DE102016211285A1 - Vehicle and circuit arrangement for switching electrical energy in a vehicle electrical system of a means of transport between two voltage-sensitive energy sources - Google Patents

Abstract

An electrically drivable means of locomotion as well as a circuit arrangement for switching electrical energy in an electrical system of a means of locomotion (10) between a first voltage-soft power source (3) and a second voltage-soft power source (4) comprising:
A first transistor (T2),
- an inductance (L) and
- an evaluation unit (6)
wherein the transistor (T2) and the inductance (L) form a switching power supply, and the evaluation unit (6) is set up, a clocked operation of the first transistor (T2) in response to the detection of a predefined operating state (Z1) of the means of transport (10) with continuous current flow through the inductance (L) to prevent.

Description

State of the art

The present invention relates to a means of locomotion as well as a circuit arrangement for the transmission of electrical energy in a vehicle electrical system of a means of locomotion between a first voltage-soft power source and a second voltage-soft power source. In particular, the present invention relates to the use of the knowledge of certain operating states to avoid unnecessary switching operations and to simplify the DC / DC converter used.

In a fuel cell system, according to the current state of the art, a fuel cell is coupled to a high-power battery by means of a DC-DC converter (DC / DC) converter. This is in turn switched to a drive inverter to provide traction energy. The DC / DC converter adjusts the voltages of the fuel cell system to the voltage of the battery and thus regulates the flow of current through the fuel cell depending on the respective state of the vehicle. While the battery is set up to provide different voltage and current quantities with substantially no time delay, a fuel cell system is subject to some inertia until appropriate electrical characteristics are provided. Therefore, the battery is preferably used for recuperation and inertia compensation (dynamic increase). In addition, by means of the battery, a Stromgradientenbegrenzung the fuel cell flow to avoid increased wear of the fuel cell. If the system is designed so that either the voltage of the fuel cell or the voltage of the battery is higher (overlapping voltage bands) depending on the system condition, a sophisticated boost converter / buck converter topology is used (see 3 ).

The DC / DC converters, which are always designed for a bilateral energy flow direction in the prior art, usually have a substantially symmetrical structure with respect to the input side and the output side, wherein in the single-phase design at least two capacitors, a choke coil and four transistors are used in a clock mode to allow the energy stored in the choke coil to allow current to flow towards the drive inverter. It is an object of the present invention to reduce the switching losses as well as the ohmic losses in the transmission of electrical energy. It is a further object of the present invention to provide a simpler, less expensive, and lighter construction for a DC / DC converter.

Disclosure of the invention

The above identified object is achieved by a circuit arrangement for switching electrical energy in a vehicle electrical system of a means of locomotion between a first low-voltage power source and a second low-voltage power source. The first voltage-soft power source may be for example a battery or an accumulator. The second voltage-soft power source may be, for example, a fuel cell. To mediate the energy in the single-phase design, a first transistor, (preferably also a second transistor) and an inductance are provided. An evaluation unit is set up to control the first transistor (and possibly also the second transistor). The transistor or the transistors and the inductance form a switching power supply, by means of which at least in one direction electrical energy of a first lower voltage level can be converted to a second higher voltage level. This is usually done by a counterclockwise operation of the respective transistor when using at least two transistors, wherein in a first step, a current flow is provoked by the inductor towards ground and after a switching operation in a second step, the inductor current flow in the direction of higher voltage drives. According to the invention, the evaluation unit is set up to prevent a clocked operation of the first transistor in response to the detection of a predefined operating state of the means of locomotion. The operating state has the necessary condition that a current flows through the inductance. The operating state can be, for example, an operating state of the vehicle electrical system of the means of locomotion, which is recognized in particular on the basis of a driving state variable (speed and / or load state and / or acceleration or the like). In other words, the evaluation unit determines from a reference that it falls below or exceeds a characteristic which is determined over time. The parameter can be provided, for example, by a vehicle bus and / or by a sensor. The parameter may, for example, characterize the relative voltage position between the first energy source and the second energy source. Alternatively or additionally, the parameter may represent an energy consumption of an electrical consumer of the vehicle electrical system (eg all consumers, in particular comprising the electric drive train). Alternatively or additionally, the core size may be the power from the battery fuel cell unit (DC link current) or the SOC of the battery. As a result, switching operations and associated losses in certain Operating conditions of the means of transport are avoided.

The dependent claims show preferred developments of the invention.

