WO2020074383A1

WO2020074383A1 - Charging device and electric drive system comprising a charging device of said type

Info

Publication number: WO2020074383A1
Application number: PCT/EP2019/076901
Authority: WO
Inventors: Katja Stengert
Original assignee: Thyssenkrupp Ag
Priority date: 2018-10-08
Filing date: 2019-10-04
Publication date: 2020-04-16
Also published as: DE102018124787A1; DE212020000285U1; CN216467384U

Abstract

The invention relates to a charging device for charging a battery (7) of a motor vehicle fitted with an electric drive motor (2), having at least one inductance, and a drive converter (3) which converts a direct voltage of the battery (7) for the electric drive motor (2) when the motor vehicle is being driven, and comprises an intermediate circuit centre point (5). The at least one inductance, together with the drive converter (3), is used as a step-up converter for charging the battery (7). For optimizing the power, the intermediate circuit centre point (5) is connected or can be connected permanently or temporarily to an input voltage of a charge source (8) and/or the inductance.

Description

Charging device and electric drive system with such

Loading device

description

The invention relates to a charging device for charging a battery of a motor vehicle designed with an electric drive motor and an electric drive system with such a charging device.

Different charging concepts are used to charge electric vehicles. Charging with alternating current via the house socket is available almost everywhere, but only has a low charging power of less than 5 kW.

In contrast, when charging snow from DC sources (DC charging), for example using special charging stations, much higher outputs are possible (50 kW and above). However, this requires adjustment of the voltage if that

Voltage level of the charging station, typically 400 V DC, is lower than the voltage level of the vehicle battery, especially of future generations with typically 800 V DC.

To adjust the voltage level, step-up converters, also known under the terms “step-up converter”, “boost converter” or “step-up converter”, can be used as separate structural units. However, it is also possible to use an already existing inverter referred to as "inverter") of the traction or electric motor as a step-up converter

To use DC voltage conversion. In order not to have to use additional inductors for the step-up position in the inverter, it is

known to be possible to use the windings of the traction motor as charging inductors:

DE 10 2016 209 905 A1 shows a rapid charging unit for an electric vehicle, the inverter of the traction motor serving as a step-up converter in connection with the motor coils.

DE 10 2009 052 680 A1 shows the connection of a step-down converter in front of the inverter.

DE 10 2016 218 304 B3 shows a 3-level inverter in an NPC configuration (abbreviation for "neutral point clamped") for an electric vehicle, which in the Fast charging mode can be operated as a step-up converter, external inductors being used for the step-up position.

In addition to the 2-level inverters, which have 2 voltage levels, e.g. B. OV and 800V, there are also 3-level inverters for electric vehicles, which also have a third voltage level, e.g. B. 0V, 400V and 800V.

In particular with 3-level inverters with NPC topology, the voltages applied to the switching elements of the half bridges are reduced

Blocking direction to about half of the nominal voltage, z. B. 400V. Accordingly, these are only designed for this reverse voltage. At the same time, the permissible reverse voltage prohibits switching states in which a voltage higher than the permissible reverse voltage is present. Such an impermissible state exists, for example, if only one switching element blocks while the others are all switched on. This also applies in operation as a step-up converter.

Since a simultaneous switching of two switching elements is practically not possible, the switching elements must be switched to target states at different times, e.g. B. first an inner and then an outer switching element are switched. During this time, a current flows into the center of the intermediate circuit and undesirably and further charges it (or its capacitor) with each switching cycle. Exceeds the tension of the

DC link center point the permissible reverse voltage of the switching elements or diodes or if the voltage of the DC link center point exceeds the permissible voltage of the capacitor, the element concerned will fail and lead to a defect in the inverter. This must be avoided.

In order to charge a battery of an electric vehicle with existing DC charging stations, an adaptation element in the form of a DC / DC converter is desired on the vehicle side. Now comes a 3-level NPC as the switching topology

Inverters are used and if you want to use them as DC / DC converters at the same time, a solution for voltage balancing of the DC link center voltage (in the DC link center between two DC link capacitances CI and C2), i.e. maintaining or maintaining a DC link center point voltage.

