DE102016220541A1 - Method for operating a drive system for a vehicle - Google Patents

Abstract

The invention relates to a method for operating a drive system (10) for a vehicle, comprising a battery (14) for storing electrical energy, a DC link capacitor (16) and at least one main switch (21, 22), by means of which the DC link capacitor (16) in parallel switchable to the battery (14) and from the battery (14) is separable. The method comprises the steps of precharging the intermediate circuit capacitor (16), closing the at least one main switch (21, 22) and measuring an electrical charge which flows through the at least one main switch (21, 22) in a defined time interval.

Description

The invention relates to a method for operating a drive system for a vehicle, wherein the drive system comprises a battery for storing electrical energy, an intermediate circuit capacitor and at least one main switch, by means of which the intermediate circuit capacitor is switchable parallel to the battery and separable from the battery.

State of the art

It is becoming apparent that in the future, especially in vehicles such as electric vehicles (EV), hybrid vehicles (HEV) and plug-in hybrid vehicles (PHEV), more and more electrical and electronic systems are being used that combine new energy storage technologies with electric drive technology. Such vehicles have drive systems for controlling an electric drive motor, which serves to drive the vehicle.

A generic drive system includes, for example, a rechargeable battery for storing electrical energy, which comprises a plurality of battery cells, and power electronics. The drive motor is usually designed as a three-phase electric motor and controlled by the power electronics. The power electronics is designed, for example, as an inverter, which is also referred to as an inverter. In the inverter, a DC voltage supplied by the battery is converted to a three-phase AC voltage.

A generic drive system further comprises a main switch, by means of which the battery can be switched to the rest of the drive system and switched off from the rest of the drive system. The main switch is designed in particular as a contactor, so as a controllable electromechanical relay.

To stabilize the DC voltage supplied by the battery, an intermediate circuit capacitor is provided, which is connected in parallel to inputs of the power electronics. By means of the main switch thus the DC link capacitor can be connected in parallel with the battery and disconnected from the battery.

The main switch has electrical contacts which are subject to wear. Such wear manifests itself, for example, by sticking of the contacts, whereby the main switch can not be securely closed and opened. The main switch should therefore be replaced before such failure due to wear of the contacts occurs. Such wear is particularly dependent on the switching current, that is, the current flowing through the contacts immediately after closing the main switch.

From the US 2013/0054071 A1 For example, a monitoring device for a battery module is known, which has an integrated circuit (IC). The integrated circuit includes a charging counter circuit which measures the amount of power consumed by the integrated circuit. To this end, the charging counter circuit includes a module configured to measure the power consumption of the integrated circuit during a time interval.

The document US 2013/0066575 A1 discloses a voltage measurement circuit. The circuit also includes a charge counter, which has means for measuring current as well as for integral formation. To measure a voltage between two terminals of a battery while the current flow is measured by a measuring resistor, the measured current flow is integrated, and from the integrated value, an average value is calculated. The voltage is then determined from the calculated mean value and value of the measuring resistor.

Disclosure of the invention

A method is proposed for operating a drive system for a vehicle, wherein the drive system comprises a battery for storing electrical energy, an intermediate circuit capacitor and at least one main switch. By means of the main switch, the DC link capacitor can be connected in parallel with the battery and disconnected from the battery. The inventive method comprises several steps, which are explained below.

In a step a), the intermediate circuit capacitor is pre-charged. In this case, an electrical charge is applied to the DC link capacitor by applying an electrical voltage to the DC link capacitor. The pre-charging takes place in a period of less than a second.

After precharging, a capacitor voltage, which approximately corresponds to the voltage of the battery, is applied to the intermediate circuit capacitor.

In a subsequent step b), the at least one main switch is closed. The voltage of the battery is at this time still slightly higher than the capacitor voltage of the DC link capacitor. Therefore, now a switching current flows from the battery through the Main switch to the DC link capacitor. As a result, an electric charge from the battery flows to the link capacitor, and the capacitor voltage of the link capacitor is thus further adjusted to the voltage of the battery.