If, as described above, only a first transistor (without a second transistor) is provided in the switched-mode power supply, an undesired short circuit during the first step can be prevented by the use of a diode. The diode may be an inherent diode of the second transistor (if provided). The use of the second transistor instead of a single diode allows use of the circuit arrangement according to the invention also in the case that the current direction between the input and output are reversely oriented. Moreover, it is possible to further reduce the conduction losses by using the second transistor.

The predefined operating state can mark, for example, a partial load operation of the electrical system or of the means of locomotion. Alternatively or additionally, a journey below a predefined maximum speed, in particular below 50 km / h, can be characterized by the predefined operating state. Such an operating state permits, for example, the assumption that the battery is not discharged or even deeply discharged during a parallel connection with the fuel cell (eg via the choke coil or the inductance), since the fuel cell can always provide sufficient energy to supply the drivetrain or power train to supply the vehicle electrical system with the necessary electrical energy. Even if the first energy source is not discharged in a parallel connection with the second energy source, it can be sensed or otherwise detected and used to detect the predefined operating state.

Outside the predefined operating state, the circuit arrangement can be set up to adopt a second operating state by means of the evaluation unit, in which the first and the second transistor are operated in a clocked manner. The second operating state may prevail, in particular in the case of a higher power consumption of the means of locomotion or the electrical system, in order to ensure a reliable, albeit with higher losses, relative voltage position between the first energy source and the second energy source. Moreover, the circuit arrangement can assume a third operating state in which the first transistor and the second transistor are open, in other words, have no conductivity in one direction.

As is conventional in the art, smoothing capacitances may be provided in parallel with the first power source and the second power source to smooth the voltages generated by the circuitry.

According to a second aspect of the present invention, an electrically driven means of transport is proposed which comprises a circuit arrangement according to the first aspect of the invention. The circuit arrangement may in particular be provided between an electrochemical energy source (eg battery, accumulator, or the like) and a fuel cell. A bus system and / or a sensor are connected in terms of information technology to the circuit arrangement in order to enable the inventive activation of the predefined operating state in response to predefined operating conditions by a corresponding control of the transistors.

Brief description of the drawings

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the drawings:

1 a schematic overview of components of an embodiment of a means of transport according to the invention;

2 a schematic representation of a vehicle electrical system with an embodiment of a circuit arrangement according to the invention;

3 a schematic representation of a vehicle electrical system with a second embodiment of a circuit arrangement according to the invention;

4 a schematic representation of a vehicle electrical system with a third embodiment of a circuit arrangement according to the invention;

5 an operating map illustrating voltages of a fuel cell and of an electrochemical energy store as a function of the state of charge and when the vehicle is at a standstill;

6 a comparison of the battery or fuel cell currents as a function of the DC link current;

7 an operating map illustrating voltages of an electrochemical energy store in response to its state of charge and a fuel cell; and

8th one opposite 4 simplified circuit according to another embodiment of the present invention.

Embodiments of the invention

1 shows a car 10 as an embodiment of a means of transport according to the invention, which via a circuit arrangement according to the invention 1 coming from a battery 3 as a first energy source or from a fuel cell 4 traction energy derived from a second energy source for use in an electric motor 2 as an example of a vehicle electrical system 2 taught.

2 shows the schematic structure of a vehicle electrical system according to the present invention, in which the electric motor 2 as a three-phase electric machine via an inverter 5 supplied from a DC electrical system with traction energy. A circuit arrangement according to the invention 1 in the form of a DC / DC converter conveys the voltage levels between a battery 3 with a terminal voltage U _Bat and a fuel cell 4 with a clamping voltage U _BZ . An evaluation unit 6 controls the aforementioned components and ensures the exchange of information. In particular, either a desired voltage U _1soll , a desired power P _1soll and a desired current I _1soll to the circuit _{arrangement according} to the invention 1 outputted to set the switching states of the transistors (not shown) accordingly.

3 shows a circuitry known from the prior art arrangement in which the circuit arrangement 1 is symmetrical. Two smoothing capacities C _Bat , C _BZ are the connections for the battery 3 or the fuel cell 4 connected in parallel. Between the capacitances C _Bat , C _BZ is a full bridge of four transistors T1, T2, T3, T4, wherein the common nodes of each two transistors are electrically connected together by the inductance L. According to the prior art, at a terminal voltage of the fuel cell 4 U _BZ larger U _Bat the second transistor T1 is closed, the first transistor T2 is opened and the transistors T3, T4 operated in a clocked manner. This results in the transistors T3, T4 switching losses and line losses. Line losses also occur in the second transistor T1. In a state in which the terminal voltage of the fuel cell U _{BZ is} smaller than U _Bat , the transistors T1, T2 are operated in a clocked manner, the transistor T3 is closed and the transistor T4 is opened. Accordingly occur in the transistors T1, T2 switching losses and conduction losses and additional line losses in the transistor T3.

