POWER SUPPLY SYSTEM AND METHOD FOR POWER SUPPLY

Description

[0001] The invention relates to an energy supply system and a method for energy supply.

[0002] To date, batteries and fuel cells have been used in electrical systems as grid power supplies only in very different sizes in terms of capacity. Since in such cases only one component primarily supplies the electrical grid, energy management is not provided.

[0003] In systems where the electrical grid is primarily supplied by a battery, the considerably smaller fuel cell is only installed for backup purposes. Any negative impact on the battery, e.g. by overcharging the battery with the fuel cell, is technically almost impossible. Due to the small size of the fuel cell, this would require a great deal of time and gas. Energy management is not installed in these systems. For example, submarines have a large battery that supplies the electrical grid and a fuel cell that is connected to the power supply system via a DC / DC converter. The capacity of the fuel cell is in the thousandths of an inch compared to the capacity of the battery. The fuel cell is used either to maintain the battery or, in exceptional cases, to supply part of the on-board electrical system.The main battery charging is usually done via generators, since the fuel cell cannot supply the required current. The fuel cell system is typically controlled via an automation system.

[0004] Conversely, in systems where the fuel cell supplies the electrical grid almost exclusively, only a small battery is installed, which is intended solely for starting the system. After the start-up process, the battery is recharged in parallel with the system's power supply from the fuel cell. A simple charge controller monitors the charging process and stops it as soon as the battery is full. Since the system is essentially powered only by the fuel cell, energy management is not provided here either. Such constellations can be found, for example, in the so-called mobility sector, where larger fuel cells are installed to power the vehicle and the drive. The battery only supplies the energy for starting the system and the fuel cell.While the fuel cell supplies the vehicle and the drive, the battery is recharged, just as the alternator recharges the battery during operation in a conventional vehicle. In this application, there is only one fuel cell and one battery. Multiple, similar supply systems are not planned.

[0005] US 2001 / 018138 A1, for example, discloses a system that operates a fuel cell at a high energy conversion efficiency point. A control unit calculates the required power of an inverter.

[0006] In supply systems with multiple energy producers or suppliers of comparable capacity or with multiple similar components, an energy management system usually ensures that the load from the electrical grid is distributed evenly among the energy suppliers installed in the electrical grid, such as generators and / or batteries. Such a system with a central control system is used, for example, in US 2016 / 297544 A1 to ensure the stability of an aircraft. If the energy is also generated by generators, this energy management system starts or stops the respective generators depending on the load. In any case, it would be indispensable without a higher-level energy management system, especially when lithium batteries are used. Overcharging the battery, which can quickly happen with components of approximately the same capacity, would significantly reduce the service life of the battery or even destroy it.Fuel cells also have certain limits that must be observed to avoid reducing their lifespan or damaging them. Overloading or backfeeding energy into the fuel cell also reduces its lifespan or even destroys it. In any case, an overarching energy management system must be adapted to the type and number of components installed in the system.

[0007] The object of the invention is to provide a power supply system that enables improved power supply with regard to flexibility, safety, and the service life of the components. Furthermore, the object of the invention is to provide a corresponding method for power supply.

[0008] The invention solves the problem directed at an energy supply system by providing that the energy supply system comprises mutually independent, in particular with regard to control, self-sufficient, parallel-connected energy supply modules, the energy supply modules each comprising consumer connections, a battery which couples directly to the consumer connections, a fuel cell which couples to the consumer connections via a DC / DC converter, and further an energy management system with which the operating point of the fuel cell or the operating point of the DC / DC converter can be controlled depending on a charge state of the battery.

[0009] In particular, for each energy supply module, the operating point of the fuel cell or the operating point of the DC / DC converter can be controlled exclusively depending on the battery charge state.

[0010] The self-sufficient energy management system of each power supply module of the energy supply system controls the operating point of the respective DC / DC converter so that, together with the respective battery, there is always sufficient power available for a consumer.

[0011] At the same time, the energy management systems of the power supply modules ensure that the charge level of each battery remains within specified limits. This ensures the maximum service life of all components.

