BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a switching arrangement, in particular a DC-DC voltage converter, for charging the electrical energy store of a vehicle.

Vehicles having electrical propulsion (e.g., a plug-in hybrid electric vehicle (PHEV), or a battery electric vehicle (BEV)) comprise electrical energy stores (e.g., batteries) that can be connected to a charging station by means of a charging apparatus of the vehicle and charged. To charge the electrical energy stores of such electric and/or hybrid vehicles, various conductive, i.e., wired, charging technologies exist. In the case of what is known as AC charging or alternating current charging, the charger producing the direct current (also referred to as DC current) for charging the electrical energy store is located in the vehicle. A charging cable between the charging station and the vehicle is used to transfer an AC (alternating current) current. In the case of what is known as DC charging or direct current charging, the charger producing the direct current for charging the electrical energy store is located in the charging station. The charging cable is therefore used to transfer DC (direct current) current.

At the present time, DC charging typically involves a maximum voltage of 500 V and a maximum current of 120 A being used, charging currents of 350 A being meant to be possible in future. In order to increase the charging power further, the charging voltage is also meant to be increased to 800 V or 1000 V (for a maximum charging current of 350 A). As a result, the onboard electrical system voltage of a high voltage system of a vehicle is also increased to 800 V or 1000 V, which means that the vehicle cannot readily be charged at a 500 V charging station.

The present document is concerned with the technical object of enabling an at least partly electrically propelled vehicle having a relatively high onboard electrical system voltage (e.g., 800 V or 1000 V) to be charged at a charging station having a relatively low charging voltage (e.g., 500 V) in an efficient manner.

The object is achieved by the features of the independent patent claims. Advantageous embodiments are described in the dependent claims, inter alia. It is pointed out that additional features of a patent claim dependent on an independent patent claim are able, without the features of the independent patent claim or only in combination with a subset of the features of the independent patent claim, to form a separate invention, independent of the combination of all of the features of the independent patent claim, that can be made the subject matter of an independent claim, of a divisional application or of a subsequent application. This applies in the same manner to technical teachings described in the description that are able to form an invention independent of the features of the independent patent claims.

According to one aspect, a switching arrangement for a vehicle (in particular for a road motor vehicle) is described. The vehicle can comprise an electrical energy store for storing electrical energy. In addition, the vehicle can comprise an electrical machine that can be operated using energy from the energy store. The electrical machine can be used to propel the vehicle. The energy store can provide electrical energy at an onboard electrical system voltage. In this case, the onboard electrical system voltage can be, for example, in a region of 800 V or 1000 V.

The switching arrangement comprises a switching unit having multiple switches. In this case, a switch can comprise a transistor, in particular an IGBT (insulated gate electrode bipolar transistor) or a MOSFET (metal oxide semiconductor field effect transistor), and/or a semiconductor diode. At least some of the switches in this case can be arranged in series in order to form a half-bridge.

The switching unit is configured to couple at least one phase of the electrical machine (e.g., a three phase synchronous machine) of the vehicle to the DC onboard electrical system voltage of the vehicle in different configurations in order to generate an AC phase voltage and/or an AC phase current for the phase of the electrical machine. The switching unit can be part of an inverter configured to generate from the DC onboard electrical system voltage a three phase current for operating a three phase machine. The switching arrangement can have, e.g., L switching units for L different phases of the electrical machine, where L>1, e.g., L=3.

Additionally, the switching arrangement comprises at least one coil and isolating switches (e.g., two isolating switches per phase). The isolating switches in this case can be configured to couple the switching unit to a DC charging voltage or to decouple said switching unit from the charging voltage (or to couple it to a charging interface, for example, a charging socket, of the vehicle or to decouple it from the charging interface) via the coil. The charging voltage can be lower than the vehicle electrical system voltage.

A first isolating switch can couple or decouple a first point inside the switching unit to or from a first pole of the charging voltage via the coil. In addition, a second isolating switch can couple or decouple a second point inside the switching unit (possibly directly) to or from a second pole of the charging voltage. An isolating switch can comprise, e.g., an IGBT, a relay or a MOSFET. The isolating switches can therefore be used to provide a connection between the switching unit (and therefore between the onboard electrical system voltage) and the charging voltage. The coil and the switching unit can then be used in combination as a DC-DC voltage converter between the charging voltage (which is, e.g., in the region of 500 V) and the onboard electrical system voltage.