It is therefore an object of the present invention to improve

Charger for charging a battery with an electric motor to provide trained motor vehicle. Particular care should be taken to ensure that the voltage at the center of the DC link does not shift to a technically relevant extent during charging, especially not beyond the permissible reverse voltage of the semiconductors.

According to the invention, a charging device according to claim 1 is used for this purpose

provided. In particular, it is a charging device for charging a battery of a type which is designed with an electric drive motor

Motor vehicle, with an inductance and a drive converter, which in

Drive operation of the motor vehicle converts the DC voltage of the battery for the electric drive motor and has an intermediate circuit center, the inductance together with the drive converter for one

Charging operation of the battery serves as a step-up converter. Here is the

Intermediate circuit center point with an input voltage of a charge source and / or the inductance via a compensating conductor in charging operation permanently or temporarily interconnectable or interconnectable. Here, under one

permanent or temporary interconnection can be understood that e.g. B. there is no switch or a switch to interrupt the compensating conductor.

This prevents the intermediate circuit capacitors used for symmetrical voltage distribution from being charged too differently during the charging process and the capacitor and / or

Switching elements or diodes occurs. Via the compensating conductor, a

Equalization current, which would otherwise accumulate in the capacitor and in extreme cases would charge it up to battery voltage, is discharged.

In order for the drive converter to act as a step-up converter, this, in particular its switching units in the form of transistors,

can be controlled accordingly to the input voltage (that of the

Charge source) to a higher output voltage (that of the vehicle battery). The switching units are opened and closed periodically. According to the intermediate circuit center is interconnected such that a compensating current can flow off and one

Pre-charge voltage is maintained. B. happen that a compensating conductor is connected to the inductor starting from the intermediate circuit center. The compensating conductor is preferably separable, for. B. carried out by means of a circuit breaker. This allows the compensating conductor for the

Ferry operations are separated so that no leakage currents can flow when driving.

The intermediate circuit center point is preferably connected or connectable to the input voltage via a resistor. It is therefore ensured that the current to the intermediate circuit center and the charge source and / or inductance is limited.

The resistor is preferably designed as a PTC resistor (positive temperature coefficient), so that the current flowing through the compensating conductor is limited, in particular in the event of a fault.

It has also proven to be advantageous if the inductance has at least one winding of the electric drive motor or is formed by at least this. This saves additional components and thus reduces costs and space requirements.

A plurality of inductors are preferably provided, all more preferably as windings for exciting the drive motor, in the form of coils or

Wave winding are formed. With the aim of controlling the electric motor for ferry operation and efficient voltage conversion in the

To provide charging, the drive converter has three

Voltage phases a 3-level inverter, especially with one

Half bridge for each of the three phases. Each 3-level inverter is connected to one of the three windings of the electric drive motor. This also has the advantage of being able to use all three windings for one step-up converter, in particular individually or simultaneously, and thus to increase the maximum possible charging power.

The 3 half bridges preferably have the same intermediate circuit center. The windings of the motor windings used for the step-up position preferably have a common star point. Thus, the interconnection of the DC link center and inductors or motor windings is only one line possible, which also saves components and materials.

In a further advantageous embodiment, the intermediate circuit center is arranged between two capacitors connected in series. In addition, at least one additional capacitance can be connected in parallel and / or in series to at least one of the capacitances in order to change the size of the capacitance in charging mode and / or ferry mode.

The charging device preferably has a control circuit for controlling the drive converter, in particular its half-bridges, as a step-up converter for the charging operation and as an inverter for the driving operation. The control circuit can thus operate the drive converter in both operating modes and thus save costs for additional components.

The disconnector can advantageously be opened and closed cyclically in charging mode. This means that the DC link center point voltage can be cyclically shifted (increased and decreased) without exceeding a permissible reverse voltage. The DC link center point voltage can be raised on average. An increase in

DC link center point voltage in charging operation can have an advantageous effect on the efficiency. For this reason, an increased intermediate circuit center voltage, which is however below the permissible reverse voltage, can

be desired.

