Composite power supply system and method

Abstract

The invention discloses a composite power supply system, which comprises a storage battery, a fuel cell, a DC / DC controller, a DC bus, a DC / AC and a power supply distribution unit, and is characterized in that the storage battery and the fuel cell are electrically connected to the DC bus through the DC / DC controller; the direct current bus supplies power to the load through the DC / AC, the direct current bus is connected to one load through one DC / AC, the power supply distribution unit is configured to utilize the power of the fuel cell as much as possible, and the power characteristic of the storage battery and the endurance of the fuel cell are both considered.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply, and in particular to a composite power supply system and method. Background Art

[0002] Batteries and fuel cells have been widely used in fields such as ships.

[0003] As a common lithium battery in batteries, its dynamic characteristics of power output are b See also Figure 1 The advantage is that I b It is better, which means that it can change from 0 power to full power (or from full power to 0 power) immediately.

[0004] As a common hydrogen fuel cell among fuel cells, its dynamic characteristics of power output are fc See also Figure 2 The advantage is that it can achieve a longer driving range, and the disadvantage is that I fc Very poor, usually requires slow loading, about 30 seconds from 0 power to full power (or from full power to 0 power).

[0005] Therefore, in order to solve the respective shortcomings of the above-mentioned storage battery and fuel cell, the present invention provides a composite power supply system and method. Summary of the invention

[0006] The object of the present invention is to provide a composite power supply system and method, which takes into account the power characteristics of the battery and the endurance of the fuel cell.

[0007] To achieve the above object, the present invention is implemented by adopting the following technical solutions: A first aspect of an embodiment of the present invention provides a composite power supply system, which includes: Batteries; Fuel cells; DC / DC controller; A DC bus, the battery and the fuel cell are electrically connected to the DC bus through the DC / DC controller; DC / AC; The DC bus supplies power to the load through the DC / AC; A power distribution unit configured as follows: If the power supply power of the fuel cell meets the load power, the DC / DC controller controls the fuel cell to supply power and the DC / DC controller controls the battery to not supply power; If the power supply power of the fuel cell does not meet the load power, the DC / DC controller controls the fuel cell to supply power at full power, and the DC / DC controller controls the battery to supply power at partial power.

[0008] Furthermore, the DC / DC controller is integrated with a DC bus voltage control module, and the DC bus voltage control module is configured as follows: Based on the actual sampling feedback current value I of the battery b Control the voltage V of the DC bus b-ref , and I b The bigger the V b-ref The smaller.

[0009] Furthermore, the DC bus voltage control module also includes a current sensor and a PI controller, wherein: The current sensor is configured as follows: Collect the current reference value I of the battery b_ref ; Collection I b ; The DC / DC controller is further configured to: compare I b with I b_ref To calculate the error value between the two; The PI controller is configured to: compare the error value with the actual sampled feedback voltage value V of the battery b Add together to get V b-ref .

[0010] Furthermore, the DC / DC controller is further configured to: adjust I b To compensate V dc changes.

[0011] Furthermore, the DC bus is divided into two sections and connected by a solid-state switch, and the solid-state switch includes: An on / off module configured to control the on / off of the DC bus as a whole; The overcurrent disconnecting module is configured to control the DC current to be disconnected as a whole when the current is overloaded.

[0012] Furthermore, the power distribution unit is integrated with an EMS, wherein: The EMS configuration is: Obtaining the state of charge SOC of the battery; If SOC ≥ SOC 上限 , the DC / DC controller controls the fuel cell to not supply power, and the DC / DC controller controls the battery to supply power, SOC 上限 is the default value; If SOC≤SOC 下限 , the DC / DC controller controls the fuel cell to supply power at full power, and the DC / DC controller controls the battery to not supply power, SOC 上限 is the default value.

[0013] Furthermore, the power distribution unit is also integrated with an FCU, and the FCU is configured to send the fuel cell's: Maximum allowable operating current I EMS_Ref , discharge current change rate.

[0014] Furthermore, the EMS is also configured to EMS_Ref Sent to FCU, which is configured to compute I fc_Ref and sent to EMS, which is also configured to send I fc_Ref Sent to the DC / DC that controls the fuel cell.

[0015] Furthermore, the storage battery is a lithium battery, and / or the fuel cell is a hydrogen fuel cell.

