DE102014216020A1 - Monitoring a power supply when charging an electrical energy storage of a motor vehicle - Google Patents

Abstract

A method for monitoring a power supply of a charger is described. In the method, a first voltage value of an electrical voltage applied to the charger is detected before a charging process is started. Furthermore, a charging process is started and a second voltage value of the electrical mains voltage applied to the charger is detected during the charging process. Based on the recorded voltage values, a network impedance is determined. A monitoring device and a charger are also described.

Description

The invention relates to a method for monitoring a power supply when charging an electrical energy storage device of a motor vehicle. Furthermore, the invention relates to a monitoring device. Finally, the invention relates to a charger.

Electric vehicles or plug-in hybrid vehicles have as energy storage a rechargeable battery that has to be charged depending on the type of battery via an electric charger with a specific charging characteristic. Electric chargers for charging batteries of electric vehicles or plug-in hybrid vehicles are connected to an AC mains when charging and receive the electric power for charging the battery from the AC mains. Such chargers are usually integrated in the electric vehicle and are connected to a charging station via a usually about 5 m long highly flexible charging cable and a plug for a household socket or a plug type 1 or type 2 or a CEE plug with a charging station. Depending on the vehicle type and power consumption, a 1-phase connection or a 3-phase connection is possible. The charging cable or supply line itself has a resistance at which a voltage drops during charging of the battery. The voltage drop leads to a heating of the supply line. If the supply line is not dimensioned accordingly, it can lead to defects or even accidents. In particular, in old or aged and non-standard installations or the use of extension cables or multiple sockets may occur at the line and contact resistances higher voltage drops and thus power losses, which can lead to overheating and even fires.

In DE 10 2010 003 470 A1 a method for determining the temperature change of a power supply of a charger is described. In the method, an electromagnetic input pulse is coupled into the power supply line. The input electromagnetic pulse can be reflected in the power supply line and the reflected part returns to the charger as a reflected electromagnetic output pulse. Subsequently, the pulse shape of the electromagnetic output pulse is determined. The determined pulse shape of the reflected electromagnetic output pulse is compared with a reference pulse shape. From the comparison of the two pulse shapes is finally concluded on a temperature change.

It is therefore an object of the invention to develop a method and a device with which a safe charging of batteries of electrical energy storage of motor vehicles is possible.

This object is achieved by the method according to claim 1, a monitoring device according to claim 7 and a charger according to claim 9.

In the method according to the invention for monitoring a power supply of a charger, a first voltage value of an electrical mains voltage applied to the charger is first detected before a charging process is started. The first measured value is therefore the mains voltage measured without load on a consumer. Then, the charging process is started and, at the same time, more precisely, during the increase of the charging current, a second voltage value of the electrical mains voltage applied to the charger is detected. Under load, the measured voltage value is reduced by the voltage drop across the power supply or the charging cable. Finally, a network impedance is detected on the basis of the detected voltage plants. The grid impedance provides information about the status of the power supply, so that countermeasures can be taken if the grid impedance is outside the nominal range. From the network impedance can be concluded that there is a power loss at the current charging current. Too high values of the network impedance indicate a defect or at least a deterioration in the conductivity of the charging cable.

The monitoring device according to the invention has a voltage detection unit which is set up to detect a first voltage value of a mains voltage applied to a charger before the start of a charging process and a second voltage value of the mains voltage applied to the charger during the charging process. It is also possible to measure several voltage values during the charging process. For example, voltage values of the mains voltage can be measured at predetermined regular time intervals. In addition, the monitoring device according to the invention has a determination unit which is set up to determine a network impedance on the basis of the detected voltage values. Furthermore, the monitoring device according to the invention comprises a comparison unit, which is set up to compare the determined network impedance with a maximum value of the impedance. The determination unit and comparison unit can work analog or digital. For example For example, the measured values can be processed analogously directly with the aid of operational amplifiers or similarly operating analog circuits, ie the determination unit and / or the comparison unit can be analogous data processing units. Alternatively, a conversion of the measured values into digital data by means of a digital / analog converter is possible. The digital-to-analog converter may, for example, be connected between the voltage detection unit and the detection unit or be part of one of the units, ie the voltage detection unit, the detection unit or the comparison unit, in which case the units connected downstream of the digital / analog converter operate digitally , Finally, the monitoring device according to the invention comprises an output interface, which is set up to output a warning message or a control command on the basis of a comparison result determined by the comparison unit. The units mentioned can also be implemented as a software solution in an existing hardware unit, so that the expense for the realization of the monitoring device according to the invention is minimized.

