DE102012008626A1 - Method and arrangement for error detection in a pre-charging process - Google Patents

Abstract

The invention relates to a method for fault detection of a precharging process for an electrical load (8) having a capacitive element, in particular an intermediate circuit capacitor (6), comprising the following steps: - starting (S2) the precharging operation by closing a circuit through the electrical load (8) by means of a precharge circuit (10); - detecting (S3) an indication of a current flow through the precharge circuit (10); and - detecting (S4) an error if the indication of the current flow does not fall below a predetermined threshold within a predetermined period of time after the start of the precharge operation.

Description

Technical area

The invention relates to electric drive systems, in particular for driving electric or hybrid vehicles. Furthermore, the present invention relates to measures for performing switching operations for connecting battery systems.

State of the art

Electric or hybrid vehicles usually have as a source of energy a battery system, in particular a high-voltage battery system with Li-ion cells, a fuel cell or the like. Such energy sources often have a very low internal resistance, which leads to very high currents when the battery system is connected to a load buffered with a DC link capacitance, as is the case, for example, with a traction network with one or more electric motors. This is especially true when the DC link capacity of the power electronics of the traction network is completely discharged. Such a current pulse can lead to excessive loading, damage or destruction of components.

One way to reduce such current spikes is to provide a precharge circuit as is known from the references DE 10 2009 012 901 A1 . DE 102 20 255 A1 . DE 10 2009 053 712 A1 and DE 10 2007 048 620 A1 is known. Such precharging circuits comprise a series connection of a switching element and a precharge resistor, which are arranged in parallel with a main switch, such as a relay, contactor or the like. Prior to the switching of the main switch, the switching element of the precharge circuit is closed, so as to be able to perform a charging of the DC link capacitance by the precharging resistor with a lower current.

During pre-charging, appreciable currents can flow through the precharging resistor, in particular in the event of a short circuit within the traction network, which can lead to damage in the precharging circuit or a component of the traction network. From the DE 10 2007 048 620 A1 For example, when connecting a high voltage power source, it is known to first close the switch of the precharge circuit and then measure the voltage applied to a high voltage power load. The voltage applied to the high voltage power load is used to determine if there is a short circuit or open circuit. When a deviation of the voltage applied to the high voltage power load is detected, the high voltage power source is disconnected to protect the vehicle and its users.

From the DE 102 20 255 A1 It is known that a Vorladefehler is signaled when the change in voltage over time is less than 2 V in 10 seconds, so that a charging process, the DC link capacity by decoupling the Vorladeschaltschützes (precharge switch) is terminated. In particular, in the case of short-circuit detection, it must be checked in the above cases whether the applied voltage falls below a certain voltage threshold value, this check being activated only if pre-charging by means of the pre-charging circuit is active. However, a realization of such a query is complicated and it is therefore an object of the present invention to carry out a simplified determination of a short circuit in the traction network.

Disclosure of the invention

This object is achieved by the arrangement for detecting an error in an electrical load a traction network of a motor vehicle according to claim 1 and by the motor system and the method according to the independent claims.

Further advantageous embodiments of the present invention are specified in the dependent claims.

• – Starten des Vorladevorgangs durch Schließen eines Stromkreises durch die elektrische Last mithilfe einer Vorladeschaltung;
• – Erfassen einer Angabe über einen Stromfluss durch die Vorladeschaltung; und
• – Erkennen eines Fehlers, wenn die Angabe über den Stromfluss nicht innerhalb einer vorbestimmten Zeitdauer nach dem Starten des Vorladevorgangs unter einen vorgegebenen Schwellenwert fällt.

According to a first aspect, a method for error detection in a precharging process for an electrical load with a capacitive element, in particular an intermediate circuit capacitor, is provided, which comprises the following steps:

• - starting the precharge by closing a circuit by the electrical load by means of a precharge circuit;
• - detecting an indication of a current flow through the precharge circuit; and
• Detecting an error if the indication of the current flow does not fall below a predetermined threshold value within a predetermined period of time after the start of the pre-charging process.

An idea of the above method is to define a current threshold for a current flow through the precharge circuit, wherein an error is detected when the current flow through the precharge circuit does not fall below the current threshold within the predetermined time period. Thus, it is possible to detect a fault in an electrical load, wherein before a low-resistance connection between a power source and the electrical load, a precharge with a pre-charge resistance is performed first to charge a capacitive element of the electrical load. If the current value does not reach the current value indicated by the current threshold within the predetermined period of time, this can be interpreted as the presence of a low-impedance current path in the electrical load. This is especially the case when there is a short circuit in the electrical load.

Furthermore, as the indication of the current flow, a voltage on a precharge resistor of the precharge circuit can be detected.

According to one embodiment, the precharge circuit may be disposed between a power source and the electrical load, wherein as the indication of the current flow, a voltage difference between a power source voltage of the power source and a voltage on the electrical load is detected.