[0016] A second aspect of an embodiment of the present invention provides a composite power supply method, which is applied to any composite power supply system as claimed in any one of the claims.

[0017] The beneficial effects of the present invention are as follows: If the power supply power of the fuel cell meets the load power, the DC / DC controller controls the fuel cell to supply power and the DC / DC controller controls the battery to not supply power; if the power supply power of the fuel cell does not meet the load power, the DC / DC controller controls the fuel cell to supply full power and the DC / DC controller controls the battery to supply partial power, thereby avoiding the shortcomings of poor power output characteristics of the fuel cell and poor battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 The dynamic characteristics of lithium battery power output in the prior art; Figure 2 The dynamic characteristics of power output of hydrogen fuel cells in the prior art; Figure 3 It is a schematic diagram of an embodiment of a composite power supply system; Figure 4 Schematic diagram of a power supply system consisting of a single lithium battery and a single hydrogen fuel cell; Figure 5 It is a schematic diagram of an embodiment of lithium battery DC bus voltage control; Figure 6 This is the relationship diagram between the reference current and DC voltage of the lithium battery; Figure 7It is the relationship diagram between fuel cell current and battery SOC; Figure 8 A schematic diagram of an embodiment of a fuel cell control; Fig. 9 A system topology diagram of an embodiment of a composite power supply system; Fig.10 It is the FCU current diagram; Fig.11 A topological diagram of a solid-state switch embodiment; Fig.12 for Figure 3 An energy flow diagram of an embodiment of a composite power supply system. DETAILED DESCRIPTION

[0019] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0020] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship are based on the orientation or position relationship shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0021] The first aspect of the embodiment of the present invention discloses a composite power supply system, see Figure 3 and Figure 4 , which includes batteries, fuel cells, DC / DC controllers (also known as choppers), DC bus, DC / AC (also known as inverters) and power distribution units.

[0022] The battery and fuel cell are electrically connected to the DC bus through a DC / DC controller; the DC bus supplies power to the load through DC / AC. The battery can be a lithium battery, lithium iron phosphate battery, etc., and the fuel cell can be a hydrogen fuel cell. For the sake of example, the battery is a lithium battery and the fuel cell is a hydrogen fuel cell. See the system diagram for details. Figure 3 The system consists of 4 lithium batteries and 2 hydrogen fuel cells as power sources. The output is daily power (connected to the daily power distribution board through a transformer) and 2 propulsion motors (when installed on a ship, the propulsion motor drives the propeller to rotate).

[0023] The DC bus is then connected to a load (for example, a motor driving a propeller or a household load) through a DC / AC (sometimes called an inverter). The power distribution unit is configured as follows: if the power supply of the fuel cell meets the load power, the DC / DC controller controls the fuel cell to supply power and the DC / DC controller controls the battery to not supply power; if the power supply of the fuel cell does not meet the load power, the DC / DC controller controls the fuel cell to supply power at full power and the DC / DC controller controls the battery to supply power at partial power. This takes into account the endurance of the fuel cell and the power output characteristics of the battery.

[0024] In order to illustrate the control method of hydrogen fuel cells, Figure 3 This is a system diagram of a hydrogen fuel cell actually used in a project, but for the sake of clarity, continue to refer to Figure 4 , which is an enlarged partial view of a hydrogen fuel cell and a lithium battery.

[0025] A hydrogen fuel cell is connected to the DC bus through a DC / DC (on the right side of the picture, sometimes also called a chopper), which can control the power of the hydrogen fuel cell. At the same time, a lithium battery is also connected to the DC bus through a DC / DC (on the left side of the picture), which can control the power of the lithium battery.

[0026] The DC bus is in turn connected to a load (for example, a motor driving a propeller or a household load) through a DC / AC (sometimes called an inverter).

[0027] Based on the advantages of lithium batteries and hydrogen fuel cells, the inventors have conceived the following solution: The DC bus voltage is controlled by the DC bus voltage control module integrated in the DC / DC controller. Figure 5 The control of the DC bus voltage first requires a reference value (set to V b-ref ), this reference value adopts the droop method, that is, by collecting the DC current I b The larger the current, the higher the V b-ref The lower.

