WO2008081133A2

WO2008081133A2 - Method for the management of energy flows in an electric power supply device

Info

Publication number: WO2008081133A2
Application number: PCT/FR2007/052467
Authority: WO
Inventors: Guillaume Cherouvrier; Eric Prada
Original assignee: Peugeot Citroën Automobiles SA
Priority date: 2006-12-29
Filing date: 2007-12-10
Publication date: 2008-07-10
Also published as: FR2911015A1; WO2008081133A3; FR2911015B1; EP2094524A2

Abstract

The invention relates to an energy flow management process in an electric power supply device comprising at least one main energy storage device and a secondary storage device, the process comprising the following steps: - distributing, when the electric power supply device receives an electric power supply demand, the power demand between the main device and the secondary device, - measuring the state of the charge (35) of the main storage device, - depending on this measure, ordering an electrical energy exchange between the main energy storage device and the secondary energy storage device.

Description

METHOD FOR MANAGING FLOWS IN A DEVICE

POWER SUPPLY

The present invention relates to the management of a power supply device, in particular intended to be installed in a vehicle.

In systems requiring a power supply capable of providing significant electrical powers and energies, particularly motor vehicles, the power devices generally include one or more types of energy storage devices. These storage devices are, for example, electrochemical batteries or supercapacitors.

When several storage elements are present, it is known to use one of these elements, called the main device, to effectively provide the energy necessary for the operation of the system to be powered. In this case, the secondary element (s) are used to load or unload the main device, in order to enable it to provide optimal power to the system.

However, it has been found that, in some cases, the main device is not sufficiently sized to be able to supply all the energy required by the system. Furthermore, it has also been found that, in order to obtain optimal operation of an electrical power supply system, it was necessary for the energy exchanges taking place between the different storage devices to be adapted according to the state of charge of the power supply. main device.

The invention thus proposes a method for managing energy flows in a power supply device comprising at least one main energy storage device and a secondary storage device, making it possible to improve the optimization of the operation of such a device. power system, in terms of flexibility and performance. The method comprising the following steps:

A step during which the demand for power between the main device and the secondary device is distributed, when the power supply device receives a demand for electrical power, a step during which the state of charge is measured. the main storage device, and

, a step during which it is controlled from this measurement, an exchange of electrical energy between the main energy storage and the secondary energy storage.

The main energy storage device is generally a device called "power", that is to say a device with the ability to provide or store a large power over a very short time. The secondary device, meanwhile, is usually a device called "energy"; it can therefore be used to provide energy for a longer period.

All the features and embodiments presented below will preferably be implemented in using a power device and an energy device as defined above. Throughout the remainder of the description, the term "storer" will be equivalent to the term "storage device".

These devices are, for example, in the form of an electrochemical battery of Lead oxide-Sulfuric acid, Nickel-Hydride or Lithium-ion type.

There are two types of electrochemical torque batteries: "power" type batteries, which can, for example, be used for the main storage device, and "energy" type batteries, usable for the secondary device. The difference between these two types lies in the amount of active ingredient contained in these batteries. Indeed, the more a battery contains active material, the more it is able to provide or store energy but, in return, it is even more cumbersome.

Thus, energy type batteries, which contain a large amount of active material, can provide an energy of about 40 to 100 amperes per hour. "Power" type batteries, on the other hand, are less bulky and have a capacity of the order of a few amperes only. On the other hand, they allow to provide a strong power during a very short time.

The power supply device is intended to be installed in the or near the system that it supplies, for example a vehicle. Thus, the management method described here can be part of a global energy supply method of a system, in particular a hybrid motor vehicle.

This method, as mentioned above, is implemented in a power supply device comprising two separate storage devices. The purpose of this method is to use mainly that of the two storage devices having the largest specific power, and to use the second device to maintain the first device in working condition and, optionally, to provide or store a portion of the energy required by the system powered by this power device.

This objective can be achieved by implementing different utilization strategies that depend in particular on the characteristics of the two storage devices.

