DE102015122690A1 - Method for overvoltage protection - Google Patents

Abstract

The invention relates to methods (100) for overvoltage protection in a DC link (200) of an electric drive (50) of a vehicle, wherein
the electrical intermediate circuit (220) comprises at least one drive component (60), and the intermediate circuit (220) is electrically connected to at least one electrical energy storage unit (40) via a DC-DC converter (250), wherein
an overvoltage protection device (10) via an electronic switching unit (11) electrically connects the intermediate circuit (220) and the energy storage unit (40) parallel to the DC-DC converter (250), and
an intermediate circuit voltage of the intermediate circuit (220) is monitored by the overvoltage protection device (10), and
the switching unit (11) is controlled as a function of the monitoring of the intermediate circuit voltage.

Description

The present invention relates to a method and a system for overvoltage protection in an electrical DC link in an electric drive of a vehicle.

It is known from the prior art that in vehicles with an electric drive, an intermediate circuit, in particular a traction network, is used, which in particular comprises the electric drive and optionally further drive components and consumers. The intermediate circuit can be directly connected to an energy source and / or sink, such as a battery. Alternatively, a connection via a DC-DC converter with one or more energy sources and / or sinks is known. In the latter case, there is a decoupled voltage intermediate circuit on the drive side. In particular, in fuel cell vehicles also a fuel cell is connected as an energy source via the DC-DC converter with the intermediate network.

From the DE 10 2014 107 093 A1 For example, a method of implementing a short circuit as a countermeasure in a rotary polyphase electrical machine is known. Here, an error condition is detected, initially commanding a rectifier / inverter module to an electrically open state.

From the DE 10 2004 023 505 A1 a method for energy management in an electrical system of a hybrid vehicle is known. The document describes an electric machine which can be operated by an internal combustion engine or by recuperation as a generator.

It has proven to be a disadvantage that when using a DC-DC converter for decoupling the DC link overvoltages can be dissipated insufficiently on the DC link. The DC-DC converter is often unable to react quickly enough to the overvoltages and to transfer the energy into a sink (for example a battery connected to the DC-DC converter), with the result that a transient voltage peak occurs at the voltage intermediate circuit. The overvoltage occurs, for example, by a load shedding of the electric machine (wheel spin). The overvoltages can cause, for example, a shutdown and / or destruction of components in the traction network or in the DC link.

It is known to use a so-called chopper for overvoltage protection, wherein an additional braking resistor is used to absorb energy. However, this option requires a higher space requirement and possibly cooling. Furthermore, this known solution often has only insufficient efficiency for overvoltage protection.

It is an object of the present invention to remedy the aforementioned disadvantages at least partially. In particular, it is an object of the present invention to enable a reliable overvoltage protection, and in particular to simultaneously reduce the space requirement. Next, preferably, the cost of providing the overvoltage protection can be reduced by a low-cost DC converter can be used without concomitant reduction of overvoltage protection can be used.

The above object is achieved by a method having the features of claim 1 and by a system having the features of claim 6. Further features and details of the invention will become apparent from the respective dependent claims, the description and the drawings. In this case, features and details that are described in connection with the method according to the invention, of course, also in connection with the system according to the invention, and in each case vice versa, so that with respect to the disclosure of the individual invention aspects always reciprocal reference is or can be.

The object is achieved in particular by a method for overvoltage protection in an electrical DC link in an electric drive of a vehicle. In this case, it is provided in particular that the intermediate circuit comprises at least one drive component, and the intermediate circuit is electrically connected to at least one electrical energy storage unit via a DC-DC converter. It can be provided that an overvoltage protection device and / or an overvoltage protection system by means of an electronic switching unit electrically interconnects the intermediate circuit and the energy storage unit parallel to the DC-DC converter, wherein an intermediate circuit voltage of the intermediate circuit is monitored by the overvoltage protection device, in particular by a monitoring unit, and the switching unit in Depending on the monitoring of the DC link voltage, in particular by the monitoring unit, is controlled. In other words, an overvoltage protection is achieved in particular by using the switching unit as a bypass to the DC-DC converter. The switching unit thus preferably forms a switchable bypass, which energy from the intermediate circuit to the energy storage unit bypassing and / or can run independently without involvement of the DC-DC converter, the energy storage unit is thus used as a power sink. It can be made possible in this way a reliable overvoltage protection for the electrical system. Furthermore, for example, a total of at least two and / or at least three and / or at least four and / or at least five and / or at least six energy sources and / or sinks, such as energy storage units, in particular electrically connected in each case via a separate terminal of the DC-DC converter to the DC-DC converter be.

