motor load is connected in parallel to the DC bus, which can consume electric energy or feedback electric energy, and the electric energy flows bidirectionally between the DC bus and the load, and Pd is the load demand power, which can flow bidirectionally.

[0052] In order to ensure the stability of the system, the DC bus voltage needs to be maintained at a constant value, and the output power of each power supply is controlled by the energy management controller to stabilize the DC bus. The energy management controller collects the state information of each power supply and the load, including current information, voltage information, power information, working mode, speed information, etc., and then sends instruction current, droop coefficient, hysteresis bandwidth and other control instruction information to each power supply and the corresponding DC / DC controller by executing the energy management method of the application, to realize unified management of system energy.

[0053] ​​​The energy management method of a marine direct-current hybrid power system is to adjust the working instructions of each power supply and the control mode of the DC / DC converter corresponding to each power supply according to the working condition of the ship running, so that the hybrid power system switches between 11 working modes, timely allocates the flow of energy in the hybrid power supply, and ensures the stability of the DC bus. The control mode of the DC / DC converter corresponding to each power supply includes that the unidirectional DC / DC converter connected with the fuel cell works in the constant current discharge mode, the bidirectional DC / DC converter connected with the lithium battery works in the droop charge / discharge mode, and the bidirectional DC / DC converter connected with the super capacitor works in the droop charge / discharge mode.

[0054] The fuel cell DC / DC adopts a constant current control mode, and sets a minimum output power value Pfc_min. If the load demand power is lower than Pfc_min, the fuel cell outputs in constant current according to the current instruction corresponding to Pfc_min. In the acceleration condition, the fuel cell first outputs according to the instruction current corresponding to the power before acceleration, and then outputs according to the current corresponding to the new high-speed power after entering the uniform speed condition after acceleration is completed; while in the deceleration condition, the fuel cell directly outputs according to the current corresponding to the new low-speed power.

[0055] The lithium battery system and the super capacitor system constitute an energy storage power supply. The energy storage power supply is connected in parallel with the bus through DC / DC, and the DC / DC adopts a droop control mode. By adjusting the voltage hysteresis bandwidth of the lithium battery and the super capacitor DC / DC, the output order of the lithium battery and the super capacitor is determined; by adjusting the droop coefficient of the DC / DC, the charging and discharging current of the lithium battery and the super capacitor is adjusted. In the steady state condition (uniform speed condition), the energy storage power supply preferentially uses the lithium battery to supplement the power difference after the demand power is subtracted from the output power of the fuel cell. In the dynamic condition (acceleration condition or deceleration condition), the energy storage power supply preferentially uses the super capacitor for charging / discharging to supplement the rapidly changing demand power difference, and if the charging reaches the upper limit value SOCsc_max of the state of charge of the super capacitor or the state of charge reaches the lower limit value SOCsc_min during discharging, the lithium battery is used for charging / discharging.

[0056] When the ship runs in the uniform speed condition, the direct-current hybrid power system runs in mode 1 to mode 3; when the ship runs in the acceleration condition, the direct-current hybrid power system runs in mode 4 to mode 6, and when the ship runs in the deceleration condition, the direct-current hybrid power system runs in mode 7 to mode 11.

[0057] The detailed control process of each working condition is as follows:

[0058] (1) Uniform speed condition. As shown in Figure 7The energy management control flow chart of the marine DC hybrid power system in the uniform speed working condition of the ship is shown. In the uniform speed working condition, the fuel cell and the lithium battery provide power for the load, and the super capacitor is on standby. The fuel cell discharges according to the constant current according to the demand power size table calculated according to the uniform speed rate, and the lithium battery charges / discharges to supplement the power difference required by the load, while stabilizing the bus voltage.

