HARNISCH, Sten (Hermann-Gmeiner-Weg 9, München, 81929, DE)
DE ROCHE, John (Winkstr. 1, München, 81373, DE)
JÄKEL, Jürgen (Forstweg 11, Taufkirchen, 82024, DE)
HARNISCH, Sten (Hermann-Gmeiner-Weg 9, München, 81929, DE)
DE ROCHE, John (Winkstr. 1, München, 81373, DE)
| Claims 1. Energy supply unit for a vehicle comprising a set of energy storage contacts for connecting at least two stacks (5, 6) of electrical energy storage and supply means (Cl, ... CnI, C2, ... Cn2 ) , a set of energy supply contacts for connecting an energy source (17), a set of motor contacts for connecting a motor, and a switch device (UMl, UM2 ) operable in a first switching state and in a second switching state, wherein in the first switching state, the set of energy supply contacts and the set of energy storage contacts transfer energy from the energy source (17) to the first stack while the set of energy storage contacts and the set of motor contacts supply energy from the second stack to the motor and in the second switching state, the set of energy supply contacts and the set of energy storage contacts transfer energy from the energy source (17) to the second stack while the set of energy storage contacts and the set of motor contacts supply energy from the first stack to the motor. 2. Energy supply unit according to claim 1 further comprising at least two stacks (5, 6) of electrical energy storage and supply means (Cl, ... CnI, C2, ... Cn2) . 3. Energy supply unit according to claim 2, wherein the electrical energy storage means (Cl, ... CnI; C2, ... Cn2 ) comprises at least one battery unit. 4. Energy supply unit according to claim 3, wherein the battery unit comprises at least one lithium ion battery. 5. Energy supply unit according to any of the preceding claims further comprising a decision unit for providing the switches (UMl, UM2 ) in one of the first switching state and the second switching state . 6. Energy supply unit according to any of claims 2 to 5, characterised in that more than two stacks are provided in the vehicle, at least one stack is connected in parallel to the first stack (5) or in parallel to the second stack (6) . 7. Vehicle comprising an energy supply unit according to one of claims 1 to 6 with at least two stacks (5, 6) of electrical energy storage and supply means (Cl, ... CnI, C2, ... Cn2 ) , with an energy source (17), and with a motor for driving at least one wheel of the vehicle. 8. Vehicle according to claim 7, characterised in that the energy source (17) comprises an on-board fuel cell. 9. Vehicle according to claim 7, characterised in that the energy source (17) comprises an on-board solar cell. 10. Method for operating of an energy storage and supply unit in a vehicle, wherein the energy storage and supply unit comprises at least two stacks (5, 6) of electrical energy storage means (Cl, ... CnI, C2, ... Cn2), each stack (5, 6) is capable of providing energy to drive the vehicle, the method comprising a) charging the first stack (5) by an energy source (10) while the second stack (6) drives [or operates] the vehicle and b) charging the second stack (6) by the energy source (10) while the first stack (5) drives the vehicle. 11. Method according to claim 10 further comprising charging at least two electrical energy storage means (Cl, ... CnI, C2, ... Cn2) of one stack (5, 6) to the same voltage. 12. Method according to claim 10 or 11, characterised in that a decision on whether to perform the step a) or the step b) is made using a state of charge of the electrical energy storage means (Cl, ... CnI, C2, ... Cn2) of the stacks (5, 6) . 13. Method according to one of the claims 10 to 12, characterised in that the decision on whether to perform the step a) or the step b) is made using an age of the electrical energy storage means (Cl, ... CnI, C2, ...Cn2) of the stacks (5, 6) . 14. Method according to any of the claims 10 to 13, characterised in that the decision on whether to perform the step a) or the step b) is made using a capacity of the electrical energy storage means (Cl, ... CnI, C2, ...Cn2) of the stacks (5, 6) . 15. Method according to any of the claims 10 to 14, characterised in that the decision on whether to perform the step a) or the step b) is made using a current consumption of the vehicle . |
Method for the operation of an energy storage arrangement in a vehicle and vehicle with an energy storage arrangement
This application relates to a method for the operation of an energy storage arrangement in a vehicle and to a vehicle with an energy storage arrangement. Storage batteries are used to store electric energy and can be both charged and discharged.