A first strategy is, in the case where the dimensioning of the main device allows to respond to any power demand from the powered system, to let this main device supply or store all the requested current. In this case, the secondary device is used only to maintain the main device in a state to supply and store, at any moment, the maximum current that its capacity allows. For this purpose, in one embodiment, the power demand is distributed in such a way that only the main storage device is requested to respond to this request.

In a second strategy, advantageously used when the dimensioning of the main device is insufficient to respond to any power demand from the powered system, the secondary device is used to supply or store a portion of the requested power.

In this case, it is necessary to distribute the power between the storage devices. An example of a possible distribution is a limitation in the form of a clipping of the power demand experienced by the storage system. For this purpose, in one embodiment, the distribution is performed by setting a power limitation threshold provided by the main device, the secondary device providing a power amount corresponding to the difference between this limitation threshold and the requested amount.

The value of this threshold is, for example fixed according to at least one parameter included in the group comprising the size of the main and secondary storage devices, the state of charge of the secondary device, parameters representative of the state of the devices. elements forming the storage devices, and the operating state of the system powered by the supply device.

This distribution by clipping will be described in detail later using power scaling graphs in the two storage devices.

The parameters representative of the state of the elements forming the storage devices are, for example, the state of wear of these elements, or their temperature. In the case where the method is implemented in a power supply device installed in a vehicle, the operating state of the system corresponds, for example, to vehicle life phases such as a rolling phase with a gear ratio. constant speed, a gearshift phase, or a stopping phase. This operating state can also take into account the vehicle power supply mode, for example for a hybrid vehicle that can operate either in pure electric mode, or in thermal mode, or both.

Moreover, regardless of the choice of the strategy, it is necessary that the two storage devices are maintained in an optimal operating state, especially in terms of charging and discharging, in order to optimize the performance of the power supply device. Thus, during the implementation of the method, energy exchanges take place between the main storage device and the secondary device. These energy exchanges must be made taking into account the state of charge of each of the devices in order, for example, to recharge the main device if its state of charge is insufficient to ensure proper operation of the power device.

For this purpose, it is therefore necessary to measure the state of charge of the storage devices. In one embodiment, this measurement is performed by determining the percentage of energy stored in this device relative to the maximum amount that can be stored.

In the case where a storage device takes the form of a supercapacitor, this determination is, in particular, performed by measuring the voltage across this supercapacity.

After measuring the state of charge of the main device, it is advantageous to use predetermined data to determine the energy exchange to be controlled between the devices.

For this purpose, in one embodiment, the method comprises the step of determining, from the measurement of the state of charge and of a predetermined variation law, the exchange of energy to be controlled between the main device and the secondary device.

Examples of laws of variation will be given later. These variation laws are established, for example, from tests carried out beforehand on different storage elements, according to at least one parameter included in the group comprising: the size of the main and secondary storage devices, the state charging the secondary device, parameters representative of the state of the elements forming the storage devices, and the operating state of the system powered by the supply device. In one embodiment, the method is such that when the state of the main device is less than a predetermined value, an energy exchange is controlled corresponding to a load of the main device and a discharge of the secondary device.

The invention also relates to a device for implementing the method defined above. This device comprises: a main energy storage device, a secondary energy storage device, means for measuring the state of charge of a storage device, and means for controlling and distributing the flows. energy.

The control and distribution means take for example the form of a microprocessor. Thus, in one embodiment, the variation laws used to determine the exchanges of energy to be controlled are recorded in a memory connected to the microprocessor.

In one embodiment, these control and distribution means are in the form of an electrical coupling member.

In a preferred embodiment, the main storage device and the secondary storage device are separate and are included in the group comprising: a "power" type electrochemical battery, an "energy" type electrochemical battery, and a supercapacity.