[0012] Advantageously, the power supply modules each further comprise a bus system for communication between the energy management system and a battery management system of a power supply module, for communication between the energy management system and a fuel cell controller of the power supply module, and for communication between the energy management system and the DC / DC converter of the supply module. All data, control values, warnings, and error messages necessary for the operation of the power supply module are transmitted between the energy management system and the individual components via this bus system.

[0013] The power supply module thus enables the construction of a power supply system from one or more similar, self-sufficient and independent supply components with regard to control, without the need for a higher-level control system, while ensuring the maximum service life of the components in the components.

[0014] The object directed to a method for energy supply is achieved by a method in which a required base load can be provided by an energy supply system comprising parallel-connected and each independently controlled energy supply modules, wherein for each energy supply module energy can be provided both directly from a battery and via a DC / DC converter from a fuel cell, as well as jointly from the battery and fuel cell, wherein for each energy supply module a state of charge of the battery is determined and an operating point of the fuel cell or an operating point of the DC / DC converter is controlled depending on the state of charge of the battery.

[0015] As already explained regarding the power supply system, the operating point of the DC / DC converter is controlled so that, together with the battery, sufficient power is always available for a load. According to the invention, the battery's charge level always remains within specified limits. This approach ensures the maximum service life of all components.

[0016] Advantageously, transient load peaks are covered only by the battery because the battery does not have a lead time until energy can be supplied, as would be the case with the fuel cell.

[0017] Furthermore, it is advantageous if the battery's state of charge always remains within defined limits. Any deep discharge damages a battery. Typically, this damage accumulates. However, even at the upper end of the state of charge scale, care should be taken to ensure that the battery is not regularly charged to 100%. A state of charge of 80 to 90% as an upper limit is appropriate in this case.

[0018] The two charging end points for the battery, both the lower charging end point SoC min and the upper charging end point SoC max, are selected so that the maximum service life of the battery is achieved at the maximum usable capacity, and sufficient control reserve is available for the fuel cell.

[0019] It is also useful to control the operating point of the DC / DC converter so that, together with the battery, sufficient power is always available. The operating point of the DC / DC converter can be used to easily adjust the total power of the power supply module and the load on its components.

[0020] It is advantageous if the data, control values, warnings, and error messages required for the process are transmitted via a bus system. This enables bidirectional operation and allows multiple components to be securely connected to each other via the same set of cables.

[0021] As already mentioned, excessive battery discharge should be avoided. Therefore, if the battery's state of charge (SoC) is detected to fall below a predefined threshold (SoC min), the operating point of the DC / DC converter should be increased until the battery enters the state of charge.

[0022] Likewise, if the battery changes from charging to discharging before it has reached its upper charging end point SoC max, it is advisable to increase the operating point of the DC / DC converter until the battery is charged again or the maximum output current of the fuel cell is reached.

[0023] Furthermore, when charging the battery, it is advisable to adjust the operating point of the DC / DC converter so that the maximum permissible charging current into the battery is not exceeded. Otherwise, the battery will overheat and be damaged.

[0024] It is advantageous that when the battery has reached the preset upper charging point SoC max, the operating point of the DC / DC converter is lowered until the current drawn from the battery reaches a preset percentage of a permissible continuous discharge current of the battery and that a load is covered by the fuel cell and the battery together.

[0025] In an advantageous form of the embodiment of the method according to the invention, if a load requirement does not change and the battery reaches its upper final charge value SoC max, the fuel cell is switched off and kept in standby mode until the SoC value of the battery approaches the lower final charge value SoC min and only then is the fuel cell started again.

[0026] When a load decreases, it is advisable to lower the operating point of the DC / DC converter until a current from the battery has again reached approximately the set percentage of a continuous discharge current.

[0027] The operating point of the DC / DC converter, and thus also of the fuel cell, is advantageously only changed when a new load is present for longer than a configurable dead time. This prevents a constant change or oscillation of the fuel cell's operating point. In addition, the speed at which the DC / DC converter changes the operating point and thus the current from the fuel cell is limited by the fuel cell's specifications for the maximum permissible current change rates. This process further protects the fuel cell and thus extends its service life.

[0028] The fuel cell's output power cannot be reduced arbitrarily, as this would also negatively impact its service life. The permissible, continuous minimum load of the fuel cell, P BZmin, is specified by the manufacturer.