Overvoltage protection means in particular that the components (such as the drive components or other consumers) are protected in the intermediate circuit from a functional impairment and / or destruction due to overvoltages, in particular transient voltage peaks. The intermediate circuit is, for example, a DC voltage intermediate circuit and / or an (electric) traction network of the vehicle, and is in particular connected via the DC-DC converter (DC / DC converter) to the energy storage units or the energy storage unit and / or an energy source. The connection is preferably decoupled, wherein the decoupling is carried out without galvanic isolation or with galvanic isolation. The overvoltage protection function or the overvoltage protection therefore preferably does not lead to an error state, but represents a regular operating state (operating state).

In this case, the DC-DC converter preferably connects (electrical) networks, such as the intermediate circuit and / or the at least one energy storage unit and / or the energy source, to each other, the networks each having different voltage levels. The voltage applied to the terminal of the DC-DC converter voltage of the intermediate circuit (that is, in particular the DC link voltage) may preferably be in the range between 200 V and 1000 V, preferably between 380 V and 800 V, more preferably between 400 V and 600 V. The rated voltage of the energy storage unit, that is to say in particular the voltage applied to the terminal of the DC voltage converter of the respective energy storage unit, may preferably be between 150 V and 850 V, preferably between 200 V and 600 V, particularly preferably between 250 V and 400 V. The voltage at the output of the fuel cell and / or the voltage applied to the terminal of the DC voltage converter of the fuel cell may preferably be in the range between 200 V and 800 V, more preferably between 230 V and 430 V, preferably between 300 V and 330 V. This makes it possible, for example by the use of the DC-DC converter, that the vehicle drive can be operated by a fuel cell and / or one or more energy storage units. The vehicle may be embodied, for example, as a motor vehicle and / or a passenger vehicle and / or a truck and / or a fuel cell vehicle and / or an electric vehicle.

For overvoltage protection, an overvoltage is preferably detected by the monitoring and then passed or removed by driving the switching unit, the energy which leads to the overvoltage to a power sink. In this case, in particular the DC-DC converter is bypassed in that the switching unit or the overvoltage protection device forms a bypass to the DC-DC converter, that is, is connected in parallel thereto. The power sink is preferably formed by a (in particular a single) energy storage unit, which is preferably the strongest loadable by electrical current. Alternatively, it may be provided that a plurality of energy storage units form the power sink and / or a plurality of switching units are provided in order to electrically connect the respectively different energy storage units to the DC link. These multiple switching units may then optionally be operated simultaneously for overvoltage protection according to the method of the invention, or alternatively only one of these switching units, for example to achieve redundancy.

The energy storage unit is formed, for example, as an electrical energy storage, such as a (rechargeable) battery, and may preferably be both an electrical sink and an electrical source. The electrical sink can absorb electrical energy via the DC-DC converter and the electrical source can deliver energy to the DC-DC converter or deliver via the DC-DC converter to other connected to the DC-DC converter networks. The energy source can be designed, for example, as a pure energy source, in which case a (re) supply of energy via the DC-DC converter to the energy source is prevented. This allows, for example, the connection of a fuel cell for feeding the DC link. Thus, only a unidirectional energy transfer to the DC-DC converter can be provided for the pure energy source, while in the energy storage units, for example, a bidirectional energy transfer (that is, both energy intake and energy output or both use as a source and as a sink) is provided.