Other advantages and features of the invention will become apparent with the description of some of its embodiments, this description being given without limitation by means of the figures in which: FIGS. 1a and 1b show examples of architecture of a power supply device according to the invention, FIGS. 2a, 2b and 2c represent the consequence of the implementation of a clipping on the power signals seen by a device according to the invention, FIGS. 3a, 3b, 3c, 3d, and 3e represent variation laws that can be used to determine the exchanges of energy to be controlled during a process according to the invention.

Figures 1a and 1b show power supply device architectures comprising a main storage device 10a (resp.lOb) and a secondary storage device 12a (respectively 12b). These devices, main and secondary, are coupled by an electric coupling member 14a (respectively 14b).

This coupling member 14a (or 14b) is, for example constituted by a switching member, or a DC / DC converter (DC / DC), or a combination of several DC / DC converters. DC current (DC / DC).

The coupling member is used to couple the main and secondary device, but also to distribute the power demand between these two devices, in particular according to the dimensioning of the devices.

This device is also used, in some embodiments, to control the energy exchanges between the main device and the secondary device.

As described above, the main storage devices 10a (respectively 10b) and secondary storage devices 12a (respectively 12b) are distinct and each comprised in the group comprising: a "power" type electrochemical battery, an electrochemical battery of "energy" type, and a supercapacity.

Thus, combinations of the type: battery "power" / battery "energy", - battery "power" / supercapacity, battery "energy" / supercapacity.

The embodiment illustrated in Figure la is advantageously used to implement the first feeding strategy described above. Indeed, in this first strategy, the main storage device is allowed to respond to any power demand.

However, in FIG. 1a, it appears that the coupling member 14a is placed in such a way that the main storage device 10a is permanently connected to the system to be powered, the member 14a being used solely to manage the contributions of the device secondary 12a.

On the other hand, it was previously mentioned that one way of implementing the second power strategy was to perform a power demand clipping in order to distribute the demand on the two storage devices. This clipping process is illustrated by the graphs shown in Figures 2a, 2b and 2c. The graph of FIG. 2a represents the evolution of the power demand received by a device according to the invention, during a cycle of operation. This solicitation corresponds, for example, to the energy requirements of a motor vehicle, and the variations in the load are therefore representative of the different phases of vehicle life (rolling phase at constant speed ratio, shifting phase gear ratio , and stop phase).

The sizing of the main device sometimes requires that the power demand be limited to destination of this device. For this, it is useful to have a limitation threshold to distribute the demand between the two devices. This threshold is, for example, determined beforehand according to the characteristics of the device, and entered in a memory of a microprocessor used to implement the method.

Thus, a quantity of energy less than or equal to the limitation threshold will be provided by the main device, and the missing amount will, if necessary, be provided by the secondary device.

Thus, in the case shown in FIGS. 2a to 2c, the limitation threshold is set to 10000 W in absolute value. Thus, the power demand is distributed in such a way that the main storage device responds to a load corresponding to that shown in FIG. 1b, ie a load that remains lower, in absolute value, than the limit threshold of 10000 W. However, in graph 2a, it can be seen, for example, in points 20a and 22a, that the overall load of the powered system exceeds this absolute value of 10,000 W (between a minimum threshold of 5000 W and a maximum threshold of 5000 W). In this case, the main device supplies or stores the maximum quantity, namely 10,000 W. in absolute value (20b and 22b, Fig. 2b), and the complement is supplied or stored by the secondary device (20c and 22c, fig. 2c) On the other hand, when the bias remains below this limit threshold, the main device can supply or store all the energy required, and in this case the secondary device provides only a very small quantity, or even a zero quantity. , energy.

Moreover, whatever the power strategy used, it is useful that the two storage devices are maintained in an optimal state to be able to respond to any request. For this purpose, energy exchanges take place between the main device and the secondary device. These energy exchanges are, for example, governed by variation laws as illustrated in FIGS. 3a to 3e. These variation laws represent, as a function of the state of charge of the main device, expressed as a percentage, the power exchanged between the devices. This exchanged power corresponds to the electrical power that can pass between the two devices.