[0029] To protect the battery, it is advisable to increase the operating point of the DC / DC converter when the maximum permissible long-term discharge current of the battery is reached or exceeded, until the long-term discharge current drops below its maximum value again. The short-term discharge current of the battery is usually several times the long-term discharge current, so brief exceedances of the long-term discharge current or current peaks do not have a negative impact on the battery's service life.

[0030] If a single power supply module cannot meet the required load alone, it is advantageous to connect several power supply modules in parallel. The power supply system constructed from several power supply modules then consists of self-sufficient, similar components, without the need for a higher-level power supply system. If several of these power supply modules operate in parallel in a network, all of them behave identically, e.g., like parallel-connected batteries or regulated power supplies. All participating power supply modules supply the network equally.

[0031] If the parameters of the individual energy supply modules are not set the same, e.g. the SoC max of one system is set higher than that of the other supply modules, it can happen that energy is fed from the consumer system into the battery for a longer period of time and the battery is also charged by the consumer system. In this case, the operating point of the DC / DC converter is reduced to its minimum value. If more energy is required from the system within this time, the operating point of the DC / DC converter changes according to the procedure described above. If the load requirement from the system does not change and the battery reaches its upper end charge value, SoC max, the fuel cell is switched off. The fuel cell remains in standby mode until the SoC value of the battery approaches the lower end charge value SoC min. Only then is the fuel cell restarted.Because all batteries are connected in parallel, they have the same voltage level and approximately the same state of charge. Accordingly, all supply systems in the network behave the same.

[0032] The energy supply system according to the invention, with the energy supply modules and the corresponding method for energy management between the battery and fuel cell, enables a consumer system to be supplied with energy in the most effective manner while simultaneously ensuring the maximum service life of the components. The energy supply system and the corresponding method offer the following advantages: The respective energy management of each individual energy supply module ensures that none of the limit values ​​of the individual components in the supply component are exceeded, which could cause damage to the components.

[0033] The energy supply system behaves towards the consumer system like any other energy supply system, only with a considerably larger capacity, which is determined solely by the number of energy supply modules.

[0034] Since all rapid current changes that can occur in the system, e.g. when switching consumers on or off, are carried by the battery, no soft start circuits or components to limit the inrush currents in the consumer system are necessary.

[0035] The base load is supplied by both components, the battery and the fuel cell. Oversizing the battery is unnecessary.

[0036] When needed, the fuel cell ensures that the battery is charged in addition to the mains supply. The energy management system ensures that the battery's maximum charging current is not exceeded.

[0037] Energy management prevents the fuel cell from having to change its output too often and too quickly, which has a negative impact on the service life of the fuel cell.

[0038] Because all supply components are identical, manufacturing is simplified. Only the same size power supply module needs to be built, using the same components, regardless of the actual size of the consumer system. This means that there is hardly any design effort required for new systems.

[0039] All combinations of battery and fuel cell operate autonomously.

[0040] Any number of these combinations can be connected in parallel without the need for a higher-level control system that has to be adapted to the respective system.

[0041] High redundancy is achieved and high flexibility is achieved at low completion costs.

[0042] The invention is explained in more detail by way of example with reference to the drawings. They show schematically and not to scale: Figure 1 shows an energy supply module of an energy supply system according to the invention, Figure 2 shows an energy supply system comprising several energy supply modules, and Figure 3 shows time profiles of the fuel cell power and the battery charge state as a function of a load requirement.

[0043] The Figure 1shows schematically and by way of example a power supply module 1 of a power supply system 10 according to the invention, which is coupled to a consumer 11. The power supply module 1 comprises consumer connections 2, a battery 3, which couples directly to the consumer connections 2, a fuel cell 4, which couples to the consumer connections 2 via a DC / DC converter 5, and an energy management system 6, with which the operating point of the fuel cell 4, or the operating point of the DC / DC converter 5, can be controlled depending on a charge state of the battery 3. Control is via a bus system 7, which ensures communication between the energy management system 6 and a battery management system 8, communication between the energy management system 6 and a controller 9 of the fuel cell 4, and communication between the energy management system 6 and the DC / DC converter 5. All data necessary for the method, such asfrom the current measurement at the consumer connections 2, control values, warnings and error messages are transmitted via this bus system 7.