It is also conceivable within the scope of the invention that the monitoring and / or control of the switching unit takes place in such a way that a voltage value of the intermediate circuit voltage is determined (that is to say measured in particular) by the monitoring, whereby a current flow between the intermediate circuit and the energy storage unit is permitted if the determined voltage value is greater than a (pre-stored) maximum voltage value, and a current flow between the intermediate circuit and the energy storage unit (partially or completely) is suppressed if the determined voltage value is less than or equal to the maximum voltage value. The switching unit may preferably be designed such that, for allowing the current flow, an electrical resistance of an electrical connection, in particular of the switching unit, between the intermediate circuit and the energy storage unit is reduced. For suppressing the current flow, for example, the electrical resistance can be increased. For this purpose, the switching unit may be embodied for example as an electronic switch. Allowing the current flow can, for example, clocked and / or take place only for a given pulse and thus last only for a certain time. Subsequently, the monitoring and control can take place again (possibly after a further intermediate time). If appropriate, this process, that is to say in particular a renewed (cyclic) pulse-like permitting of the current flow, is then carried out repeatedly until the determined voltage value lies below or corresponds to the maximum voltage value. This has the advantage that a switchable bypass to the DC-DC converter can be realized quickly and with little space.

It can be provided within the scope of the invention that the control of the switching unit and / or allowing the current flow clocked and / or pulsed or alternatively permanent, and in particular carried out for a first predetermined period of time and then interrupted for a second predetermined period of time. The monitoring, in particular the voltage measurement, preferably takes place permanently and / or analogously. In particular, the activation is only carried out when the monitoring indicates that the maximum permitted voltage (that is to say the maximum voltage value, for example) has been exceeded. In this context, clocked triggering is understood in particular to mean that the permitting and / or suppressing of the current flow (between the DC link and the energy storage unit) is clocked. For example, to control the current flow, it is possible to enable (and subsequently prevent again) only for a defined pulse when the determined voltage value is greater than the maximum voltage value. The activation can preferably be repeated until the intermediate circuit voltage (the determined voltage value) is less than or equal to the maximum voltage value. For monitoring, the measured voltage value, in particular the intermediate circuit voltage, which in particular is applied to the DC-DC converter, is preferably compared with a reference voltage (for example, corresponding to the maximum voltage value). The clocking can be done, for example, with a frequency between 1KHz and 100KHz, preferably between 10KHz and 50KHz. The first and / or the second predetermined time period may, for example, be in a range between 10 μs and 1 ms, preferably between 100 μs and 500 μs. It is also conceivable that the control takes place electronically, for which purpose the monitoring unit and / or the switching unit has electronic components. Such electronic components preferably comprise at least one integrated circuit and / or a microprocessor and / or a microcontroller and / or semiconductor components. This allows, inter alia, a flexible and fast control and monitoring with a high efficiency.

Furthermore, it is conceivable that, depending on the activation of the switching unit, a current flow between the intermediate circuit and the energy storage unit is permitted or suppressed for a predetermined pulse duration. The predetermined pulse duration can lie in a range which has been described above for the first and second predetermined time periods. This enables efficient and reliable overvoltage protection.

It is also conceivable that the predetermined pulse duration is predetermined in dependence on a thermal limit of the switching unit or is. It may be possible that the predetermined pulse duration is pre-stored electronically, for example as a digitally stored value in an electronic memory unit. The predetermined pulse duration can preferably be selected such that it lies below a pulse duration which would result in damage to the switching unit over a longer period of time. Furthermore, it can also be provided that a temperature monitoring of the switching unit is provided. As a result, the life of the overvoltage protection device can be improved.

The invention also relates to a system for overvoltage protection in an electrical DC link in an electric drive of a vehicle, wherein the intermediate circuit comprises at least one drive component, and preferably the DC link is electrically connected via a (in particular only a single) DC-DC converter with at least one electrical energy source. It is preferable provided that at least one electrical energy storage unit is connected via this DC-DC converter with the intermediate circuit and the power source. It is conceivable here that an overvoltage protection device electrically connects the intermediate circuit and the or at least one of the energy storage unit (s) to one another via an electronic switching unit in parallel to the DC voltage converter. Thus, the system according to the invention brings the same advantages as have been explained in detail with reference to a method according to the invention. In addition, the system can be operated in particular according to a method according to the invention.