DE 10 2007 013 699 describes an electric industrial truck comprising a fuel cell unit and a transaction battery. The transaction battery can be charged with the aid of the fuel cell unit. With a coupling between the transaction battery and the fuel cell unit, a transaction battery charged by the fuel cell unit can be released and installed into another vehicle.
Storage batteries are subject to the problem that their life time largely depends on the type of charging and discharging process. For lithium ion batteries, for example, certain life time values are predicted. Whether the predicted life time is actually reached depends to a great extent on the way in which the batteries are operated, i.e. how much energy is taken from them. As lithium ion batteries are very expensive, an increase in their life time is very desirable.
The current subject matter provides a method and a device for the operation of an energy storage arrangement which ensures a longer life time for the batteries.
It is provided a method for the operation of an energy storage arrangement in a vehicle. The arrangement comprises an energy source and two stacks of electrical energy storage means.
Within the stacks, the electrical energy storage means are connected in series. Each stack may or may not individually take over the energy supply for the operation of the vehicle.
The following steps a) and b) are performed alternatively. In step a) , the first stack is charged from an energy source carried on the vehicle, while energy is simultaneously taken from the second stack for driving or operating the vehicle. Essentially, no energy is taken from the first stack for the driving the vehicle.
In step b) , the second stack is charged while energy for the driving the vehicle is taken from the first stack. In step b) essentially no energy is taken from the second stack for the operation of the vehicle.
Only one of the stacks is charged at any one time, while the other stack is discharged. Charging and discharging one of the stacks simultaneously is avoided, if possible. It has been shown that in particular the lifetime of lithium ion batteries can be extended if there is not too much alternation between charging and discharging cycles. The alternative provision of steps a) and b) therefore extends the lifetime of lithium ion batteries significantly, so that they have to be replaced less frequently. The process also allows a gentle charging of the batteries, as they can be charged with low currents .
When a cell is charged or discharged, the battery cells are extended and compressed. The mechanical stress deriving from the extension and compression on the cells is reduced using the disclosed method. The management of the battery control becomes easier. The battery management calculates after each charge cycle and each discharge cycle the current state of charge (SOC) of the battery cells. As the disclosed method reduces the number of cy- cles, there are less calculation steps, usually addition steps or subtracting steps. As each calculation step includes rounding errors, a reduction of the number of steps means a higher precision when determining the state of charge. The disclosed method is especially applicable for lithium ion batteries. Such batteries are known for a limited number of charge cycles.
In the first stack, a device for charging individual storage batteries is preferably provided for each storage battery. While the storage batteries are charged and while energy is taken, this device is operated such that the storage batteries of the stack are charged to the same voltage. In this way, none of the storage batteries is overcharged or charged too little, which can destroy the storage batteries in the worst case. At the same time, it is ensured that the storage batteries of a stack age at the same rate as far as possible, because a defect in one storage battery of a stack would necessitate the replacement of the whole stack.
The same device is provided in the second stack to ensure that the storage batteries of this second stack are likewise operated as gently as possible. If the energy source includes an on-board fuel cell, energy can be generated continuously whatever the environmental conditions are. As an alternative or in addition, the energy source further includes an on-board solar cell, so that energy can be generated without a regular fuel supply. In a further embodiment, the energy source comprises a recuperation device generating electrical energy from the rotational energy of the wheels of the vehicle.
In one embodiment, the decision on whether to use step a) or step b) is determined by the state of charge of the stacks. In this way, it can for example be ensured that the storage batteries are discharged evenly.
In a further embodiment, the decision on whether to use step a) or step b) is determined by the aging of the storage batteries of the stacks. In this way, newer storage batteries with a higher capacity in particular can compensate for high peak loads . The decision on whether to use step a) or step b) may also be determined by the capacity of the storage batteries of the stack. In this way, it can for example be ensured that storage batteries with a low capacity are used only for minor loads. In a further embodiment, more than two stacks are provided in the vehicle, one stack being parallel-connected with either the first or the second stack. In this way, the method according to the application is made available for more than two stacks. As a result, the vehicle can be designed with a higher overall capacity.
The decision on whether to use step a) or step b) is preferably determined by the current consumption of the vehicle, so that the most suitable stack can be selected in accordance with the load.
