DE102009033514B4 - Method for operating an energy storage arrangement in a vehicle and vehicle with an energy storage arrangement - Google Patents

Abstract

The invention relates to a method for operating an energy storage arrangement in a vehicle and to a vehicle having an energy storage arrangement. The assembly includes an energy source and at least two stacks (5, 6) of lithium-ion accumulators. Each of the stacks (5, 6) can individually take over the power supply for the operation of the vehicle. In the method, the following steps are alternatively performed. a) Charging the first stack (5) and simultaneously removing energy from the second stack (6) for the operation of the vehicle, wherein no energy for the operation of the vehicle from the first stack (5) is removed. In step b), the second stack (6) is charged and at the same time energy is taken from the first stack (5) for the operation of the vehicle, with no energy for the operation of the vehicle from the second stack (6) is removed.

Description

The invention relates to a method for operating an energy storage arrangement and a vehicle having an energy storage arrangement. Accumulators are used to store electrical energy and can both be charged and discharged.

The DE 10 2007 013 699 A1 describes an electric hall vehicle having a fuel cell unit and a transaction battery. The transaction battery can be charged using the fuel cell unit. With a coupling between the transaction battery and the fuel cell unit, a transaction battery charged by the fuel cell can be released and installed in another vehicle.

For accumulators, the problem arises that the life depends very much on the type of loading and unloading. For example, certain lifetimes are predicted for lithium-ion batteries. However, whether this lifetime is actually achieved depends very much on how the accumulators are operated, ie. H. How much energy is taken from each of them. Since the lithium-ion batteries are expensive, it is desirable to increase the lifetime as possible.

The DE 10 2007 013 072 A1 shows a multiple power supply device with a generator and a first battery. The first battery can be charged by an electrical output signal of the generator. A second battery operates to add electrical power to an electrical load installed in the vehicle. Electrical energy is supplied to the first battery based on at least one of the electrical output of the generator and a charge level. This ensures that the second battery is sufficiently charged. However, here too the problem of irregular loading and unloading processes arises.

The DE 27 40 438 C2 shows a vehicle with electric motor drive, the vehicle having solar cells and batteries. The solar cells are arranged so that the individual battery blocks are charged by the solar cells about the same with changing light.

The DE 699 20 585 T2 shows a battery control method for spacecraft with two parallel batteries, which are disabled for certain times by being discharged and cooled to a lower temperature range. This extends the life of the spacecraft as the batteries are partially deactivated. Nevertheless, the problem of lifetime reduction arises here with frequent load changes.

The object of the invention is therefore to provide a method and a device for operating an energy storage device, which allows a longer life of the intended energy storage accumulators.

According to the invention, this object is achieved with the subject matter of the independent patent claims. Advantageous developments of the invention are subject matters of the dependent claims.

The invention relates to a method for operating an energy storage arrangement in a vehicle. The assembly includes a power source and two stacks of lithium-ion batteries. In the stacks, the lithium-ion batteries are each connected in series. Each stack can individually take over the power supply for the operation of the vehicle. In the method, the following steps a) and b) are alternatively performed. In step a), the first stack is loaded from an energy source carried by the vehicle, while at the same time energy for the operation of the vehicle is taken from the second stack. In this case, no energy for the operation of the vehicle is taken from the first stack.

In step b), however, the second stack is charged and at the same time energy is taken from the first stack for the operation of the vehicle. In this case, no energy for the operation of the vehicle is removed from the second stack in step b).

The method has the advantage that only one of the stacks is loaded while the other of the stacks is being unloaded. This means that it is not possible for one of the stacks to be loaded and unloaded at the same time. It has been found that the life span of lithium-ion batteries in particular can be increased if the changes between the charging cycles and discharge cycles do not pile up too much. The alternative provision of steps a) and b) thus increases the life of the lithium-ion batteries considerably, so that they need to be replaced less frequently. The procedure also allows a gentle charging of the batteries, since the charging can be done with low currents.

Preferably, a device for charging the individual accumulators is provided in the first stack per accumulator. During charging of the batteries and removal of energy, this device is operated in each case so that the accumulators of the stack are charged to the same voltage. This ensures that none of the accumulators is over- or underloaded, which can destroy the accumulators in the worst case. At the same time, it is ensured that the aging of the accumulators of a stack is as uniform as possible, since a defect of one of the accumulators of a stack entails the replacement of the entire stack.