The DC-DC converter preferably has a plurality of terminals, which may each be designed as unidirectional or bidirectional terminals. The energy storage unit is connected, for example, with a bidirectional connection, so that an energy flow in both directions is possible. The power source is connected, for example, to a unidirectional terminal, so that the energy transfer is only possible from the power source to the equality converter and is blocked in the reverse direction. The DC-DC converter can have, for example, at least three, at least four or at least five terminals, wherein, for example, at least one or at least two or at least three electrical energy storage unit (s) are each connected to a terminal. In this case, one or more energy storage unit (s) form, in particular, a power sink to which energy can be conducted from the intermediate circuit upon detection of an overvoltage by the overvoltage device. An overvoltage system is thus formed by the overvoltage device and the power sink, that is, the at least one electrical energy storage unit, which is used as a power sink. As a result, a reliable and efficient surge protection is possible.

It may further be possible for the overvoltage protection device to form a common component with the DC-DC converter, in particular with common connections for the energy storage unit and / or the intermediate circuit and / or the energy source, and preferably (completely) functionally independently from the DC-DC converter with its own monitoring unit for monitoring the DC link voltage is executed. Alternatively, it is also conceivable that the overvoltage protection device is functionally dependent on a pilot control. It is also conceivable that the overvoltage protection device outputs an electrical signal, in particular a status, to the DC-DC converter and / or another vehicle control device. In addition, it may be possible that the feedforward control is provided by the DC-DC converter and / or the vehicle control device. For this purpose, the DC-DC converter and / or the vehicle control device may, for example, be electrically connected to the overvoltage protection device. The DC-DC converter is guided, for example, as an electronic component, which in particular also comprises a housing. The overvoltage device can in this case be integrated in this electronic component and / or have a common housing with the DC-DC converter or the electronic component. Thus, no additional space requirement for the overvoltage device is necessary. The monitoring unit comprises, for example, at least one electronic component, in particular at least one semiconductor switch, preferably a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and / or an IGBT (Insulated Gate Bipolar Transistor), and / or at least one reference voltage source and / or at least one comparator , Thus, the DC link voltage can be reliably measured by the monitoring unit.

• – mindestens einen Wechselrichter, welcher insbesondere mit mindestens einer elektrischen Maschine elektrisch verbunden ist,
• – mindestens eine elektrische Maschine, vorzugsweise einen Elektromotor zum Antreiben des Fahrzeuges,
• – mindestens ein Nebenaggregat, bevorzugt einen Turboverdichter zum Verdichten der Luft für eine Brennstoffzelle und/oder eine Zusatzheizung für den Fahrzeuginnenraum.

Another advantage within the scope of the invention can be achieved if the drive component comprises at least one of the following components:

• At least one inverter, which is in particular electrically connected to at least one electric machine,
• At least one electric machine, preferably an electric motor for driving the vehicle,
• - At least one auxiliary unit, preferably a turbo compressor for compressing the air for a fuel cell and / or an auxiliary heater for the vehicle interior.

The additional heater is designed for example as a PTC heating element. The drive components, in particular the drive, are for example high voltage components. The power of the electric machine is in particular 50kW to 150kW, preferably 80kW to 100kW and the power of the fuel cell is preferably 50kW to 200kW, preferably 80kW to 100kW and the battery power is preferably 20kW to 150kW, more preferably 25kW to 100kW. By the overvoltage protection device while a reliable protection of these drive components is possible. It is conceivable that the overvoltage protection device is also integrated in at least one of these drive components and / or forms a common component with at least one of these drive components and / or is connected thereto.

Further advantage may be provided that the overvoltage protection device at least one electrical filter unit, in particular a throttle, having, in particular, the switching unit as a power semiconductor, in particular as a MOSFET and / or IGBT, is formed. The electric filter unit serves in particular to prevent an absolute short circuit and is preferably designed as a high-pass filter. The filter unit is used in particular for filtering the current flow permitted according to the activation of the switching unit. As a result, the overvoltage protection can be further improved.

