DE102020007368A1 - Method for pre-charging a high-voltage electrical system of an electrically operated vehicle - Google Patents

Abstract

The invention relates to a method for precharging a high-voltage electrical system (100) of an electrically operated vehicle, the high-voltage electrical system (100) comprising a high-voltage energy store (10) which is coupled to an intermediate circuit capacitance (32) via at least one switch (12), the intermediate circuit capacitance (32) is coupled to a low-voltage energy store (26) via a DC / DC converter (20), the method comprising at least the steps of (i) determining (S100) a charge amount required for precharging the intermediate circuit capacitance (32); (ii) pre-charging (S102) the intermediate circuit capacitance (32) with a first charging power until a first amount of charge is reached, the at least one switch (12) being open, the first amount of charge being smaller than the required amount of charge; (iii) continuing (S104) the pre-charging with a second charging power; (iv) determining (S106) a voltage (16) present at the intermediate circuit capacitance (32); (v) closing (S108) the at least one switch (12) of the high-voltage energy store (10) as soon as the voltage (16) applied to the intermediate circuit capacitance (32) has reached a predetermined nominal voltage (40); (vi) terminating (S110) the precharge.

Description

The invention relates to a method for precharging a high-voltage electrical system of an electrically operated vehicle.

High-voltage components, such as high-voltage (HV) energy storage devices, DC-DC converters, on-board chargers, inverters, electric motors, heaters and refrigerant compressors, and the like, form the high-voltage electrical network in vehicles with electric drives, including battery electric vehicles (BEV), plug-in hybrid vehicles (plug-in hybrid vehicles = PHEV), hybrid vehicles (hybrid electric vehicles = HEV) and fuel cell vehicles (fuel cell = F -Cell) count. The term high voltage includes all voltages according to the ECE R 100 standard that have a potential of greater than 60 V DC or 30 V AC rms.

The high-voltage energy store is coupled to the high-voltage on-board network and thus to the vehicle's electric drive via an electrical intermediate circuit, which for example includes an intermediate circuit capacitance as an essential component. So that no excessively high currents flow when the high-voltage energy store is switched on via at least one switch, the intermediate circuit capacitance is charged to a predetermined nominal voltage before the switch is closed. This process is known as a subpoena.

When precharging the high-voltage intermediate circuit of a vehicle with a component outside the high-voltage energy store, e.g. a 12V DC / DC converter, communication between the high-voltage energy store, which has switches, for example in the form of contactors, and the precharging component is important.

On the one hand, the precharge voltage must be set with sufficient accuracy so that the switches of the high-voltage energy storage device are not damaged by currents in the intermediate circuit capacities when they are switched on. This requires a high level of accuracy for the voltage sensors in the high-voltage energy store and the precharging component. On the other hand, the time synchronization of the measured values must also be taken into account, since high voltage gradients of greater than 1V / msec can occur during the pre-charging process.

The DE 102013225884 A1 discloses a method for operating an on-board electrical system of a motor vehicle with an intermediate circuit store, a high-voltage energy store coupled to the intermediate circuit store, and a low-voltage energy store coupled to the intermediate circuit store via a voltage converter. The method includes voltage-regulated pre-charging of the intermediate circuit store via the voltage converter using electrical energy from the low-voltage energy store. The voltage converter sets a target voltage. After the precharge has been completed, the contactors of the high-voltage energy store are switched on.

One object of the invention is to provide an improved method for precharging a high-voltage on-board network of an electrically operated vehicle.

The aforementioned object is achieved with the features of the independent claim.

Favorable configurations and advantages of the invention emerge from the further claims, the description and the drawing.

According to one aspect of the invention, a method for precharging a high-voltage on-board network of an electrically operated vehicle is proposed, the high-voltage on-board network comprising a high-voltage energy store, which is coupled to an intermediate circuit capacitance via at least one switch, the intermediate circuit capacitance being coupled to a low-voltage energy store via a DC / DC converter is. The method comprises at least the following steps (i) determining a charge quantity required for precharging the intermediate circuit capacitance; (ii) pre-charging the intermediate circuit capacitance with a first charging power until a first amount of charge is reached, the at least one switch being open, the first amount of charge being smaller than the required amount of charge; (iii) continuing the pre-charging with a second charging power; (iv) determining a voltage applied to the intermediate circuit capacitance; (v) Closing the at least one switch of the high-voltage energy store as soon as the voltage applied to the intermediate circuit capacitance has reached a predetermined setpoint voltage; (vi) End the subpoena.

