Process for determination of the charge consumption of a storage battery

ES 2 300 528 T3

DESCRIPTION

Procedure for determining the charge absorption of an accumulation battery.

The invention relates to a method for determining the charge absorption of a storage battery starting from an initial state of charge at the beginning of charge absorption.

The invention further relates to a monitoring device for storage batteries with a battery temperature measurement unit and with calculation means for determining the charge absorption of the storage battery according to the above-mentioned method.

The invention further relates to a computer program with program coding means for carrying out the aforementioned method.

In the operation of accumulator batteries, in particular starter batteries in automobiles, there is a need to determine the momentary state of the accumulator battery and to anticipate a future state with the assumed environmental and state conditions of the battery. In this case it is also desired to determine the load absorbed in the load operation.

For this, it is known to measure the battery current continuously during the operating time of the accumulator battery. From the converted current, the charge entering the storage battery or the charge removed from the storage battery can be calculated and the state of charge can be determined by balancing.

Furthermore, it is known to determine the variation in the state of charge of an accumulation battery by means of mathematical models, such as, for example, with equivalent schemes.

In this method, the battery current has to be measured disadvantageously. This is costly, particularly in the case of starter batteries with relatively high starter motor currents. From document US5936313A it is known to determine a charge absorption by means of an exponential function with a time constant that depends on the battery temperature.

Thus, the object of the invention is to create an improved method for determining the charge absorption of an accumulator battery, with which the charge absorbed during charging operation can be determined without battery current measurement. part of the storage battery as accurately as possible and with a low measurement cost.

The objective is achieved with the generic method according to the invention thanks to the fact that the charge absorption is determined as a function of an exponential function with a time constant. In this case, it is proposed that the time constant is set at least as a function of the type of storage battery and the temperature of the battery or the electrolyte.

Through tests, it has been shown, in particular, that the charge absorbed by a storage battery approaches exponentially asymptotically to a defined state of total charge, that is, to the nominal capacity. The nominal capacity is already given by the manufacturer for storage batteries. In this case, it has surprisingly been shown that the time constant of the exponential function depends fundamentally on the type of storage battery and on the temperature of the battery or the electrolyte. The influence of the state of charge at the beginning of the absorption of charge, as well as of the average charge voltage, on the other hand, is much less, and does not have to be considered necessarily. All other influences are totally negligible.

This reduces the measurement cost for determining the absorbed charge in a battery or electrolyte temperature measurement, the measured battery or electrolyte temperature being used in a function set for the storage battery for the calculation. of the time constants. This function can be determined, for example, experimentally for each accumulator battery.

Preferably, the time constant is further set as a function of the state of charge at the beginning of the charge absorption. It is particularly advantageous that the time constant is also set as a function of the load voltage, an average load voltage or a nominal load voltage.

In this way, the time constant can be determined with three factors that are multiplied between them, calculating the first factor with a function that depends on the type of accumulator battery and the charging voltage or the average charging voltage or the the nominal charge voltage, the second factor with a function dependent on the state of charge at the beginning of the charge housing, and the third factor with a function that depends on the temperature of the battery or electrolyte.

ES 2 300 528 T3

The absolute charge absorption of the storage battery can be calculated, for example, as a function

<img file="ES2300528T3_D0001.tif" />

with nominal capacity Q₀ accumulation battery and initial charge Q_S accumulation battery at the beginning of charge absorption.

However, a relative state of charge can also be calculated based on the nominal capacity Q₀ of the storage battery as a function

The third factor as a function of the battery or electrolyte temperature can be, for example, a first correction factor τ_τ for the time constant τ, which is determined according to the formula with the electrolyte temperature T₀ battery, a nominal electrolyte temperature T_to,₀ and the constants a and b. With this first correction factor τ_τ the influence of the electrolyte temperature on the charge absorption of the storage battery is taken into account. This function is based on Arenius's law, since the limiting physicochemical reactions are dissolution reactions. For a time constant τ normalized at room temperature of approximately 20 ° C, a constant a with the value 2 with a tolerance of ± 0.5 and a constant b with a value of 10 and a tolerance range of ± 1.

