VALAYER, Richard (19 rue Dian Fossey, Genas, F-69740, FR)
MILLET, Michael (61 rue Daniel Rops, La Motte Servolex, F-73290, FR)
VALAYER, Richard (19 rue Dian Fossey, Genas, F-69740, FR)
| CLAIMS 1. System for controlling the charge and discharge cycles of a battery set (8) connected to an electrical system (ES), comprising : - means (ECU) for evaluating the actual sequence of the battery, either charge or discharge, according to the electrical system behaviour; and - shifting means interposed between the electrical system and the battery set and adapted to : - when the battery is in a charge sequence (CS), interrupt the charge sequence with at least one discharge pulse (DP); - when the battery is in a discharge sequence (DS), interrupt the discharge sequence with at least one charge pulse (CP). 2. Control system according to claim 1 , wherein the charge (CS), respectively discharge (DS), sequence is repeatedly interrupted with reversing pulses respectively discharge pulses (DP) or charge pulses (CP), and comprises forward periods, respectively charge or discharge periods, alternating with reversing pulses. 3. Control system according to claim 2, wherein the duration of each reversing pulse (CP, DP) is chosen so that during the reversing pulse the state of charge of the battery set (8) varies in the range of 0,01 % and 1 % of the total state of charge. 4. Control system according to claim 2 or 3, wherein the duration of each forward period is chosen so that during the forward period the state of charge of the battery set (8) varies in the range of 1 % and 10 % of the total state of charge. 5. Control system according to any of claims 2 to 4, wherein the duration of each reverse pulse and/or forward period is a function of the state of charge variation during the forward periods. 6. Control system according to any of claims 1 to 5, wherein the shifting means comprise : - auxiliary discharge means (16) for discharging the battery set and absorbing electricity of the electrical system during the discharging pulse (DP); - auxiliary electrical energy providing means (16) for charging the battery set (8) and providing electricity to the electrical system (ES) during charging pulse (CP); - electronically controlled switching means (22,23,24) between the electrical system (ES), the battery set (8), the auxiliary discharge means (16) and the auxiliary electrical energy providing means (16); - an electronic control unit (ECU) adapted to evaluate the electrical system behaviour and to control the switching means (22,23,24) in order to induce the discharging and charging pulses during respectively the charging and discharging sequences. 7. Control system according to claim 6, wherein the auxiliary discharge means (16) and the auxiliary electrical energy providing means (16) comprise capacitors and/or ultra-capacitors. 8. Control system according to claim 7, wherein the auxiliary discharge means and the auxiliary electrical energy providing means comprise a same capacitor and/or ultra-capacitor set (16). 9. Control system according to claim 7 or 8, further comprising a step-up converter (28) for charging the capacitors and/or the ultra-capacitors before each charging pulse (CP). 10. Control system according to any of claims 6 to 9, further comprising filtering means (30,31 ) on the electrical system side and on the battery set side adapted to filter at least disturbances generated by the switching means. 11. Control system according to claim 10, wherein the filtering means comprise passive electric components. 12. Vehicle comprising an electric drive system including an electric driving motor (5) connected to a driving battery set (8) by a driving circuit (7) further comprising a control system according to any of claims 1 to 11 situated between the driving battery set (8) and the driving motor (5). 13. Method for managing the charging and the discharging of a battery set comprising at least one battery and being connected to an electrical system comprising the steps of: - When the battery is in a discharging sequence and the electric system demanding electricity, interrupt the discharging sequence of the battery with at least one charging pulse during which electricity is provided to the battery set; - When the battery is in a charging sequence and the electric system providing electricity, interrupt the charging sequence of the battery with at least one discharging pulse during which electricity is taken from the battery set. 14. Method according to claim 13, wherein : - during each charging pulse, electricity is provided to the electrical system; - during each discharging pulse, electricity is taken from the electrical system. |
The invention relates to the management of charging and discharging cycles of battery sets and in a preferred but not limitative application, to the management of the charging and discharging of battery sets on electric or hybrid vehicles. BACKGROUND ART
It is well known that battery or battery sets have a given life time and can support a limitative number of full charge and discharge cycles. This is a major drawback for transportation application as if a battery set for electrical or hybrid vehicles may support an high number of charge and discharge cycles its lifetime is always much shorter than the lifetime of the whole vehicle. The lifetime and numbers of cycles supported by a battery depends on the chemical technology used and on how deeply the battery is discharged before being recharged. For example, on battery sets designed for providing high level of energy on short periods such as for hybrid vehicles, in order to provide a sufficient lifetime, battery set are not deeply cycled and therefore the battery are oversized inducing a high weight and a high cost. Therefore, there is a need for increasing the lifetime of a battery without increasing its weight and/or size or its price. SUMMARY OF THE INVENTION