wobei U die am Zwischenkreis anliegende Spannung, Q die Ladungsmenge, C die Zwischenkreiskapazität und I den Ladestrom darstellt, welcher über die Zeit t integriert wird. Eine zugehörige Energiemenge E lässt sich daraus ebenfalls bestimmen über die Beziehung E=1/2*C*U².According to the method according to the invention, the amount of charge required for the pre-charging is predicted and then the pre-charging is carried out with a first output, which corresponds to a maximum output of the DC / DC converter and / or low-voltage energy store, until a little less than the predicted amount of charge is reached. The amount of charge reached can be determined by the current integral, from which the voltage applied to the intermediate circuit can be determined directly via the following relationship: $$\text{U}=\text{Q / C}=\text{1/}\mathrm{C.}{\displaystyle \int \mathrm{I.}dt}$$

where U is the voltage applied to the intermediate circuit, Q is the amount of charge, C is the Intermediate circuit capacitance and I represents the charging current which is integrated over time t. An associated amount of energy E can also be determined from this using the relationship E = 1/2 * C * U ² .

Subsequently, the pre-charging is continued with reduced power. The at least one switch, or in particular both switches in a double contactor, of the high-voltage energy store are closed independently as soon as the desired precharge voltage is reached and the high-voltage energy store is thus connected to the high-voltage on-board network.

In contrast to the prior art, the DC / DC converter is given a setpoint charge quantity or a setpoint power with which the precharge is carried out. The connection of the contactor (s) of the high-voltage energy store takes place autonomously during the pre-charging process as soon as the voltage at the intermediate circuit capacitance has reached the specified target voltage.

This advantageously simplifies the synchronization between the high-voltage energy store and the DC / DC converter. There is no real-time requirement for bus communication between the high-voltage energy store and the precharging component.

Voltage sensors with lower accuracy can be used. The error chain of the voltage measurements does not extend over two components with different environmental conditions, in particular a different temperature. This means that fewer requirements are placed on the sensors.

The pre-charging time is advantageously reduced. This enables faster pre-charging and faster vehicle start-up.

According to an advantageous embodiment of the method, the intermediate circuit capacitance can be precharged from the low-voltage energy store via the DC / DC converter.

The low-voltage energy store for precharging the intermediate circuit capacity can be designed, for example, as a battery of a low-voltage electrical system of a hybrid vehicle. For example, it can be a conventional 12V lead-acid battery, a 24V battery, or a battery from a 48V on-board network. Such a low-voltage energy store can also be used to supply low-voltage consumers in the motor vehicle. For example, an existing low-voltage battery that is already used to supply low-voltage consumers in the motor vehicle can be used as the low-voltage energy store. This has the advantage that it is not necessary to install an additional low-voltage energy store for precharging the intermediate circuit store. Alternatively, however, it is also possible to provide a special battery for the purpose of pre-charging.

According to an advantageous embodiment of the method, the closing of the at least one switch of the high-voltage energy store can be carried out autonomously. In particular, the at least one switch of the high-voltage energy store can be closed independently by the high-voltage energy store as soon as the voltage applied to the intermediate circuit capacitance has reached a predetermined setpoint voltage. The predefined setpoint voltage can, for example, correspond to the operating voltage of the high-voltage energy store. Closing of the at least one switch, for example one or the two main contactors of the high-voltage energy store, can be controlled by the battery control device of the high-voltage energy store or another control device of the high-voltage on-board network.

According to an advantageous embodiment of the method, the setpoint voltage can correspond to an operating voltage of the high-voltage energy store. If the voltage of the intermediate circuit corresponds to the operating voltage of the high-voltage energy store, the high-voltage energy store can be safely connected to the high-voltage on-board network without excessive currents flowing when the switch is closed and thus damaging the switch or other components of the high-voltage on-board network.

According to an advantageous embodiment of the method, the second charging power can be smaller than the first charging power. In particular, the second charging power can be at most 20%, preferably at most 10% of the first charging power. In this way, lower voltage gradients occur shortly before the specified target voltage of the intermediate circuit is reached. As a result, lower demands can be placed on the voltage measurement, as a result of which the voltage sensors can be designed more simply.

