High-voltage system and a method for its operation

Abstract

The invention relates to a method for heating a high-voltage battery (2) of a high-voltage system (1) of an electrically powered vehicle, wherein the high-voltage system (1) comprises an inverter (3) and an intermediate circuit capacitor (Cx) associated with the inverter (3), wherein the inverter (3) has two high-voltage potentials (HV+, HV-) as DC voltage terminals and three phase terminals to which an electric machine (5) is connected, wherein the inverter (3) has a plurality of semiconductor switches (S1 to S6), wherein, using the semiconductor switches (S1 to S6), a resonant resonant circuit, comprising the intermediate circuit capacitor (Cx) and motor inductances (L1, L2, L3) of the electric machine (5) and / or inductances of the inverter (3) and / or a high-voltage cable between the high-voltage battery (2) and the inverter (3), is excited to transfer energy between the high-voltage battery (2) and the to recharge the intermediate circuit capacitor (Cx).

Description

[0001] The invention relates to a high-voltage system for an electrically powered vehicle according to the preamble of claim 5 and a method for operating it according to the preamble of claim 1.

[0002] Electrically operated vehicles with a high-voltage system and a high-voltage battery, a drive inverter and a DC link capacitor associated with the inverter are known in the prior art.

[0003] A cold high-voltage battery can only accept a very low charging current. Therefore, it is necessary to heat the battery before or during a charging process.

[0004] It is known to induce an AC current in a battery cell to heat the cell via the power loss generated at its AC resistance. In this process, a certain amount of charge is transferred to a capacitor, and subsequently the capacitor is discharged back into the battery cell.

[0005] Furthermore, an impedance heating method via an inverter, a star point tap of the electric machine and a battery center tap is known.

[0006] In impedance heating, a cold battery is charged and then discharged using an AC current. The charging frequency is greater than 1 Hz, for example, 100 Hz, to prevent charging and discharging processes from occurring within the battery cell chemistry. This avoids battery aging. Waste heat from the charging process is generated directly within the battery cell at the battery's internal resistance. The current waveform (sine wave or PWM) can be adjusted via the inverter. The waste heat from the electric motor and the inverter can also be used to heat the battery via the cooling water.

[0007] CN 118700899 A describes a battery heating circuit, a control method, a controller, a power supply system, and electrical equipment. The battery heating circuit comprises a resonant circuit, an inverter, and an AC drive motor, wherein the resonant circuit is used for electrical connection to a battery, the inverter is electrically connected to the resonant circuit, and the AC drive motor is electrically connected to the inverter; and the inverter is used to control a series current of the AC drive motor such that it changes along a preset PWM waveform to generate a resonant current for heating the battery between the resonant circuit and the battery.

[0008] From DE 10 2022 100 433 A1, a vehicle is known comprising an electric machine, a battery, an inverter coupled between the electric machine and the battery, and a control unit programmed to switch the inverter at a switching frequency selected to generate an alternating current for heating the battery, to set a d-axis current of the electric machine to increase battery heating power without changing the switching frequency selected to generate the alternating current for heating the battery, and to set a q-axis current of the electric machine according to the set d-axis current.

[0009] From DE 10 2021 126 347 A1, a method for preparing a traction battery for a selected battery operation is known, in which the traction battery is used as an electrical energy storage device for an electric drive of a motor vehicle and an inverter circuit is provided for electrically coupling the traction battery with the electric drive, wherein the inverter circuit is operated in an inverter mode to supply at least one phase of the electric drive with an alternating current as a phase current, in which at least one switching element of the inverter circuit is operated according to a predetermined first clock pattern and / or a predetermined first clock frequency in a first frequency range, wherein an alternating component of an intermediate circuit current with which the traction battery is supplied in the inverter mode is filtered.A DC link capacitor with a predetermined impedance function is connected between the traction battery and the inverter circuit, wherein the impedance of the DC link capacitor, according to the impedance function for the first frequency range, encompasses a global minimum within a predetermined minimum value range, wherein, to prepare the traction battery for the selected battery operation, the inverter circuit is operated in heating mode under a predetermined operating condition to heat the traction battery to a predetermined heating temperature value, wherein, in heating mode, the at least one switching element is operated according to a predetermined second clock pattern and / or a predetermined second clock frequency in a second frequency range, and the impedance of the DC link capacitor, according to the impedance function for the second frequency range, encompasses a global minimum within a predetermined heating value range.which is disjoint from the minimum value range.

[0010] From DE 10 2022 106 506 A1, a method for controlling a vehicle inverter is known, comprising the steps of determining information about the heating requirement of a battery of the vehicle electrically and thermally coupled to the inverter, controlling the inverter in a first mode in which an electric motor of the vehicle, electrically coupled to an AC connection of the inverter, is powered by a current supplied by the battery, and controlling the inverter in a second mode, which represents a freewheeling of the inverter in which a freewheeling current flowing through inverse diodes of semiconductor switches of the inverter leads to the heating of the battery thermally coupled to the inverter, wherein the first mode and the second mode are switched repeatedly at least until the heating requirement of the battery is met, and the control of the inverter is carried out in such a manner.that an average current flowing through the electric motor corresponds to a direct current which does not produce any torque in the electric motor, and that respective switching times for the recurring change between the first mode and the second mode are determined depending on the heating requirements of the battery.

[0011] The invention is based on the objective of providing a novel high-voltage system for an electrically operated vehicle and a novel method for its operation.

[0012] The problem is solved according to the invention by a high-voltage system for an electrically operated vehicle with the features of claim 5 and by a method for operating it with the features of claim 1.