[0059] The specific control logic is that the energy management controller estimates the demand power Pd_constant according to the uniform speed running value. The estimation method is to calculate according to the corresponding relationship between the motor speed and the power value. In this example, the relationship between the motor and the power is: In the formula, P N is the rated power of the motor, n N is the rated speed of the motor, and n is the running speed of the motor. The fuel cell outputs current according to the table corresponding to the power value. The table is prepared according to the corresponding characteristics of the fuel cell output power and current. Considering that the fuel cell has very low running efficiency at low power, in order to improve the efficiency of the fuel cell, the minimum power Pfc_min allowed for the fuel cell to work is set. If the demand power Pd_constant is greater than Pfc_min, the fuel cell outputs constant current according to the demand power value table, otherwise, the fuel cell outputs constant current according to the minimum power Pfc_min allowed for working. By setting the bandwidth of the super capacitor DC / DC voltage hysteresis loop to be greater than the bandwidth of the lithium battery DC / DC voltage hysteresis loop, the super capacitor is on standby, and the lithium battery charges and discharges to supplement the difference between the demand power Pd_constant and the output power Pfc of the fuel cell. If the bus voltage value is higher than the upper limit value U H1_bat of the lithium battery DC / DC voltage hysteresis loop, the hybrid energy storage system works in mode 1, that is, the fuel cell discharges according to the current instruction corresponding to the demand power table, the lithium battery automatically charges in droop, and the super capacitor is on standby; if the bus voltage value is lower than the lower limit value U L1_bat of the lithium battery DC / DC voltage hysteresis loop, the hybrid energy storage system works in mode 3, that is, the fuel cell discharges according to the current instruction corresponding to the demand power table, the lithium battery automatically discharges in droop, and the super capacitor is on standby; if the bus voltage value is within the lithium battery DC / DC voltage hysteresis loop, the hybrid energy storage system works in mode 2, that is, the fuel cell discharges according to the FC current instruction corresponding to the demand power table, the super capacitor is on standby, and the lithium battery is on standby.

[0060] (2) Acceleration working condition. Figure 8is a flow chart of energy management control of the DC hybrid power system of the ship in the acceleration condition of the ship. In the acceleration process, the fuel cell still outputs constant current according to the current instruction corresponding to the steady-state rotating speed before acceleration, and the super capacitor or lithium battery provides the power difference required for acceleration. The super capacitor and lithium battery DC / DC are operated in the droop mode when discharging.

[0061] The specific control logic is that after the energy management controller receives the acceleration instruction, the fuel cell still outputs constant current according to the current instruction corresponding to the steady-state rotating speed before acceleration, and then reads the SOC state of charge value SOCsc of the super capacitor. If the SOCsc is lower than the minimum SOC value SOCsc_min allowed for discharging of the super capacitor, the super capacitor is not allowed to discharge any more, at this time, mode 6 is operated, that is, the super capacitor is in standby, the lithium battery is discharged in the droop mode, and the lithium battery provides the power difference required for acceleration. If the SOC value of the super capacitor is greater than the minimum SOC value SOCsc_min allowed for discharging, the super capacitor can discharge, at this time, the power value Pd_new corresponding to the target rotating speed is estimated according to the acceleration instruction, and the power difference Pd between the power Pd_new corresponding to the new rotating speed and the demand power Pd_old corresponding to the original rotating speed is calculated. Pd is compared with the maximum discharging power Psc_max of the super capacitor. If the demand power difference is less than the maximum discharging power Psc_max of the super capacitor, the lithium battery can be in standby, and only the super capacitor itself provides the power difference (mode 5); otherwise, the super capacitor and the lithium battery need to be discharged through the DC / DC droop (mode 4) to meet the acceleration demand of the load. When the super capacitor and the lithium battery are discharged at the same time, the discharging current of the super capacitor is greater than the discharging current of the lithium battery by adjusting the droop coefficient of the super capacitor DC / DC to be greater than the droop coefficient of the lithium battery DC / DC.

[0062] In the discharging process, the energy management controller still needs to read the SOC value SOCsc of the super capacitor in real time to judge whether it reaches the minimum SOC value SOCsc_min allowed for discharging. If it reaches, the super capacitor is in standby by increasing the voltage hysteresis width of the super capacitor DC / DC, and the lithium battery is discharged in the droop mode (mode 6); otherwise, the super capacitor is always discharged until the load reaches the stable target rotating speed and enters the uniform speed condition.

[0063] (3) deceleration condition. Figure 9is a flow chart of energy management control of the DC hybrid power system of the ship in the deceleration condition of the ship. In the deceleration process, the fuel cell outputs constant current according to the current instruction corresponding to the latest target rotating speed, if the bus voltage rises, the super capacitor is charged preferentially, and after the super capacitor is charged to the upper limit, the lithium battery is charged; if the bus voltage is too low, the super capacitor is discharged preferentially to supplement the power difference, and if the lower limit of the super capacitor discharge is reached, the lithium battery is discharged.

[0064] DC hybrid power system 11 kinds of working mode:

[0065] Mode 1: fuel cell discharges, lithium battery charges, and super capacitor is in standby mode; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the steady rotating speed, and the lithium battery charges according to the droop curve automatically.