The influence of the state of charge at the beginning of the charge absorption can be expressed by means of a second correction factor to_s/ Q_or for the time constant τ, whose interval of values ​​must go from 1 to 1 - Q_s/ Q₀. The quotient Q_s/ Q₀ is the charge Q_s initial referred to nominal capacity Q₀ at the beginning of load absorption.

The objective is further achieved by means of a monitoring device that has calculation means for carrying out the procedure described above. The calculation means can be implemented, for example, as a computer program running on a processor, for example a central vehicle computer of an automobile. The aim is further achieved by means of a computer program with program coding means which are shaped to carry out the method described above.

The invention is explained in more detail below from the accompanying drawings. It shows:

Fig. 1 Diagram of the relative accumulated load absorptions measured and determined according to the method according to the invention as a function of the initial state of charge;

Fig. 2 Diagram of the relative accumulated load absorptions measured and determined according to the method according to the invention as a function of the initial state of charge, in which the time constant of the exponential function is corrected with a correction factor dependent on the temperature;

Fig. 3 Diagram of the relative accumulated charge absorption for an electrolyte temperature of 25 ° C as a function of the initial state of charge and time with a constant charge voltage of a lead-acid automobile battery;

Fig. 4 Diagram of the relative accumulated charge absorption for an electrolyte temperature of -10 ° C as a function of the initial state of charge and the charging time with a constant charge voltage of a lead-acid car battery.

Figure 1 allows us to recognize a diagram of the relative accumulated charge absorption Δζ? (/) / Q = - ⁷__—

0o for initial states of charge Q_s/ Q₀ initials of 50% SOC and 70% SOC (SOC = State of Charge). Charge absorption is represented as a function of the charging process time and is carried out with battery or electrolyte temperatures of 25 ° C.

In this case, the charge absorption has been determined experimentally and in comparison with it has been calculated using the method according to the invention. The load absorptions determined experimentally

ES 2 300 528 T3 are represented by the curves indicated with circles. The load absorptions determined according to the invention are represented by means of the curves characterized by cross lines.

It can be recognized that the curves determined according to the invention and experimentally determined of the relative accumulated charge absorption have a good agreement with each other.

At time t = 0, the accumulation battery has an initial charge Q_s and an initial state of charge Q_s/ Q₀ referred to nominal capacity Q₀. The initial state of charge Q_s/ Q₀ It has a value, for the first case a) of 50% SOC and for the second case b) of 70% SOC. The remaining 50% or 30% charge that could be absorbed, at least, until reaching the full state of charge with a nominal capacity Q0 is absorbed by the accumulator battery over time in a charging process that it runs approximately exponentially.

Load absorption AQ (t) / Q_or The relative value shown corresponds to the absolute load absorption referred to the nominal capacity Q0 during the charging process.

The relative load absorption is determined, according to the invention, proportionally to the formula:

<img file="ES2300528T3_D0002.tif" />

where t is time and τ is a specific time constant. The time constant is, according to the invention, a function of the type of storage battery, the temperature of the battery or the electrolyte T_s, from initial state of charge Q_S/ Q₀ and the load voltage U_L. The load voltage U can be used as the load voltage._L(t) over time, an average load voltage U_L or a nominal load voltage U_L,₀, or similar.

The bottom line is that the time constant τ is a function of the battery and electrolyte temperature and the type of storage battery. The dependence of the optimal time constants τ or of the exponential function, on the contrary, depends only relatively slightly on the initial state of charge Qs / Q0 at the beginning of charge absorption, as well as on the charge voltage uL. The charging voltage UL can already be entered as a specific value of the storage battery type when a function for determining the time constants τ as a function of the storage battery type is experimentally determined.

