Patent ID: 12261556

DETAILED DESCRIPTION

FIG.1shows a schematic of a motor vehicle1according to the disclosure, in the present instance an electric motor vehicle. The electric motor vehicle1comprises, in a drive train not otherwise shown, an electric machine, which is configured here as an externally excited synchronous machine2, also serving as the electric motor for the electric motor vehicle1. The externally excited synchronous machine2comprises a rotor having an exciter winding, not otherwise shown here for clarity of the drawing, as is the case for the stator windings of the stator, there being provided one for each of the three phases. The exciter winding is connected across a high-voltage component3, comprising an exciter circuit4, to a high-voltage network5of the motor vehicle1, having a higher voltage than a low-voltage network of the motor vehicle1, not being shown here. The operating voltage of the high-voltage network5can lie for example in a range of over 200 Volt, especially 350 to 860 Volt, this being a DC voltage network. It is fed from a battery6.

The stator windings of the externally excited synchronous machine2are connected across a power electronics layout7, comprising an inverter8, to the high-voltage network5. Of course, further high-voltage components or network components can also be provided in the high-voltage network5and connected to it, such as a DC voltage converter provided between the low-voltage network and the high-voltage network5, an onboard charger for the battery6, an electric air conditioning compressor and/or an electric heater. In the present instance, at least the power electronics layout7with the inverter8comprises an intermediate circuit having an intermediate circuit capacitor, while such electric energy storing capacitors, which may include suppression capacitors as well as intermediate circuit capacitors, can also be provided in other components, being hooked up in parallel.

The motor vehicle1moreover comprises a cooling device9, which also includes a cooling circuit for a cooling fluid, to be further explained below, bringing about a cooling of the inverter8and the exciter circuit4by way of a common cooling element.

The operation of the high-voltage network and the high-voltage components connected to it is controlled in the present instance by a central control device10, which is also designed in particular to carry out the method according to the disclosure.

FIG.2shows as an example a cooling element11of the cooling device9, which in the present instance comprises at least one duct and/or at least one cavity, not otherwise shown, through which the cooling fluid in the cooling circuit flows. Fastened on the cooling element11and thermally connected to it for heat dissipation are not only the power modules12for each phase, together forming the inverter8, but also an exciter power module13, in which the exciter circuit4is accommodated in a housing, so that this can also be cooled by way of the cooling element11.

The power modules12can have housings containing the corresponding power electronics components, especially including semiconductor switches. In the present instance, the power terminals14of the power modules12at the high-voltage network5as well as the power terminals15to the stator windings for the individual phases as well as corresponding actuation terminals16are also shown. These are not shown here for the exciter power module13, for sake of clarity of drawing.

FIG.3shows schematically a circuit diagram of the power electronics layout7with the inverter8as a circuit diagram. As can be seen, the inverter8comprises a B6 bridge circuit with corresponding components for each of three phases U, V and W, which are connected to corresponding stator windings17(here only suggested) of the stator of the externally excited synchronous machine2. In the present case, as an example, two intermediate circuit capacitors19are shown for the high-voltage network5, cf. the terminals18, although configurations are also conceivable in which the inverter8comprises only one intermediate circuit capacitor19or more than two intermediate circuit capacitors19.

In fault situations, during accidents, and for repair purposes, and possibly also in other cases where the user safety and functional safety must be assured, the intermediate capacitors19must be actively discharged as soon as possible, so that the least possible voltage remains in the high-voltage network5. This discharging is done in the present instance across the exciter circuit4, which is designed accordingly, as shown by the circuit diagram ofFIG.4.

As can be seen, the exciter circuit4comprises, between the terminals20for the high-voltage network and connection points21for the exciter winding24, indicated here by its inductance22and its resistance23and corresponding to the rotor winding, a bridge circuit25in the manner of a slightly modified half-bridge. This comprises four branches26,27,28,29, in each of which there are provided freewheeling diodes30. In order to obtain a half-bridge, the semiconductor switches31,32are provided in the branch27and in the branch28, bridging over the freewheeling diodes30, and which can be MOSFETs or IGBTs, for example. However, in the present case, the corresponding freewheeling diode30in the branch29is also bridged over by a semiconductor switch33, which can likewise be a MOSFET or IGBT.

In this way, the branches27and29produce the indicated discharge section34between the terminals20for the high-voltage network5, since current can flow with low impedance between the terminals20when the semiconductor switches31,33are closed by way of actuation by the control device10, so that the intermediate circuit capacitors19are discharged. The discharge resistance is provided by the operation of one of the semiconductor switches31,33in the linear region (ohmic region). If the semiconductor switch32is also closed at the same time, the exciter winding24is short circuited, so that the branches28and29together form a short circuit section35.

Now, if a signal indicating the need for an active discharging is present in the control device10, which can also actuate the semiconductor switches31,32,33of the exciter circuit4, this can make the discharge section34low-impedance conducting by closing the semiconductor switch31and33, so that, as shown schematically by the arrow36inFIG.5, the charge of the intermediate circuit capacitors19, shown here schematically by only one capacitor, can drain away. The semiconductor switch33remains permanently closed, in order to maintain undisturbed the active short circuit of the exciter circuit24existing on account of the just closed semiconductor switch32. However, as indicated inFIG.5, the semiconductor switch31is actuated by pulse width modulation, and the control device10has chosen the duty cycle in dependence on the voltage being discharged and the temperature measured on the semiconductor switch31by a measuring unit37only suggested inFIG.4, so that no thermal overload occurs and an active discharging is made possible for many cycles by way of the exciter circuit4. A discharge resistance is provided by a linear operation of one of the semiconductor switches31,33, here being likewise the semiconductor switch31.

In parallel with the active short circuit of the exciter winding24, the stator windings17are also switched to an active short circuit condition, either by closing all low side semiconductor switches of the B6 bridge of the inverter8(so-called low side ACS) or by closing all high side semiconductor switches (high side ACS). Thanks to these active short circuits (ACS) of both the stator windings17and the exciter winding24, no energy is fed back into the high-voltage network5during the active discharging by the rotating externally excited synchronous machine2. Thanks to the connection of the exciter circuit4to the active cooling by way of the cooling element11, which also cools the inverter8, this cooling is also active during the active discharging and this function can be implemented in a distinctly smaller and more cost-effective manner. Besides the integration of the “active discharging” function in the exciter circuit4, this is at the same time able, thanks to appropriate actuation by way of the control device10, to bring about the active short circuit (ACS) for the exciter winding24, so that a safe condition of the externally excited synchronous machine2obtains and a discharging can be done quickly and without complications.

German patent application no. 102022112558.0, filed May 19, 2022, to which this application claims priority, is hereby incorporated herein by reference, in its entirety.

Aspects of the various embodiments described above can be combined to provide further embodiments. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.