In order to achieve this, an object of the invention is a method for managing the charging and the discharging of a battery set comprising at least one battery being connected to an electrical system. According to the invention, the method comprises the steps of:
- when the battery is in a discharging sequence and the electric system requiring electricity, interrupt the discharging sequence of the battery with at least one charging pulse during which electricity is provided to the battery set; - when the battery is in a charging sequence and the electric system providing electricity, interrupt the charging sequence of the battery with at least one discharging pulse during which electricity is taken from the battery set. By reversing, during the short pulses, the chemical process which takes place into the battery either charging of discharging, the invention allows a reduction of the non interrupted variation window of the state of charge between two pulses. As a consequence, it is possible to increase the total battery state of charge window, without affecting the initial lifetime and as a result reduce the battery size / capacity / cost of the battery having its charge and discharge cycles managed according to the invention. Therefore for a given lifetime, the invention allows a size reduction of the battery sets, whereas for a same size the invention allows a lifetime enhancement for an equivalent energy capacity. According to an embodiment of the invention, during each charging pulse, electricity is provided by auxiliary means to the electrical system whereas during each discharging pulse, electricity is taken from the electrical system by auxiliary means. By implementing such an embodiment, the method according to the invention has almost no consequence for the electrical system connected to the battery set, so that the original behaviour of the electrical system connected to the battery set would be unchanged. The implementation of the invention is thus transparent when viewed from user side.
Another object of the invention is a system for controlling the charge and discharge cycles of a battery set connected to an electrical system. According to the invention, the control system comprises:
- means for evaluating the actual sequence of the battery, either charge or discharge, according to the electrical system behaviour; and
- shifting means interposed between the electrical system and the battery set and adapted to : - when the battery is in a charge sequence, interrupt the charge sequence with at least one discharge pulse;
- when the battery is in a discharge sequence, interrupt the discharge sequence with at least one charge pulse.
By implementing the method of the invention, the control system achieves a lifetime enhancement of the battery set to which it is associated. According to the invention, the managing control system may be a stand alone device interconnected between an electrical system and a battery set. The control system according to the invention can also be embedded either with the electrical system or the battery set.
According to an embodiment of the invention, the charge, respectively discharge, sequence is repeatedly interrupt with discharge, respectively charge, pulses. Therefore each charge, respectively discharge, sequence comprises charge, respectively discharge, periods alternating with discharge, respectively charge, pulses. In the context of the invention, charge and discharge pulses may be designated as reversing pulses whereas the discharge and charge periods may designated as forward periods. According to the invention the wording pulse implies that the reversing pulses are much shorter than the forward periods. Each reversing pulse may have for example duration inferior to two second preferably inferior or equal to one second.
According to an implementation of the invention, the parameters of the reversing pulses, including duration, intensity and frequency, are determined depending on the variation of the state of charge of the battery. The speed of the variation of the state of charge can for example be estimated by monitoring the intensity of the current circulating in the battery set and the reversing pulses parameters may be adjusted according to the forward current value during the forward periods. The duration of the reversing pulse may be a function of the forward current value such as a linear function.
The duration and/or the intensity of each reversing pulse can for example be chosen so that during the reversing pulse the state of charge of the battery set varies in the range of 0,01 % and 1 % of the total state of charge. In a same manner the duration of the forward periods i.e. the time interval between two consecutive reverse pulses, may be chosen according to the variation of the state of charge of the battery set. The time interval between two consecutive reverse pulses may be chosen according to the current value.