Advantageously, it can be provided within the scope of the invention that the energy source is designed as a fuel cell and / or as a range extender. It is also conceivable that the energy source is designed as a further energy storage unit. A range extender is understood to mean, in particular, internal combustion engines that drive a generator that supplies power to an energy storage unit and / or an electric motor. The Range Extender is used in particular to increase the range of the vehicle. It is also conceivable that a plurality of energy sources, in particular also different energy sources, are connected to the DC-DC converter.

Further advantages, features and details of the invention will become apparent from the following description in which, with reference to the drawings, embodiments of the invention are described in detail. The features mentioned in the claims and in the description may each be essential to the invention individually or in any desired combination. Show it:

1 : a schematic representation of a system according to the invention 200 .

2 : a schematic representation of the visualization of a method according to the invention 100 ,

In 1 is schematically a system according to the invention 200 which is an overvoltage protection device 10 includes. The overvoltage protection device 10 comprises at least one switching unit 11 , at least one filter unit 12 and at least one monitoring unit 13 , Next is a DC-DC converter 250 shown connecting several networks together. Such a network is, for example, an intermediate circuit 220 which at least one drive component 60 like a drive 50 includes. Other networks are at least one energy storage unit 40 , which via the DC-DC converter 250 with the DC link 220 connected is. This is visualized by the double arrow that the DC link 220 and the at least one energy storage unit 40 each at a connection 251 of the DC-DC converter 250 are connected, which allows a bidirectional power transmission. Of course, other sources and / or sinks, in particular further energy storage units 40 , preferably via their own connections 251 of the DC-DC converter 250 , with the DC-DC converter 250 be connected (electrically). For example, a total of at least two and / or at least three and / or at least four and / or at least five wells and / or sources with the DC-DC converter 250 be connected. In contrast, there is an energy source 30 , which is designed for example as a fuel cell, via a unidirectional connection 251 with the DC-DC converter 250 connected, as shown by the arrow in accordance with only one direction. Of course, other sources of energy can also be used 30 , in particular in each case via own (unidirectional) connections 251 of the DC-DC converter 250 , with the DC-DC converter 250 be connected (electrically). As visualized by a dashed line, the overvoltage protection device is 10 with the DC link 220 and at least one energy storage unit 40 electrically connected. This connection can preferably also unidirectionally only in the direction of the energy storage unit 40 be executed. This connection can be a flow of current from the DC link 220 to the energy storage unit 40 be admitted, preferably only if the monitoring unit 13 detected an overvoltage. For this purpose, it may be provided that the overvoltage unit 13 the switching unit 11 electrically and / or electronically activates and thus enables the flow of current. Further, it is conceivable that the overvoltage protection device 10 a common component 14 with the DC-DC converter 250 forms and thus to the outside common connections 252 with the DC-DC converter 250 having.

In 2 schematically is a method according to the invention 100 visualized. Here, according to a first method step 100.1 monitors a DC link voltage, wherein according to a second method step 100.2 a current flow between the DC link 220 and the energy storage unit 40 in particular only (possibly clocked) is allowed if the determined voltage value is greater than a maximum voltage value. According to a third method step 100.3 becomes a current flow between the DC link 220 and the energy storage unit 40 suppressed when the detected voltage value is less than or equal to the maximum voltage value. Subsequently, the activation and / or monitoring can again (in particular after a certain time and / or cyclically repeated) in the first method step 100.1 kick off.

The above explanation of the embodiments describes the present invention solely by way of example. Of course, individual features of the embodiments, if technically feasible, can be combined freely with one another, without departing from the scope of the present invention.

LIST OF REFERENCE NUMBERS

10

 Surge protector

11

 switching unit

12

 Filter unit, throttle

13

 Monitoring unit, voltage monitoring unit

14

 common component

30

 Energy source, fuel cell

40

 Energy storage unit

50

 drive

60

 drive component

100

 method

100.1

 First process step

100.2

 Second process step

100.3

 Third procedural step

200

 system

220

 DC

250

 DC converter

251

 connection

252

 common connection

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 102014107093 A1 [0003]
• DE 102004023505 A1 [0004]

Claims (11)