The charger according to the invention has the monitoring device according to the invention and a current control device. The current control device comprises a receiving unit that is configured to receive a control command transmitted by the monitoring device, and a control unit that is configured to reduce or limit the charging current in dependence on the control command.

The dependent claims relate to advantageous developments of the invention, in particular the possibility exists to develop the claims of one category according to the dependent claims of another category of claims.

In a preferred variant of the method according to the invention, the determined network impedance is compared with a predetermined maximum value of the network impedance. The maximum value may, for example, depend on certain specifics of the power supply, such as the cable diameter, the cable length and the line material. Furthermore, the maximum value of the impedance may also depend on a maximum power loss, a maximum charging current and a temperature correlated with the variables mentioned Charging cable are set at the maximum charging current. The maximum value can be set as the absolute maximum value based on these physical quantities.

In a particularly easy-to-implement embodiment of the method according to the invention, a warning message is issued to an operator if the maximum value of the impedance is exceeded. For example, in response to the alert, the operator may cancel the charging process or replace a power supply cable.

In an alternative embodiment of the method according to the invention, if the maximum value is exceeded, a charging current is reduced to a value at which a maximum power loss corresponding to the maximum value is not exceeded. For example, a maximum power loss due to the voltage drop across the charging cable as a threshold value can be determined in advance. Then, based on the voltage measurements and the associated currents, it may be determined if this maximum power dissipation is exceeded, and if so, the current flow when charging the battery is reduced or limited to a value below the power dissipation threshold becomes.

Alternatively, a control method can be used to reduce the charging current through the power supply, whereby a power loss is achieved below a predetermined maximum value of power loss. For example, a stepwise increase of the charging current can be carried out in each case by a predetermined value and the last increase of the charging current can be withdrawn if the maximum value of the power loss is exceeded. Eventually, the step size of the charging current increase can be adjusted afterwards, ie. H. can be reduced and the charging current can be increased again, if the maximum value of the power loss is exceeded.

The network impedance or the value of the network impedance results from the quotient of the difference between the first voltage value and the second voltage value and the charging current. The second voltage value can also be understood to be an arbitrary voltage value measured according to the second voltage value. The first voltage value is preferably measured not only before the start of the charging process, but also in the further course of the charging process, wherein short charge interruptions are made. This detects any changes in the quiescent voltage and prevents the value for the impedance from changing unnoticed.

In addition, the monitoring device can have a control command generation unit which generates a control command as a function of the comparison result which was determined by the comparison unit. The control command is forwarded to the output interface, which issues the control command.

In the drawing, an embodiment of the invention is shown. Show it:

1 a diagram illustrating the temporal behavior of the voltage applied to a charger of an electric vehicle and the charging current,

2 a flow chart showing a method for monitoring a power supply of a charger according to an embodiment of the invention,

3 a schematic representation of a monitoring device according to an embodiment of the invention,

4 a schematic representation of a charger according to an embodiment of the invention.

In 1 a diagram is shown which illustrates the time course of a voltage applied to a charger power supply voltage U and the course of a charging current I _L as a function of time. Before the start of the charging, at a time t ₁ , when the charging current I _L still has the value zero, the mains voltage U is at a value which is referred to below as the rest voltage U _rest . If the charging current I _L is subsequently increased, the impedance of the charging cable of the charging device and of the supply lines causes a drop in the mains voltage U applied to the charger, which becomes all the stronger the greater the charging current I _L. For example, U _network is measured at the time t ₂ a measured compared to that at time t _1, voltage U _resting reduced voltage. If the charging current is constant over time, the mains voltage applied to the charger is also constant over time.