The points 30 and 32 shown in the graphs 3a to 3d respectively define optimum operating zones of the supply device.

Graph 3 illustrates a case in which the optimal operating area is reduced to a point 33.

Indeed, at all times, the main device must be able to respond to a request from the powered system, and for this it is useful that it is at a state of charge corresponding preferably, but not necessarily, to a half-load to be able to supply or store energy.

Thus, on these curves, the upper half-planes, defined by a state of charge of the main device greater than 50%, correspond to a discharge of the main storage in the direction of the secondary device which is then loaded.

In the same way, the lower half-planes correspond to a discharge of the secondary device towards the main device which then charges.

On these graphs, the values 34 and 36 represent the maximum values accepted in charge and in discharge by the energy storage devices.

The values 34 and 36, as well as the positions of the points 30 and 32 may be, in some embodiments, variable as a function of parameters representing the technical characteristics of the storage devices. FIG. 3e represents the particular case of a law of variation in which the optimum operating zone of the system is reduced to a point 33.

Thus, during the implementation of a method according to the invention, the state of charge of the main storage device is measured and, from this measurement and a law of variation, for example such that the one of those shown in FIGS. 3a to 3e, the energy exchanges that must be made between the main device and the secondary device are determined.

Claims

A method of managing energy flows in a power supply device comprising at least one main energy storage device (10a, 10b) and a secondary storage device (12a, 12b), the method comprising the steps of: the power demand between the main device (10a, 10b) and the secondary device (12a, 12b) is distributed, when the power supply device receives a demand for electrical power, the load state of the device of the device is measured. storage (10a, 10b), from this measurement, an electrical energy exchange is controlled between the main energy store (10a, 10b) and the secondary energy store (12a, 12b), the method being characterized in that, to distribute the power demand,

determining a threshold for limiting the power supplied by the main device, according to the characteristics of the main device, and

- Clipping of the power demand of the main device at the limiting threshold.

2. Method according to claim 1 wherein the power demand is distributed in such a way that only the main storage device (10a, 10b) is requested to respond to this request.

3. Method according to claims 1 or 2 wherein the secondary device (12a, 12b) provides a power amount corresponding to the difference between this limitation threshold and the amount requested.

4. Method according to one of the preceding claims wherein the value of the limitation threshold is predetermined according to at least one parameter included in the group comprising: the size of the main storage devices (10a, 10b) and secondary storage (12a , 12b), the state of charge of the secondary device (12a, 12b), parameters representative of the state of the elements forming the storage devices, and the operating state of the system powered by the supply device.

5. Method according to one of claims 1 to 4 wherein, for measuring the state of charge of the main device, the percentage of energy stored in this device is determined relative to the maximum quantity that can be stored in this device.

6. Method according to one of claims 1 to 5 comprising the step of determining, from the measurement of the state of charge (35) and a predetermined variation law, the exchange of energy to be controlled between the main device (10a, 10b) and the secondary device (12a, 12b).

7. The method of claim 6 wherein the variation law is determined beforehand according to at least one parameter included in the group comprising: the size of the main (10a, 10b) and secondary storage devices (12a, 12b) , the state of charge of the secondary device, parameters representative of the state of the elements forming the storage devices, and the state of operation of the system supplied by the supply device.

8. Method according to claim 6 or 7 wherein the law of variation is such that when the state of charge (35) the main device (10a, 10b) is less than a predetermined value, an energy exchange corresponding to a load of the main device (10a, 10b) and a discharge of the secondary device (12a, 12b) is controlled.

9. Device for implementing a method according to one of the preceding claims, this device comprising: a main storage device (10a, 10b), - a secondary storage device (12a, 12b), measuring means of the state of charge (35) of a storage device (10a, 10b) and means for controlling and distributing electrical exchanges.

10. Device according to claim 9 wherein the main storage device (10a, 10b) and the secondary storage device (12a, 12b) are separate and are each included in the group comprising: a "power" type electrochemical battery, an electrochemical battery of "energy" type, and a supercapacity.