The duration of each forward period between two reverse pulses can be chosen so that, during this continuous forward period, the state of charge of the battery set varies in the range of 1 % and 10 % of the total state of charge.
By using such ratio for the charge or discharge pulses are long enough to allow an effective reversal of the chemical process occurring before the pulse, but short enough not to affect a behaviour of the running of the electrical system connected to the battery set though the control system according the invention.
According to an embodiment of the invention, the shifting means of the control system comprise: - auxiliary discharge means for discharging the battery set during each discharging pulse;
- auxiliary electrical energy providing means for charging the battery set during each charging pulse;
- electronically controlled switching means between the electrical system, the battery set, the auxiliary discharge means and the auxiliary electrical energy providing means;
- an electronic control unit adapted to evaluate the electrical system behaviour and to control the switching means in order to induce each discharging and charging pulses during respectively the charging and discharging sequences. According to the invention, the auxiliary discharge means may be formed by any appropriate electrical system or device. For example, the auxiliary discharge means may comprise a dedicated resistive device to which the battery set is connected during the discharging pulse. The auxiliary discharge means may also comprise a circuit electrical to which electrical consumers are connected.
The auxiliary electrical energy providing means may also be of any appropriate kind and comprise for example: an electric generator or an electricity storage system.
According to an embodiment of the invention, the auxiliary discharging means comprises an electricity storage system, which will accumulate the energy from the battery set during the discharging pulse in order to reduce as much as possible the energy wasted during the discharging pulse. The energy from the battery set during the discharging pulse will be therefore at least partly reusable. According to the invention, the auxiliary electrical energy providing means are the same electricity storage system as the one forming the auxiliary discharge system.
According to an embodiment of the invention, the auxiliary discharge means and the auxiliary electrical energy providing means comprise capacitors and/or ultra capacitors. The use of such device allows a high rate of energy recovering with a small sized and light system.
According to an embodiment of the invention, the same set of capacitor and or ultra capacitor is used as auxiliary discharge means and auxiliary electrical energy providing means.
According to an embodiment of the invention, the auxiliary discharge means are adapted to absorb the electricity provided by the electrical system during the discharge mean whereas the auxiliary electrical energy providing means are adapted to provide electricity to the electrical system during the charging pulse.
According to an embodiment of the invention, when capacitors and /or ultra capacitors are used as electrical energy providing means, the control systems comprise a step-up converter for charging the capacitor and/or ultra-capacitor in order to reach the voltage high enough for charging the battery set during the charging pulses.
According to another embodiment to the invention, in order to reduce as much as possible the effects of the switching on both the electrical system and the battery set, the control system further comprises filtering means on the electrical system side and on the battery set side. These electrical filtering means are adapted to filter at least the electrical disturbances generated by the switching means.
According to the invention, the filtering means may comprise any appropriate electrical components or electrical system either active or passive.
According to a preferred embodiment, the filtering means comprise passive components such as capacitors and inductive coils.
Another object of the invention is a vehicle comprising an electric drive system including an electric driving motor connected to a driving battery set by a driving circuit further comprising a control system according to the invention
Such electric vehicle can be either a full electric vehicle or a hybrid vehicle comprising an internal combustion engine and/or a fuel electric cell.
Naturally the method according the invention and the control can also be implemented on various electrical system or devices using batteries such as personal computers, phones or smart phones or other portable tools or devices. The various above aspects, embodiments or objects of the invention may be combined in various ways with each others provided the combined aspects, embodiments or objects are not incompatible or mutually exclusive.
DESCRIPTION OF THE FIGURES Other aspect and advantages of the present invention will be apparent from the following detailed description made in conjunction with the accompanying drawing illustrating schematically a non-limitative embodiment of the invention.
- The figure 1 is a schematic view of a hybrid vehicle implementing a control system for controlling the charge and discharge cycles of the driving battery set according to the invention.
- The figure 2 illustrates the state of charge evolution of the driving battery set over the time with the implementation of the control method according to the invention.