The switching arrangement further comprises a controller (e.g., a microprocessor). The controller is programmed so as, in a converter mode of the switching arrangement, to prompt the isolating switches to couple the switching unit to the charging voltage via the coil. It is therefore possible for a connection to be set up between the charging voltage (i.e., to the charging interface of the vehicle) and the switching arrangement and hence indirectly to the onboard electrical system voltage (i.e., to the energy store of the vehicle). Additionally, the controller is programmed so as, in the converter mode of the switching arrangement, to operate the switching unit such that the coil is used to convert electrical energy at the charging voltage into electrical energy at the onboard electrical system voltage. In particular, the switching unit can be operated in combination with the coil as a DC-DC voltage converter, e.g., as a boost converter, in particular as a three level boost converter.

Secondly, the controller is programmed so as, in an inverter mode of the switching arrangement, to prompt the isolating switches to decouple the switching unit from the charging voltage. The onboard electrical system voltage can therefore be decoupled from the charging voltage and/or from the charging interface in order to allow undisturbed inverter operation of the switching unit. The controller is further programmed so as, in the inverter mode of the switching arrangement, to operate the switching unit such that the onboard electrical system voltage is taken as a basis for generating the phase voltage and/or the phase current for the phase of the electrical machine.

A switching arrangement for a vehicle is therefore described that can provide both an inverter function and a DC-DC voltage converter function in a manner efficient in terms of installation space, weight and cost. This can allow 800 V energy stores in a vehicle to be charged using a 500 V charging station in an efficient manner.

The switching unit can comprise at least one first switch (e.g., at least one high side switch) configured to couple or decouple the phase of the electrical machine to or from a first pole (e.g., to or from a positive pole) of the onboard electrical system voltage. In addition, the switching unit can comprise at least one second switch (e.g., at least one low side switch) configured to couple or decouple the phase of the electrical machine to or from a second pole (e.g., to or from a negative pole) of the onboard electrical system voltage. In this case, the one or more first and second switches can form a half-bridge for the onboard electrical system voltage. This means that the one or more first and second switches can be arranged in series with one another between the two poles of the onboard electrical system voltage. The phase of the electrical machine can then be coupled to a midpoint of the half-bridge.

Such a half-bridge can provide at least one two level inverter in which the midpoint of the half bridge is coupled to the first pole or to the second pole of the onboard electrical system voltage in order to replicate an AC voltage (e.g., a sinusoidal AC voltage).

Secondly, such a half bridge in combination with the coil can provide at least one two level DC-DC voltage converter, in particular a boost converter, between the charging voltage and the onboard electrical system voltage. For this purpose, the coil can be arranged between the midpoint of the half bridge and the first pole of the charging voltage (via the first isolating switch). In addition, the second pole of the onboard electrical system voltage can be coupled to the second pole of the charging voltage (via the second isolating switch). Alternating activation of the first switch or the second switch in a sequence of PWM (pulse width modulation) periods can then effect a DC-DC voltage conversion.

An efficient combination of an inverter and a DC-DC voltage converter is therefore made possible.

The controller can be configured so as, in a converter mode, to actuate the switching unit in order to take the charging voltage as a basis for sequentially arranging the coil directly or indirectly between the first and second poles of the charging voltage in a first portion of a PWM period in order to magnetize the coil, and arranging the coil between the first pole of the onboard electrical system voltage and the first pole of the charging voltage in a second portion of a PWM period in order to demagnetize the coil. This sequence of portions can be repeated periodically in order to transfer electrical energy from the charging socket of the vehicle to the electrical energy store.

The switching arrangement can have one or more capacitors that are arranged between the first and second poles of the onboard electrical system voltage. The one or more capacitors can be used both in the converter mode and in the inverter mode to smooth the onboard electrical system voltage.

In particular, the switching arrangement can comprise a capacitive voltage divider having at least two series capacitors. The at least two series capacitors can be arranged in series between the two poles of the onboard electrical system voltage, and can split the onboard electrical system voltage into two or more (possibly identical) voltage elements. The use of a capacitive voltage divider can provide more than two voltage levels. This is advantageous both for the converter mode and for the inverter mode. In particular, this allows uniform operation of the electrical machine, on the one hand, and a uniform charging current, on the other hand, to be provided.

The switching unit can comprise at least two first series switches (in particular high side switches) configured to couple or decouple the phase of the electrical machine (i.e., the midpoint of the half bridge) to or from the first pole of the onboard electrical system voltage. In addition, the switching unit can comprise a first neutral switch configured to couple or decouple a voltage division point between the two capacitors of the capacitive voltage divider to or from the midpoint between the two first series switches. Such an arrangement of switches can provide a neutral voltage level (between the potential of the first pole and the potential of the second pole of the onboard electrical system voltage).

