WO2010106257A1

WO2010106257A1 - Battery recharging system

Info

Publication number: WO2010106257A1
Application number: PCT/FR2010/050233
Authority: WO
Inventors: Francis Roy; Jean-Claude Dolhagaray
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2009-03-17
Filing date: 2010-02-11
Publication date: 2010-09-23
Also published as: FR2943473B1; FR2943473A1

Abstract

The invention relates to a method for recharging an electric battery (2) including a set of cells (3), including the step of measuring the voltage at the terminals of each of said cells (3) and determining the voltage at the terminals of the cells having the highest charge and the successive charge of the less charged cells until the voltage at the terminals of the highest charged battery is reached.

Description

BATTERY RECHARGING SYSTEM

The present invention claims the priority of the French application 0951667 filed March 17, 2009 whose content (text, drawings and claims) is here incorporated by reference.

The invention relates to electric energy storage batteries, and in particular battery charging systems having several contiguous cells.

The use of batteries to power an electric motor of a motor vehicle is known. Such batteries typically include Li-ion cells connected in series. Due to manufacturing dispersions, these cells have in practice different characteristics. These differences, relatively minor when the battery is new, increase with the wear of the battery. The charge of the battery is supervised by a control device from voltage measurements on the different cells.

[0oo4] Figure 1 illustrates the voltage of different cells of a battery at the end of a conventional charging method of the state of the art. The voltage across the different cells is representative of the charge of these cells. The operating range of a Li-ion type cell is typically between 2.7 V and 4.2 V. Use outside this range induces irreversible damage to the cells of the battery. Since an overload can lead to cell destruction, the load of all cells is interrupted when the most charged cell reaches the high limit Vmax of the operating range. The voltage of the least charged cell is then equal to a voltage Vinf which is less than Vmax. The control device also interrupts the discharge of the battery when the least charged cell reaches the low limit Vmin of the operating range. The useful capacity of the battery is defined by the difference of the capacitance values corresponding to the voltages Vinf and Vmin. Therefore, the larger the dispersions between cells, the lower the capacity of the battery. With a reduced operating range, the capacity of the battery can be relatively limited in the presence of strong dispersions between the cells. This decrease in capacity multiplies the number of charge / discharge cycles to restore a given amount of energy. [oooδ] Patent Application US6157165 describes a method of recharging a battery. Prior to recharging all the cells, the method comprises a phase of balancing the voltage of the different cells. The charge of each of the cells is sequentially measured by transiently connecting them to a capacitor. After disconnecting the capacitor cell, the voltage across this capacitor is measured. Then, when a less charged cell is connected to the capacitor, energy is transferred from the capacitor to the cell until their voltages are balanced. Then, when a more charged cell is connected to the capacitor, energy is transferred from the cell to the capacitor until their voltages are balanced. The step of measuring the voltages thus induces load balancing. A charging phase of all the cells is then initiated. During this charging phase, resistors are connected in parallel on some cells whose charging speed is higher than the others. Thus, when a resistor is connected in parallel, the charging speed of the corresponding cell is reduced. The voltage across the different cells is therefore regularly measured to connect or not a resistance in parallel with a cell.

Such a method, however, has drawbacks. In practice, the balancing and measuring phase occupies a significant amount of time. In addition, energy is lost by Joule effect during successive transfers between the capacitor and the different cells, as well as when connecting resistors in parallel.

The invention aims to solve one or more of these disadvantages. The invention thus relates to a method of recharging an electric battery comprising a set of cells, comprising the steps of measuring the voltage across each of said cells and determining the voltage across the most charged cell; and successively charging less charged cells until the voltage reaches the terminals of the most charged cell.

[oooδ] According to one variant, the order of the successive charges is defined by loading the least charged cell. According to another variant, light energy is converted into electrical energy, wherein this electrical energy is applied to said cells during successive charges. According to another variant, all the cells are charged simultaneously until the voltage across a cell exceeds a maximum threshold.

According to yet another variant, the electrical energy used for the simultaneous charging comes from the sector or an alternator driven by an internal combustion engine.

According to one variant, the voltage measurement and the successive charges are carried out when the battery is at rest.

The invention also relates to a charging system of an electric battery comprising a set of cells and, the system comprising means for measuring the voltage across the cells; means for determining the voltage across the most heavily loaded cell; and, charging means successively charging less charged cells to reach the voltage across the most charged cell.

According to a variant, the charging means successively charge the cells by charging the least charged cell.

According to another variant, the system comprises photovoltaic cells supplying the measuring means, determining and charging system of the cell or cells to recharge when the current generated by the photovoltaic cells is sufficient. The invention also relates to a motor vehicle comprising a battery and a battery charging system as described above and further comprising photovoltaic cells applying a voltage across a cell of the battery during successive charges.