The application further relates to a vehicle with an energy storage arrangement. The vehicle contains an energy source, and the arrangement comprises at least two stacks of lithium ion batteries. Each of the stacks is capable of individually taking over the energy supply for the operation of the vehicle. The arrangement is provided with a changeover switch for setting either a position a) or a position b) . In position a), the first stack is charged from the energy source while energy for the operation of the vehicle is simultaneously taken from the second stack. No energy is taken from the first stack for the operation of the vehicle.
In position b) , on the other hand, the second stack is charged from the energy source while energy for the operation of the vehicle is taken from the first stack. No energy is taken from the second stack for the operation of the vehicle. In the pro- posed vehicle, the storage batteries are used particularly gently, thus extending their life time.
The present application is particularly suitable for lightweight vehicles, i.e. vehicles weighing no more than 350 kg without the mass of the batteries and having an electric motor with a rated power of up to 4 kW. In such vehicles, the weight of the batteries and a reliable energy supply are critical.
In an alternative embodiment, the vehicle is a watercraft, in a further embodiment, the vehicle is an airplane especially a sailplane .
In summary, the application provides an energy supply unit for a vehicle. The energy supply unit includes a set of energy storage contacts, a set of energy supply contacts, a set of motor contacts, and a switch device.
The set of energy storage contacts is used for connecting two or more stacks of electrical energy storage and supply means. The set of energy supply contacts is used for connecting an energy source. The set of motor contacts is used for connecting a motor. In particular, the switch device is operable in a first switching state and in a second switching state.
In the first switching state, the set of energy supply contacts and the set of energy storage contacts transfer energy from the energy source to the first stack while the set of energy storage contacts and the set of motor contacts supply energy from the second stack to the motor. No energy for operating the vehicle is taken from the first stack. Similarly, in the second switching state, the set of energy supply contacts and the set of energy storage contacts transfer energy from the energy source to the second stack while the set of energy storage contacts and the set of motor contacts supply energy from the first stack to the motor, No en- ergy for operating the vehicle is taken from the second stack.
This configuration has an advantage of providing a longer life time for the electrical energy storage and supply means. This will be explained more fully in the application.
The energy supply unit can include two or more stacks of electrical energy storage and supply means. One stack of electrical energy storage means often refers to multiple electrical energy storage means arranged in a column or in a matrix although other arrangements are also possible.
Each of the electrical energy storage means can include one or more battery units. In addition, the battery unit can include one or more lithium ion batteries. Other alternatives are also possible. For example, the battery unit can include metal hydride or lead-acid batteries. The energy supply unit can include a decision unit for providing, setting, or configuring the switches to operate in the first switching state or in the second switching state.
In certain cases, the vehicle is provided with more than two stacks, wherein one or more stacks are connected in parallel to the first stack or in parallel to the second stack.
The application provides a vehicle. The vehicle includes the above energy supply unit with two or more stacks of electrical energy storage and supply means, with an energy source, and with a motor for driving one or more wheels of the vehicle.
In particular, the energy source can include an on-board fuel cell. The fuel cell can be provided as a combustion engine range extender. The energy source can also an on-board solar cell.
The application provides a method for operating of an energy storage and supply unit in a vehicle. The energy storage and supply unit includes two or more stacks of electrical energy storage means. Each stack is capable of individually providing energy to drive or to operate the vehicle. The method includes a first step of charging the first stack by an energy source. The energy source is carried on the vehicle. At the same time, the second stack provides energy to drive or operate the vehicle. No energy is taken from the first stack for operating or for driving the vehicle.
Similarly, the method includes a second step of charging the second stack by the energy source while simultaneously the first stack drives or operates the vehicle. No energy is taken from the second stack for operating or driving the vehicle.
The multiple electrical energy storage means of one stack is often charged to the same voltage. Several ways of deciding on whether to perform or to carry out the first step or the second step are possible. In one implementation, a decision on whether to perform or to carry out the first step or the second step is made using or can be dependent on a state of charge of the electrical energy storage means of the stacks. In a further implementation, the decision on whether to perform the first step or the second step is made using an age of the electrical energy storage means of the stacks. In yet a further implementation, the decision on whether to perform the first step or the second step is made using a capacity of the electrical energy storage means of the stacks. In another implementation, the decision on whether to perform the first step or the second step is made using a current consumption of the vehicle. The subject matter of the application is explained below with reference to an embodiment. Of the drawings,
Figure 1 is a circuit diagram of the electric drive system of a vehicle; Figure 2 is a flow chart of a section of the method for the operation of an energy storage arrangement in a vehicle; and
Figures 3 and 4 show the state of charge of batteries over the time in a waveform diagram.