In particular, upon detection of the fault, the pre-charging operation can be interrupted by opening the circuit.

Furthermore, at least after the start of the precharge process, a temperature in the precharge circuit can be detected and a further fault can be detected if the detected temperature exceeds a predetermined temperature threshold.

It can be provided that, upon detection of the further fault, the precharging process is interrupted by opening the electric circuit and a new precharging process is not started before the temperature in the precharge circuit is cooled below the predetermined temperature threshold.

• – eine Einrichtung zum Erfassen einer Angabe über einen Stromfluss durch die Vorladeschaltung;
• – eine Steuereinheit, die ausgebildet ist, um den Vor ladevorgang durch Schließen eines Stromkreises durch die elektrische Last mithilfe einer Vorladeschaltung zu starten; und einen Fehler zu erkennen, wenn die Angabe über den Stromfluss nicht innerhalb einer vorbestimmten Zeitdauer nach dem Starten des Vorladevorgangs unter einen vorgegebenen Schwellenwert fällt.

According to a further aspect, an arrangement for fault detection in a precharging process for an electrical load with a capacitive element, in particular an intermediate circuit capacitor, is provided, comprising:

• - means for detecting an indication of current flow through the precharge circuit;
• A control unit configured to start the pre-charge operation by closing a circuit by the electrical load by means of a precharge circuit; and detect an error if the indication of the current flow does not fall below a predetermined threshold within a predetermined period of time after the start of the precharge operation.

Furthermore, the above arrangement may be provided with the precharge circuit, wherein the precharge circuit comprises a series connection of a precharge switch and a precharge resistor and is disposed between an electric power source and the electric load.

Brief description of the drawings

Preferred embodiments of the present invention will be explained in more detail with reference to the accompanying drawings. Show it:

1 a schematic representation of a system for operating a traction network in a motor vehicle;

2 a flowchart for illustrating a method for detecting an electrical fault in the traction network.

Description of embodiments

1 shows a system 1 for driving a motor vehicle with an electrical load, such. B. a traction network 2 and a power source system 3 , The energy source system 3 includes a battery unit as the power source 4 ,

The battery unit 4 has battery cells 41 and a first and a second battery unit connector 42 . 43 on to electrical energy via a switching unit 5 to the traction network 2 provide. The switching unit 5 has a first main switch 51 for connecting the first battery unit connector 42 with a first power source connection 31 and a second main switch 52 for connecting the second battery unit port 43 with a second power source connection 32 on. The main switches may be formed by or include a semiconductor switch or a relay or contactor.

The traction network 2 is at the first power source connection 31 and at the second power source terminal 32 connected, so that this is supplied with electrical energy. The traction network 2 includes a DC link capacitor 6 and a driver circuit 7 to operate a load 8th , such as an electronically commutated electrical machine.

When switching the main switch 5 for providing electrical energy in the traction network 2 must depend on the state of charge of the DC link capacitor 6 initially a charge of the DC link capacitor 6 on the from the power source system 3 provided power source voltage done. This can be done in completely discharged state of the DC link capacitor 6 due to a low internal resistance of the battery unit 4 lead to a high current flow.

Because such a high current flow leads to a damaging load on components in both the power source system 3 as well as in the traction network 2 Therefore, is to provide electrical energy to the traction network 2 initially provided a pre-charge. This is a precharge circuit 10 parallel to the first main switch 51 connected. The precharge circuit 10 includes a precharge switch 11 , For example, in the form of a semiconductor switch or a relay or a contactor, and a pre-charge resistor connected in series 12 ,

The precharge resistor 12 is dimensioned so that the DC link capacitor 6 when closing the precharge switch 11 can be fully charged within a predetermined period of time. At the same time, the pre-charging resistor is used 12 to do this, the current flow out of the battery cells 4 into the traction network 2 to limit.

The switch-on process, in which electrical energy to the power source system 3 is created by a control unit 15 controlled. The control unit 15 can according to an external switch-on initially the second main switch 52 and the precharge switch 11 in a suitable manner to close, so that a current flow through the power source terminals 31 . 32 is effected.

Furthermore, the control unit performs 15 the method for detecting an error, which is described below with reference to the flowchart of 2 will be described in more detail.

In the interrogation step S1, it is first queried whether a connection of the battery unit 4 with the traction network 2 should be done to provide this electrical energy. If this is the case (alternative: yes), the method is continued with step S2, otherwise (alternative: no), the query of step S1 is repeated until a connection of the energy source 3 with the traction network 2 is requested.

In step S2, controlled by the control unit 15 , the precharge switch 11 and the second main switch 52 closed, allowing a current flow through the pre-charge resistor 12 into the traction network 2 takes place, wherein the DC link capacitor 6 is charged.