Other features and advantages of the invention will become apparent from the description which is given below, by way of indication and in no way limiting, with reference to the accompanying drawings, in which:

FIG. 1 is a representation of the charge of different cells of a battery at the end of a charging process according to the prior art;

FIG. 2 is a representation of the charge of different cells at the beginning of a balancing phase; FIG. 3 is a schematic representation of a battery charging system according to the invention;

FIG. 4 is a representation of the electrical circuit of the system of FIG.

The invention provides a method and a battery charging system. The voltages across the individual cells of a set of cells are measured. In particular, the voltage across the terminals of the most charged cell is determined. Less charged cells are then successively charged until the voltage reaches the terminals of the most charged cell.

Thus, following these successive charges, the voltage across the cells is balanced before starting a recharge or discharge of all cells. When the cells are then recharged, the recharge is interrupted when one of the cells will have reached its maximum charge. Because of the balancing, all the cells will have almost reached their maximum load at the time of the interruption of charge. As a result, the overall capacity of the battery will be increased. When the cells are then discharged, the discharge is interrupted when one of the cells has reached its minimum load. Due to the balancing, all the cells will also have almost reached their minimum load. As a result, the overall capacity of the battery will be increased. The battery life is also increased since the number of charge / discharge cycles of the battery is decreased by this increase in capacity. Moreover, the frequent balancing loads according to the invention make it possible to avoid the use of shunts inducing losses by heat dissipation. The balancing phase according to the invention is feasible from electric sources based on renewable energies. Figure 3 schematically shows a charging system 1 of a battery 2 comprising a set of cells 3 of electrical energy accumulation. The cells 3 may be of the electrochemical type, for example of the Li-ion, NiMH, NiCD or Pb type, or electrical energy storage for example by supercapacities. The charging system 1 also includes a supervision module 4 of the battery charge. The supervision module 4 comprises a module 5 for measuring the voltage at the terminals of each of the cells 3. The charging system 1 also advantageously comprises a protection module 6 of the battery 2. The battery 2 is connected to the electrical consumers 1 1 and to a charger 12 powered by the mains via the protection module 6.

In addition, the charging system 1 comprises an annex 8 electrical source and a main power source 7. The electrical source annex 8 may in particular be made of photovoltaic cells. The electrical source annex 8 may also be constituted by a wind turbine. For an automobile application of the charging system, the use of such an auxiliary power source makes it possible to balance the charge of the battery 2 while benefiting from renewable energy. Figure 4 shows more precisely the circuit diagram of the charging system 1. The battery 2 comprises a set of cells 3 connected in series. The supervision module 4 can control the measurement module 5 to individually measure the voltage across each of the cells 3. The supervision module 4 is connected to the electrical source 7 and to the electrical source 8 via diodes 13 The electrical sources 7 and 8 can apply to the module 4 a voltage of between 12 and 14 V. The supervision module 4 can recover from the measurement module 5 the voltage level of the most charged cell and identify the least cell. loaded. The supervision module 4 controls a multiplexing module 10 for selecting the cell to be loaded or whose voltage is to be measured. The recharging system 1 comprises a charging module 9. The supervision module 4 selectively applies the voltage supplied by the electrical source 7 or the voltage supplied by the electrical source 8 via the charging module 9 to adapt the voltage. The load module comprises a DC / DC converter for adapting the voltage received from the module 4 to the voltage level required for the load of a cell. The charging voltage supplied by the module 9 is selectively applied by the multiplexing module 10 to the terminals of a selected cell. The charging current and the voltage of the load cell can be measured to determine the energy transferred by the module 9 to a cell. The diagram of Figure 2 shows the load of different cells 31 to 39 at the beginning of a balancing phase. At the beginning of the balancing phase, all the voltages of the cells 31 to 39 are measured. The voltage C max at the terminals of the most heavily loaded cell is determined. In this case, it is the Voltage at the terminals of the cell 33. The less charged cells are then successively charged until these reach the voltage Cmax. The successive charges are interrupted when the cells reach this voltage Cmax. The balancing phase ends when all the cells have reached the voltage. Only one cell at a time is loaded during successive loads.

To define the order of successive loads, systematically load the least loaded cell systematically. In the example illustrated, the least charged cell is initially the cell 34 with a voltage Cmin. The cell 34 is thus charged up to Cmax as illustrated by the shaded area. The voltage of the cell can be measured at regular intervals during charging. Then, the cell 31 becomes the least charged cell and therefore undergoes a load up to Cmax. It may be noted that even when the successive charges are interrupted before all the cells have reached the charge Cmax, a partial balancing of the charges has been achieved since the least charged cell has benefited from a recharge. Even then, the Cmin value will be raised. Thus, even if the balancing refill is interrupted by the user who solicits the battery charging by the sector or discharges to feed for example the power train, the balancing phase has benefited the capacity of the battery.