[0044] Figure 2 shows a power supply system 10 according to the invention. It comprises power supply modules 1 that are independent of one another with respect to a control system and connected in parallel.

[0045] Figure 3 The lower part shows an example of a time course of a load requirement PL .

[0046] Directly above, in the middle of the Figure 3, a battery charge level is shown. The three most important values ​​for the battery charge level are shown: full charge level (SoC 100%), the ideal maximum charge level for the battery's service life (SoC max), and the recommended minimum charge level (SoC min). The charge level (SoC) of battery 3 essentially always remains within the specified limits (SoC max and SoC min). Briefly falling below SoC min is harmless.

[0047] Above the battery charge level is in the Figure 3 a corresponding fuel cell power P BZ is shown. The fuel cell power curve lies between a maximum fuel cell power P BZmax and a minimum fuel cell power P BZmin .

[0048] In the following, the Figure 3 The curves shown explain in more detail the behavior of a power supply module 1 under different load conditions or load developments.

[0049] From time t 8 onward, the curves show an example of how transient load peaks are covered only by battery 3. In general, the operating point of DC / DC converter 5 is controlled so that, together with battery 3, sufficient power is always available.

[0050] At time t 3 it is determined that the state of charge of the battery (SoC) falls below the predefined threshold value SoC min . As a result, the operating point of the DC / DC converter 5 is increased and the battery 3 switches to the state of charge. At time t 9 the state of charge of the battery (SoC) also falls below the predefined threshold value SoC min . However, the load requirement increases comparatively quickly here, so that the fuel cell 4 alone cannot provide sufficiently more power. The battery state of charge therefore briefly falls below the lower limit SoC min until at time t 10 the load requirement falls and the power that can be provided by the fuel cell 4 is sufficiently high to both cover the power demand of the consumer 11 and recharge the battery 3.

[0051] At time t 4 , battery 3 switches from charging to discharging, before it has reached its upper charging end point SoC max. If the maximum output current of fuel cell 4 has not yet been reached, the operating point of DC / DC converter 5 is increased until battery 3 is recharged or the maximum output current of fuel cell 4 is reached. In the example of Figure 3 At time t 4 , the fuel cell is already running at maximum, which is why the operating point of the DC / DC converter is no longer changed. However, at time t 5 , when the load demand begins to decrease, the operating point is maintained and battery 3 is charged until the maximum SoC is reached at time t 6 .

[0052] Generally, when charging battery 3, the operating point of DC / DC converter 5 is adjusted so that the maximum permissible charging current to battery 3 is not exceeded. This can be seen, for example, at time t 7 , when battery 3 is being charged, but not at the maximum power of fuel cell 4.

[0053] When the battery 3 has reached the preset upper charging point SoC max, for example at time t 6 , the operating point of the DC / DC converter 5 is lowered until the current drawn from the battery 3 reaches a preset percentage of a permissible continuous discharge current of the battery 3 and a load is covered by the fuel cell 4 and the battery 3 together.

[0054] Alternatively, in the event that a load requirement does not change and the battery 3 reaches its upper charge limit value SoC-max, the fuel cell 4 could be switched off and remain in standby mode until the SoC value of the battery 3 approaches the lower charge limit value SoC min and only then would the fuel cell 4 be started again.

[0055] It is also useful to lower the operating point of the DC / DC converter 5 so that when the load is reduced, the current from the battery 3 again reaches approximately the set percentage of a continuous discharge current.

[0056] Out of Figure 3It can also be seen that the operating point of the DC / DC converter 5, and thus also of the fuel cell 4, only changes when a new load is present for longer than a settable dead time. At time t 6 , for example, the load begins to increase, but only the state of charge of battery 3 follows instantly; a change in the fuel cell power is delayed.

