FR2790148A1 - Flexible energy source for traction, telephone, lap-top or other mobile equipment, comprises two parallel-batteries, one for base load, one for short-term peaks - Google Patents

Abstract

The batteries' nominal operating voltages are identical, but one is designed for a much higher power/energy ratio than the other. (In practice, one or both parallel sources represents a set of two or more similar batteries; the effect of a unit failure is thus reduced.). Thus one source is regarded as essentially energy providing, the other as power providing. Each branch is independently switched, but satisfactory operation does not require an overall electronic controller. In an example given, the energy source (E1) is rated at 50 Ah, the power source (P1) at 5 Ah, the respective power/energy ratios being 2 and 20. If each source comprises 40 component batteries, this makes available 28 kW and 5 kWh power and energy capacities for a gross weight of 60 kg, compared with 140 kg if the same capacities are to be achieved with low ratio elements only, or 100kg with high ratio only.

Description

FLEXIBLE BATTERY SYSTEM.

  The present invention relates to the field of the storage of electrical energy with a view to its restitution to organs consuming energy, such as a traction motor of an electric or hybrid propulsion vehicle, portable electronic components such as a microphone. - computer or telephone or any other consumer item

  that you want to power with a battery.

  Traction batteries for electric and hybrid vehicles are currently produced at high cost. The batteries developed for automobile manufacturers are specific for each of them and for each application, which translates into a cost price.

  high of the elementary battery cell.

  Any battery must meet specifications in terms

  mass energy and mass power.

  The placing in series or the placing in parallel of the elements of a traction battery for electric or hybrid vehicles is usually chosen according to the desired energy, power and voltage. Dissociating the energy source and the power source has often been a research avenue in order to optimize the system in terms of power, energy and lifespan. The series connection of a lead-acid battery (energy source) and a supercapacitor (power source) has been studied for an application to electric vehicles,

  in order to reduce the demand for power sent to the battery.

  However, this type of assembly has two main drawbacks: - the period during which a reduction in the average power for the energy source is obtained is very short, - the supercapacitor requires the presence of a system of

recharging when the vehicle is stopped.

  To overcome these problems, one can imagine the parallel connection of a lead-acid battery with a supercapacitor. The energy required to pull the vehicle is supplied by the accumulator to the

  lead and power calls are satisfied by the supercapacitor.

  The distribution of the traction current between these two elements is managed by electronic components, themselves controlled by a battery management unit. This system also requires power electronics which can drive either the battery or the supercapacitor in order to decrease the average power for the energy source, which would lead to an improvement in the service life of the assembly. However, the gain in service life, which results in a cost saving, is partially compromised by the cost of the associated electronics and by the importance of the

  implementation of an order management strategy.

  Furthermore, the supercapacitors do not meet a high demand for power for a period compatible with that of an acceleration of the vehicle, of the order of 10 seconds, due to the rapid decrease in the voltage observed at the terminals of the

supercapacitor.

  The object of the present invention is to provide a flexible battery system which can be adapted and optimized according to the needs of the user, using energy source or energy source elements.

identical technology power.

  The energy storage system according to the invention comprises at least two electrochemical generators capable of storing energy in chemical form and of releasing it in the form of electrical energy. The energy storage system comprises at least two branches arranged in parallel, each branch comprising at least one electrochemical generator, the branches being of equal nominal voltages and of

  different power-to-energy ratios.

  Advantageously, the branches are connected to each other

  directly without associated electronics.

  In one embodiment of the invention, the system may include means for electrically isolating each branch from the

other branches.

  In one embodiment of the invention, the system consists of a branch of power to low energy ratio and a plurality of

  high power-to-energy ratio branches.

  In one embodiment of the invention, the system consists of a plurality of branches of low power-to-energy ratio and a

  high power-to-energy ratio branch.

  Advantageously, the different power-to-energy ratios of the branches are at least two. In other words, the system has two or more groups of branches, with different power-to-energy ratios. Advantageously, the electrochemical generators of a

branch are identical.

  The present invention also relates to a transport system such as an electric vehicle, an unmanned cart or a satellite, an electronic system such as a toy, a mobile telephone or a portable microcomputer and a stationary system such as an organ. backup or medical machine, equipped with a system

as described above.