4 shows a modification of the invention in 3 illustrated arrangement in which the circuit arrangement 1 is designed asymmetrically. In this case, the transistor T4 is removed and the transistor T3 is replaced by a short circuit. Despite overlapping voltage bands on the illustrated DC / DC converter (ie, the terminal voltage of the battery U _Bat is greater or smaller than the terminal voltage of the fuel cell U _BZ ) a Hochsetzstellertopologie (also multi-phase possible) is used. The control / control of the boost converter is designed so that it can be divided into three states in principle. In a first state, the second transistor T1 is closed, while the first transistor T2 is opened (blocks). In a second operating state, both transistors T1, T2 are operated in a clocked manner, while in a third operating state both transistors T1, T2 are operated open / closed. Is the second transistor T1, as shown by an optional, in the direction of the battery 3 replaced by the diode D, which fulfills the function of the inherent diode of the second transistor T1, the aforementioned states of the rigid coupling (predefined first state) and the switched-off state are identical. If a predefined operating state of the means of locomotion is detected, the state of the rigid coupling is actively selected, whereby a clocking is prevented.

5 shows a map in a state of low power consumption of the drive train, at the same time the battery is charged by means of a fuel cell. Here, the fuel cell is rigidly coupled to the battery (predefined first state). Accordingly, a compensation current flows into the battery, whose characteristics are plotted for different states of charge (SoC). The fuel cell charges the battery with a maximum current of approx. 30 A on the charge curve I (t) shown. The transhipment is completed when the battery has reached the quiescent voltage of the fuel cell.

6 shows two maps for the currents of the fuel cell (I _BZ ) and the battery (I _Bat ) over the DC link current I _ZK in the case of a normal driving operation with an empty battery (SOC _Min ). A first operating point AP1 lies on the edge contour of the hatched marked operating fields. The edge contour characterizes the predefined state of a rigid coupling without cyclic operation. In partial load operation, the DC / DC converter according to the invention can be operated in the state of rigid coupling. The currents are defined by the edge contour of the two operating maps. Up to a DC link current of approx. 40 A, which corresponds to a load current of 15 kW, the battery will in no case run flat because the battery is being charged (negative currents IBat). In full load operation or in operating states above the operating point AP1, the DC / DC converter can be operated in a clocked manner (eg operating point AP2). The currents I _Bat , I _BZ within the system can be regulated and both the fuel cell and the battery extended to the load limits.

• – „I_DYNCHA” einen Strom, welcher in einem Ladezustand nur kurzzeitig mit hoher Stärke fließt,
• – „I_CHA” einen Strom, welcher in einem Ladezustand längerfristig mit hoher Stärke fließt,
• – „I_DIS” einen Strom, welcher in einem Entladezustand längerfristig mit hoher Stärke fließt und
• – „I_DYNDIS” einen Strom, welcher in einem Entladezustand nur kurzzeitig mit hoher Stärke fließt.

7 shows a map to illustrate the requirements in the system design. The rest voltage of the battery must be greater than the rest voltage of the fuel cell at a maximum state of charge. It should be noted that the standby voltage of the battery is a function of the state of charge (SoC). To fully utilize the overall system performance over the full range of battery different states of charge, the voltage of the battery must be greater than the voltage of the fuel cell at a dynamic current output of the fuel cell at a dynamic discharge current of the battery. In addition, the equalizing current must not overload the battery or the fuel cell at standstill. Mark in the diagram

• - "I _DYNCHA " a current which flows in a state of charge only for a short time with high intensity,
• - "I _CHA " a current that flows in a state of charge in the long term with high strength,
• - "I _DIS " a current which flows in a discharge state in the long term with high strength and
• - "I _DYNDIS " a current which flows in a discharge state only for a short time with high strength.

8th shows one opposite 4 simplified circuit in which only a first transistor T2, a diode D and an inductance L between the battery 3 and the fuel cell 4 are provided, which form a unidirectional DC / DC converter. In dependence on a predefined operating state of the means of locomotion or its vehicle electrical system, a clocked operation of the first transistor T2 is prevented in order to reduce switching losses.