[0057] Finally, the Figure 3 It can be seen that the operating point of the DC / DC converter 5 is increased when the maximum permissible long-term discharge current of the battery 3 is reached or exceeded, until the long-term discharge current drops below its maximum value again. This is evident in the curve progression around times t 1 , t 2 , and t 3 . At point t 2 , the gradient of the load requirement increases, the state of charge of the battery 3 decreases more rapidly, and the power curve of the fuel cell 4 changes from a sideways movement to an upward movement.

Claims

1. An energy supply system (10) comprising energy supply modules (1) connected in parallel and each autonomously controlled, the energy supply modules (1) each comprising load terminals (2), a battery (3) directly coupled to the load terminals (2), a fuel cell (4) coupled to the load terminals (2) via a DC / DC converter (5), wherein the operating point of the fuel cell (4) and / or the operating point of the DC / DC converter (5) within an energy supply module (1) are controllable by an energy management system (6) depending on a state of charge of the battery (3).

2. The energy supply system (10) according to claim 1, wherein the energy supply modules (1) each comprise a bus system (7) for communication between the energy management system (6) and a battery management system (8), for communication between the energy management system (6) and a controller (9) of the fuel cell (4), and for communication between the energy management system (6) and the DC / DC converter (5).

3. A method for supplying energy, wherein a required base load may be provided by an energy supply system (10) comprising energy supply modules (1) connected in parallel and each autonomously controlled, wherein, at each energy supply module (1), energy may be provided directly by a battery (3) or by a fuel cell (4) via a DC / DC converter (5) or jointly by both the battery (3) and the fuel cell (4), wherein a respective state of charge of the battery (3) is determined and an operating point of the fuel cell (4) and / or an operating point of the DC / DC converter (5) is controlled depending on the state of charge of the battery (3).

4. The method according to claim 3, wherein transiently occurring load peaks are covered by the battery (3) only.

5. The method according to any one of claims 3 or 4, wherein a state of charge of the battery substantially is substantially within predetermined limits.

6. The method according to any one of claims 3 to 5, wherein the operating point of the DC / DC converter (5) is controlled such that, in combination with the battery (3), sufficient power always is available.

7. The method according to any one of claims 3 to 6, wherein data, control values, warnings, and error messages required for the method are transmitted via a bus system (7).

8. The method according to any one of claims 3 to 7, wherein, when the state of charge (SoC) of the battery is determined to fall below a predefined threshold SoCmin, the operating point of the DC / DC converter (5) is increased until the battery (3) switches to the state of charge.

9. The method according to any one of claims 3 to 8, wherein, when the battery (3) switches from charging to discharging prior to having reached its upper charging end point SoCmax, the operating point of the DC / DC converter (5) is increased until the battery (3) is charged again or the maximum output current of the fuel cell (4) is reached.

10. The method according to any one of claims 3 to 9, wherein, upon charging the battery (3), the operating point of the DC / DC converter (5) is adjusted such that a maximum allowed charging current to the battery (3) is not exceeded.

11. The method according to any one of claims 3 to 10, wherein, when the battery (3) has reached the preset upper charging point SoCmax, the operating point of the DC / DC converter (5) is lowered to where the current drawn from the battery (3) reaches a preset percentage of an allowed continuous discharge current of the battery (3) and a load is covered jointly by the fuel cell (4) and the battery (3).

12. The method according to any one of claims 3 to 11, wherein, when a load requirement does not change and the battery (3) reaches its upper charging end point SoCmax, the fuel cell (4) is turned off and remains in standby mode until the SoC value of the battery approaches the lower charging end value SoCmin, by which point the fuel cell (4) is restarted.

13. The method according to any one of claims 3 to 12, wherein the operating point of the DC / DC converter is lowered until a current from the battery (3) has reached approximately the adjusted percentage of a continuous discharge current as a load decreases.

14. The method according to any one of claims 3 to 13, wherein the operating point of the DC / DC converter (5), and thus also of the fuel cell (4), are changed only when a new impending load is impending for a time longer than an adjustable idle time.

15. The method according to any one of claims 3 to 14, wherein the operating point of the DC / DC converter (5) is increased when the maximum allowed long-term discharge current of the battery (3) is reached or exceeded until the long-term discharge current falls again below its maximum value.

16. The method according to any one of claims 3 to 15, wherein multiple energy supply modules (1) are connected in parallel.