Also the considered temperature of the battery and the electrolyte can be determined, for example, as a momentary value measured at the beginning of the charging process, and can be kept constant for the next charging process. Thus, the time constant τ for a charging process can have a constant value. Alternatively, the time constant τ can also be adapted as a function of time during the charging process.

Figure 2 allows us to recognize a diagram of the relative charge absorption AQ (t) / Q₀ = Q (t) - Q_s/ Q₀ with an electrolyte temperature of 0 ° C and initial charge constants Q_s/ Q₀ 50% SOC and 70% SOC. In turn, the values ​​for the relative load absorption have been determined experimentally, and have been determined in numerical comparison according to the method according to the invention. In the example shown, the time constant τ has been corrected by means of a first correction factor τ_Τ, which reflects the dependence of the time constants τ on the electrolyte temperature. Since the limiting physico-chemical reactions are dissolution reactions, starting from Arenius's law a correction quantity has been defined

<img file="ES2300528T3_D0003.tif" />

and thus the influence of the electrolyte temperature on the charge absorption of the accumulation battery has been taken into account. In this case, T_s is the temperature of the electrolyte, and T_to,₀ is a nominal electrolyte temperature. The constants a and b are quantities that are determined experimentally. The constant a must have a value of approximately 2 with a tolerance interval of ± 0.5, and the constant b must have a value of approximately 10 with a tolerance interval of ± 1.

From Figure 2 it can be recognized that with a time constant τ corrected in this way there is a relatively good match of the calculated relative accumulated charge absorptions with the measured relative accumulated charge absorptions. By optimizing the constants a and b, the result of the determination of the charge absorption can be further optimized as a function of the type of storage battery.

The dependence of the time constant τ with respect to the relative state of charge Qs / Q0 at the beginning of the charge absorption is very low, since during charging the reduction of the internal resistance R, of the accumulation battery is compensated according to the product τ = R, x C by the increase in the capacity C of the accumulation battery. When calculating a time constant, an initial relative state of charge Qs / Q0 is preferably determined by means of a second correction factor.

ES 2 300 528 T3

<img file="ES2300528T3_D0004.tif" />

in which the second correction factor tQ_s/ Q₀ must take a value between 1 and (1 - Q_s/ Q₀).

With this, the time constant τ can be determined according to the relation:

τ ~ R_T0(accumulation battery type, U_L) · why_s/ Q₀ Τ_Τ = t_rt0 (accumulation battery type, U_L) F (Qs / Qo f (Te) where t_rto is a time constant at room temperature that depends only on the type of storage battery and the charging voltage U_LThis part t_rto of a time constant t can be determined experimentally for accumulator batteries of one type and for vehicles of a manufacturer in relation to the charging voltage U_Lexperimentally, so that for the determination of the charge absorption only a temperature measurement is required

Figure 3 shows a diagram of the relative accumulated charge absorption AQ (t) / Q₀ as a function of the initial relative state of charge Q_s/ Q₀ at the beginning of the charge absorption and the charging time t with a constant charging voltage of 14.2 V and an electrolyte temperature of 10 ° C in the example of a lead acid car battery. It is shown that the charge absorption shows an exponential evolution. In the wide range of an initial relative state of charge Q_s/ Q₀ ranging from approximately 0% to 0.7%, a great linearity can be recognized in the different exponential curves that limit the initial states of charge. This means that the influence of the initial relative state of charge on the evolution of the curves is small.

Figure 4 allows us to recognize the relative accumulated charge absorption AQ (t) / Q₀ depending on the state of charge Q_s/ Q₀Initial relative to the start of charge absorption and time t with a constant charge voltage of 14.2 V and an electrolyte temperature of 25 ° C. It is shown, in comparison with the evolution of the curves in Figure 3, that the evolution of charge absorption with electrolyte temperatures T_s varied is clearly modified. The evolution of the curves, however, again follows an exponential function.