Method for regulating a charging current in a charging path between a battery of an electric vehicle and a connector of a charging station

Abstract

The invention relates to a method (1) for controlling a charging current (I) in a charging path between an electric vehicle battery and a charging station connector during a charging process. At the start of the charging process, battery and connector currents (I_BAT1, I_BAT2, I_EVSE1, I_EVSE2) and battery and connector voltages (U_BAT1, U_BAT2, U_EVSE1, U_EVSE2) are determined before and after the application of a test current (I_PRB), and from this, an electrical resistance (R_LADEPFAD) of the charging path and a maximum safe charging current (I_SAVE) are calculated. The maximum safe charging current (I_SAVE) is then set in the charging station.

Description

The invention relates to a method for regulating a charging current in a charging path between a battery of an electric vehicle and a connector of a charging station during a charging process according to the preamble of claim 1.Rapid charging of an electric vehicle requires high charging currents, which can be realized only with a low electrical resistance of the charging path. In particular, the connector or the charging socket of the charging station can have a high electrical resistance, for example, due to corrosion. If the high charging current is set at the high electrical resistance, dangerous heat development can occur.DE 10 2019 129 799 A1 describes a method for regulating a charging current, wherein here a maximum charging current for the next charging process is determined on the basis of the determined electrical resistance of the charging path during the current charging process.The object of the invention is therefore to specify an improved or at least alternative embodiment for a method of the generic type, in which the described disadvantages are overcome.This object is achieved according to the invention by the subject matter of independent claim 1. Advantageous embodiments are the subject of the dependent claims.The present invention is based on the general idea of determining the resistance of the charging path and defining this as a maximum value of the power loss at the connector or charging socket for determining the charging current.The method according to the invention is provided or designed for regulating a charging current in a charging path between a battery of an electric vehicle and a connector of a charging station during a charging process. When the charging process is started, the battery of the electric vehicle and the connector of the charging station are electrically conductively connected to one another. In other words, a communication is established between the battery of the electric vehicle and the connector of the charging station. This can be effected in particular by plugging a charging plug of the battery into the connector or a charging socket of the charging station. A first battery current and a first battery voltage are then detected at the battery and a first connector current and a first connector voltage are detected at the connector. A sample current is then set as charging current in the charging station and an end of a transient process of the sample current is waited. The sample current can be suitably small and, for example, equal to 50A. A second battery current and a second battery voltage are then detected at the battery and a second connector current and a second connector voltage are detected at the connector. An electrical resistance of the charging path is now calculated from the detected battery currents and the detected connector voltages. From the known maximum permissible heat input into the connector and the calculated electrical resistance of the charging path, a maximum safe charging current is then calculated. In other words, the electrical resistance and the maximum safe charging current are determined from the ratios of the currents and the voltages in the battery and in the connector. The maximum safe charging current is then set as charging current in the charging station.In the method according to the invention, the electrical resistance is assigned to the connector or the charging socket as a worst-case consideration. Since the maximum permitted energy input or the maximum permitted heat input into the connector or the charging socket is known, a safe current limit or the maximum safe charging current can be calculated with the knowledge of the electrical resistance of the connector or the charging socket. In the method, the electrical resistance of the charging path and, from this, the maximum safe charging current can be determined particularly quickly. The maximum safe charging current can then be set in the charging station and the charging process can be started with the maximum safe charging current correspondingly quickly. In particular, this eliminates conventional adjustment of the charging current and enables a rapid charging start. In addition, the charging process can be carried out particularly safely, since the maximum safe charging current is calculated on the basis of the current values of the electrical resistance.Prior to calculating the electrical resistance of the charging path, the reliability of the sensed battery and connector currents and sensed battery and connector voltages may be checked. The electrical resistance of the charging path can be calculated only when the detected battery and connector currents and the detected battery and connector voltages are reliable. The reliability of the detected battery and connector currents and the detected battery and connector voltages is accordingly a prerequisite for a correct determination of the electrical resistance of the charging path and corresponding to the maximum safe charging current.Reliability may be when the first connector current has increased by an expected value. In other words, the reliability may be given when the difference of the second connector current and the first connector current is an expected value. Reliability may be when the first connector voltage has not dropped. In other words, the reliability can be given if the first connector voltage and the second connector voltage do not differ or do not differ insignificantly. The reliability may be given if the first connector voltage and the first battery voltage differ by not more than 20%, preferably not by more than 10%. In the method, all or only individual ones of the stated requirements for reliability can be checked.The electrical resistance of the charging path may be calculated from a ratio of a difference of the second connector voltage and the first connector voltage and a difference of the second battery current and the first battery current. In other words, the electrical resistance of the charging path can be calculated from the following relationship by means of a differential method:In this case, R_CHARGE PATH is the electrical resistance of the charge path, U_EVSE 1 is the first connector voltage, U_EVSE 2 is the second connector voltage, I_BAT 1 is the first battery current and I_BAT 2 is the second battery current.The maximum permissible heat input into the charging path corresponds to a