According to an advantageous embodiment of the method, the intermediate circuit capacitance can be discharged if the voltage applied to the intermediate circuit capacitance exceeds a predetermined limit voltage before the at least one switch is closed. If the appropriate connection time for closing the switch of the high-voltage energy storage unit was missed and the voltage at the intermediate circuit capacitance is already above the specified nominal voltage, the intermediate circuit capacitance can be discharged again and the voltage in the intermediate circuit capacitance can be reduced again. If the target voltage is reached, the switch of the high-voltage energy store can then be closed.

According to an advantageous embodiment of the method, the required amount of charge can be determined by means of a prognosis method. For example, depending on the state parameters of the high-voltage energy store, ambient conditions or other boundary conditions of the high-voltage on-board network, the amount of charge that will be necessary to achieve the specified target voltage for switching on the switch of the high-voltage energy store during pre-charging can be estimated.

According to an advantageous embodiment of the method, the prognosis method can be carried out by means of a self-learning algorithm to adapt the amount of charge required for pre-charging. For example, an aging condition of the high-voltage energy store, ambient conditions or other boundary conditions of the high-voltage on-board network can particularly advantageously be included in order to estimate the amount of charge that will probably be necessary to achieve the specified target voltage for switching on the switch of the high-voltage energy store during pre-charging.

According to an advantageous embodiment of the method, the DC / DC converter can be designed as a bidirectional converter with a first operating mode in which electrical energy is transferred from the low-voltage energy storage device to the intermediate circuit capacity and with a second operating mode in which electrical energy is transferred from the intermediate circuit capacity to the Low-voltage energy storage is transferred. The method can advantageously include switching between the first operating mode and the second operating mode, in particular as a function of a difference between the voltage at the intermediate circuit capacitance and an output voltage of the DC / DC converter.

The DC / DC converter is advantageously designed as a bidirectional converter, since its actual function is to supply low-voltage components from the high-voltage vehicle electrical system. In order to be able to carry out the pre-charging function, the DC / DC converter must enable an energy flow from the low-voltage network into the high-voltage on-board network and can therefore advantageously be designed to be bidirectional. You could use a separate converter for this. However, such a solution would be less favorable in terms of both costs and installation space.

In this way, energy can advantageously be loaded from the low-voltage energy store into the intermediate circuit capacitance and also be charged back into the low-voltage energy store from the intermediate circuit capacitance. If, for example, the appropriate connection time for closing the switch of the high-voltage energy store was missed and the voltage on the intermediate circuit capacitance is already above the specified target voltage, the intermediate circuit capacitance can be discharged again and the voltage in the intermediate circuit capacitance can be reduced again.

Further advantages emerge from the following description of the drawings. In the drawings, an embodiment of the invention is shown. The drawings, the description and the claims contain numerous features in combination. The person skilled in the art will expediently also consider the features individually and combine them into useful further combinations.

• 1 eine schematische Darstellung eines Hochvoltbordnetzes für die Ausführung des erfindungsgemäßen Verfahrens zum Vorladen des Hochvoltbordnetzes eines elektrisch betreibbaren Fahrzeugs;
• 2 ein Flussdiagramm des erfindungsgemäßen Verfahrens; und
• 3 einen Spannungsverlauf beim Vorladen des Hochvoltbordnetzes nach dem erfindungsgemäßen Verfahren.

Show:

• 1 a schematic representation of a high-voltage on-board network for carrying out the method according to the invention for precharging the high-voltage on-board network of an electrically operated vehicle;
• 2 a flow chart of the method according to the invention; and
• 3 a voltage curve when precharging the high-voltage electrical system according to the method according to the invention.

Identical or similar components are numbered with the same reference symbols in the figures. The figures show only examples and are not to be understood as restrictive.

1 shows a schematic representation of a high-voltage electrical system 100 for performing the method according to the invention for precharging the high-voltage electrical system 100 an electrically operated vehicle.