In 2 is a procedure 200 for monitoring a power supply of a charger according to an embodiment of the invention. At the step 2.I Before the start of the charging process or in a short charge break a _rest voltage U _rest , ie measured before the start or in a charge break in the absence of charging current to the charger mains voltage. Subsequently, at the step 2.II the charge current increases slowly. For example, the charging current I _{L is} increased by a predetermined value I _s . Illustrated clearly, for example, a step size I _{s is set in} advance, with the charging current I _L stepwise, ie once in the step 2.II and at each loop pass in the step 2.VII of the described method is increased. The mentioned loop comprises the steps 2.VII and 2.VIII , The charging current I _L is thus (n + 1) * I _s after n loop _passes . At the step 2.III a mains voltage U _{network is} measured. The mains voltage depends on the impedance of the charging cable as well as the height of the current charging current I _l . At the step 2.IV the network impedance Z _Netz or the impedance of the charging cable is determined. It results as follows:

At the step 2.V it is determined whether the determined value of the network impedance Z _network exceeds a maximum value Z _max . The maximum value Z _max results from the maximum power loss P _max to be tolerated. The relationship between the maximum tolerable power dissipation P _max and the maximum value Z _{max of} the impedance is as follows: P _max = I 2 / L, max * Z _max (2)

The maximum value Z _max is therefore dependent on the strength of a predetermined maximum charging current I _{L, max} . If the determined value of the network impedance Z _net exceeds the maximum value Z _max , which is in 2 marked with "j", then at the step 2.VI the maximum value of the charging current I _{L, max} newly determined according to the following formula:

Subsequently, the step becomes 2.VII passed. If the determined value of the network impedance Z _net does not exceed the maximum throw Z _max , which is in the 2 marked with "n", goes directly to the step 2.VII passed over and the charging current I _L further increased by the predetermined value I _s . The following will be at the step 2.VIII determines whether the maximum value of the charging current I _{L, max is} reached. If that is not the case, what in 2 marked with an "n" becomes the step 2.VII returned and the charging current I _L further increased. Will at the step 2.VIII determines that the maximum value of the charging current I _{L, max is} reached, which is in 2 is marked with a "j", then at the step 2.IX determines whether a criterion for completion of the charging is satisfied, for example, it is determined whether a predetermined amount of energy or charging time is reached. If that's the case, what's in 2 marked with a "j" is at the step 2.X the charging process is finished. If the mentioned criterion is not met, what is in

2 marked with "n", the process goes to step 2.XI continued. At the step 2.XI it is determined whether a predetermined time interval has elapsed after the charging process is interrupted and a new measurement of the rest voltage U _rest should be performed. If that is not the case, what in 2 marked with "n", then becomes the step 2.IX returned. If the predetermined time interval has elapsed, which is in 2 marked with "j" is at the step 2.XII charging stops and it is determined in the following if the value of the open circuit voltage has changed U _peace. If that's the case, what's in 2 marked with a "j", then becomes the step 2.II returned and the following steps are performed with the newly determined rest voltage U _rest . Has not changed the value of the rest voltage U _rest , what in 2 marked with an "n", then becomes the step 2.VII returned and the loading process continued. Alternatively, those in the steps 2.V and 2.VI determined values Z _max and I _{L, max can} also be read from a characteristic field, which in 3 is shown.

In 3 is the maximum charging current I _{L, max applied} as a function of the network impedance Z _network . Furthermore, the maximum value of the network impedance Z _{max is} plotted, up to which no change of the charging current I _L must be made. If the value of the network impedance Z _network is greater than Z _max, the maximum load current I _{L has, max} adjusted according to the determined value of the line impedance Z _AC, ie reduced.