In a step S3, the voltage becomes above the precharge resistance 12 tapped and the control unit 15 an appropriate indication supplied. This can be done by a separate or in the control unit 15 integrated analog-to-digital converter.

Once it is determined in the subsequent step S4 that the voltage drop across the precharge resistor 12 within a predetermined period of time falls below a predetermined voltage threshold (alternative: yes), the pre-charge is recognized as successful and the process continues with step S5. Instead, it determines that the voltage is above the precharge resistance 12 is not within the predetermined period of time falls below the voltage threshold (alternative: no), the method proceeds to step S6.

That the voltage drop across the pre-charge resistor 12 within a predetermined period of time falls below a predetermined voltage threshold, is determined by means of a in the control unit 15 arranged timer. The timer signals the expiration of the predetermined period of time after switching on the pre-charge switch 11 , so the voltage across the precharge resistor 12 detected and compared with the voltage threshold. Below the voltage above the pre-charge resistance 12 the voltage threshold, the process proceeds to step S6.

In step S5, upon detection of proper precharge, the DC link capacity becomes 6 the not yet closed first main switch 51 closed.

In step S6, when abnormal precharge is detected, the DC link capacity becomes 6 the precharge is aborted as unsuccessful because there must be a fault, such as a short circuit within the traction network 2 , This is the preload switch 11 and / or the second main switch 52 opened and signaled in step S7 a corresponding error.

Instead of measuring the voltage across the precharge resistor 12 can also be another current measurement by the Vorladeschaltung 10 respectively.

Alternatively or additionally, it can be checked whether the voltage difference between the battery unit 4 , ie the voltage across the battery unit U _Batt , and the intermediate circuit voltage, ie the voltage of the DC link capacitor 6 , changed as soon as the preload process is started. The precharge is recognized as successful if the voltage difference falls below a voltage difference threshold within a further predetermined period of time. Otherwise, an error is detected during the pre-charging process.

Furthermore, using a temperature sensor, the temperature of the pre-charging resistor 12 recorded and depending on a warming of the Vorladewiderstands 12 during the precharge process, an error is detected when the temperature of the precharge resistor 12 rises above a threshold temperature before the predetermined time has expired.

LIST OF REFERENCE NUMBERS

1

system

2

traction power

3

Energy System

31, 32

Energy Connections

4

battery unit

41

battery cells

42, 43

Battery cell terminals

51, 52

first, second main switch

6

Link capacitor

7

driver circuit

8th

electrical load

10

precharge circuit

11

precharge

12

precharging

15

control unit

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 102009012901 A1 [0003]
• DE 10220255 A1 [0003, 0005]
• DE 102009053712 A1 [0003]
• DE 102007048620 A1 [0003, 0004]

Claims (8)

Method for fault detection of a precharging process for an electrical load ( 8th ) with a capacitive element, in particular a DC link capacitor ( 6 ), comprising the following steps: - starting (S2) the pre-charging process by closing a circuit by the electrical load ( 8th ) by means of a precharge circuit ( 10 ); Detecting (S3) an indication of a current flow through the precharge circuit ( 10 ); and - detecting (S4) an error if the indication of the current flow does not fall below a predetermined threshold within a predetermined period of time after the start of the precharge operation. The method of claim 1, wherein as the indication of current flow, a voltage on a pre-charge resistance ( 12 ) of the precharge circuit ( 10 ) is detected. Method according to claim 1, wherein the precharge circuit ( 10 ) between an energy source ( 4 ) and the electrical load ( 8th ), wherein, as the indication of the current flow, a voltage difference between a power source voltage of the power source (FIG. 4 ) and a voltage at the electrical load ( 8th ) is detected. Method according to one of claims 1 to 3, wherein upon detection of a fault, the pre-charging is interrupted by opening the circuit. Method according to one of claims 1 to 4, wherein at least after the start of the pre-charging a temperature in the Vorladeschaltung ( 10 ) is detected and another error is detected when the detected temperature exceeds a predetermined temperature threshold. The method of claim 5, wherein upon detection of the further fault, the precharge is discontinued by opening the circuit and a recharge is not started before cooling the temperature in the precharge circuit below the predetermined temperature threshold. Arrangement for fault detection of a precharging process for an electrical load ( 8th ) with a capacitive element, in particular a DC link capacitor ( 6 ), comprising: means for detecting an indication of current flow through a precharge circuit ( 10 ); A control unit ( 15 ), which is designed to prevent the precharging operation by closing a circuit by the electrical load by means of the precharge circuit ( 10 ) to start; and detect an error if the indication of the current flow does not fall below a predetermined threshold within a predetermined period of time after the start of the precharge operation. Arrangement according to Claim 7, with the precharge circuit ( 10 ), wherein the precharge circuit ( 10 ) a series connection of a precharge switch ( 11 ) and a pre-charge resistance ( 12 ) and between an electrical energy source ( 4 ) and the electrical load ( 8th ) is arranged.

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