[0066] Mode 2: fuel cell discharges, lithium battery and super capacitor are in standby mode; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the steady rotating speed.

[0067] Mode 3: fuel cell and lithium battery discharge simultaneously, and super capacitor is in standby mode; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the steady rotating speed, and the lithium battery discharges according to the droop curve automatically.

[0068] Mode 4: Fuel cell, lithium battery, super capacitor discharge simultaneously; wherein the fuel cell discharges according to the current instruction corresponding to the steady-state power before the ship accelerates; the lithium battery and the super capacitor automatically discharge according to the droop curve, and the droop coefficient is adjusted so that the super capacitor discharge current is greater than the lithium battery discharge current;

[0069] Mode 5: Fuel cell and super capacitor discharge simultaneously, lithium battery standby; wherein the fuel cell discharges according to the current instruction corresponding to the steady-state power before the ship accelerates; the super capacitor automatically discharges according to the droop curve;

[0070] Mode 6: Fuel cell and lithium battery discharge simultaneously, super capacitor standby; wherein the fuel cell discharges according to the current instruction corresponding to the steady-state power before the ship accelerates; the lithium battery automatically discharges according to the droop curve;

[0071] Mode 7: Fuel cell discharges, lithium battery charges, super capacitor standby; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the new target speed after deceleration; the lithium battery automatically charges according to the droop curve;

[0072] Mode 8: Fuel cell discharges, super capacitor charges, lithium battery standby; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the new target speed after deceleration; the super capacitor automatically charges according to the droop curve;

[0073] Mode 9: Fuel cell discharges, lithium battery and super capacitor standby; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the new target speed after deceleration;

[0074] Mode 10: Fuel cell and super capacitor discharge simultaneously, lithium battery standby; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the new target speed after deceleration; the super capacitor automatically discharges according to the droop curve;

[0075] Mode 11: Fuel cell and lithium battery discharge simultaneously, super capacitor standby; wherein the fuel cell discharges according to the current instruction corresponding to the demand power at the new target speed after deceleration; the lithium battery automatically discharges according to the droop curve.

