DE19943466B4 - Power supply system with multiple energy storage - Google Patents

Abstract

In a power supply system consisting of multiple energy stores and at least one consumer, energy is transferred between the energy stores in times of non-usage of the system in such a way that the total loss of the system of stored energy is minimized by parasitic operations. At least one of the energy stores is an electrochemical accumulator and the system is located in a vehicle. The system has a central processing unit in which, depending on the design of the individual storage system and its current energy content and possibly their current temperature and other factors, a decision about the transfer of energy from one system to another takes place.

Description

electrochemical Memories that are charged to some degree show one so-called self-discharge, in which also without external electrical load by stored in its interior parasitic processes the stored electrical energy is gradually reduced. The self-discharge rate, d. H. the relative loss of state of charge per unit of time depends both from the state of charge as from the temperature. Furthermore, the Aging condition of the memory and the previous operating conditions an influence on the Have self-discharge rate.

in the Generally, the self-discharge rate increases with increasing temperature drastically. The dependence the self-discharge rate of the temperature is due to the temperature dependence the parasitic causing them Reactions conditionally, in most cases, in a rough approximation Doubling of the reaction rate per 10 ° temperature increase recognized can be. If several parasitic self-discharge reactions are effective at the same time, so can a complex temperature dependence of self-discharge when the activation energies of the various Processes are significantly different.

The dependence however, the self-discharge rate from the current state of charge is generally complex. So there are electrochemical stores whose self-discharge rate is in the fully loaded state has a maximum, such. NiMH and Ni / Cd, but also systems whose self-discharge increases as soon as a certain one Charging state is undershot.

The Magnitude the self-discharge rate depends in addition to the state of charge and the temperature in particular of the type and the electrochemical system of the memory. So lie to Example alkaline storage systems NiMH and Ni / Cd with 10-20% loss on state of charge within 1 month at room temperature at significantly higher values as, for example, the lead-acid battery in which the losses under same conditions of the order of magnitude only 3% per month.

A change the Selbstentladeverhaltens with increasing service life and aging of the Electrochemical storage, for example, by changing the inner surface of active materials, by change (especially degradation) of excipients, through change the substrate surfaces or even through the formation of microscopic inner fine closures.

One the self-discharge electrochemical storage analog behavior show other types of energy storage such as capacitors. In mechanical energy storage, such as flywheels occurs also by parasitic (Friction) losses a decline the energy stored in them with the storage duration. The Rate of these losses is many orders of magnitude for flywheels higher than in electrochemical storage.

The Self-discharge of storage is very annoying for longer storage times. she leads at a loss of energy and reduces the useful life of the powered by them system. In individual cases It can also be complete Failure of the system will come if this again after the storage time to be put into operation.

Of the The invention is therefore based on the object, the losses of a system, which is located in a vehicle, stored energy as possible to keep small.

The The object is achieved by the features cited in claim 1. In the Subclaims are advantageous embodiments of the invention described.

at a motor vehicle, the phenomenon is well known that after a long time Service life of the charge state of the starter battery is no longer sufficient to to give sufficient power to start the internal combustion engine.

has such a vehicle, however, more than an energy storage system, so according to the invention results in a degree of freedom to reduce the loss of electrical energy during storage. Especially the subject of the invention is a system of several energy stores, which differ in their self-discharge properties. By the displacement of the invention of stored energy from one store to another can do so the energy loss of the entire system can be reduced.

According to the invention will, depending on Parameters such as the state of charge, the temperature, the type, the Aging, the history of the operation etc. of the various (in particular, but by no means necessarily electrochemical) Store energy from higher self-discharge rate storage transmit those with low self-discharge rate, so the losses of the overall system.

In each case, the advantage of this measure by reducing the losses in the storage against the disadvantage of the loss of energy in the contracting of energy from a memory to to weigh others. If, for example, two electrochemical accumulators are connected in one system, losses will occur in the transfer of energy from one to the other during both the discharging and the charging processes, and also the conversion by, for example, a DC / DC converter can not be lossless.

It is therefore advantageous, knowing the Selbstentladeverhaltens, the state of charge and the temperature and possibly other Characteristics of the Energy storage, as well as taking into account the past and, where appropriate, the expected future operating conditions Decision over the transfer of energy at all, as well as over the timing and rate of transmission hold true.

Especially at (compared to the Selbstentladeraten) short stoppages you will renounce the application, as with states with absolutely low self-discharge rates (for example at low temperatures). Farther is generally slow in electrochemical storage Rate of overpass chosen because then both the discharged and the loaded memory as possible works close to its rest voltage and so the internal losses the overpass small being held.

Next The reversible self-discharge, although a loss of current stored energy, which, however, by recharging again can be compensated, are also with longer life of accumulators occurring adverse processes known to damage the Storage properties that are either completely irreversible or not under normal operating conditions can be reversed.

to belong to the first group Loss of storage capacity as with lithium-ion batteries when stored at elevated Temperature occur to the second group the so-called sulfation at partially discharged lead accumulators and the so-called memory effect in alkaline Accumulators.

Also in these phenomena there is a dependence of the extent of damage from the state of charge and the temperature, so that by displacement according to the invention the stored energy between two or more energy stores a condition brought about that can be for that Overall system with the least drawbacks is connected.

An inventive power supply system is basically as in 1 constructed, in which schematically a 2-battery electrical system for motor vehicles is shown.