  In other words, the system according to the invention consists in putting in parallel at least two branches of generators of identical technology which have a different power / energy ratio for each of them. One of the generators is considered to be the source of energy and the other the source of power. The use of the same technology for the parallelization of the energy and power branches is interesting for at least three reasons: - the system makes it possible to meet a demand for average power corresponding to the acceleration of a vehicle, while overcoming the presence of power electronics for

traction applications.

  - the energy and power branches have the same operating voltage. - the battery system is easily adjustable according to the user's needs in terms of space, energy, power and

lifetime.

  An energy battery / power battery coupling makes it possible to respond to power calls lasting approximately 20 seconds, for example with a current of 80 Amps. The distribution of the current is spontaneously balanced, that is to say without control electronics, between the energy source and the power source.

  For comparison, a simulation of a battery-

  supercapacitor shows that the system can only respond to power calls lasting less than 0.5 seconds and during which there is no equilibrium between the sources of energy and power. Indeed, the current of the power source decreases extremely quickly. One of the two sources of energy and power works

at the expense of the other.

  On the contrary, according to the invention, the two energy and power generators, of identical technology, evolving in the same voltage range, the current evolution curve is similar for the source

  of energy and the source of power.

  The present invention will be better understood on reading the

  detailed description of some embodiments taken as

  in no way limiting examples and illustrated by the appended drawings, in which: - Figure 1 is a schematic view of the parallel connection of two battery branches according to the invention; and

  - Figures 2 and 3 illustrate variants of Figure 1.

  The distribution of the current between the two parallel branches of energy and power generators during a charge / discharge cycle characteristic of an acceleration, a running at stabilized speed, a

  regenerative braking and stopping the vehicle, is shown in the table below

  below. The energy generator has a capacity of 50 Ah (low power / energy ratio), while the power generator has a

  capacity equal to 5 Ah (high power / energy ratio).

  Sequences Generator Energy Factor Generator (50 Ah) Power (5 Ah) Power / Acceleration% I - 58.5 - 41.5 (10 sec.)% APdd - 0.3 - 1.8 6 Stabilized speed% I - 74 - 26 (20 sec.)% APdd - 0.2 - 0.6 3 Regenerative braking% I + 46.4 + 53.6 low% APdd + 0.06 + 0.7 11

1 0 _ _ _ _ _ _ _ _ _ _ _ _ _ _

  Recuperative braking% I + 31.6 + 68.4 strong% APdd + 0.02 + 0.5 25 Vehicle stop% I 50 50% APdd - 0.04 + 0.4 10 Balance charge / discharge% APdd - 0, 4 - 0.8 2 For large current calls caused during acceleration, it is the power source which intervenes mainly with a variation in the depth of discharge APdd six times greater than that of the energy source . This variation is only three times higher for lower current calls characteristic of a stabilized speed. During regenerative braking, the two generators are recharged but the variation in the depth of discharge is, here again, greater for the power source. The factor obtained for the variation APdd between the power source and the energy source is

  the higher the braking is strong.

  Stopping the vehicle generates a self-balancing of the distribution of currents since an identical current, in absolute value, crosses each of the two branches in parallel. So the source

  of energy is discharged and the power source is recharged.

  An assessment of the variation in the depth of discharge can be made from acceleration to the stop of the vehicle. It indicates that the power source intervenes globally twice as much as the source

of energy.

  Regarding the service life of the battery system, it is

  directly related to the evolution of each of the elements.

  On the one hand, the current calls caused during the charge / discharge cycles as described above, cause a voltage dispersion which increases as a function of the depth of discharge of the battery. The paralleling of the energy and power elements contributes to reducing the current on each of the branches and therefore to reducing the voltage dispersion of the elements at the end of discharge. Such a system makes it possible to better manage the discharge curve and to optimize the capacity of

  the battery, i.e. the battery cost.

  On the other hand, the system uses power elements that work exclusively to generate power, and energy elements to generate energy. The discharge profile is therefore perfectly suited to the design of the battery, which leads to a

improvement of its lifespan.

  In order to reduce battery production costs, it is interesting to use standard elements. We can imagine two types of elements: one specific to a high demand for energy (low power / energy ratio) and the other specific to a high demand for power (high P / E ratio). The proposed solution allows,

  thanks to the parallelization of one or more of the standard elements mentioned above

  above, to obtain a generator system having an intermediate P / E ratio capable of meeting an average demand for energy and

in power.

  As an example illustrated in FIG. 1, we can connect in parallel an energy element denoted E 1, with P / E ratio equal to 2, with a power element denoted P1, with P / E ratio equal to 20. The battery system thus obtained is shown diagrammatically below. It has an average ratio between 2 and 20, calculated from the characteristics described

in the following table.