In a subsequent step c), an electrical charge is then measured, which flows through the at least one main switch from the battery to the intermediate circuit capacitor in a defined time interval. The measured electrical charge is dependent on the time course of the switching current.

Advantageously, the drive system of the vehicle further includes a precharge resistor and a precharge switch. In this case, in the aforementioned step a), the intermediate circuit capacitor is precharged by the precharge switch is closed, whereby a precharge current flows from the battery to the intermediate circuit capacitor. The precharge resistor limits the amount of precharge current.

However, the DC link capacitor does not necessarily have to be precharged by the mentioned battery of the drive system. It is also conceivable that another battery in the vehicle or outside the vehicle is used to pre-charge the DC link capacitor.

Preferably, the precharge resistor and the precharge switch are connected in parallel to the at least one main switch. The precharge current thus flows parallel to the main switch. After closing the main switch, the switching current flows through the main switch, which has a significantly lower resistance than the pre-charging resistor and thus bridges it. Advantageously, the precharge switch is then opened after closing the at least one main switch in step b). Thus, the battery can be turned off later by opening the main switch.

The drive system preferably comprises a further main switch. For example, a first main switch is connected to a positive terminal of the battery, and a second main switch is connected to a negative terminal of the battery. In this case, the other main switch is first closed before the intermediate circuit capacitor is pre-charged in step a).

According to an advantageous embodiment of the invention, in step c) the electrical charge is measured by integrating a switching current flowing through the at least one main switch over the defined time interval. This means that measured values of the switching current are measured, and the said measured values of the switching current are then integrated over the defined time interval.

In particular, the switching current is integrated by sampling the switching current and thereby adding current samples obtained to a charge value. The charge value thus obtained represents a measure of the electrical charge that has flowed through the at least one main switch in the defined time interval.

In order to determine the charge value and thus the electrical charge which has flowed through the at least one main switch in the defined time interval, it is advisable to obtain a sufficiently high number of current sampled values, that is to sample the switching current with a sufficiently high sampling frequency. It has proven to be advantageous if the switching current is sampled at a sampling frequency of at least 20 kHz.

According to a preferred embodiment of the invention, step a), step b) and step c) are carried out repeatedly. The charge values obtained in each case are added to a total charge value. Particularly preferably, step a), step b) and step c) are always executed when the drive system is switched on and the vehicle is started.

The total charge value represents a measure of the electrical charge that has flowed through the at least one main switch in the said plurality of time intervals, preferably after each start of the vehicle. Thus, the total charge value is also a measure of the sum of the currents that have flowed through the at least one main switch in the said time intervals.

According to a preferred embodiment of the invention, the total charge value thus obtained is compared with a predetermined threshold value. The threshold is an empirical value, which represents a measure of the wear of the contacts of the main switch. In particular, the said threshold value is predetermined in such a way that, when the threshold value is reached, an exchange of the main switch is proposed in order to prevent a failure of the main switch by gluing the contacts.

The method according to the invention advantageously finds use in an electric vehicle (EV), in a hybrid vehicle (HEV) or in a plug-in hybrid vehicle (PHEV).

Advantages of the invention

The inventive method are currents and electrical charges, the flowing directly after closing the main switch through the contacts of the main switch, very accurately detectable. The wear of the contacts of the main switch is thus very accurately determined. In particular, a failure of the main switch can be predicted in good time before sticking of the contacts, and thus a timely replacement of the main switch can be proposed.

For carrying out the method, measuring devices and control units already present in the drive system and in the vehicle can be used. So there are no costs for additional hardware. The said measuring devices and control units have powerful analog-to-digital converters and arithmetic unit and memory. As a result, the sampling of the switching current, the integration and the addition as well as the comparison with the threshold value are relatively simple but nevertheless precise.

list of figures

• 1 eine schematische Darstellung eines Antriebssystems und
• 2 einen beispielhaften Zeitverlauf von Strom und Kondensatorspannung des Antriebssystems aus 1,
• 3 ein beispielhaftes Zeitdiagramm des Antriebssystems aus 1.