Figure 1 is a circuit diagram of an electric drive system 3 of a vehicle. The vehicle may for example be a bicycle with pedals operated by human effort and with an electric drive unit. Both the pedals and the electric drive unit cause the movement of a chain and thus of the rear wheel of the bicycle. The electric drive system comprises a first transformer 121, a second transformer 122, a microprocessor 13, a dc-dc converter 14, a fuel cell 10, a voltage measuring circuit 15, a current measuring circuit 16, a first changeover switch UMl, a second changeover switch UM2 and a motor 17. The fuel cell 10, which may for example be a methanol fuel cell, generates a voltage U B of 24 V. From this voltage, the dc-dc converter 14 generates the so-called first voltage Ul of 40 V, which is applied between a node Kl and ground 36. A second voltage U2 provided between the node Kl and ground 36 is applied to the motor 17. The second voltage U2 is further connected to the voltage measuring circuit 15, which also includes circuits for energy management. This voltage measuring circuit 15 measures the second voltage U2 and receives infor- mation on the consumption to be expected. Depending on the value of the second voltage U2 and the value of the consumption to be expected, the voltage measuring circuit controls the dc-dc converter in order to increase the first voltage Ul. The energy provided by the fuel cell 10 is stored in the stacks 5 and 6. Stack 5 contains the storage batteries CIl to CnI, which are stacked in series. One end of this series connection is connected to ground 36, while another end of the series connection is connected to a first terminal of the changeover switch UMl. The second stack 6 contains the storage batteries C12 to Cn2 and is connected between ground 36 and a first terminal of the changeover switch UM2. The storage batteries CIl to CnI and C12 to Cn2 are lithium ion batteries. In stack 5, a first terminal of the battery CIl is connected to ground 36, while its second terminal is connected to the first terminal of the second battery C21. A second terminal of the second battery C21 is connected to a first terminal of the battery C31, to which the series of the remaining batteries is connected. In the selected embodiment, the number of storage batteries n=10, so that each of the storage batteries CIl to CnI stores an electric charge at a voltage of 4 V. The stack 6 with its storage batteries C12 to Cn2 is constructed in the same way as the stack 5.
It is important to ensure that individual cells of any battery are not overcharged. If too high a voltage is applied to one of the batteries, it becomes defective, with the result that no energy is stored in the entire series of batteries.
In order to ensure an equal charge for the storage batteries CIl to CnI, the transformer 121 is provided. The transformer 121 has a magnetic core 111. Around this core 111, a primary coil NpI is wound, which has 90 windings in the illustrated embodiment. A first terminal Al of the primary coil NpI is connected to the first terminal of the changeover switch UMl, while a second terminal of the primary coil NpI is connected to a first terminal of the primary switch SpIl, the second terminal of which is connected to ground 36. The primary switch SpIl has a switching input. Depending on this switching input, a connection is broken or made between the first terminal and the second terminal of the primary switch SpIl.
The transformer 121 further comprises n secondary coils. In Figure 1, the first secondary coil Nil, the second secondary coil N21, the third secondary coil N31 and the nth secondary coil NnI are shown explicitly. Each of these secondary coils Nil to NnI has three windings wound around the core 111. The core 111 is magnetisable and transfers energy from the primary coil to one or more of the secondary coils Nil to NnI. Each of the secondary coils Nil to NnI can be connected in parallel to one of the storage batteries CIl to CnI. Each of the secondary coils Nil to NnI has a first and a second terminal located at the ends of the winding assembly. The first terminal of a secondary coil Nil is connected to a second terminal of the storage battery CIl, while the second terminal of the secondary coil Nil is connected to a first terminal of a secondary switch SIl, the second terminal of which is connected to a first terminal of the storage battery CIl. A switching input of the secondary switch SIl controls the establishment or the break of the electric connection between the first terminal and the second terminal of the secondary switch SIl.