[0028] Continue to see Figure 5 , we can see that the current reference value of the lithium battery is I b_ref (determined by the DC voltage, explained below) and the actual sampling feedback current value I of the lithium battery b The error value is compared with the actual sampled feedback voltage value V of the lithium battery by a PI controller.b (This value can be obtained by sampling the voltage sensor and sent to the PLC that controls the DC / DC of the lithium battery) Add together to get the output voltage V of the DC / DC b_ref The determined value of .

[0029] Figure 5 All implementations are carried out by controlling the DC bus voltage control module (such as PLC) of the DC / DC integrated in the lithium battery, and the output is the output voltage V of the DC / DC b_ref The setting ensures that the lithium battery can output the appropriate voltage. Figure 5 Medium DC voltage V dc Any changes can be instantly adjusted b To quickly compensate and control, if the DC voltage is low, it means that the load has increased and the battery discharge needs to be increased, so the battery discharge current I is increased accordingly. b_Ref On the other hand, if the DC voltage rises, it means the load has become smaller, and the battery discharge needs to be reduced, or even switched to charging mode.

[0030] In order to give a specific example of setting the lithium battery current reference value, it is assumed that the rated power of the lithium battery is 500kW and the rated voltage is 772.8V, then the rated current is approximately 500000 / 772.8=647A.

[0031] See also Figure 6 When a DC voltage (V DC ) is 1050V (sampled by the voltage sensor and sent to the PLC that controls the DC / DC of the lithium battery), I b_ref is 0A; when the DC voltage is detected to decrease gradually, the battery reference current increases linearly. When the DC voltage reaches 1000V, the battery current reference value I b_ref When the DC voltage continues to drop, the discharge current of the lithium battery is always limited to 647A, ensuring that the lithium battery and its DC / DC do not overheat.

[0032] Continue to see Figure 6 , if the detected DC voltage (V DC ) exceeds 1050V, the battery current reference value I b_ref When the voltage drops to a negative value, charging begins, and as the voltage increases, the charging current increases. When the DC voltage reaches 1100V, the battery current reference value I b_ref It is charged at -647A. When the detected voltage exceeds 1100V, the charging current of the lithium battery is always maintained at -647A to ensure that the lithium battery and its DC / DC do not overheat.

[0033] In this control, the lithium battery is in the main control position, that is, any sudden increase or decrease in load (propeller or daily power supply) will cause the lithium battery to respond quickly by adjusting its own current.

[0034] According to the requirements of CCS "Guidelines for Inspection of Ship DC Integrated Power Systems 2023", the DC busbar should be divided into at least two independent sections, and a busbar tie switch should be used in the middle to protect the DC busbar. Conventional busbar tie switches use a combination of isolating switches + fuses. This system uses solid-state switches, which have a faster fault removal time response. The solid-state switch includes: an on-off module, which is configured to control the on and off of the DC bus as a whole; an overcurrent disconnect module, which is configured to control the overall disconnection of the DC bus when the current is overloaded.

[0035] The topology of a solid-state switch embodiment is shown in FIG. Fig.11 The solid-state switch is essentially a frequency converter, including an on-off module, which is configured to control the on and off of the DC bus as a whole; an overcurrent disconnection module, which is configured to control the overall disconnection of the DC current when the current is overloaded. The on-off module mainly implements the on-off of the upper tube of the IGBT half-bridge, and the lower tube is in the off state for a long time. If a short circuit fault occurs, by detecting the current at both ends of the solid-state switch, when the overcurrent occurs, all IGBTs inside the module are turned off, and the PLC fault is reported at the same time, the opposite module of the same solid-state switch is turned off, and after a small delay, the mechanical switch is turned off. The mechanical switch is usually placed at the connection between the solid-state switch and the bus on both sides, and must have a remote opening and closing function, mainly for isolation.

[0036] Continue to see Fig.11 The working principle of the overcurrent segmentation module is that when a short-circuit fault occurs, the entire system will autonomously perform instant fault isolation. The entire process has a fast response time, and the fault disconnection time is only 0.1ms. The short-circuit current at the fault point is only a few kA, which is negligible and will not cause a significant drop in the bus voltage. In addition, the solid-state switch itself is equipped with a DC reactor L, which has a small energy storage function. When a short-circuit fault occurs, it has sufficient short-circuit current support capacity, and the current will last for a sufficient time to ensure that the circuit breaker or fuse in the load circuit can be selectively triggered.

