Method of charging accumulators

State of the art

p0001The invention relates to a method for charging rechargeable batteries according to the generic type of claim 1, as well as a charging device for accumulators according to the preamble of claim 5.

p0002In electrical devices, batteries are replaced by alternating accumulators, for example in power tools. The accumulators have individual cells connected in series, for example NiCad cells but also NiH cells. For detecting the cell temperature, suitable sensors, for example NTC resistors or diodes, are introduced between the cells. When the accumulators are recharged, different cut-off criteria are taken into account, for example, temperature, voltage or time cut-off. Also, several criteria are often combined. Damage to the cells could also be avoided even if an error occurred during charging times of up to one hour when one of the switch-off criteria was taken into account.

p0003From US Pat. No. 4,308,493, a charger for alkaline batteries is known in which the temperature of the rechargeable battery is measured during charging. As the temperature increases, the charging current also increases and vice versa. If a predefined voltage value is reached during charging, the charging current is switched off.

p0004US Pat. No. 4,370,606 discloses a charging device in which a reference voltage for a thermistor is formed. The reference voltage depends on the ambient temperature and the battery temperature. The reference voltage is used to control the control input of a thyristor, which supplies the charging current for the battery. The charging current is switched off when the voltage difference between the reference voltage and the charging voltage is less than the switching voltage of the thyristor.

Advantages of the invention

p0005The method according to the invention with the features mentioned in claim 1, as well as the device according to claim 5, have the advantage that gentle loading cycles are ensured which extend the service life of the cells, even if the charging time is substantially shortened.

p0006Through the use of the fuzzy logic, various boundary conditions can be taken into account and a very gentle charging process can be realized without substantially increasing the effort involved in implementing the method.

p0007According to the method according to the invention, the voltage and temperature of the accumulator or its cells as well as the temporal derivation of these measured values ​​are detected. With the help of relatively few signals, a very gentle charging process can already be realized.

p0008Also preferred is an embodiment of the method in which various charging processes can be distinguished according to whether the temperature of the accumulator is high or low or whether the temperature of the accumulator or of the cells rises or falls. By taking these measured values ​​into consideration, a gentle charging of the accumulator can be ensured in a simple manner.

p0009Further embodiments are evident from the remaining subclaims.

p0010The charging device for carrying out the method is characterized in that a fuzzy processor is provided. By using such a processor, the charger is particularly suitable for charging accumulators gently in order to extend the service life of the individual cells.

p0011The use of the method or of the charger for charging NiCad batteries and / or NiH batteries has proved particularly advantageous.

drawing

p0012The invention is explained in more detail in the following appendix of the drawing. Show it:<dl id="dl0001"><dt>FIG</dt><dd>A block diagram of a charger;</dd><dt>FIG</dt><dd>A diagram for illustrating the implementation of the method for charging accumulators;</dd><dt>FIG</dt><dd>Membership functions of input variables and</dd><dt>FIG</dt><dd>The membership function of an output.</dd></dl>

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

p0013FIG. 1 shows a schematic block circuit diagram of a charging device 1 for landing an accumulator 3. The charging device can be connected to a suitable mains supply. The tapped voltage is smoothed by a filter circuit 5 and fed to a rectifier 7. Its output signal is passed via a DC converter 9 to a current controller 11, to whose output terminals 13 the accumulator 3 is connected.

p0014The accumulator is provided with a temperature sensor, which in this case is embodied as an NTC resistor 15 and which is connected, by way of example, with its one end to a connection of the accumulator 3. On the other hand, the NTC resistor 15 is connected to an input terminal 17 of the charging device 1.

p0015The charger 1 has a microprocessor 19, which comprises a fuzzy logic circuit 21. The voltage U applied to the rechargeable battery 3 to be charged, the discharge of which after the time, referred to as dU, is the temperature T of the accumulator as well as the derivative thereof, which is designated as dT, according to time.

p00161 that the microprocessor 19 is provided with a measured value processing stage 20 in which the time derivative of the voltage dU / dt and the time derivative of the temperature dT / dt are generated. Moreover, a smoothing of the signals is carried out in the signal conditioning stage 20 in order to ensure error-free further processing.

p0017The input signals are evaluated by the logic circuit and the charging current I which the current regulator 11 specifies for the charging process of the accumulator 3 is calculated therefrom. The microprocessor 19, or its fuzzy logic 21, is therefore connected to the current regulator 11 via a control line 23.