LIST OF REFERENCE NUMBERS

1

circuitry

2

Electric machine

3

battery

4

fuel cell

5

inverter

6

evaluation

10

car

S1 to S4

Sagittarius

T1 to T4

transistors

I _ZK

DC link current

I _BZ

A fuel cell power

I _Bat

battery power

U _Bat

battery voltage

U _BZ

fuel cell voltage

C _Bat , C _BZ

smoothing capacitors

P _1soll

power

I _1soll

Target current

U _1soll

Target voltage

SoC

State of charge, state of charge

IdynCha

Short term possible charging current limit

I

Trickle charge current limit

IDIS

Dauerentladestromgrenze

IdynDis

Short term possible discharge current limit

Claims (11)

Circuit arrangement for switching electrical energy in a vehicle electrical system of a means of transportation ( 10 ) between a first low-voltage energy source ( 3 ) and a second low-voltage energy source ( 4 ) comprising: - a first transistor (T2), - an inductance (L) and - an evaluation unit ( 6 ) wherein the first transistor (T2) and the inductance (L) form a switching power supply, and the evaluation unit ( 6 ) is set up, a clocked operation of the first transistor (T2) in response to the detection of a predefined operating state (Z1) of the means of transport ( 10 ) with continuous current flow through the inductance (L) to prevent. Circuit arrangement according to claim 1 further comprising - a second transistor (T1) as part of the switched-mode power supply, wherein the evaluation unit ( 6 ), a clocked operation of the first transistor (T2) and the second transistor (T1) in response to the detection of a predefined operating state (Z1) of the means of transport ( 10 ) with continuous current flow through the inductance (L) to prevent. Circuit arrangement according to claim 2, wherein - The first transistor (T2) has an inherent diode, and / or - The second transistor (T1) has an inherent diode. Circuit arrangement according to Claim 2 or 3, wherein - a first terminal of the second transistor (T1) is connected to a first terminal for the first energy source ( 3 ) is electrically connected, - a second terminal of the second transistor (T1) with - a first terminal of the inductance (L) and - a first terminal of the first transistor (T2) is electrically connected, - a second terminal of the first transistor (T2) with - the second connection for the first energy source ( 3 ) and - a second connection for the second energy source ( 4 ) is electrically connected, A second terminal of the inductance (L) with a first terminal for the second energy source ( 4 ), wherein - the second transistor (T1) and the first transistor (T2) in dependence on a driving state variable by the evaluation unit ( 6 ) are energized to receive electrical energy from the first energy source ( 3 ) and / or the second energy source ( 4 ) into a connection for the on-board network of the means of transport ( 10 ) bring to. Circuit arrangement according to one of claims 2 to 4, wherein the arrangement is set up, In a third operating state (Z3) to block the second transistor (T1) and the first transistor (T2), - In the predefined operating state (Z1) to turn on the second transistor (T1) conductive and the first transistor (T2) to lock and - To operate in a second operating state (Z2) the first and the second transistor (T1, T2) clocked. Circuit arrangement according to one of the preceding claims, wherein - the predefined operating state (Z1) - a partial load operation and / or - a travel below 50 km / h of the means of locomotion ( 10 ) and / or - in response to the detection of the predefined operating state (Z1), the first voltage-soft energy source ( 3 ) and the second voltage-soft energy source ( 4 ) are permanently electrically connected by means of the inductance (L). Circuit arrangement according to one of the preceding claims, wherein the first energy source ( 3 ) and the second energy source ( 4 ) are provided for supplying a traction machine and set up. Circuit arrangement according to one of the preceding claims, wherein the predefined operating state (Z1) is characterized by a low on-board network load or a predefined state of charge (SoC) of the first energy source (Z1). 3 ). Circuit arrangement according to one of the preceding claims, wherein - the first energy source ( 3 ) - an accumulator and / or - a fuel cell and / or - a supercap and - the second energy source ( 4 ) - a fuel cell and / or - an accumulator and / or - a fuel cell with an inverter ( 5 ) for an electric traction machine ( 2 ) and / or - an accumulator with an inverter ( 5 ) for an electric traction machine ( 2 ). Circuit arrangement according to one of the preceding claims, wherein - a first capacitance (C _Bat ) having a first connection to the first connection for the first energy source ( 3 ) and with a second connection to a second connection for the first energy source ( 3 ), and / or - a second capacitance (C _BZ ) having a first terminal at the first terminal for the second energy source ( 4 ) and with a second connection to a second connection for the second energy source ( 4 ) is provided. Electrically drivable means of locomotion ( 10 ) comprising a circuit arrangement ( 1 ) according to any one of the preceding claims.

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