The same device is provided analogously in the second stack, so that the batteries of this second stack can also be operated as gently as possible.

If the energy source contains a fuel cell carried along with the vehicle, energy can be generated continuously substantially independently of the environmental conditions.

Alternatively or additionally, the energy source contains a solar cell carried along with the vehicle, so that energy can be generated without the need for regular fuel supply.

In one embodiment, the decision as to whether step a) or b) is performed depends on the state of charge of the accumulators of the stacks. This can for example ensure that the batteries are discharged evenly.

In another embodiment, the decision as to whether step a) or b) is made depends on the aging of the accumulators of the stacks. This makes it possible in particular for younger, and therefore more receptive, accumulators to compensate for large load peaks.

In addition, the decision as to whether step a) or b) is performed can be made dependent on the capacities of the accumulators of the stacks. This can z. B. also be ensured that those low-capacity batteries are used only for small loads.

In a further embodiment, more than two stacks are provided in the vehicle and at least one stack is connected either parallel to the first stack or parallel to the second stack. Thus, the inventive method is provided for more than two stacks. Thus, the vehicle can be formed with a larger total capacity.

Preferably, the decision as to whether step a) or b) is carried out is made dependent on the power consumption of the vehicle, whereby the most favorable stack can be selected according to the load.

The invention also relates to a vehicle with an energy storage arrangement. The vehicle includes a power source and the assembly includes at least two stacks of lithium-ion batteries. Each of the stacks can individually take over the power supply for the operation of the vehicle. In the arrangement, a switch is provided in such a way that either a position a) or a position b) is adjustable. In this case, in position a), the first stack is charged by the energy source and at the same time energy is taken from the second stack for the operation of the vehicle. In this case, no energy for the operation of the vehicle is taken from the first stack.

In the position b), however, the second stack is charged by the power source and at the same time taken energy from the first stack for the operation of the vehicle. In this case, no energy for the operation of the vehicle is taken from the second stack. With the presented vehicle, a particularly gentle use of the batteries is possible, which extends their life.

Particularly suitable is the present invention for light vehicles, d. H. Vehicles, of a weight not exceeding 350 kg, without the mass of the batteries, fitted with an electric motor with a maximum rated power not exceeding 4 kW. In such vehicles, pay special attention to the weight of the batteries and reliable power supply.

The invention will now be illustrated with reference to the figures with the aid of an embodiment. It shows

1 a circuit diagram of the electric drive system of a vehicle;

2 a flowchart of a portion of the method for operating an energy storage device in a vehicle.

1 shows a schematic diagram of an electric drive system 3 of a vehicle. For example, the vehicle is a bicycle with pedals powered by human power and an electric drive unit. The pedals and the electric drive unit both cause the movement of a chain and thus of the rear wheel of the bicycle.

The electric drive system has 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 UM1, a second changeover switch UM2 and a motor 17 on. The fuel cell 10 , which is designed for example as a methanol fuel cell, generates a voltage U _B of 24 V. The DC-DC converter 14 generates from this voltage the so-called first voltage U1 of 40 V, which is between a node K1 and the ground 36 is applied.

At the engine 17 is a second voltage U2, which is between the node K1 and the ground 36 provided. Also to the second voltage U2 is the voltage measuring circuit 15 , which also contains circuits for energy management, connected. This voltage measuring circuit 15 measures the second voltage U2 and receives information about the expected consumption. In accordance with the magnitude of the second voltage U2 and the magnitude of the expected consumption, the voltage measuring circuit drives the DC-DC converter to increase the first voltage U1.

The fuel cell 10 Provided energy is in stacks 5 and 6 saved. stack 5 contains the accumulators C11 to Cn1, which are stacked in series. One end of this series connection is with the ground 36 and another end of the series connection is connected to a first terminal of the changeover switch UM1. The second batch 6 contains the accumulators C12 to Cn2 and is between the mass 36 and a first terminal of the switch UM2 connected.

The accumulators C11 to Cn1 and C12 to Cn2 are each lithium-ion accumulators. In the pile 5 is a first terminal of the accumulator C11 with the ground 36 while its second terminal is connected to the first terminal of the second accumulator C21. A second terminal of the second accumulator C21 is connected to the first terminal of the accumulator C31, followed by the series of the remaining accumulators. In the selected embodiment, the number of accumulators is n = 10, so that each of the accumulators C11 to Cn1 stores electric charge at a voltage of 4V each. The stack 6 with its accumulators C12 to Cn2 is analogous to the stack 5 built up.