DESCRIPTION OF THE INVENTION On the embodiment shown on figure 1 , the system S for controlling the charge and discharge circle of a battery set is implemented on a hybrid vehicle designated as whole by reference number 1. The hybrid vehicle 1 comprises a drive system which includes an internal combustion engine unit 2 powering a mechanical dhveline 3. The internal combustion engine unit 2 is associated with an engine electronic control unit 4 providing at least a state of the engine unit 2 to a vehicle control unit VCU. The drive system comprises also an electric drive motor system 5 which is as well operatively connected to the driveline 3. The electric drive motor system 5 is associated with a motor electronic control unit 6 connected to the vehicle control unit VCU. The mechanical driveline or the drive system can be of different types such as of a parallel or series type or implement a planetary gear system. In the same manner, the electric drive motor system 5 may comprise a single electric motor or a plurality of electric motors combined with a single electric generator or a plurality of electric generators in order to recover energy during slowing down phases of the hybrid vehicle. As the electric motor and the electric generator may be mutually separate, they also can be combined as a single motor/generator which selectively functions as an electric motor or an electric generator. The hybrid vehicle 1 comprises a driving circuit 7 which provides electricity at least to the electric drive motor system 5 and which comprises a driving battery set 8 comprising at least one driving battery not shown. The driving battery set 8 may of course comprise a plurality of driving batteries either connected in series or in parallel depending on capacity or the nominal voltage of the driving battery set. The driving battery set 8 is preferably of a medium or a high nominal voltage, for example being in the range of 120 V to 1000 V. Furthermore, each driving battery is preferably a battery with a low internal resistance optimized for efficient low duration high current output, for example a lithium-ion battery.
The hybrid vehicle 1 comprises also a service circuit 10 which provides electricity at least to the engine unit 2 but also to other electrical consumers 12 schematically depicted as a light bulb and a ventilator on the figure. The service circuit 10 comprises a service battery set 13 which comprises at least one service battery not individually shown on the figures. The service battery set 13 is of a low nominal voltage, for example being in the range of 12 V to 72 V. Each service battery is preferably a battery optimized for deep cyclic uses and for total energy capacity but can also be of a dual type being a compromise between an energy battery and a power battery. The service circuit 10 further comprises an electric generator operatively connected to the engine unit 2 and therefore driven by internal combustion engine unit 2. The service circuit 10 is also connected to the driving circuit 7 through a driving converter 15, the driving converter 15 mainly works as a step-down converter lowering the voltage of the driving circuit 10 in order to provide electricity to the service circuit 7 and more particularly in order to charge the service battery set 8. The driving converter 15 can also be of a step-up/step-down type in order to reciprocally derive power from the service circuit 10 for providing electricity to the driving circuit 7.
On the show embodiment, the system S is interposed between the driving battery set 8 and the rest of the driving circuit 7, which may be designated as a whole as the electrical system ES. The system S therefore controls the charge and discharge cycles of the driving battery set 8.
The control system S comprises a super-capacitor set 16 connected to a main internal circuit 17 by two internal branches 18, 19. The main internal circuit 17 is also connected on the one hand to the driving circuit 7 and on the other hand to the driving battery set 8. The main internal circuit 17 comprises also electronically control switching means 22 situated between the connecting points of the internal branches 18, 19. Each of two internal branches 18, 19 comprises also electronically controlled switching means, respectively 23, 24, interposed between the super-capacitor set 16 and the main internal circuit 17. The electronically controlled switching means 22, 23 and 24 may be formed in any appropriate manner. For example, each electronically controlled switching means may comprise an assembly of transistors or thyhstors. The switching means 22, 23, 24 are controlled by an electronic controlled unit ECU. The assembly of the switching means 22, 23 and 24, and the ECU forms what may be called the shifting means of the system S as the ECU is adapted to induced pulses during which the chemical process within the battery set is reversed with respect to the chemical process occurring during the period preceding the pulse according to the working state of the electrical system ES during this preceding period.
