Method for checking the plausibility of an electronic circuit for time measurement of an electrochemical energy storage system

Abstract

Method for checking the plausibility of an electronic circuit for time measurement of an electrochemical energy storage system by means of a cooling behavior of at least one electrochemical energy store during non-use of the electrochemical energy store.

Claims

1. A method for checking the plausibility of an electronic circuit for time measurement of an electrochemical energy storage system by means of a cooling behavior of at least one electrochemical energy store during non-use of the electrochemical energy store, the method comprising the following steps: a) detecting an ambient temperature T.sub.Env of the electrochemical energy store; b) detecting a temperature T.sub.t0 of the electrochemical energy store at the beginning of the non-use of the electrochemical energy store; c) detecting a temperature T.sub.t1 of the electrochemical energy store at the beginning of a restart of the electrochemical energy store; d) calculating a period toff of the non-use of the electrochemical energy store in accordance with the formula $t_{\mathrm{off}}=-\tau *\ln \left(\frac{T_{t1}-T_{\mathrm{Env}}}{T_{t0}-T_{\mathrm{Env}}}\right),$ wherein τ is a system constant, which comprises material properties of the electrochemical energy store in accordance with $\tau =\frac{m*c_p}{\alpha *A},$ wherein m is a mass, A is a contact area, α is a thermal conductivity and c.sub.p is a specific thermal capacity of the electrochemical energy store; e) determining an overall error in the calculation of the period t.sub.off of the non-use of the electrochemical energy store in accordance with the formula Δt.sub.off.sup.err=Δt.sub.1+Δt.sub.2+Δt.sub.3, wherein Δt.sub.1 is a temperature measurement error during the restart of the electrochemical energy store, Δt.sub.2 is a temperature measurement error at the beginning of the non-use of the electrochemical energy store and Δt.sub.3 is a temperature measurement error of the ambient temperature; f) checking the plausibility of the electronic circuit for time measurement by comparing a period t.sub.off.sup.Clock of the non-use of the electrochemical energy store, which period is measured by the electronic circuit for time measurement, with the calculated period t.sub.off of the non-use of the electrochemical energy store; g) identifying an error in the electronic circuit for time measurement when Δt.sub.off.sup.err<|t.sub.off.sup.Clock−t.sub.off|; and h) generating at least one selected from a group consisting of an electrical signal, an optical signal, an acoustic signal, and a haptic signal when an error is identified in the electronic circuit for time measurement.

2. An electrochemical energy storage system comprising at least one electrochemical energy store, at least one sensor for detecting at least one selected from a group consisting of a temperature of the electrochemical energy store and an ambient temperature of the electrochemical energy store, an electronic circuit for time measurement and at least one means configured to carry out the steps of the method according to claim 1.

3. An electronic battery management control device executing a computer program, comprising commands, which, when the computer program is executed by an electronic battery management control device, cause the electronic battery management control device to execute the method according to claim 1.

4. A non-transitory, machine-readable storage medium, on which a computer program is stored, and which, if the computer program is executed by an electronic battery management control device, causes the electronic battery management control device to execute the method according to claim 1.

5. An electrochemical energy storage system comprising at least one electrochemical energy store, at least one sensor for detecting at least one selected from a group consisting of a temperature of the electrochemical energy store and an ambient temperature of the electrochemical energy store, an electronic circuit for time measurement and an electronic battery management control device configured to carry out the steps of the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Exemplary embodiments of the invention are illustrated in the drawing and explained in more detail in the following description.

(2) In the drawing:

(3) FIG. 1 shows a schematic illustration of a temperature profile of an electrochemical energy store during non-use; and

(4) FIG. 2 shows a schematic illustration of a temperature-dependent period of the non-use of an electrochemical energy store.

(5) Identical reference signs denote identical apparatus components in all of the figures.

DETAILED DESCRIPTION

(6) FIG. 1 shows a schematic illustration of a temperature profile of an electrochemical energy store during non-use. Development of heat in an electrochemical energy store, in particular a high-voltage or low-voltage system, can be described by means of the following differential equation:

(7) $m*c_p*\frac{d{T}_{\mathrm{cell}}}{\mathrm{dt}}={\stackrel{.}{Q}}_{\mathrm{heat}}+\alpha *A*\left(T_{\mathrm{Env}}-T_{\mathrm{cell}}\right)$

(8) During use, for example during a charging or discharging process, of the electrochemical energy store, a power loss {dot over (Q)}.sub.heat is produced on account of an internal resistance of the electrochemical energy store and the electrochemical energy store assumes a somewhat higher temperature than the environment T.sub.Env. During non-use, the power loss {dot over (Q)}.sub.heat is essentially zero and a temperature profile is dependent on a heat exchange with an environment of the electrochemical energy store and on a mechanical design of the electrochemical energy store with specific material properties, for example a mass m, a contact area A, a thermal conductivity α and a specific thermal capacity c.sub.p of the electrochemical energy store.

(9) A period of non-use of the electrochemical energy store can be calculated by means of a cooling behavior of the electrochemical energy store during non-use.