product of the squared maximum safe charging current and the electrical resistance of the charging path.In other words, the following relationship applies for the maximum permissible heat input:Q_MAX is the maximum permissible heat input into the charging path and I_AVE is the maximum safe charging current. The maximum permissible heat input into the charging path is known or assumed, so that the maximum safe charging current can be calculated from the maximum permissible heat input into the charging path on the basis of the calculated electrical resistance of the charging path.After the charging process has been started and the maximum safe charging current has been set as charging current, the charging current can be regulated via the thermal capacitance of the connector of the charging station. This can be done in a manner known to the skilled person.It goes without saying that the calculations carried out in the method can be carried out, for example, by means of a microcontroller. It is also understood that the values measured or recorded in the method and / or calculated in the method can be temporarily stored in a memory and used as required. The memory and the microcontroller can be installed, for example, in a coherent control unit. The battery of the electric vehicle is a high-voltage battery.Further important features and advantages of the invention are evident from the dependent claims, from the drawings and from the associated description of the figures with reference to the drawings.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Preferred exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description, wherein the same reference numerals refer to the same or similar or functionally the same components.In each case, diagrammatically show: FIG. 1 shows a flow diagram of a method according to the invention for regulating a charging current; FIG. 2 shows a time profile of a charging current and a temperature of a connector when carrying out the method according to the invention.FIG. 1 shows a flow diagram of a method 1 according to the invention. Method 1 is provided or designed for regulating a charging current I in a charging path between a battery of an electric vehicle and a connector of a charging station during a charging process. In the method 1, a plurality of individual steps S 1 to S 11 are carried out one after the other in the sequence shown.In step S 1, a communication is set up between the battery of the electric vehicle and the connector or charging box of the charging station. For this purpose, a charging plug of the battery can be electrically conductively connected to the connector or the charging socket of the charging station.In step S 2, the first battery current I_BAT 1 and the first battery voltage U_BAT 1 of the battery of the electric vehicle are detected and stored. In step S 3, the first connector current I_EVSE 1 and the first connector voltage U_EVSE 1 of the connector or of the charging socket of the charging station are detected and stored.In step S 4, a comparatively small sample current I_PRBis set rapidly as charging current I in the charging station and the sample current I_PRBis waited for from settling. The sample current I_PRB is comparatively small and can be, for example, equal to 50 A.In step S 5, the second battery current I_BAT 2 and the second battery voltage U_BAT 2 of the battery of the electric vehicle are detected and stored. In step S 6, the second connector current I_EVE 2 and the second connector voltage U_EVE 2 of the connector or of the charging socket of the charging station are detected and stored.In step S 7, the reliability of the values acquired in steps S 2, S 3, S 5, S 6 is checked, since the reliability is the prerequisite for a correct measurement.In a substep S 7.1 of step S 7, it is checked whether the first connector current I_EVSE 1 has increased by approximately the requested value. If yes, the measurement is reliable. In a substep S 7.2 of step S 7, it is checked whether the first connector voltage U_EVSE 1 has not fallen. If yes, the measurement is reliable. In a substep S 7.3 of step S 7, it is checked whether the first connector voltage U_EVSE 1 is in the vicinity of the first battery voltage U_BAT 1, i.e. for example within a 10% tolerance. If yes, the measurement is reliable.If the reliability is given, then in step S 8, an electrical resistance R_CHARGE PATH of the charge path is calculated by means of the differential method. The following relationship is used for this purpose:In step S 9, the maximum safe charging current I_AVE is calculated from the presumed or known maximum permissible heat input Q_MAX into the charging path and the calculated R_LADE PATH. The following relationship is used for this purpose:In step S 10, the maximum safe charging current I_AVEis set as charging current I in the charging station. In step S 11, the charging current I is then regulated via the thermal capacity of the connector of the charging station until the end of the charging process. This can be done in a manner known to those skilled in the art.Steps S 1-S 10 are carried out once when the charging process is started. After the charging process is started, the charging current is carried out in a plurality of loops as described in step S 11.FIG. 2 shows time curves of an ACTUAL charging current I_EV_IST and a TARGET charging current I_EV_SOLL at the connector of the charging station and an ACTUAL temperature T_EV_IST of the connector of the charging station. The connector of the charging station must not exceed the maximum temperature T_EVE_MAX. The charging current I must then not exceed the maximum charging current I_MAX. The maximum charging current I_MAX is not known when starting the charging process.In a phase P0, all the contactors are closed. In the subsequent phase P 1, the ACTUAL charging current I_EV_IST of the connector is compensated according to mesh rule. In the time phase P 2, steps S 1-S 5 of method 1 are carried out and the electrical resistance R_CHARGE PATH of the charge path is determined. In the subsequent phase P 3, the steps S 6-S 11 are now carried out. In this case, the maximum safe charging current I_AVE is determined and set from the thermal consideration and the known maximum permissible heat input Q_MAX. Subsequently, the charging current I can be regulated in step S 11 in a manner known to the person skilled in the art. For this purpose, the thermal response of the connector can be waited for and a regulation with a new thermal capacity can take place.In method 1, the maximum safe charging current I_AVEis quickly determined in steps S 1-S 9 and set in step S 10. This eliminates conventional adjustment of the charging current I. Consequently, a rapid charging start with the maximally safe charging current I_AVEis possible and the setpoint temperature of the connector is quickly reached. Overall, the charging process can thereby be shortened and carried out particularly safely. It is also advantageous that the current limits or the current specifications change as rarely as possible and a DC current sensor is not necessary in the charging path.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedDE 10 2019 129 799 A1