In the same way, the second terminal of the second storage battery C21 is connected to the first terminal of the secondary coil N21. The first terminal of the switch S21 is connected to the second terminal of the second secondary coil N21, its second terminal being connected to a first terminal of the second storage battery C21. The connection between storage batteries, secondary coils and switches is established in the same way for the other storage batteries C31 to CnI. The microcontroller controls states of the switches SpIl and SIl to SnI of the transformer 121. By closing one of the secondary switches SIl to SnI, the secondary coil is connected in parallel with a storage battery. Although in the description, the state of the switch may be called "position", the switches can be provided by solid-state elements which have switching states. The switching position is then represented by switching state. The transformer 122 comprises the same elements as the transformer 121. These elements are likewise interconnected and connected to the storage batteries of the stack 6. The corresponding elements of the transformer 122 are distinguished from the elements of the transformer 121 by the last digit 2.
The changeover switches UMl and UM2 have second and third terminals. The second terminal is connected to the node Kl, while the third terminal is connected to the node K2. In this way, the changeover switch UMl establishes either a connection be- tween the first terminal of the stack 5 and the node Kl or a connection between the first terminal of the stack 5 and the node K2. In the same way, the changeover switch UM2 establishes either a connection between the first terminal of the stack 6 and the node Kl or a connection between the first terminal of the stack 6 and the node K2. The changeover switches are coupled such that they adopt opposite switch positions. If the changeover switch UMl connects the first node Kl to the first terminal of the stack 5 in position a) , the second changeover switch UM2 connects the second node K2 to the first terminal of the stack 6.
In the second position b) , the first changeover switch UMl connects the node K2 to the first terminal of the stack 5, while the second changeover switch UM2 connects the node Kl to the first terminal of the stack 6. As a result, one of the stacks 5 and 6 is charged while the other drives the motor 17 and the peripheral circuits like engine control, gear control and user display. Further electrically operated units of the vehicle may be connected in parallel to the motor, for example electric display systems, transmission or motor controllers. While a stack is being charged, no current is taken from it. This offers the advantage that the life time of the stack is increased. It is nevertheless possible to use the total capac- ity of the vehicle, because positions a) and b) can be alternated. Figure 1 shows position b) .
It should be noted that during the switching of the changeover switch, between positions a) and b) , there is for a short pe- riod in which the power supply of the engine may be interrupted for a short time. Therefore, it is preferred to switch the changeover switch during an halt of the vehicle.
A typical consumption of a driving engine is between 600 W (Watt) and 700 W, but can also include powers of up to 4 or 5 kW (kilowatt) .
In place of the transformers, other buffer storage devices for energy may be used. These may for example be capacitors, coils or further batteries.
Figure 2 illustrates in a flow chart how the decision on whether to switch the changeover switches UMl and UM2 to position a) or b) is made. The explanation is based on the follow- ing example. The individual lithium ion batteries have an expected life time of X cycles. The usual values for lithium ion cells are presently 300 to 500 cycles, up to 2000 cycles in exceptional cases. In the course of time, the capacity of the storage batteries is reduced. Irrespective of any attempts to charge the storage batteries of a stack, e.g. CIl to CnI, as simultaneously as possible using active balancing, the ageing processes for the individual storage batteries of a stack differ as a result of production differences. Depending on the number of cycles completed, some capacity differentials are tolerated. If a stack has completed first 0.1*X cycles, the capacity of any one storage battery in a stack should not deviate by more than 2% from the average capacity of all storage batteries in the stack. At higher cycle numbers, larger deviations are tolerated.
These requirements are illustrated in the table below.
This means that in age stage III 0.2*X to 0.4*X cycles, i.e. charge and discharge processes, have been completed as a rule, that capacity may have been reduced to 80% of the original value and that the capacity differential of a storage battery from the average capacity value of all storage batteries of the stack may be 4%.
Two values are stored for each stack. For the first value, a first counter is provided in which the number of charge and discharge cycles is stored. In the second, the age stage of the stack is stored. If the number of actual cycles of a stack corresponds to the requirements of the table, the age stage is stored in the age stage counter. If there is any deviation, the values are upgraded or downgraded accordingly. If the cy- cle counter for example indicates 2500 and the differential is 5%, the stack is rated in age class V.