With the accumulators must be taken care that a single cell is not overloaded. If too high a voltage is applied to one of the accumulators, the accumulator is defective, so that no energy is stored through the entire series connection of the accumulators.

In order to ensure that the accumulators C11 to Cn1 are charged evenly, the transformer is 121 intended. The transformer 121 has a magnetizable core 111 on. To this core 111 is wound a primary coil Np1, which has 90 windings in the embodiment. A first terminal A1 of the primary coil Np1 is connected to the first terminal of the changeover switch UM1, while a second terminal of the primary coil Np1 is connected to a first terminal of the primary switch Sp11, whose second terminal is connected to ground 36 connected is. The primary switch Sp11 also has a switching input. Depending on this switching input, a connection between the first terminal and the second terminal of the primary switch Sp11 is opened or closed.

The transformer 121 also has n secondary coils. In the 1 the first secondary coil N11, the second secondary coil N21, the third secondary coil N31 and the nth secondary coil Nn1 are explicitly drawn. These secondary coils N11 to Nn1 each have three windings around the core 111 are laid. The core 111 is magnetizable and serves to transfer energy from the primary coil to the secondary coil or to several of the secondary coils N11 to Nn1. Each of the secondary coils N11 to Nn1 is to one of the accumulators C11 to Cn1 in parallel switchable. The secondary coils N11 to Nn1 each have a first and a second terminal, which are located at one end of the entirety of the turns. The first terminal of a secondary coil N11 is connected to a second terminal of the accumulator C11, while the second terminal of the secondary coil N11 is connected to a first terminal of a secondary switch S11 whose second terminal is connected to a first terminal of the accumulator C11. A switching input of the secondary switch S11 controls whether the electrical connection of the first terminal to the second terminal of the secondary switch S11 is closed.

Similarly, the second terminal of the second accumulator C21 is connected to the first terminal of the first secondary coil N21. The first terminal of the second switch S21 is connected to the second terminal of the second secondary coil N21, and its second terminal is connected to a first terminal of the second battery C21. The connection between accumulators, secondary coils and switches takes place in the same way for the remaining accumulators C31 to Cn1.

The microcontroller controls the switches Sp11 and S11 to Sn1 of the transformer 121 each on. By closing one of the secondary switches S11 to Sn1, a secondary coil is connected in parallel with an accumulator.

The transformer 122 contains the same elements as the transformer 121 , The elements are also corresponding to one another and to the accumulators of the stack 6 connected. The corresponding elements of the transformer 122 differ by the final digit 2 from the elements of the transformer 121 ,

The switches UM1 and UM2 each have second and third ports. The second terminal is connected to node K1, while the third terminal is connected to node K2. Thus, the switch UM1 either connects between the first port of the stack 5 and node K1 or a connection between the first port of the stack 5 with the knot K2 ago. Similarly, the switch UM2 either provides a connection between the first port of the stack 6 and node K1 or a connection between the first port of the stack 6 with the knot K2 ago. The switches are coupled together so that they occupy opposite switch positions. In position a), the switch UM1 connects the first node K1 to the first terminal of the stack 5 , the second switch UM2 connects the second node K2 to the first port of the stack 6 ,

In the second position b), the first switch UM1 connects the node K2 to the first terminal of the stack 5 while the second switch UM2 connects node K1 to the first port of the stack 6 combines. Thus, each one of the stack 5 and 6 loaded while the other the engine 17 operates. In parallel to the engine, further electrically operated units of the vehicle may be provided, for example electric indicator systems, transmission control units or engine control units. During the charging of the one stack, power is not taken from it at the same time. This has the advantage that the life of the stack increases. Nevertheless, the total capacity of the vehicle can be used, since alternately between the positions a) and b) can be switched. The 1 shows the position b).

Instead of the transformers, other buffers for energy can be used. These buffers can be, for example, by capacitors, coils or other batteries.