In a corresponding manner, the switching unit can comprise at least two second series switches (in particular two low side switches) configured to couple or decouple the phase of the electrical machine (i.e., the midpoint of the half bridge) to or from the second pole of the onboard electrical system voltage. Additionally, the switching unit can comprise a second neutral switch configured to couple or decouple the voltage division point to or from the midpoint between the two second series switches.

Overall, it is therefore possible for a switching unit for a 3 level inverter to be provided. This switching unit can then be used to provide a 3 level DC-DC voltage converter, in particular a 3 level boost converter. The controller can be programmed so as, in the inverter mode, to actuate the switching unit to take the onboard electrical system voltage as a basis for generating a positive, a negative and a neutral level for the phase voltage. As such, stable operation of the electrical machine can be made possible.

Secondly, the controller can be programmed so as, in the converter mode, to actuate the switching unit to take the charging voltage as a basis for sequentially magnetizing the coil via a first of the capacitors; demagnetizing the coil via the capacitors of the capacitive voltage divider; magnetizing the coil via a second of the capacitors; and demagnetizing the coil via the capacitors of the capacitive voltage divider. This succession can be repeated in a sequence of PWM periods in order to convert electrical energy at the charging voltage into electrical energy at the onboard electrical system voltage. As such, a stable charging current for charging the energy store of the vehicle can be provided.

The coil can be coupled firstly to the midpoint between the two first series switches and secondly, in particular via the first isolating switch, to the first pole of the charging voltage. In addition, the midpoint between the two second series switches can be coupled, in particular via the second isolating switch, to the second pole of the charging voltage.

The controller can be programmed so as, in the converter mode, to actuate (in particular to open) a first switch and a second switch in order to decouple both the coil and the second pole of the charging voltage from the midpoint of the half bridge (and hence from the phase of the electrical machine). In particular, the first switch coupled directly to the midpoint of the half bridge and the second switch coupled directly to the midpoint of the half bridge can be opened in the converter mode. As such, particularly energy-efficient DC-DC voltage converter operation can be made possible, since the switching unit is decoupled from the electrical machine.

The switching arrangement can comprise L switching units for L phases of the electrical machine, where L>1 (e.g., L=3). In addition, the switching arrangement can comprise L coils and L sets of isolating switches that are each coupled to one of the L switching units and to the charging voltage. The controller can be configured so as, in the converter mode, to operate the L switching units such that L parallel DC-DC voltage converters are provided between the charging voltage and the onboard electrical system voltage. As such, the charging power transferred via the switching arrangement can be increased. The DC-DC voltage converters can be operated in phase-shifted fashion (e.g., with a phase offset of 360°/L). This allows the ripple in the charging current to be reduced.

According to a further aspect, a method for operating a switching arrangement described in this document is described. The method comprises ascertaining whether the switching arrangement is meant to be operated in a converter mode or in an inverter mode. By way of example, it is possible to ascertain whether a charging process is meant to be performed or whether the vehicle is in driving mode. The method comprises, when the switching arrangement is meant to be operated in the converter mode, prompting the isolating switches to couple the switching unit to the charging voltage via the coil. Additionally, the method comprises operating the switching unit such that the coil is used to convert electrical energy at the charging voltage into electrical energy at the onboard electrical system voltage.

Secondly, the method comprises, when the switching arrangement is meant to be operated in the inverter mode, prompting the isolating switches to decouple the switching unit from the charging voltage. The method further comprises operating the switching unit such that the onboard electrical system voltage is taken as a basis for generating the phase voltage for a phase of the electrical machine.

According to a further aspect, a vehicle (in particular a road vehicle, e.g., a passenger vehicle, a truck or a motorcycle) is described that comprises the switching arrangement described in this document.

According to a further aspect, a software (SW) program is described. The SW program can be configured to be executed on a processor and to thereby carry out the method described in this document.

According to a further aspect, a non-transitory computer-readable storage medium is described. The storage medium can have an SW program configured to be executed on a processor and to thereby carry out the method described in this document.

It should be borne in mind that the methods, apparatuses and systems described in this document can be used either on their own or in combination with other methods, apparatuses and systems described in this document. In addition, any aspects of the methods, apparatuses and systems described in this document can be combined with one another in a wide variety of ways. In particular, the features of the claims can be combined with one another in a wide variety of ways.

The invention is described more specifically below on the basis of exemplary embodiments. In the drawing,

Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.