Embodiments of the invention will be explained in more detail with reference to the drawings and the description below. Show it:

• 1 a schematic representation of a drive system and
• 2 an exemplary time course of current and capacitor voltage of the drive system 1 .
• 3 an exemplary timing diagram of the drive system 1 ,

Embodiments of the invention

In the following description of the embodiments of the invention, the same or similar elements are denoted by the same reference numerals, wherein a repeated description of these elements is dispensed with in individual cases. The figures illustrate the subject matter of the invention only schematically.

In 1 is a drive system 10 shown schematically for a vehicle. The drive system 10 includes a battery 14 which has several battery cells 2 having. In the present case are the battery cells 2 connected in series. The drive system 10 further includes an inverter 30 for driving a drive motor, not shown here. The inverter 30 converts the battery 14 DC voltage supplied to an AC voltage.

The drive system 10 further comprises an intermediate circuit capacitor 16 , The DC link capacitor 16 is parallel to the inputs of the inverter 30 connected. Above the DC link capacitor 16 drops a capacitor voltage U from.

The drive system 10 also includes a first main switch 21 which is connected to a positive terminal of the battery 14 as well as with the DC link capacitor 16 connected is. Also includes the drive system 10 a second main switch 22 which is connected to the negative terminal of the battery 14 and with the DC link capacitor 16 connected is.

The drive system 10 also includes a precharge switch 20 and a precharge resistor 25 , The precharge switch 20 and the pre-charge resistance 25 are connected to each other in series and are parallel to the first main switch 21 connected.

The drive system 10 also includes a measuring resistor 34 which is present between the negative terminal of the battery 14 and the second main switch 22 is arranged. The measuring resistor 34 is by means of test leads 36 with a control unit 32 connected.

The control unit 32 includes an integrated circuit, such as a Freescale MC33771 , The integrated circuit is set up, one on the measuring resistor 34 to measure falling voltage. By means of the voltage thus measured is a through the measuring resistor 34 flowing current I can be determined. The integrated circuit in this case has a charge counter, which is set up, the said at the measuring resistor 34 to sample the falling voltage with a sampling frequency of 20 kHz and to integrate the values obtained or to add them together.

2 shows an exemplary time course of the by the measuring resistor 34 flowing current I and the above the DC link capacitor 16 sloping capacitor voltage U of the drive system 10 out 1 during the execution of the method according to the invention. 3 shows an exemplary timing diagram of the state of several components of the drive system 10 out 1 during the execution of the method according to the invention. The inventive method will now be described with reference to the illustration in the 2 and 3 explained.

part 3a shows the state of the second main switch 22 , The second main switch 22 will be closed first. Subsequently, at a start time t0, the precharge switch becomes 20 closed. Then a pre-charge current flows 53 through the pre-charge resistor 25 to the DC link capacitor 16 , The state of the precharge switch 20 is in the part 3b shown.

After closing the precharge switch 20 a precharge current flows 53 from initially about 10 A through the precharge resistance 25 , The said value for the precharge current 53 results from an exemplary battery voltage of 400 V and a precharge resistor 25 with a value of about 40 Ω. By the flow of the precharge current 53 becomes the DC link capacitor 16 charged, whereby the capacitor voltage U increases. With increasing capacitor voltage U, the voltage difference between the battery 14 and the DC link capacitor 16 smaller. This will also cause the precharge current 53 smaller.

At a first time t1 is the precharge current 53 significantly decreased, and the capacitor voltage U has grown to a value of, for example, 350 volts. The precharge switch 20 is reopened at the first time t1.

At the first time t1 becomes the first main switch 21 closed. Then a switching current flows 52 through the first main switch 21 to the DC link capacitor 16 , The state of the first main switch 21 is in part 3c shown.

Immediately before closing the first main switch 21 at the first time t1, a current measurement is made in the integrated circuit of the control unit 32 started. For this purpose, the charge counter of the integrated circuit by means of a in part 3d Reset RESET signal shown reset.