For example, when the electrical system and more particularly the drive system is in a driving or a traction sequence, the driving battery set 8 is providing electricity to driving motor 5. Information concerning this traction sequence may be provided to the ECU by VCU or deducted by ECU from the voltage of the driving circuit 7. During such a traction sequence, the state of charge of the driving battery set 8 will globally be managed as it is shown on the part DS of the graph figure 2. This traction sequence corresponds to a discharge sequence DS of the driving battery set 8. During this discharge sequence DS, the ECU will control the switching means 22 to 24, in order to induce at least one and according to the shown example two reversing pulses, here charging pulses CP by deriving energy from the super-cap set 16. During these charging pulses the chemical reactions within the driving battery set 8 will be reversed by comparison to the chemical reaction taking place just before the charging pulse i.e. during what might be called a forward period. When a charge pulse CP is needed, the ECU pilots the opening of the switching means 22 and the closing of the switching means 23 and 24. The super-capacitor set 16 will be thus connected both to the driving circuit 7 and to the battery set 8 and will induce a charging pulse CP in the battery set, whereas it provides energy to the driving motor so that the driving system will not be affected by the charging pulse CP. At the end of the charging pulse CP, ECU pilots the closing of switching means 22 and the opening of the switching means 23, 24 so that the battery set 8 resumes the discharging sequence.
The energy of the super-capacitor set 16 used during the charging pulses CP might have been stored during a previous braking phase of the vehicle. The super-capacitor set 16 may also have been charge during the discharge period preceding the charging pulse. In order to charge the super-capacitor set 16 up to a voltage high enough to charge the battery set 8 i.e. higher than the discharge voltage of the battery set 8, the control system S preferably comprises a step-up converter 28 controlled by the electronic control unit ECU. The step-up converter 28 will charge the super-capacitor set 16 with energy derived from a driving battery set 8 during the discharge sequence. The step-up converter 28 pre- charges the super-capacitor set 16 for the next charging pulse CP during each discharge period.
The ECU repeats the charging pulses CP during the discharging sequence DS at various moments of this charging sequence DS, preferably on a regular basis. Each charging pulse has for example a duration shorter than two seconds, such as a few milliseconds or a few tens of milliseconds.
When the vehicle is in a slowing or braking sequence, the electric drive system is designed to recover electrical energy from the braking or slowing, in order to charge the driving battery set 8. Therefore such a braking or slowing sequence can be considered when viewed from the battery set has a charging sequence CS. Similarly to what is provided for the discharging sequence DS, the ECU of the control system S will interrupt this charging sequence CS with at least one and preferably several reversing pulses, here discharging pulses DP. In order to achieve this, the ECU will open the switch 22 and close the switches 23 and 24, the electricity provided by the driving circuit 7 will be used for charging the super-capacitor set 16 and the driving battery 8 will also charge the super-capacitor set 16 so that energy losses are very low during the discharging pulse DP. The implementation of these charging pulse during the discharging sequence DS and discharging pulse DP during the charging sequence CS will allow dividing the cycling percentage by the number of interruptions leading to less impact on the driving battery set 8 aging due to cycling. It should be noted that electricity accumulated in the super-capacitor 16 during the discharging pulses can be recovered using the step up converter 28 in order to be provided to the circuit for charging the driving battery set 8.
Furthermore, in order to reduce the electrical disturbances induced by the pulses and the current inversion, the control system may also be provided with filters 30, 31 , one on the driving circuit side and the other on the driving battery set side. These filters are preferably of a passive type comprising capacitors and inductive coils. These filters will dampen the effects of the switching and guarantee a smooth running of the driving system and during driving sequences corresponding to discharge sequences as viewed from the driving battery set side.
In the previously described embodiment the parameters for the reversing pulses and the forward periods are preset fixed parameters of the ECU but according to the invention these parameters can be dynamically determined by the ECU according to the working conditions of the battery set 8. For example, the ECU can monitor the forward current value circulating through the battery set 8 during the forward period and adjust the duration and/or intensity of the reserving pulses and the forward periods i.e. the reversing pulses' repetitiveness according to the forward current value.
Furthermore, the duration and/or intensity of each reversing pulse CP, DP can be chosen so that the variation dSoC of the state of charge during said reversing pulse in the range of 0,01 % and 1 % of the total state of charge.
In a same manner, the duration of each forward period FP can be chosen so that the variation ΔSoC of the state of charge during said forward period FP in the range of 1 % and 10% of the total state of charge. While the invention has been shown and described with reference to certain embodiments thereof, it would be understood by those skilled in the art that changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims
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