(10) FIG. 1 shows a temperature profile of an electrochemical energy store, for example a 48 volt battery pack. The electrochemical energy store has been heated at an ambient temperature T.sub.Env of 20° C. through use, for example through a discharging process, to a temperature T.sub.t0 of 50° C. Non-use of the electrochemical energy store begins at a time t.sub.0. The temperature profile illustrated corresponds to a cooling curve during non-use of the electrochemical energy store up to a time t.sub.1 at which the electrochemical energy store is set in operation again. The electrochemical energy store is cooled at the time t.sub.1 to a temperature T.sub.t1 of 30° C.

(11) The period t.sub.off of non-use of the electrochemical energy store can be calculated in accordance with the formula

(12) $t_{\mathrm{off}}=-\tau *\ln \left(\frac{T_{t1}-T_{\mathrm{Env}}}{T_{t0}-T_{\mathrm{Env}}}\right),$
wherein τ is a system constant, which comprises the material properties of the electrochemical energy store in accordance with

(13) $\tau =\frac{m*c_p}{\alpha *A}.$
The system constant τ can be determined, for example, analytically or experimentally. In the case of the experimental determination, the electrochemical energy store at a given ambient temperature T.sub.Env can thus be brought to a higher temperature. By means of observing and measuring a temperature profile at a plurality of times during non-use of the electrochemical energy store, the system constant τ can be identified by way of a standard method, for example least square. Ideally, the experimental parameter determination is carried out after the electrochemical energy store has been installed, for example in a vehicle. This can minimize measurement and model inaccuracies.

(14) An accuracy of the identified period t.sub.off of non-use can be identified by means of methods for error propagation. A first partial error

(15) $\Delta t_1=\left|\frac{-\tau }{T_{t0}-T_{\mathrm{Env}}}\right|*\Delta T_{t1}$
is caused by a temperature measurement error upon restart of the electrochemical energy store, a second partial error

(16) $\Delta t_2=\left|\frac{\tau }{T_{t0}-T_{\mathrm{Env}}}\right|*\Delta T_{t0}$
is caused by a temperature measurement error at the beginning of non-use of the electrochemical energy store and a third partial error

(17) $\Delta t_3=\left|\frac{-\tau *\left(T_{t1}-T_{t0}\right)}{\left(T_{t1}-T_{\mathrm{Env}}\right)*\left(T_{t0}-T_{\mathrm{Env}}\right)}\right|*\Delta T_{\mathrm{En\nu }}$

(18) is caused by a temperature measurement error of an ambient temperature of the electrochemical energy store. An overall error Δ.sub.off.sup.err in the calculation of the period t.sub.off of non-use of the electrochemical energy store results from a sum of all of the partial errors t.sub.off=Δt.sub.1+Δt.sub.2+Δt.sub.3.

(19) The inaccuracies of the individual input variables ΔT.sub.t3, ΔT.sub.t0, ΔT.sub.Env can be determined experimentally, for example in a vehicle, since the measurement inaccuracy of a temperature of the electrochemical energy store increases when no power loss is produced in the electrochemical energy store in a short period of time, usually a few minutes, and a homogenous temperature distribution in the electrochemical energy store can be assumed.

(20) A check for the plausibility of an electronic circuit for time measurement of an electrochemical energy storage system is effected by means of a cooling behavior of at least one electrochemical energy store during non-use of the electrochemical energy store in one advantageous embodiment by means of comparing a period t.sub.off.sup.Clock of non-use of the electrochemical energy store, which period is measured by the electronic circuit, with the calculated period t.sub.off of non-use of the electrochemical energy store.

(21) A difference between the measured period t.sub.off.sup.clock and the calculated period t.sub.off must be within a tolerance range of the overall error Δt.sub.off.sup.err, otherwise the electronic circuit for time measurement has an error.

(22) electronic circuit for time measurement functions in a fault free manner:
Δt.sub.off.sup.err≥|t.sub.off.sup.Clock−t.sub.off|

(23) electronic circuit for time measurement is faulty:
Δt.sub.off.sup.err<|t.sub.off.sup.Clock−t.sub.off|

(24) FIG. 2 shows a schematic illustration of a temperature-dependent period of the non-use of an electrochemical energy store. A difference T.sub.t1−T.sub.Env between a temperature T.sub.t1 of the electrochemical energy store at the beginning of a restart of the electrochemical energy store and an ambient temperature T.sub.Env of the electrochemical energy store is plotted on the abscissa. A difference T.sub.t0−T.sub.Env, between a temperature T.sub.t0 of the electrochemical energy store at the beginning of non-use of the electrochemical energy store and an ambient temperature T.sub.Env of the electrochemical energy store is plotted on the ordinate. For the illustration of the period of non-use calculated in accordance with the invention, as values for example 4 hours is assumed for the system constant τ and ΔT.sub.t1=3 kelvins, ΔT.sub.t2=6 kelvins and ΔT.sub.Env=1.5 kelvins are assumed for the temperature measurement accuracies.

(25) In a first example, a temperature difference T.sub.t0−T.sub.Env is 40 kelvins at a time of non-use of the electrochemical energy store. Upon restart, a temperature difference T.sub.t1−T.sub.Env is 10 kelvins. A temperature-dependent period 201 of non-use of the electrochemical energy store is approximately 5 hours.

(26) In a second example, a temperature difference T.sub.t0−T.sub.Env is 30 kelvins at a time of non-use of the electrochemical energy store. Upon restart, a temperature difference T.sub.t1−T.sub.Env, is 20 kelvins. A temperature-dependent period 202 of non-use of the electrochemical energy store is approximately 3 hours.