The current measurement is in part 3e shown. The current measurement starts at the first time t1 and is during a time interval 51 performed, which ends at a second time t2. During the time interval 51 the capacitor voltage U rises at the DC link capacitor 16 continues and reaches a value of approximately 400 V, which is the voltage of the battery 14 equivalent. The switching current 52 initially reaches a relatively high value of about 600 A. The switching current 52 falls during the time interval 51 clearly off.

After the second time t2, at which the current measurement ends, the charge counter of the integrated circuit by means of in part 3d reset signal shown again reset.

During the said time interval 51 an electric charge flows 50 from the battery 14 through the first main switch 21 on the DC link capacitor 16 , The said electrical charge 50 is the integral of the switching current 52 over the time interval 51 , In the illustration after 2 corresponds to the electric charge 50 the hatched area below the switching current 52 ,

The integrated circuit in the control unit 32 scans the switching current 52 with a sampling frequency of 20 kHz. As a result, current samples are obtained in the integrated circuit, which are then added to a charge value. Said addition of the obtained current samples corresponds mathematically to an integration of the switching current 52 over the time interval 51 , Thus, at the second time t2, so after the expiration of the time interval 51 , the electric charge 50 , which on the DC link capacitor 16 has flowed, measured and stored in the integrated circuit.

The described method is repeated every time the vehicle is started. The charge values obtained in each case are added to a total charge value. The total charge value also becomes in the integrated circuit of the control unit 32 stored. Furthermore, after each addition of a further charge value, the existing total charge value is compared with a predetermined threshold value. If the total charge value exceeds the predetermined threshold, a corresponding warning is issued on a display of the vehicle, after which replacement of the first main switch is recommended.

The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, within the scope given by the claims a variety of modifications are possible, which are within the scope of expert action.

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

• US 2013/0054071 A1 [0007]
• US 2013/0066575 A1 [0008]
• MC 33771 [0034]

Claims (10)

Method for operating a drive system (10) for a vehicle, comprising a battery (14) for storing electrical energy, an intermediate circuit capacitor (16) and at least one main switch (21, 22), by means of which the intermediate circuit capacitor (16) is connected in parallel with the battery ( 14) and separable from the battery (14), comprising the following steps: a) precharging the intermediate circuit capacitor (16), b) closing the at least one main switch (21, 22), c) measuring an electrical charge (50) which flows in a defined time interval (51) through the at least one main switch (21, 22). Method according to Claim 1 wherein the drive system (10) further comprises a precharge resistor (25) and a precharge switch (20), and wherein in step a) the link capacitor (16) is precharged by closing the precharge switch (20), thereby generating a precharge current (53). from the battery (14) to the DC link capacitor (16) flows. Method according to Claim 2 wherein the precharge resistor (25) and the precharge switch (20) are connected in parallel with the at least one main switch (21, 22), and wherein the precharge switch (20) is opened after closing the at least one main switch (21, 22) in step b) becomes. Method according to one of the preceding claims, wherein the drive system (10) comprises a further main switch (21, 22), and wherein the further main switch (21, 22) is closed, before the intermediate circuit capacitor (16) is pre-charged in step a). Method according to one of the preceding claims, wherein in step c) the electrical charge (50) is measured by integrating a switching current (52) flowing through the at least one main switch (21, 22) over the defined time interval (51) , Method according to Claim 5 wherein the switching current (52) is integrated by sampling the switching current (52) and thereby adding current samples obtained to a charge value. Method according to Claim 6 wherein the switching current (52) is sampled at a sampling frequency of at least 20 kHz. Method according to one of Claims 6 to 7 wherein step a), step b) and step c) are carried out repeatedly, and wherein the respectively obtained charge values are added to a total charge value. Method according to Claim 8 , wherein the total charge value is compared with a predetermined threshold value. Use of the method according to one of the preceding claims in an electric vehicle (EV), in a hybrid vehicle (HEV) or in a plug-in hybrid vehicle (PHEV).

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