The high-voltage electrical system 100 includes a high-voltage energy store 10 , which has a number of series-connected battery cells and two switches 12th , especially the main contactors of the high-voltage energy storage system 10 , with the electric drive 30th the vehicle is paired. The electric drive 30th has an intermediate circuit capacitance parallel to the input 32 on, which in turn parallel to the input of a DC / AC inverter for controlling an electric motor 36 is arranged. The high-voltage electrical system also includes 100 further ancillary units 38 , which, for example, On Board Charger = OBC), heaters and refrigerant compressors.

The intermediate circuit capacity 32 is via a DC / DC converter 20th with a low-voltage energy store 26th coupled, which has a number of series-connected battery cells and, for example, an output voltage of 12 V, 24 V or 48 V can have.

In the high-voltage energy storage 10 becomes a tension 14th directly as the output voltage of the battery cells, as well as a voltage 16 on the output side after the two switches 12th measured. The voltage 16 corresponds to the voltage at the intermediate circuit capacitance 32 .

An output voltage is generated in the DC / DC converter 24 as well as the electricity 22nd measured.

The procedure for pre-charging a high-voltage vehicle electrical system 100 an electrically operated vehicle, which is shown as a flow chart in 2 comprises the steps described below.

In a first step S100 becomes one for pre-charging the DC link capacitance 32 required amount of charge determined. The required amount of charge can be estimated, for example, by means of a prognosis method. In particular, a self-learning algorithm can be used to adapt the amount of charge required for pre-charging.

After that, in step S102 the intermediate circuit capacity 32 via the DC / DC converter 20th from the low-voltage energy storage 26th with an initial charging capacity 50 pre-charged until a first charge is reached. There are the switches 12th opened so that the high-voltage energy storage 10 from the high-voltage electrical system 100 is disconnected. The first charging power 50 can use the maximum available charging power from the DC / DC converter 32 and low-voltage energy storage 26th correspond.

The first amount of charge is smaller than the amount of charge required.

If the first amount of charge is reached, the pre-charging in step S104 with a second charging capacity 52 continued. The second charging power 52 is less than the first charging power 50 , for example, the second charging power is 52 at most 20%, preferably at most 10% of the first charging power 50 .

Doing so in step S106 those at the DC link capacitance 32 applied voltage 16 certainly. The voltage 16 however, it can alternatively also be determined continuously during the entire precharge process.

As soon as the DC link capacitance 32 applied voltage 16 a predetermined nominal voltage 40 will be in step S108 the two switches 12th of the high-voltage energy storage 10 closed.

The closing S108 the desk 12th of the high-voltage energy storage 10 is carried out independently. In particular, the closing S108 the desk 12th of the high-voltage energy storage 10 for example through the high-voltage energy storage 10 self-sufficient, as soon as the DC link capacity 32 applied voltage 16 a predetermined nominal voltage 40 has reached.

The target voltage 40 can, for example, the operating voltage of the high-voltage energy store 10 correspond.

This is the high-voltage energy storage 10 to the high-voltage electrical system 100 connected and pre-charging can be done in step S110 be terminated.

If the on the DC link capacitance 32 applied voltage 16 before closing the switch 12th a predetermined limit voltage, which is above the target voltage 40 is exceeded, the DC link capacitance 32 can also be discharged again.

The DC / DC converter can do this 20th be advantageously designed as a bidirectional converter with a first operating mode in which electrical energy from the low-voltage energy store 26th into the intermediate circuit capacitance 32 is transmitted and with a second operating mode in which electrical energy from the intermediate circuit capacitance 32 in the low-voltage energy storage 26th is transmitted. It is expedient to switch between the first operating mode and the second operating mode, in particular as a function of a difference in voltage 16 at the DC link capacitance 32 and an output voltage 24 of the DC / DC converter 20th , respectively. In this way, the DC link capacitance 32 can also be discharged again. In addition, the DC / DC converter 20th advantageously fulfill its actual function, namely the low-voltage components of the vehicle from the high-voltage electrical system 100 to supply.

3 shows a voltage curve 16 as a function of time t when precharging the high-voltage electrical system 100 according to the method according to the invention.

At a time t1 becomes the preload process with step S100 as previously described with the pre-charging of the DC link capacitance 32 with an initial charging capacity 50 started. The one at the DC link capacitance 32 applied voltage 16 increases with a high voltage gradient over time.