Rather than interrupting the charge of a cell by measuring its voltage, it is also possible to define beforehand an electrical energy leading approximately to a charge of this cell up to Cmax. For this, we can apply a charging time of the cell function of the instantaneous power measured and delivered by the converter 9 to the cell. The supervision module 4 can control the charge current of the cell and adapt it according to the state of charge of the cell or the electric power supplied by the source 8.

The supervision module 4 advantageously uses the voltage supplied by the source 8 to perform the successive charges of the cells 3. Indeed, a relatively small amount of energy is sufficient to enable the cells to be balanced 3 The voltage measurement and the successive charges of the cells 3 are advantageously performed when the battery is at rest. We will consider that the battery is at rest when it will not feed a charge connected to its terminals. Thus, the measurements of the voltages at the terminals of the cells will not be disturbed by a current draw, which will allow accurate balancing of the voltages of the different cells 3. In addition, a rest recharge can be performed in masked time for the user. . The battery 2 can be integrated in a vehicle. This battery 2 can power an electric motor 1 1 of an electric vehicle or a hybrid vehicle. Simultaneous recharging of the cells 3 up to their maximum capacity Vmax will advantageously be performed via the electrical source 12. The simultaneous recharging of the cells 3 will be interrupted when one of the cells reaches the maximum capacity Vmax.

Simultaneous charging of the cells 3 can be started following a balancing phase or when one of the cells 3 reaches the minimum capacity Vmin.

In the case of a hybrid vehicle, the electrical source 12 may be constituted by an internal combustion engine driving an alternator. In the case of an electric vehicle, the electrical source 12 may be constituted by a charger powered by the sector.

The supervision module 4 is advantageously powered by the auxiliary power source 8 when the battery 2 is at rest. When the auxiliary power source 8 generates electricity from a renewable energy, the supervision module 4 can be activated when the power produced by the source 8 is greater than the power consumed by the supervision module 4. , the supervision module 4 will only be activated when the power supplied by the source 8 is sufficient to carry out the successive charges of the different cells 3. The power supplied by photovoltaic cells may in particular be measured to determine whether the power generated by the source 8 is sufficient. It is also possible for the supervision module 4 to be powered by the source 7 and for the source 7 to provide the necessary electrical power during the balancing phase, when the electric power supplied by the source 8 is insufficient.

Outside the balancing phase of the battery 2, the supervision module 4 may be powered by the battery 7, by a voltage converter connected to a high voltage output powered by the battery 2, or by the source of energy 8. Following the balancing phase, a discharge of the battery 2 may also occur, for example to power an electric motor 1 1 of the vehicle. This discharge may continue until one of the cells reaches the minimum capacity. Following balancing, this minimum capacity will be reached later, which corresponds to an overall increase in the capacity of the battery 2.

In the illustrated embodiment, the set of cells 3 is connected in series. However, the mention also applies to a battery in which all the cells are connected in parallel.

Claims

A method of recharging an electric battery (2) comprising a set of cells (3), comprising a step of measuring the voltage across each of said cells and determining the voltage across the most charged cell and the successive charging of less charged cells until reaching the voltage across the most charged cell.

2. The method of recharging an electric battery according to claim 1, wherein the order of successive charges is defined by charging the least charged cell.

3. A method of recharging an electric battery according to claim 1 or claim 2, wherein light energy is converted into electrical energy, wherein this energetic electric is applied to said cells during successive charges.

4. A method of recharging an electric battery according to any one of the preceding claims, wherein the set of cells is charged simultaneously until the voltage across a cell exceeds a maximum threshold.

5. A method of recharging a battery according to claim 4, wherein the electrical energy used for simultaneous charging comes from the mains or an alternator driven by an internal combustion engine.

6. A method of recharging an electric battery according to any one of the preceding claims, wherein the voltage measurement and the successive balancing loads are performed when the battery is at rest.

7. System (1) for recharging an electric battery comprising a set of cells (3) and, the system comprising means (5) for measuring the voltage across the cells; means (4) for determining the voltage across the most charged cell; characterized in that it further comprises charging means (4, 8) successively charging less charged cells until reaching the voltage across the most charged cell.

8. Refilling system according to claim 7, wherein the charging means successively charge the cells (3) by charging the least loaded cell.

9. charging system according to claim 7 or claim 8, comprising photovoltaic cells (8) supplying the measuring and determining means when the current generated by the photovoltaic cells is sufficient.

10. Motor vehicle comprising a battery and a battery charging system according to any one of claims 7 to 9, further comprising photovoltaic cells (8) applying a voltage across a cell (3) of the battery (2) during successive charges.