Claims

1. A method of energy management for a marine DC hybrid power system, characterized in that, According to different working conditions of the ship, the energy management controller controls the working modes of the fuel cell system, the lithium battery system and the super capacitor system respectively, thereby controlling the flow of energy in the DC hybrid power system and stabilizing the DC bus voltage, wherein the different working conditions of the ship are: a ship running uniform speed condition, a ship running acceleration condition and a ship running deceleration condition. The energy management method for the ship running uniform speed condition is specifically: The energy management controller predicts the demand power Pd_constant according to the motor speed of the ship running at a uniform speed; The fuel cell outputs current according to the demand power Pd_constant value, sets the minimum power Pfc_min allowed to work, and if the demand power Pd_constant is greater than Pfc_min, the fuel cell outputs constant current according to the demand power value, otherwise, the fuel cell outputs constant current according to the minimum power Pfc_min allowed to work; By setting the super capacitor DC / DC voltage hysteresis bandwidth to be greater than the lithium battery DC / DC voltage hysteresis bandwidth, the super capacitor is in standby, and the lithium battery is charged and discharged to supplement the difference power after the demand power Pd_constant minus the output power Pfc of the fuel cell. If the bus voltage value Udc is higher than the upper limit value U H1_bat of the lithium battery DC / DC voltage hysteresis, the fuel cell discharges according to the required power, the lithium battery automatically charges, and the super capacitor is on standby; if the bus voltage value Udc is lower than the lower limit value U L1_bat of the lithium battery DC / DC voltage hysteresis, the fuel cell discharges according to the required power, the lithium battery automatically discharges, and the super capacitor is on standby; if the bus voltage value is within the lithium battery DC / DC voltage hysteresis, the fuel cell discharges according to the required power, the super capacitor is on standby, and the lithium battery is on standby. The energy management method for the ship running acceleration condition is specifically: After the energy management controller receives the acceleration instruction, the fuel cell outputs constant current according to the current corresponding to the steady-state speed of the motor load before acceleration, and reads the SOC value SOCsc of the super capacitor, if the SOCsc is lower than the minimum SOC value SOCsc_min allowed to discharge, the super capacitor is in standby, and the lithium battery is discharged by droop, and the lithium battery provides the power difference required for acceleration; if the SOC value of the super capacitor is greater than or equal to the minimum SOC value SOCsc_min allowed to discharge, the power value Pd_new corresponding to the speed of the motor load after acceleration is obtained, and the power difference Pd between the power Pd_new corresponding to the speed of the motor load after acceleration and the demand power Pd_old corresponding to the original speed of the motor load is calculated, Pd=Pd_new-Pd_old; If Pd is less than the maximum discharge power Psc_max of the super capacitor, the lithium battery is in standby, and the super capacitor provides the power difference, otherwise, the super capacitor and the lithium battery are discharged by the corresponding bidirectional DC / DC converter; when the super capacitor and the lithium battery are discharged at the same time, the droop coefficient of the bidirectional DC / DC converter corresponding to the super capacitor is adjusted to be greater than the droop coefficient of the bidirectional DC / DC converter corresponding to the lithium battery, so that the discharge current of the super capacitor is greater than the discharge current of the lithium battery. During discharging, the energy management controller reads the super capacitor SOC value SOCsc in real time, judges whether it reaches the minimum SOC value SOCsc_min allowed to discharge, if it reaches, makes the super capacitor standby by increasing the super capacitor DC / DC voltage hysteresis width, and changes to lithium battery droop discharging, otherwise the super capacitor discharges all the time until the motor load reaches the stable target speed and enters the uniform speed working condition; When the ship runs in the deceleration working condition, the energy management method is specifically: The energy management controller acquires the speed corresponding power value Pd_new' of the motor load after deceleration according to the received deceleration command, if the speed corresponding power value Pd_new' of the motor load after deceleration is greater than the minimum power Pfc_min allowed to work of the fuel cell, the fuel cell outputs constant current according to Pd_new', otherwise the fuel cell outputs constant current according to Pfc_min; If the bus voltage value Udc exceeds the upper and lower limit values of the lithium battery DC / DC voltage hysteresis, if the bus voltage value Udc is within the lithium battery DC / DC voltage hysteresis bandwidth, the lithium battery and the super capacitor are in standby state; if the bus voltage value Udc is higher than the upper limit value of the lithium battery hysteresis, the super capacitor and the lithium battery are charged, at this time, if the super capacitor SOC value does not reach the upper limit value, the lithium battery DC / DC voltage hysteresis bandwidth is increased to make the lithium battery standby and charge the super capacitor; if the super capacitor SOC reaches the upper limit value, the super capacitor DC / DC voltage hysteresis bandwidth is kept greater than the lithium battery DC / DC voltage hysteresis bandwidth to make the super capacitor standby and charge the lithium battery; if the bus voltage Udc is lower than the lower limit value of the lithium battery DC / DC voltage hysteresis, the lithium battery DC / DC voltage hysteresis bandwidth is set to be greater than the super capacitor DC / DC voltage hysteresis bandwidth to make the lithium battery standby and the super capacitor discharge; In this process, if the super capacitor SOC reaches the discharging lower limit, the lithium battery discharges, otherwise, the super capacitor discharges to supplement the power difference until the motor load reaches the stable target speed and enters the uniform speed working condition.

2. A DC hybrid power system for a ship for implementing the energy management method of claim 1, characterized by It comprises: The fuel cell system, the lithium battery system, the super capacitor system, the motor load, the direct current bus and the energy management controller, wherein: The fuel cell system is composed of a plurality of fuel cells and a plurality of unidirectional DC / DC converters, one fuel cell is connected with one unidirectional DC / DC converter to form a group, and a plurality of groups are connected in parallel on the direct current bus to provide power for the direct current hybrid power system; The lithium battery system is composed of a plurality of lithium batteries and a plurality of bidirectional DC / DC converters, one lithium battery is connected with one bidirectional DC / DC converter to form a group, and a plurality of groups are connected in parallel on the direct current bus to provide power for the direct current hybrid power system and charge the lithium battery; The super capacitor system is composed of one super capacitor and one bidirectional DC / DC converter, the super capacitor is connected to the direct current bus through the bidirectional DC / DC converter to provide power for the direct current hybrid power system and charge the super capacitor; The motor load is connected to the direct current bus to consume and feedback power. An energy management controller is used to collect the state information of fuel cell, lithium battery, super capacitor and motor load, and send instruction information to each power source and DC / DC controller connected therewith. The plurality of lithium batteries and a super capacitor are connected in parallel to form an energy storage power source, and the energy storage power source and a bidirectional DC / DC converter connected therewith adopt a distributed droop control mode.

3. A marine DC hybrid power system according to claim 2, characterized in that The state information includes current information, voltage information, power information, working mode and rotating speed information; and the instruction information includes instruction current, droop coefficient and hysteresis bandwidth.

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