If the differential is less than 1% and capacity still is 99.5%, the respective stack is rated in age class I.
In this way, each stack is rated in accordance with the cycles completed and with its capacity.
The decision on switching the changeover switches UMl and UM2 to position a) or b) is then based on age classes.
In a first step, the age stages A(I) for the first stack 5 and A(2) for the second stack 6 are scanned. In addition, the states of charge L(I) and L (2) for the storage batteries of the stacks 5 and 6 are scanned. These are indicated in percent, 30% meaning that the stack is 30% charged.
In the next step, the energy demand is scanned, i.e. essentially the current consumption of the motor 17 and the further control units.
In evaluating demand, a distinction is made between three cases. In the first case, the current is less than 1 A, in the second case 1 A to 5 A and in the third case more than 5 A. In the case of a bicycle with an auxiliary motor, this may be more than 20 A on an uphill grade.
In the first case, i.e. at a current consumption < 1 A, the first scan is to establish whether age stage A(I) is higher than age stage A(2) . In the first case, a further scan is started to establish whether the state of charge of the first battery is > 30%. If this is not the case, the system switches to position a), i.e. the older battery charges until the lower charge threshold of 30% is reached. If the state of charge is > 30%, the system switches to position b) , so that the stack 6 drives the motor 17. If the changeover switches remain in the same position for three minutes, the scan is repeated. If the age stage of the stack 6 is higher than or equal to the age stage of the stack 5, the state of charge of the stack 6 is first scanned. If this is > 30%, the system switches to position a), otherwise to position b) . It will also have to be established whether in this mode, which consumes relatively little current, the older battery should be discharged as a matter of principle in order to charge the newer battery as much as possible for any subsequent uphill travel.
At a medium demand between 1 A and 5 A, the quotient is first calculated from the states of charge L(I) and L (2) . If this is between 0.95 and 1.05, positions a) and b) alternate for 3 minutes each. If the differential between the states of charge is higher, it is established which of the states of charge is the higher. If the state of charge L(I) is higher than the state of charge L(2), the system switches to position a) for two minutes and to position b) for four minutes. In the opposite case, the system alternates between 4 minutes in position b) and two minutes in position a) . To summarise, it can be established that the batteries are charged and discharged as evenly as possible at a medium power consumption, while at major differences between the states of charge one of the batteries is discharged a little less long than the other. In the third case of a relatively high power consumption above 5 A, the scan establishes which of the age stages A(I) and A(2) is the higher. In the case of newer storage batteries, it is established whether the state of charge is above 30%. If this is the case, the system switches to a position in which the newer battery drives the motor while its state of charge exceeds 30%. At high power consumption, the newer battery is therefore used as long as possible.
Figures 3 and 4 show the state of charge (SOC) of one battery stack over time in waveform diagrams . Figure 3 shows a wave- form of the SOC over time for a prior art battery management system in which the battery is simultaneously connected to the load and to the on-board energy source. The waveform shows many changes between charging and discharging with varying length .
Figure 4 demonstrates the SOC of a same battery as in Figure 3 and on the same time scale but charged according to the method disclosed in this application. In the timeframe between the time 0 and t^ there are only two charging and two discharging cycles whereby Figure 3 shows over a dozen charging and over a dozen discharging cycles. The lower number of cycles means less mechanical stress for the battery cells and a more precise calculation of the state of charge. Reference Numbers
3 Electric drive unit
5 Stack
6 Stack
10 Fuel cell
111 Core
112 Core
121 Transformer
122 Transformer
13 Microcontroller
14 DC-DC converter
15 Voltage measuring circuit
16 Current measuring circuit
17 Motor
36 Ground
Al First terminal
A Age stage
L State of charσe
CIl Storage battery
C12 Storage battery
C21 Storage battery
C22 Storage battery
C31 Storage battery
C32 Storage battery
NpI Primary coil
Np2 Primary coil
Nil First secondary coil N12 First secondary coil
N21 Second secondary coil
N22 Second secondary coil
N31 Third secondary coil
N32 Third secondary coil SpIl Primary switch
Spl2 Primary switch
SIl Switch
521 Switch
S12 Switch
522 Switch
S32 Switch
Ul First voltage
U2 Second voltage
UB Fuel cell voltage
UMl First changeover switch UM2 Second changeover switch