[0037] When the system of the present invention is applied to a ship, in addition to the above-mentioned DC busbar protection, it also involves the following aspects.

[0038] Daily power station protection Since the DC system uses solid-state switches as busbar protection devices, during normal navigation, the DC busbar busbar switch is normally closed, and the AC busbar switch is normally open, and the energy flow is as follows. Fig.12 As shown in the energy flow diagram, daily power supplies T1 and T2 are divided into partitions to supply power to AC daily loads, ensuring the redundancy of the system.

[0039] Power module protection In the DC system, each power module is connected to the DC busbar with a fast fuse. When a short circuit occurs on the DC side of a power module, all power modules on the busbar will feed current to the short-circuit point, causing the fuse at the fault point to accumulate a large amount of current and quickly blow, thereby separating from the entire DC bus system and achieving coordination of the DC system.

[0040] Battery system protection When the DC output of the lithium battery pack is short-circuited, the instantaneous overcurrent protection of the corresponding inverter power module will be triggered first, and the inverter will shut down immediately. However, the short-circuit point still exists for the lithium battery pack, and the short-circuit protection mechanism of the lithium battery pack system itself is mainly used for protection. The lithium battery pack is integrated with a BMS (battery management system). The BMS is equipped with fuses and contactors on the total positive and negative poles. When the output of the lithium battery pack is short-circuited, the fuse in the BMS will blow, and then the output contactor will trip, cutting off the lithium battery pack from the short-circuit point.

[0041] Protection of propulsion motors (the motors that turn the ship's propellers) The motor AC short-circuit protection is mainly achieved by the frequency converter. When a short circuit occurs at the AC end of the propulsion motor, the instantaneous overcurrent protection of the power module will be triggered, the frequency converter will shut down immediately (stop sending pulses), and then the motor will enter the shutdown state.

[0042] Since the motor shutdown time is short enough and the main current is reactive current, it will not affect the DC bus voltage, so the motor AC short circuit and DC bus short circuit are independent of each other.

[0043] Taking into account the involvement and power distribution of hydrogen fuel cells, try to use the power of hydrogen fuel cells as much as possible and minimize the power output of lithium batteries.

[0044] In terms of specific implementation methods, in addition to the above-mentioned lithium battery control ideas, a control loop is added, namely the lithium battery SOC (state of charge) control loop. The power of the lithium battery is controlled to SOC = SOC 上限 Because such lithium batteries have lower activity and higher safety. Figure 7 and Figure 8 shown.

[0045] When SOC>=SOC 上限 When the SOC is less than 90%, the EMS sets the discharge current of the fuel cell to 0 through the DC / DC. For every 1% difference in SOC, the discharge current of the fuel cell increases by 20%. When SOC<=SOC 下限When the rated current reaches 100% (such as 85%), the discharge current of the fuel cell reaches 100% (Note: in this case, the power of the hydrogen fuel cell is 500kW and the voltage is 340V, so 100% of the rated current corresponds to 500000 / 340 = 1471A).

[0046] In other words, the power control of hydrogen fuel cells does not depend on the DC voltage, but is determined by the battery's charge. However, it should be noted that the power control of hydrogen fuel cells will affect the DC voltage. For example, if the lithium battery is discharging and the DC voltage is low, the SOC of the lithium battery will drop, and the hydrogen fuel cell will start to provide current. Under the condition of unchanged load, the DC voltage will rise, and the discharge current of the lithium battery will drop, and even enter the charging mode.

[0047] A practical benefit of doing this is that when the load suddenly increases, the lithium battery balances the load by increasing its own current output. If the lithium battery continues to provide current, the SOC will drop, and the fuel cell will therefore provide current to the DC bus through the DC / DC, and even charge the lithium battery in turn. There are four systems associated in the system of the embodiment of the present invention, see Fig. 9 , namely BMS (battery management system), FCU (hydrogen fuel cell system controller), DC / DC controller and EMS (ship energy management system), their functions are as follows: BMS manages the battery temperature, etc., and sends the SOC to the EMS in terms of control.

[0048] The FCU sends the maximum current allowed to the EMS. This current value cannot change suddenly but needs to increase slowly. The DC / DC controller of the lithium battery does not participate in the control system by controlling itself, while the DC / DC controller of the fuel cell receives the reference current value set by the EMS to control the discharge of the fuel cell.