2 shows in a flow chart how the decision whether the switches UM1 and UM2 are brought into the position a) or b) is taken. The following example is assumed. The individual lithium-ion batteries have an expected life of X cycles. Today's common values for lithium-ion cells are 300 to 500 cycles, which in exceptional cases can be increased to 2000 cycles. Over time, the capacity of the accumulators decreases. Despite the fact that with the help of active balancing is trying to accumulators of a stack z. B. C11 to Cn1 as possible to load simultaneously, the individual accumulators of a stack undergo different aging processes due to production differences. Depending on the number of cycles passed, differences in capacities are still tolerated. If a stack was operated for the first 0.1 X cycles, for any one accumulator of a stack, the capacity should be more than 2% different from the average capacity of all the accumulators of the stack. With higher cycle numbers larger deviations are accepted.

The requirements are explained in the following table. ages maximum number of cycles capacity difference I 0.1 * X 99% 2% II 0.2 * X 90% 3% III 0.4 * X 80% 4% IV 0.5 · X 70% 4.5% V 0.8 * X 60% 5% VI 0.9 * X 55% 5.5% VII X 50% 5.5%

This means that at age III, usually 0.2 X to 0.4 X cycles, i. H. Charging and discharging, have occurred, the capacity may have dropped to 80% of the original capacity and the difference of the capacity of one accumulator from the average value of the capacity of all accumulators of the stack may be 4%.

Two values are stored per batch. To the first value, a first counter is provided, in which the number of charging and discharging cycles is stored. In the second memory, the age of the stack is stored. If the number of actual cycles in a stack equals the requirements shown in the table, the corresponding age level is stored in the age counter. However, if this does not agree with the cycles, an appreciation or devaluation will be made accordingly. If, for example, the cycle counter is set to 25000, but the difference is 5%, the corresponding stack is classified in age group V.

If, on the other hand, the difference is less than 1% and the capacity is still 99.5%, the corresponding batch is classified in age group I.

So each stack is classified according to the previous cycles and according to its capacity.

Based on the age groups it is decided in which position a) or b) the switches UM1 and UM2 are switched.

In a first step, the ages A (1) for the first batch 5 and A (2) for the second stack 6 queried. In addition, the charge states L (1) and L (2) for the accumulator of the stack 5 respectively. 6 queried. These are given in percent, 30% means that the stack is loaded to 30%.

In the next step, the energy demand is queried, ie essentially the power consumption by the motor 17 and the other control devices is queried.

When assessing the need, three cases are distinguished. In a first case, the current is less than 1 A, in the second case, it is between 1 A and 5 A and in the third case, it is greater than 5 A. These may be, for example, in a bicycle with auxiliary motor more than 20 A when driving uphill ,

In the first case, ie the power consumption is <1 A, it is first queried whether the age group A (1) is greater than the age group A (2). In the first case, a further query is started, namely whether the state of charge of the first accumulator is> 30%. If this is not the case, the system switches to position a), ie the older battery charges until the lower charge threshold of 30% is reached. If the state of charge is> 30%, switch to position b), so that the stack 6 the engine 17 drives. If the switches were in the appropriate position for three minutes, the query is repeated.

If the age of the stack 6 greater than or equal to the age of the pile 5 is, first, the state of charge of the stack 6 queried. If this> 30%, the circuit a) is switched, alternatively in the circuit b). It should be noted that in this mode, in which relatively little power is consumed, basically the older battery should be discharged to charge the younger as possible for subsequent uphill driving.

In the case that an average demand between 1 A and 5 A is required, the quotient of the charge states L (1) and L (2) is first formed. If this is between 0.95 and 1.05, it will alternate for each 3 minutes in the positions a) and b) connected. If the differences between the charge states are greater, it is queried which of the charge states are greater. If the charge state L (1) is greater than the charge state L (2), two minutes is switched to the position a) and four minutes to the position b). In the other case, alternately 4 minutes is switched to position b) and two minutes to position a).

In summary, it can be stated that in the case of average power consumption, the batteries are charged and discharged as uniformly as possible, where, in the event of major inequalities of the state of charge, one of the batteries will be charged slightly less than the other one.

In the third case of the relatively high power consumption, which is larger than 5 A, it is asked which of the ages A (1) and A (2) is larger. For the younger one of the accumulators is in each case queried whether the state of charge is greater than 30%. If this is the case, it is switched so that the younger battery drives the engine as long as its state of charge is greater than 30%.

In the case of high power consumption, the younger battery is thus used as long as possible.