p0018The method for charging an accumulator is explained in more detail with reference to the functional diagram shown in FIG.

p0019When charging the charging device 1 in FIG. 1, the charging process is started in a first step Z1. Firstly, in a second step 33, a conventional initialization takes place, which serves to set the charger into a ready-to-operate state.

p0020In a third step 35, it is determined in a suitable way which type of accumulator 3 is connected to the output terminals 13 of the charging device 1.

p0021In a further step 37, the measured values ​​supplied to the charger 1 are detected and processed in the next step 39 for the evaluation logic, the fuzzy logic 21.

p0022The processed measured values ​​are processed or evaluated in the next step 41 by the fuzzy logic and the charging current I required for the charging current control is calculated. The control of the charging process is indicated by the next step 43.

p0023A query 45 is now made as to whether the accumulator 3 to be charged is full or not. If this is not the case, the system falls back into the method step 37, in which the measured values ​​are detected and processed in the fuzzy logic after a measured value processing in step 39 (step 41). After the control step 43, the query 45 again determines whether the accumulator is full or not.

p0024Finally, when the accumulator is brought to the desired charging state, a maintenance charge is carried out in a further step 47.

p0025As long as the charger 1 is not running, the maintenance charge is maintained. The query regarding the idling is performed in the method step 49.

p0026If the accumulator is disconnected from the charger 1, this is detected in the idle interrogation 49. When a new rechargeable battery is to be charged, the process returns to step 33, which is used to initialize the device. The process steps 35 to 49 described above are then carried out successively.

p0027It can be seen from FIG. 1 that the fuzzy logic circuit 21 processes various input signals. For example, the temperature T and the voltage U of the accumulator to be charged are assumed as input signals. In addition, the changes in these measured values ​​over time.

p0028FIG. 3 shows the so-called membership functions of these input variables. In the uppermost diagram, μT is the accumulator temperature above the temperature in ° C.

p0029The membership is recorded for different classes, namely for the class "small accumulator temperature", "normal accumulator temperature" and "high or large accumulator temperature". The membership is continuously plotted between the value "0" and the value "1", whereby the value "0" is assigned the statement "no affiliation" and the value "1" the 100% affiliation.

p0030The classes are arranged in such a way that the first class "small accumulator temperature" assumes the membership "1" for all values ​​below -4 ° C. The membership of this class then falls from the value "1" at -4 ° C to the value "0" at +7 ° C.

p0031The second class "Accumulator temperature normal" has an increasing degree of membership from the value "0" for -4 ° C to the value "1" at +7 ° C. The membership retains the value "1" to +45 ° C and then drops to the value "0" at +65 ° C.

p0032The third class of the accumulator temperature has a rising affinity of +45 to +65 ° C. The membership maintains the value "1" for all temperatures above +65 ° C.

p0033In the second topmost diagram according to FIG. 3, the membership function for the accumulator voltage per cell is reproduced. The designation μU * is intended to indicate that a rated voltage value for the regulation of the charging process is used here.

p0034It is here derived from the membership of two classes, namely to a first class "small accumulator voltage" and to a second class "large accumulator voltage".

p0035The membership is also indicated here by the curve course between the value "1" and "0". 100%, ie the value "1", of an accumulator voltage of ≤ 1.5 V / cell. The membership of this class then drops to the value "0" for the voltage 1.6 V per cell.

p0036The second class "large accumulator voltage" starts out from the value "0" at 1.5 V / cell and assumes the value "1" at 1.6 V / cell.

p0037The third diagram in FIG. 3 shows the change in the accumulator temperature over time, the unit being selected as mK / s.

p0038Three classes are to be distinguished: "negative temperature change", "positive temperature change" and "very large positive temperature change".

p0039The membership of the first class "negative temperature change" has the value "1" for dT / dt = -20 mK / s and falls to the value "0" to dT / dt = 13 mK / s. The membership of the second class increases from the value "0" at dT / dt = -20 mK / s to the value "1" at dT / dt = 13 mK / s and drops to dT / dt = 27 mK / s Value "0", which is reached at dT / dt = 85 mK / s.

p0040Correspondingly, the membership of the third class "very large positive temperature change" increases from "0" to "1" between dT / dt = 27 mK / s and dT / dt = 85 mK / s.