At a time t2 When the first amount of charge, which is slightly lower than the certain required amount of charge, is reached, the first charging power becomes 50 on the second charging power 52 reduced and at the same time the tension 16 continuously determined. The stress gradient over time 16 is significantly smaller than when pre-charging with the high initial charging power 50 .

When the specified target voltage is reached 40 through the tension 16 at a time t3 become the switches 12th of the high-voltage energy storage 10 self-sufficient closed, so that the high-voltage energy storage 10 to the high-voltage electrical system 100 is switched on.

The precharge process can then at the time t4 be terminated.

List of reference symbols

10

High-voltage energy storage

12

switch

14th

Voltage HV energy storage

16

Voltage high-voltage electrical system

20th

DC / DC converter

22nd

Current DC / DC converter

24

Voltage DC / DC converter

26th

Low-voltage energy storage

30th

Electric drive

32

DC link capacity

34

Inverter

36

Electric motor

38

Ancillary units

40

Target voltage

50

first charging power

52

second charging power

100

High-voltage electrical system

t1

Start preloading

t2

Reduce charging power

t3

Close switch for HV energy storage

t4

Quit preloading

S100

Determine the amount of charge required for the pre-charge

S102

Pre-charging with the first charging power

S104

Continue pre-charging with second charging power

S106

Determine the voltage applied to the DC link capacitance

S108

Autarkic closing of the switch of the high-voltage energy storage

S110

End the preload

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was 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.

Patent literature cited

• DE 102013225884 A1 [0006]

Claims (9)

Method for precharging a high-voltage on-board network (100) of an electrically operated vehicle, the high-voltage on-board network (100) comprising a high-voltage energy store (10) which is coupled to an intermediate circuit capacitance (32) via at least one switch (12), the intermediate circuit capacitance (32) via a DC / DC converter (20) is coupled to a low-voltage energy store (26), the method comprising at least the steps (i) determining (S100) a charge quantity required for precharging the intermediate circuit capacitance (32); (ii) pre-charging (S102) the intermediate circuit capacitance (32) with a first charging power (50) until a first amount of charge is reached, the at least one switch (12) being open, the first amount of charge being smaller than the required amount of charge; (iii) continuing (S104) the pre-charging with a second charging power (52); (iv) determining (S106) a voltage (16) present at the intermediate circuit capacitance (32); (v) closing (S108) the at least one switch (12) of the high-voltage energy store (10) as soon as the voltage (16) applied to the intermediate circuit capacitance (32) has reached a predetermined nominal voltage (40); (vi) terminating (S110) the precharge. Procedure according to Claim 1 , the intermediate circuit capacitance (32) being precharged from the low-voltage energy store (26) via the DC / DC converter (20). Procedure according to Claim 1 or 2 , wherein the closing (S108) of the at least one switch (12) of the high-voltage energy store (10) is carried out autarkically, in particular the closing (S108) of the at least one switch (12) of the high-voltage energy store (10) being carried out autarkically by the high-voltage energy store (10) as soon as the voltage (16) applied to the intermediate circuit capacitance (32) has reached a predetermined nominal voltage (40). Method according to one of the preceding claims, wherein the nominal voltage (40) corresponds to an operating voltage of the high-voltage energy store (10). Method according to one of the preceding claims, wherein the second charging power (52) is smaller than the first charging power (50), in particular wherein the second charging power (52) is at most 20%, preferably at most 10% of the first charging power (50). Method according to one of the preceding claims, wherein the intermediate circuit capacitance (32) is discharged if the voltage (16) applied to the intermediate circuit capacitance (32) exceeds a predetermined limit voltage before the at least one switch (12) is closed. Method according to one of the preceding claims, the required amount of charge being determined by means of a prognosis method. Procedure according to Claim 7 , the prognosis method being carried out by means of a self-learning algorithm to adapt the amount of charge required for pre-charging. Method according to one of the preceding claims, wherein the DC / DC converter (20) is designed as a bidirectional converter with a first operating mode in which electrical energy is transferred from the low-voltage energy store (26) into the intermediate circuit capacitance (32) and with a second operating mode , in which electrical energy is transferred from the intermediate circuit capacitance (32) to the low-voltage energy store (26), and the method involves switching between the first operating mode and the second operating mode, in particular depending on a difference in voltage (16) across the intermediate circuit capacitance (32) and an output voltage (24) of the DC / DC converter (20).

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