The DC link voltage is preferably around 800V and the balanced DC link center point voltage at 400V. The is in charging mode

DC link center voltage preferably increased periodically - z. B. by + 20% - because variations in the operating cycle can have a positive effect on efficiency.

The present invention also provides an electric drive system with a charging device according to the invention and a vehicle battery.

When using the charging device according to the invention or as

charging method according to the invention has proven to be advantageous if at least the following steps - in particular in this order - are carried out:

1. As soon as the engine is switched off, the DC link and thus the DC link capacitors discharge automatically.

2. The charging device is connected to a charging station with a voltage level lower than that of the vehicle battery as a direct voltage source: The charging station precharges the intermediate circuit capacitors of the drive system or the charging device to the voltage level of the charging station.

3. Only when the DC link capacitors have been precharged is the isolating switch between the DC link center and the inductor or

Charge source closed.

4. The charging process for the vehicle battery can begin.

Another charging method according to the invention is provided if the

Capacitors of the charging station must be pre-charged from the vehicle. This procedure is intended for China, for example, because there, unlike in Europe and the USA, the charging stations do not pre-charge their own DC link and vehicle DC link. The corresponding loading process provides at least the following steps - in particular in this order:

1. The engine is switched off and the intermediate circuit or the capacitors discharge themselves.

2. The charging device is connected to the charging station with a voltage level lower than that of the vehicle battery as a DC voltage source.

3. Close the isolating switch in the compensating conductor so that the

DC link center is connected to the inductance and the charge source.

4. precharging the intermediate circuit of the vehicle via a precharging resistor of the charging device, the precharging resistor preferably between

Vehicle battery and the intermediate circuit capacities is arranged and can be bridged by means of a switch for driving. At the same time, the DC link of the charging station is precharged to the voltage of the DC link center voltage via the closed compensating conductor.

4a. If necessary, the 3-level inverter can be used as a stepdown converter or stepup converter. 5. Start the loading process.

The following drawings show preferred exemplary embodiments of the charging device according to the invention, these not being used as a restriction of the invention, but essentially serving as an illustration.

Show it

1 shows a circuit diagram of an electric drive system with a charging device according to the invention;

FIG. 2 shows a circuit diagram of the electrical drive system according to FIG. 1, in this case in the charging mode;

Figure 3A shows a detailed view of the circuit diagram of the half-bridge of the

Drive converter of the electrical drive system from Figure 1 and Figure 2;

Figure 3B signal diagrams of the flow of individual components of the

Half bridge from FIG. 3A;

Figure 4 is an equivalent circuit diagram of the half-bridge with corresponding

Control elements for the transistors to act as step-up converters; and

Figure 5 shows a circuit diagram of an electric drive system with a charging device according to the invention according to another preferred embodiment.

FIG. 1 shows an electric drive system 1 which is equipped with an electric motor 2. The electric motor 2 has three inductors LI, L2 and L3 in the form of windings connected to a star point, each of which is supplied with current by means of a half bridge 4a, 4b and 4c of a drive converter 3 and the electric motor 2, in particular its rotor (not shown) , can set in rotation. The half bridges 4a, 4b and 4c are controlled in such a way that the current of the individual half bridges is in each case 120 ° in Phase is shifted towards each other. Each half-bridge 4a, 4b and 4c each has the following components: four transistors (e.g. MOSFETs or IGBTs) TI, T2, T3 and T4, each with a diode D1, D2, D3 and D4, and two diodes D5 and D6 that with an intermediate circuit center 5 of the drive converter 3

are connected. The intermediate circuit center 5 lies between the two intermediate circuit capacitors CI and C2, which are arranged parallel to the three half bridges 4a, 4b and 4c. The intermediate circuit center point 5 is electrically connected to each half bridge 4a, 4b and 4c via the corresponding diodes D5 and D6. The three inductors LI, L2 and L3 of the electric motor 2 are in one

Star connection interconnected. Furthermore, a compensating conductor 9 runs from the intermediate circuit center point 5 via a disconnector S1 and a decoupling resistor RI to the center of the star connection in FIG