In 4 is a monitoring device 40 illustrated according to an embodiment of the invention. The monitoring device 40 has a voltage detection unit 41 on. The voltage detection unit measures the voltage applied to the charger mains voltage U _network both before the start of charging when the value of the mains voltage U _{network is} at the value U _rest , as well as during charging of the battery of the vehicle. The monitoring device 40 also has an investigative unit 42 which, on the basis of the determined voltage values U _net and U _rest as well as the charging current I _{L, determines} a network impedance Z _net . Furthermore, the monitoring device 40 also a comparison unit 43 which compares the determined network impedance Z _network with a maximum value Z _max . In addition, the monitoring device 40 a control command generation unit 44 comprising a control command SB in response to the comparison result obtained by the comparison unit 43 was determined generated. Finally, the monitoring device comprises an output interface 45 that outputs the generated control command SB.

In 5 is a charger 50 according to an embodiment of the invention shown schematically. The charger 50 includes the in 3 shown monitoring device 40 and a power control device 51 , The power control device 51 includes a receiving unit 52 which control commands SB from the monitoring device 40 receives. Furthermore, in the charger 51 a control unit 53 set, which controls the charging current I _L in response to a detected control command SB. For example, the charging current I _{L is} based on one of the monitoring device 40 generated command SB reduced or limited.

It is finally pointed out once again that the method illustrated in the figures or the monitoring device described in detail and the charger described in detail are merely exemplary embodiments which can be modified in many ways. Furthermore, for the sake of completeness, it is also pointed out that the use of indefinite Article "one, one" does not exclude that the characteristics in question may also exist multiple times. Similarly, the term "unit" does not exclude that it also consists of several subunits.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102010003470 A1 [0003]

Claims (9)

Procedure ( 200 ) for monitoring a power supply of a charger ( 40 ), comprising the steps of: - detecting a first voltage value (U _rest ) of an electrical mains voltage applied to the charger before a charging process is started, - starting the charging process and detecting a second voltage value (U _network ) of a voltage applied to the charger during the charging process electrical mains voltage, - Determining a _grid impedance (Z _grid ) on the basis of the acquired voltage values (U _Rest , U _Grid ). Procedure ( 200 ) according to claim 1, wherein the determined network impedance (Z _network ) is compared with a predetermined maximum value (Z _max ). Procedure ( 200 ) according to claim 2, wherein, if the maximum value (Z _max ) is exceeded, a warning message is issued to an operator. Procedure ( 200 ) according to claim 2 or 3, wherein, if the maximum value (Z _max ) is exceeded, a charging current (I _L ) is reduced to a value at which a predetermined maximum value (P _max ) of the power loss is not exceeded. Procedure ( 200 ) according to one of claims 2 to 4, wherein, if the maximum value (Z _max ) is exceeded, the charging process is terminated. Procedure ( 200 ) according to one of claims 1 to 5, wherein the network impedance (Z _network ) is determined as a quotient of the difference between the first voltage value (U _rest ) and the second voltage value (U _network ) and a charging current (I _L ). Monitoring device ( 40 ), comprising: - a voltage detection unit ( 41 ), which is set up to detect a first voltage value (U _rest ) of a voltage applied to a charger (U) before the start of a charging process and a second voltage value (U _network ) applied to the charger mains voltage (U) during the charging process , - a determination unit ( 42 ), which is set up to determine a network impedance (Z _network ) on the basis of the acquired voltage values (U _rest , U _network ), - a comparison unit ( 43 ), which is set up to compare the determined network impedance (Z _network ) with a maximum value (Z _max ), - an output interface ( 45 ) configured to output a warning message or a control command (SB) based on a comparison result determined by the comparing unit. Monitoring device ( 40 ) according to claim 7, wherein the control command (SB) comprises a command for switching off the charger or a command for limiting or reducing a charging current (I _L ). Charger ( 50 ), comprising: - a monitoring device ( 40 ) according to one of claims 7 or 8, - a current control device ( 51 ) with a receiving unit ( 52 ), which is adapted to receive a control command (SB) transmitted by the monitoring device, and - a control unit ( 53 ) arranged to reduce or limit the charging current (I _L ) in response to the control command (SB).

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