LIST OF REFERENCE NUMBERS

3

electric drive unit

5

stack

6

stack

10

fuel cell

111

core

112

core

121

exchangers

122

exchangers

13

microcontroller

14

DC converter

15

Voltage measuring circuit

16

Current measurement circuit

17

engine

36

Dimensions

A1

first connection

A

ages

L

SOC

C11

accumulator

C12

accumulator

C21

accumulator

C22

accumulator

C31

accumulator

C32

accumulator

np 1

primary coil

p2

primary coil

N11

first secondary coil

N12

first secondary coil

N21

second secondary coil

N22

second secondary coil

N31

third secondary coil

N32

third secondary coil

Sp11

primary switch

sp12

primary switch

S11

switch

S21

switch

S31

switch

S12

switch

S22

switch

S32

switch

U1

first tension

U2

second tension

UB

fuel cell voltage

AT 1

first switch

AT 2 O'CLOCK

second switch

Claims (12)

Method for operating an energy storage arrangement in a vehicle, the arrangement comprising at least two stacks ( 5 . 6 ) of lithium-ion accumulators and each of the stacks ( 5 . 6 ) can individually take over the power supply for the operation of the vehicle, wherein in the method the following steps a) and b) are carried out alternatively: a) charging the first stack ( 5 ) from an energy source carried in the vehicle ( 10 ) and simultaneously taking energy from the second stack ( 6 ) for the operation of the vehicle, with no energy for the operation of the vehicle from the first stack ( 5 ). b) charging the second batch ( 6 ) and simultaneously extracting energy from the first stack ( 5 ) for the operation of the vehicle, with no energy for the operation of the vehicle from the second stack ( 6 ) is taken. Method according to claim 1, characterized in that in the first stack ( 5 ) for each accumulator (C1, ... Cn1) there is a device (N11, S11) for charging the accumulator, and during the charging and discharging of energy the devices (N11, S11) for charging are respectively operated in such a way that all the accumulators (C11, ... Cn1) of a stack ( 5 ) are charged to equal voltages. Method according to claim 1 or 2, characterized in that in the second stack ( 6 ) for each accumulator (C12, Cn2) there is a device (S12, N12) for charging the accumulator (C12), and during the charging and discharging of energy the devices (S11, N12) for charging are respectively operated in such a way that all the accumulators (C12, ... Cn2) of a stack ( 6 ) are charged to equal voltages. Method according to one of the preceding claims, characterized in that the energy source ( 17 ) contains a fuel cell entrained with the vehicle. Method according to one of claims 1 to 4, characterized in that the energy source ( 17 ) contains a solar cell carried along with the vehicle. Method according to one of claims 1 to 5, characterized in that the decision whether step a) or b) is carried out, the state of charge of the accumulators of the stack ( 5 . 6 ) is made dependent. Method according to claim 1, characterized in that the decision as to whether step a) or b) is carried out depends on the aging of the accumulators of the stacks ( 5 . 6 ) is made dependent. Method according to one of the preceding claims, characterized in that the decision as to whether step a) or b) is performed depends on the capacities of the accumulators of the stacks ( 5 . 6 ) is made dependent. Method according to one of the preceding claims, characterized in that in the vehicle more than two stacks are provided and at least one stack either parallel to the first stack ( 5 ) or parallel to the second stack ( 6 ) is switched. Method according to one of the preceding claims, characterized in that the decision whether step a) or b) is performed, is made dependent on the power consumption of the vehicle. Vehicle having an energy storage arrangement, wherein the vehicle is an energy source ( 17 ) and the arrangement contains at least two stacks ( 5 . 6 ) of lithium-ion accumulators and each of the stacks ( 5 . 6 ) can individually take over the power supply for the operation of the vehicle, and wherein in the arrangement switch (UM1, UM2) are provided so that either the position a) or b) is adjustable, wherein - in the position a) of the first stack ( 5 ) from the energy source ( 17 ) and at the same time energy from the second stack ( 6 ) is removed for the operation of the vehicle, with no energy for the operation of the vehicle from the first stack ( 5 ), and - in position b) the second stack ( 6 ) from the energy source ( 17 ) and at the same time energy from the first stack ( 5 ) is removed for the operation of the vehicle, with no energy for the operation of the vehicle from the second stack ( 6 ) is taken. Vehicle according to claim 11, characterized in that the vehicle is a light vehicle, being understood by light vehicle, a vehicle of not more than 350 kg, without mass of the batteries, with an electric motor whose maximum rated power is not more than 4 kW.

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