Inductors LI, L2 and L3 of the electric motor 2 and one

Plug connection 6 for a charge source (not shown). This

Plug connection 6 has two conductors and can be connected via a first one

Plug connection switch and a second plug connection switch S2 and S3 are separated from the drive system 1 - as shown in this case in FIG. 1. The switch S2 is connected to the negative pole of the battery 7

DC link capacitance C2 and the half bridges 4a, 4b and 4c connected. The battery has a voltage level of e.g. B. 800V. The switch S3 is connected to the center point of the star connection of the electric motor 2 and to the compensating conductor 9 or the decoupling resistor RI. The vehicle battery 7 is connected to the drive converter 3 and supplies it with a

DC voltage. For the drive mode, the electric drive system 1 has a controller (not shown) which is designed to control the half bridges 4a, 4b and 4c and thus their transistors TI, T2, T3 and T4, in order to generate a current which is too the other two currents are shifted by 120 ° phases. Switches S1, S2 and S3 are open during drive or travel mode.

FIG. 2 shows a circuit diagram of the electrical drive system according to FIG. 1. Here, the electrical drive system 1 is in the charging mode, whereby, in contrast to FIG. 1, the switches S1, S2 and S3 are closed and a charging source 8 is, for example, B. is connected in the form of a charging station as a DC voltage source to the connector 6. Since the charging source 8 has a voltage of 400 V (compared to a battery voltage of 800 V), this will be Drive system 1, in particular the windings LI, L2 and L3 and the

Half bridges 4a, 4b and 4c, used as step-up converters or controlled accordingly.

FIG. 3A and FIG. 3B show a half bridge 4a with the

DC link capacitors CI and C2 as well as five signal diagrams for in particular the control of transistors T3 and T4, so that the half bridge in conjunction with the inductance LI of the electric motor (not shown) acts as a step-up converter. It can be seen from the signal diagrams that an alternating current flows through the inductance LI, which is connected to the half-bridge 4a. In order to control the current from the inductance LI to the vehicle battery 7 (see FIG. 1 or 2), the transistors T3 and T4 are periodically closed. Since the transistors are not designed to block the complete voltage of the vehicle battery, and the transistors can never be switched simultaneously, transistor T4 is switched on first and then transistor T3 is closed or opened again in reverse order (see falling signal edge). In the short time in which the transistor T3 conducts and the transistor T4 is blocked or opened, a short current pulse flows through the diode D6 to the capacitor C2. This protects the transistors T3 and T4 against overvoltage; on the other hand, the current flow charges the capacitor C2 and thus changes the voltage level at the intermediate circuit center point 5. In order to prevent the intermediate circuit center point voltage from rising above the permissible reverse voltage, the compensating conductor 9 (see FIGS. 1 and 2) is used, which is controlled by the switch S1 and the Resistor RI is connected to the voltage source and thus creates a voltage equalization. As soon as the two transistors T3 and T4 are blocked, flows in

Charging current via the diode D2 and thus via Dl to the vehicle battery 7 (see FIGS. 1 and 2). The transistors TI and T2 are blocked for the entire time.

Figure 4 shows a simplified circuit diagram of the electrical drive system of the present invention. Here, only a half bridge 4a with the intermediate circuit capacitances CI and C2 is shown. Furthermore, an inductance LI is shown as an example of a winding of an electric drive motor. The switch S1 is opened and closed via a step signal 01, the switch S1 being able to send a corresponding signal to the control circuit 12 for controlling the half-bridge 4a as a step-up converter. Is the switch S1 closed, the control circuit 12 is supplied with a square-wave signal with a frequency of 20 kHz (see component A2) instead of a 0 V signal (see component Al). Here, a corresponding signal changeover switch Bl is controlled by the switch S1. The square wave signal from A2 is sent to a first one

Signal modifier ZI and a second signal modifier Z2 sent. The signal modifier ZI is connected to the transistor T3 and the signal modifier Z2 is connected to the transistor T4. Here, the signal is modified such. B. by a time shift of the signal that transistor T4 blocks first and then transistor T3.