p0041Finally, the voltage change present at the accumulator is plotted over time in the fourth diagram according to FIG. 3, the change dU / dt having the unit mV / cell, s, ie, measured in mV per cell and second.

p0042The membership of the voltage change μdU also has three classes, namely "negative voltage change", "positive voltage change" and "very large positive voltage change".

p0043The first class "negative voltage change" has the value "1" at dU / dt = -0.6 mV / cell, s and then falls to dU / dt = -0.1 mV / cell, from.

p0044Within this value range, the membership of the second class increases from the value "0" to the value "1", in order to fall between the values ​​0.6 and 1.5 mV / cell, s to the value "0".

p0045Correspondingly, an increase in the membership from the value "0" to the value "1" in the class "very large voltage changes" can be observed. Above 1.5 mV / cell, s, the value of the membership of the third class is retained.

p0046The figures for the transitional areas between two classes within the individual membership functions are, of course, merely chosen as examples. Their setting can be adapted to the accumulators to be charged.

p0047FIG. 4 shows the membership function of the output variable μI, that is to say the charging current, which is fed to the accumulator 3 via the connection terminals 13 as a function of the control signal present on the control line 23 from the current regulator 11.

p0048For the charge current I measured in amps, four classes are distinguished which are assigned charging currents of 0A, 2A, 4A and 6A.

p0049The membership of class 0A increases from the value "0" to the value "1" between -2A and 0A, in order to then assume the value "0" between 0A and + 2A.

p0050The classification of the class 2A is made from the value "0" at 0A, reaches the value "1" at + 2A, and then decreases again to the value "0" reached at 4A.

p0051Class 4A membership increases from "0" to "1" between + 2A and 4A, and then decreases to "0", which is reached at 6A.

p0052Finally, for the class 6A between 4A and 6A, an increase in the degree of membership is to be determined from "0" to "1" and then a drop to the value "0" at 8A.

p0053The charging currents which can be realized with the aid of the charging device according to FIG. 1 or the membership functions are obtained from the evaluation of the input variables, as shown in FIG. The following table shows the control set which can be determined in this case, from which the charging currents for the various charging and temperature states of an accumulator can be read. The following table shows the measured values ​​which remain without weighting.

p0054If, for example, the first line of the control set is entered in the table, it follows that the charging current I assumes the value 0A when the weighted accumulator voltage per cell is large. Neither the temperature nor its change in time nor the change in the accumulator voltage per time play a role.

p0055Other-voltage states of the accumulator marked with x remain unaffected. In this case, only the remaining input variables have an effect on the setting of the charging current. However, it is also apparent that, given a small temperature of the accumulator, the voltage change on the accumulator is not taken into account both in the case of a negative and a positive temperature change. In the first case, with a negative temperature change, a charge current of I = 4A results, a charge current of I = 6A when the accumulator temperature changes positively.

p0056Moreover, it can be inferred from the control set that the voltage change dU also has no effect at a high temperature of the accumulator. Depending on whether the temperature change of the accumulator is negative, positive or very strongly positive, a charging current of 2A, 0A and 0A occurs.

p0057In the other cases, the temperature, the change in the voltage per time, and the change in the temperature over time are included in the charging current I setting. 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p0058By using the fuzzy logic, it is possible to detect the voltage and the temperature as well as the temporal derivatives of these values ​​on an accumulator during a charging process. The term "temperature high", "temperature low", "temperature rises" or "temperature drops" is possible with the terms "high voltage", "low voltage", "voltage rise" Can also be linked with the aforementioned terms. In any case, it is ensured that, under different conditions, an optimum charging current is always set, so that a gentle charge of accumulators can be realized and a particularly long service life of the individual cells of the accumulator is ensured.

p0059Preferably, the control values ​​of the temperature and voltage of an accumulator can be averaged during the setting of the charging space, and the discharges can also be averaged over a plurality of measuring cycles in order to ensure a charging process which is as uniform as possible and thus gentle.

p0060By detecting the various boundary conditions, a careful reduction of the charging time to 15 or even 5 minutes ensures that the accumulators are protected.

p0061From the above, it is readily apparent that both the method and the charging device described are very well suited to be used in charging processes of rechargeable batteries containing NiCad or NiH cells.