[0049] EMS is mainly responsible for the stability of the ship's power station. It receives the SOC transmitted by the BMS, combines it with the allowable reference current value set by the FCU, calculates the reference current of the DC / DC controller, and ultimately ensures that the battery's SOC can reach or approach 90%.

[0050] It should be noted that the FCU does not allow the current of the hydrogen fuel cell to change suddenly, so the specific fuel cell reference current Ifc_ref is generated as follows: EMS according to Fig.10 Generates the fuel cell's limiting current I EMS_Ref , due to the sudden change of SOC, I EMS_RefIf a huge reference current change is sent directly to the DC / DC, the hydrogen fuel cell will not be able to respond quickly. EMS_Ref Send it to FCU, and FCU will calculate a reasonable I according to its actual situation fc_Ref Give it to EMS, and EMS will send this fc_Ref Sent to the DC / DC that controls the hydrogen fuel cell to ensure the orderly output of the hydrogen fuel cell power.

[0051] A second aspect of an embodiment of the present invention discloses a composite power supply method, which is used in any of the composite power supply systems mentioned above.

[0052] The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention; therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description. Therefore, it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention, and any figure marks in the claims should not be regarded as limiting the claims involved.

[0053] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A composite power supply system, characterized in that: include: Batteries; Fuel cells; DC / DC controller; a DC bus, the battery and the fuel cell being electrically connected to the DC bus through the DC / DC controller; DC / AC; The DC bus supplies power to the load through the DC / AC; A power distribution unit configured as follows: If the power supply power of the fuel cell meets the load power, the DC / DC controller controls the fuel cell to supply power and the DC / DC controller controls the battery to not supply power; If the power supply power of the fuel cell does not meet the load power, the DC / DC controller controls the fuel cell to supply power at full power, and the DC / DC controller controls the battery to supply power at partial power.

2. The composite power supply system according to claim 1, characterized in that: The DC / DC controller is integrated with a DC bus voltage control module, and the DC bus voltage control module is configured as follows: Based on the actual sampling feedback current value I of the battery b Control the voltage V of the DC bus b-ref , and I b The bigger the V b-ref The smaller.

3. The composite power supply system according to claim 2, characterized in that: The DC bus voltage control module also includes a current sensor and a PI controller, wherein: The current sensor is configured as follows: Collect the current reference value I of the battery b_ref ; Collection I b ; The DC / DC controller is further configured to: compare I b with I b_ref To calculate the error value between the two; The PI controller is configured to: compare the error value with the actual sampled feedback voltage value V of the battery b Add together to get V b-ref .

4. The composite power supply system according to claim 3, characterized in that: The DC / DC controller is further configured to: adjust I b To compensate V dc changes.

5. The composite power supply system according to claim 1, characterized in that: The DC bus is divided into two sections and connected by a solid-state switch, and the solid-state switch includes: An on / off module configured to control the on / off of the DC bus as a whole; The overcurrent disconnecting module is configured to control the DC current to be disconnected as a whole when the current is overloaded.

6. The composite power supply system according to any one of claims 1 to 5, characterized in that: The power distribution unit is integrated with an EMS, wherein: The EMS configuration is: Obtaining the state of charge SOC of the battery; If SOC ≥ SOC 上限 , the DC / DC controller controls the fuel cell to not supply power, and the DC / DC controller controls the battery to supply power, SOC 上限 is the default value; If SOC≤SOC 下限 , the DC / DC controller controls the fuel cell to supply power at full power, and the DC / DC controller controls the battery to not supply power, SOC 上限 is the default value.

7. The composite power supply system according to claim 6, characterized in that: The power distribution unit is also integrated with an FCU, which is configured to send the fuel cell to the EMS: Maximum allowable operating current I EMS_Ref , discharge current change rate.

8. The composite power supply system according to claim 7, characterized in that: EMS is also configured to EMS_Ref Sent to FCU, which is configured to compute I fc_Ref and sent to EMS, which is also configured to send I fc_Ref Sent to the DC / DC that controls the fuel cell.

9. The composite power supply system according to claim 6, characterized in that: The storage battery is a lithium battery, and / or the fuel cell is a hydrogen fuel cell.

10. A composite power supply method, characterized in that: The composite power supply system is applied to any one of claims 1 to 9.

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