FIG. 5 shows a further electric drive system 1 a

charging device according to the invention according to a further preferred

Embodiment. Compared to the electric drive system 1 from FIGS. 1 and 2, the drive system 1 a differs in that a precharge resistor 10 is arranged between the transistor CI and the car battery 7 and can be bridged via a bypass switch 11. This makes it possible to charge the capacities CI and C2 before the charging process and to raise the DC link center to a corresponding voltage level. Switch 11 is closed during travel mode. Before the charging operation, the switch 11 is opened to precharge the capacities; then the switch 11 for the charging process of the vehicle battery is closed again. In connection with the compensating conductor 9 (with the switch S1 closed), an external inductance z. B. a charging station, precharged to the intermediate circuit center voltage lying below the battery voltage.

Reference list

1 electric drive system

la electric drive system, another embodiment

2 electric motor / electric drive motor

3 inverters / drive inverters

4a First half bridge for the 1st phase

4b Second half bridge for the 2nd phase

4c Third half bridge for the 3rd phase

5 DC link center

6 plug connection

7 vehicle battery

8 charging source or charging station

9 compensating ladder

10 pre-charging resistor

11 Pre-charging resistor bypass switch

12 control circuit

LI First motor winding

L2 Second motor winding

L3 third motor winding

CI First capacitor

C2 Second capacitor

TI First transistor

T2 second transistor

T3 third transistor

T4 fourth transistor

Dl First free-wheeling diode

D2 Second free-wheeling diode

D3 Third free-wheeling diode

D4 Fourth freewheeling diode

D5 First intermediate diode

D6 Second intermediate diode

RI decoupling resistor

51 disconnector

52 First connector switch

53 Second connector switch Al OV signal

A2 square wave signal with constant frequency

Bl controlled signal switch

ZI signal reducer - starting from the beginning of the signal Z2 signal reducer - starting from the end of the signal

01 step signal

Claims

Expectations

1. Charging device for charging a battery (7) with one

electric drive motor (2) trained motor vehicle, with

- an inductance,

- A drive converter (3) which converts the DC voltage of the battery (7) for the electric drive motor (2) during drive operation of the motor vehicle and has an intermediate circuit center (5),

the inductor, together with the drive converter (3), serves as a step-up converter for charging the battery (7),

That means that

the intermediate circuit center (5) is permanently or temporarily connected to an input voltage of a charge source (8) and / or the inductance via a compensating conductor (9).

2. Loading device according to claim 1,

That means that

the intermediate circuit center (5) can be connected to the inductor via a resistor (RI).

3. Loading device according to claim 1 or 2,

That means that

the inductance (LI) is formed by at least one winding of the electric drive motor (2).

4. Loading device according to one of claims 1 to 3,

That means that

the drive converter (3) has one for three voltage phases

Half bridge (4a; 4b; 4c), each half bridge being connected to one of the three windings (LI; L2; L3) of the electric drive motor (2).

5. Loading device according to claim 4,

That means that

each half-bridge (4a; 4b; 4c) has the same DC link center (5).

6. Loading device according to one of claims 1 to 5,

That means that

the intermediate circuit center (5) is arranged between two capacitors (CI; C2) connected in series, the battery (7) being connectable parallel to the capacitors (CI; C2).

7. Loading device according to one of claims 1 to 6,

marked by

a control circuit (10) for controlling the drive converter (3), in particular its half bridge (4a; 4b; 4c), as a step-up converter.

8. Loading device according to one of claims 1 to 7,

marked by

an isolating switch (S1) for interconnecting the intermediate circuit center (5) with the input voltage of the charge source (8) and / or the inductance (LI).

9. Loading device according to claim 8,

That means that

the isolating switch (Sl) is designed in such a way that it connects to the

Charging device connected to the charging source (8) and thus the intermediate circuit center (5) with the input voltage of the

Charge source (8) and / or the inductance (LI) to connect.

10. Loading device according to one of claims 8 to 9,

That means that

the isolating switch (Sl) is designed to periodically open and close during charging.

11. Electric drive system (1) with a charging device according to one of the preceding claims.