In this case, B1 and B2 are two batteries, with V ₁ and V _2, the associated consumers and G ₁ and G _2, the batteries B1 and B2 associated energy generators. Of course, in concrete embodiments, only a single or more than two energy generators may be present.

A control unit St as a central processing unit receives information about probe temperature T ₁ and T ₂ about the temperature of the batteries and via lines SOC ₁ and SOC ₂ on the state of charge of the batteries. Furthermore, the control unit St receives information about the operating state via line B (driving, out of operation, etc.). In the control unit it is decided whether, when and in what way energy is transferred from one battery to another battery via the DC-DC converter DC / DC.

It is advantageous if the central processing unit, the signal for the transfer of Energy from one memory to another with a given time delay after completion of the supply or the removal of energy from a the memory or after the end of the use of the energy storage supplied component (s) triggers.

The Delay Time depends on from each considered energy storage, in the case of a capacitor it may be low and for example only about 1 minute.

Conveniently, is the signal for the transfer of Energy from one storage system to another only triggered when predetermined threshold values of the temperatures or energy contents of the Memory or combinations of these sizes are exceeded or fallen below. For example, no energy transfer occurs at too low Temperature values at which the power output capability of the memory is very low is, or if the energy content of a memory has become too low is.

Basically the relocation of energy from one store to another such conditions that irreversible damage to a the memory or damage that can not be reversed under other operating conditions, by this measure is reduced.

example 1

A car has an electrical system with two electrochemical storage, one Ni / MH battery and a lead-acid battery of 500 Wh electrical storage capacity. After completion of the journey, the charge state of the NiMH rechargeable battery is 80% (corresponding to 400 Wh), that of the lead-acid battery is 30% (corresponding to 150 Wh). So a total of 550 Wh are stored, ie 55% of the total storage capacity of both accumulators is used.

at an assumed business interruption of 6 weeks would turn out the charge state of the NiMH accumulator by, for example, about 30% Reduce 50%, which equals a loss of 150 Wh. The lead-acid battery loses at the same time only about 5% (based on its nominal capacity), which a loss of 25 Wh. Will now be electrical energy transferred from the NiMH accumulator in the lead-acid battery, the state of charge decreases the former and the second one are rising. Because of the strong dependence the Selbstentladereaktion of the state of charge of the NiMH accumulator In this case, the total loss of the system is significantly reduced. For example, does the state of charge of the NiMH accumulator increase by 250 Wh to 150 Wh and at the same time that of the lead-acid battery of 150 Wh increased to 400 Wh, so the loss of the former drops in 6 weeks to about 5% accordingly 25 Wh, during the Loss of the last approximate unchanged stays at 25 Wh. This will reduce the energy loss of the entire system reduced from 175 Wh to 50 Wh. The savings of 125 Wh is almost ¼ of the total in the two stores originally energy of 550 Wh. Since such a vehicle with two batteries on board usually via sensors for the Temperature and the state of charge of the batteries and also has Voltage transformers are present which provide an energy transfer from To make one system to another requires realization This invention alone, a control unit, the measured values of this Evaluates sensors and decides whether and to what extent as well as at what time and at which rate the energy of one Memory is transferred to another. The gain by reducing the losses is generally sufficient at the time of the transfer of electrical energy from one system to another occurring electrical and more than compensate for electrochemical losses.

Example 2

at the combination of electrochemical accumulators with storage very high self-discharge rate such as (electro) mechanical storage (for Example flywheels) or even with super capacitors is already after a short wait transfer the energy stored in the latter to the accumulator. Would about a flywheel after 1 hour already 90% of the energy stored in it lose, so it makes sense energetically, the stored in it To transfer energy to the accumulator after only a few minutes, if not signs of it that will be available soon to be put into operation.

is such a system installed in a motor vehicle, so this is Operation z. B. triggered once the vehicle has been parked and the driver left it and has closed.

Claims (8)

Power supply system disposed in a vehicle consisting of a plurality of energy storage devices and at least one consumer, characterized in that energy is shifted between the energy storage devices in times of non-use of the system in such a way that minimizes the total loss of the system of stored energy by parasitic processes becomes. Power supply system according to claim 1, characterized that at least one of the energy storage is an electrochemical Accumulator is. Power supply system according to one of claims 1 to 2, characterized in that the current energy content at least one of the individual memory measured and transmitted to a central processing unit becomes. Power supply system according to one of claims 2 to 3, characterized in that the current temperature at least one of the electrochemical storage is measured and transmitted to a central processing unit becomes. Power supply system according to one or more of claims 1 to 4, characterized in that it is a central processing unit contains in, depending on the design of each storage system and its current Energy content and, where appropriate, their current temperature and other factors, one Decision on the transfer of energy from one system to another takes place. Power supply system according to one of claims 1 to 5, characterized in that it is a current or voltage converter for the transfer of contains electrical energy from one memory to another. Power supply system according to one of claims 4 to 6, characterized in that the central processing unit, a signal for transferring energy from one to the other memory only with a predetermined time delay after completion of the supply or the removal of energy from one of the memories or after the termination of the use of (the) supplied by the energy storage component (s). Power supply system according to one or more of claims 4 to 7, characterized in that the central processing unit a signal for the transfer of Energy from one storage system to another only triggers when predetermined threshold values of the temperature and / or the energy contents the memory or fall below.