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Claims

Method (1) for regulating a charging current (I) in a charging path between a battery of an electric vehicle and a connector of a charging station during a charging process, characterized in that, when the charging process is started: - the battery of the electric vehicle and the connector of the charging station are electrically conductively connected to one another, - a first battery current (I_BAT1) and a first battery voltage (U_BAT1) are detected at the battery and a first connector current (I_EVSE1) and a first connector voltage (U_EVSE1) are detected at the connector, a test current (I_PRB) is set as charging current (I) in the charging station and an end of a transient process of the test current (I_PRB) is waited for, a second battery current (I_BAT2) and a second battery voltage (U_BAT2) are detected at the battery and a second connector current (I_EV2) and a second connector voltage (U_EV2) are detected at the connector, an electrical resistance (R_LADE PATH) of the charging path is detected from the detected battery currents (I_BAT1, I_BAT2) and the detected connector voltages (U_EV1, U_EVE2), - a maximum safe charging current (I_AVE) is calculated from the known maximum permissible heat input (Q_MAX) into the connector and the calculated electrical resistance (R_LADE) of the charging path, and - the maximum safe charging current (I_AVE) is set as charging current (I) in the charging station.Method (1) according to Claim 1, characterized - in that before the calculation of the electrical resistance (R_CHARGE PATH) of the charge path, the reliability of the detected battery and connector currents (I_BAT1, I_BAT2, I_EVSE1, I_EVSE2) and of the detected battery and connector voltages (U_BAT1, U_BAT2, U_EVSE1, U_EVSE2) is checked, and - in that the calculation of the electrical resistance (R_CHARGE PATH) of the charge path takes place only when the detected battery and connector currents (I_BAT1, I_BAT2, I_EVSE 1, I_EVSE 2) and the detected battery and connector voltages (U_BAT 1, U_BAT 2, U_EVSE 1, U_EVSE 2) are reliable.Method (1) according to claim 2, characterised in that - the reliability is given when the first connector current (I_EVSE1) has increased by an expected value, and / or - the reliability is given when the difference between the second connector current (I_EVSE2) and the first connector current (I_EVSE1) is an expected value, and / or - the reliability is given when the first connector voltage (U_EVSE1) has not decreased, and / or - the reliability is given when the first connector voltage (U_EVSE1) and the second connector voltage (U_EVSE2) do not differ, and / or - the reliability is given, when the first connector voltage (U_EVE1) and the first battery voltage (U_BAT1) differ by not more than 20%, preferably by not more than 10%.Method (1) according to one of the preceding claims, characterized in that the electrical resistance (R_CHARGE PATH) of the charge path is calculated from a ratio of a difference of the second connector voltage (U_EV2) and the first connector voltage (U_EV1) and a difference of the second battery current (I_BAT2) and the first battery current (I_BAT1).Method (1) according to one of the preceding claims, characterized in that the maximum permissible heat input (Q_MAX) into the charging path corresponds to a product of the squared maximum safe charging current (I_AVE) and the electrical resistance (R_LADE) of the charging path, and the maximum safe charging current (I_AVE) is calculated therefrom.Method (1) according to one of the preceding claims, characterized in that after the starting of the charging process and the setting of the maximum safe charging current (I_AVE) as charging current (I), the charging current (I) is further regulated via the thermal capacity of the connector of the charging station.

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