  Element E1 P1 E1 + P1 Element mass (kg) 1 0.5 1.5 Mass energy (Wh / kg) 100 50 83 Mass power (W / kg) 200 1000 467 Energy (Wh) 1 O0 25 125 Power (W) 200 500 700 P / E ratio (W / Wh) 2 20 5.6

APPLICATION EXAMPLE

  For the same P / E ratio equal to 5.6, it is possible to embark

  much greater energy by adding elements E1 and Pi.

  Thus, for a battery system comprising a branch of 40 elements of energy El in parallel with a branch comprising 40 elements of power Pl, the on-board energy amounts to (40 × 100 Wh) + (40 × 25 Wh) = kWh and the power at (40x200 W) + (40x500 W) = 28 kW (i.e. P / E = 28/5 = 5.6) for a mass equal to (40xl kg) + (40x0.5 kg) = 60 kg. The mass of the battery system thus formed is much lower than that which is obtained with a system composed solely of El or P1 elements. Indeed, if we consider a battery comprising elements optimized for the energy El, it is necessary, to obtain a power

  28 kW, to load a mass equal to 28 kW / 200 W / kg, i.e. 140 kg.

  A battery composed of elements optimized for the power P1 has, for an energy of 5 kWh, a mass of 5 kWh / 50

Wh / kg, i.e. 100 kg.

  It should be noted that, in each branch of energy or power, the number of elements E 1 in series must be equal to the number of elements P 1 in series since these elements, of identical technology, have the same

operating range.

  On this principle, it is possible to optimize, as needed, either the energy demand or the power demand by adding elements. In general, if we consider x the number of branches comprising specific elements of a high demand for energy (P / E = 2) and y is the number of branches of the specific elements of a strong demand for power ( P / E = 20): - the higher x, the closer the P / E ratio of the battery system to 2; - the higher there is, the higher the P / E ratio of the battery system

close to 20.

  In Figure 2, we see that we have arranged two elements P1 and a

  element El, which makes it possible to obtain a P / E ratio = 8.

  Conversely, in FIG. 3, two elements El and one have been arranged.

  element Pl, hence a P / E ratio = 4.

  From modular elements of the same nominal voltage and different P / E ratio, a battery system is formed with several parallel branches, each branch comprising one or more basic elements. The basic elements of a branch are arranged in series and are of the same type. At least one branch has elements of a different type from those of the other branches. One can design a system provided with branches having three or four different P / E ratios. We

  thus benefits from great flexibility in the construction of the system.

  The power or energy characteristics of the elements are used satisfactorily, which contributes to improving the service life, reliability and cost of the system. The voltage dispersion is reduced at the end of the battery discharge, hence an optimization of the

  capacity demand and increased battery life.

  The P / E ratio can be adjusted as needed from only two basic elements. The state of charge between the parallel branches is balanced without the need to use control electronics. The user can modify the distribution of the basic elements according to his needs. In the event of failure of a single element of a branch, the operation of the energy consuming members remains possible on the only other branches, which also results in a

  increased safety for the user.

  The invention applies in all fields using electrochemical couples: portable batteries, stationary batteries, traction batteries, etc.

Claims (9)

  1. Energy storage system comprising at least two electrochemical generators capable of storing energy in chemical form and releasing it in the form of electrical energy, characterized in that it comprises at least two branches arranged in parallel, each branch comprising at least one electrochemical generator, the branches being of equal nominal voltages and of power ratios on different energy.   2. System according to claim 1, characterized in that the branches are connected to each other directly without electronics associated.   3. System according to claim 1 or 2, characterized in that it consists of one or more branches of power to low energy ratio and one or more branches of power to low ratio high energy.   4. System according to any one of the claims   previous, characterized by the fact that the different power ratios   on energy branches are at least two.   5. System according to any one of the claims   previous, characterized in that the electrochemical generators of a branch are identical.   6. System according to any one of the claims   previous, characterized in that it can include a means for   electrically isolate each branch from the other branches.   7. Transport systems, such as for example an electric vehicle, equipped with a system according to any one of previous claims.   8. Electronic systems, such as a mobile phone, a toy or a portable microcomputer, equipped with a system   according to any one of claims 1 to 6.   9. Stationary systems, such as an electrical backup device, a medical machine, equipped with a system according to   any one of claims 1 to 6.