Procedure ( 100 ) for overvoltage protection in an electrical DC link ( 220 ) in an electric drive ( 50 ) of a vehicle, the intermediate circuit ( 220 ) at least one drive component ( 60 ), and the intermediate circuit ( 220 ) via a DC-DC converter ( 250 ) with at least one electrical energy storage unit ( 40 ) is electrically connected, wherein an overvoltage protection device ( 10 ) via an electronic switching unit ( 11 ) the DC link ( 220 ) and the energy storage unit ( 40 ) parallel to the DC-DC converter ( 250 ) and electrically connected by the overvoltage protection device ( 10 ) a DC link voltage of the DC link ( 220 ), and the switching unit ( 11 ) is driven in response to the monitoring of the DC link voltage. Procedure ( 100 ) according to claim 1, characterized in that the monitoring and / or control of the switching unit ( 11 ) is carried out such that a voltage value of the intermediate circuit voltage is determined by the monitoring, wherein a current flow between the intermediate circuit ( 220 ) and the energy storage unit ( 40 ) is permitted if the determined voltage value is greater than a maximum voltage value, and a current flow between the intermediate circuit ( 220 ) and the energy storage unit ( 40 ) is suppressed when the detected voltage value is less than or equal to the maximum voltage value. Procedure ( 100 ) according to claim 1 or 2, characterized in that the control of the switching unit ( 11 ) and / or permitting the current flow to take place clocked, and in particular carried out for a first predetermined period of time and then interrupted for a second predetermined period of time. Procedure ( 100 ) according to one of the preceding claims, characterized in that, depending on the activation of the switching unit ( 11 ) a current flow between the intermediate circuit ( 220 ) and the energy storage unit ( 40 ) is allowed or suppressed for a predetermined pulse duration. Procedure ( 100 ) according to one of the preceding claims, characterized in that the predetermined pulse duration in dependence on a thermal limit of the switching unit ( 11 ) is predetermined. System ( 200 ) for overvoltage protection in an electrical DC link ( 220 ) in an electric drive ( 50 ) of a vehicle, the intermediate circuit ( 220 ) at least one drive component ( 60 ), and the intermediate circuit ( 220 ) via a DC-DC converter ( 250 ) with at least one electrical energy source ( 30 ) is electrically connected, and at least one electrical energy storage unit ( 40 ) via the DC-DC converter ( 250 ) with the DC link ( 220 ) and the energy source ( 30 ), characterized in that an overvoltage protection device ( 10 ) via an electronic switching unit ( 11 ) the DC link ( 220 ) and the energy storage unit ( 40 ) parallel to the DC-DC converter ( 250 ) electrically interconnects. System ( 200 ) according to claim 6, characterized in that the overvoltage protection device ( 10 ) with the DC-DC converter ( 250 ) a common component ( 14 ), in particular with common connections ( 252 ) for the energy storage unit ( 40 ) and / or the intermediate circuit ( 220 ), and preferably functionally independent from the DC-DC converter ( 250 ) with its own monitoring unit ( 13 ) is carried out for monitoring the intermediate circuit voltage, with an electrical signal as status information being particularly preferred from the overvoltage protection device ( 10 ) to the DC-DC converter ( 250 ) and / or another vehicle control device can be output. System ( 200 ) according to claim 6 or 7, characterized in that the drive component ( 60 ) at least one of the following comprises: - at least one inverter, which is in particular electrically connected to at least one electric machine, - at least one electric machine, preferably an electric motor for driving the vehicle, - at least one auxiliary unit, preferably a turbo compressor for compressing the air for a fuel cell ( 30 ) and / or an additional heater for the vehicle interior. System ( 200 ) according to one of claims 6 to 8, characterized in that the overvoltage protection device ( 10 ) at least one electric filter unit ( 12 ), in particular a throttle ( 12 ), wherein in particular the switching unit ( 11 ) is designed as a power semiconductor, in particular as a MOSFET and / or IGBT. System ( 200 ) according to one of claims 6 to 9, characterized in that the energy source ( 30 ) as a fuel cell ( 30 ) and / or designed as a range extender. System ( 200 ) according to one of claims 6 to 10, characterized in that the system ( 200 ) according to a method ( 100 ) according to one of claims 1 to 5 is operable.

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