[0013] Advantageous embodiments of the invention are the subject of the dependent claims.

[0014] A method for heating a high-voltage battery of a high-voltage system of an electrically powered vehicle is proposed, wherein the high-voltage system comprises an inverter and an associated DC link capacitor, the inverter having two high-voltage potentials as DC terminals and three phase terminals to which an electric machine is connected, and the inverter having a plurality of semiconductor switches. According to the invention, a resonant circuit, comprising the DC link capacitor and motor inductors of the electric machine and / or inductors of the inverter and / or a high-voltage cable between the high-voltage battery and the inverter, is excited using the semiconductor switches to transfer energy between the high-voltage battery and the DC link capacitor.

[0015] In one embodiment, the resonant circuit is set into oscillation by time-coordinated switching operations of the inverter, in which an alternately increasing and decreasing current is generated in the motor inductors of the electric machine, leading to a voltage change at the intermediate circuit capacitor and a current change in the high-voltage cable.

[0016] In one embodiment, a current at at least one of the DC voltage terminals and / or at least one of the phase terminals of the inverter and / or a capacitor voltage across the intermediate circuit capacitor is measured and taken into account to control the switching operations of the inverter for oscillation excitation.

[0017] According to the invention, the inverter has three half-bridges, each with an upper semiconductor switch and a lower semiconductor switch, wherein one or two upper semiconductor switches are switched on and simultaneously the lower semiconductor switches of those half-bridges whose associated upper semiconductor switch is open are switched on, wherein when a predetermined threshold value of a mesh current in the motor inductors of the electric machine is reached, the previously closed semiconductor switches of the inverter are opened, wherein the mesh current impressed in the motor inductors is commutated via body diodes or freewheeling diodes of the other semiconductor switches.

[0018] In another, unclaimed embodiment, the inverter has three half-bridges, each with an upper semiconductor switch and a lower semiconductor switch, wherein an upper semiconductor switch and a lower semiconductor switch of different half-bridges are closed, wherein when a predetermined threshold value of a mesh current in the motor inductors of the electric machine is reached, the previously closed semiconductor switches are opened, wherein the mesh current impressed in the motor inductors is commutated via body diodes or freewheeling diodes of the other semiconductor switches of the same half-bridges.

[0019] In one embodiment, when the mesh current flows through the body diode or freewheeling diode, the respective semiconductor switch is closed.

[0020] According to one aspect of the present invention, a high-voltage system for an electrically powered vehicle is proposed, wherein the high-voltage system comprises an inverter and an associated DC link capacitor, the inverter having two high-voltage potentials as DC terminals and three phase terminals to which an electric machine is connected, and the inverter comprising a plurality of semiconductor switches. According to the invention, the high-voltage system is configured to carry out the method described above. For example, the method is carried out by means of a control unit that controls the inverter.

[0021] In one embodiment, the inverter is configured as a 2-level B6 inverter or as a 3-level inverter. In particular, the 3-level inverter can have a T-type, NPC, ANPC, or flying capacitor topology.

[0022] The invention relates to a high-voltage system of an electrically powered vehicle comprising a high-voltage battery, a drive inverter for operating an electric motor, and a DC link capacitor associated with the inverter. It is proposed to use the switching elements and inductors of the inverter and the electric motor to excite a resonant circuit in order to transfer energy between the high-voltage battery and the DC link capacitor, thereby heating the high-voltage battery. The proposed method can be implemented as a purely software-based solution; no additional hardware components are required compared to a conventional drive system. This allows for a particularly cost-effective method of battery heating.

[0023] The method according to the invention represents a possible implementation of impedance heating, in which the battery is heated at its ohmic internal resistance by an AC current without aging the battery.

[0024] In the proposed impedance heating method, a resonant circuit is actively excited by the switching operations of the inverter. This resonant circuit consists of the supply line inductance of the high-voltage cable between the inverter and the high-voltage battery, and the inverter's DC link capacitor. This resonant circuit is set into oscillation by time-coordinated switching operations of the inverter. These operations generate a rising and falling current in the windings of the electric machine, resulting in a voltage change across the DC link capacitor and a current change in the supply line inductance.

[0025] The solution according to the invention requires no additional hardware components compared to known drive systems to implement the battery heating function. Instead, the invention can be implemented as a purely software-based solution. Furthermore, fewer measures are necessary to comply with EMC limits, since the excitation frequency has been reduced compared to the usual switching frequency of the inverter (e.g., 10 kHz) to approximately 1 kHz, depending on inductances and capacitances. Exciting the battery with a sinusoidal current reduces EMC emissions.

[0026] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0027] This shows: Fig. 1 a schematic view of a high-voltage system of an electrically powered vehicle, Fig. 2 A schematic view of the high-voltage system during the build-up of current in motor inductors of an electric machine, Fig. 3 a schematic view of the high-voltage system during free-running current, Fig. 4 a schematic view of a simulation setup of the high-voltage system, Fig. 5 a schematic diagram of the simulation results, Fig. 6 A schematic view of the high-voltage system during the build-up of current in the motor inductors in an alternative embodiment of the method, Fig. 7 a schematic view of the high-voltage system during free-running current, and Fig. 8 a schematic diagram of the simulation results for an ideal short circuit across a supply line inductance.

[0028] Corresponding parts are marked with the same reference symbols in all figures.

[0029] Fig. Figure 1 is a schematic view of a high-voltage system 1 of an electrically powered vehicle, for example a passenger car, a commercial vehicle or a bus, with a high-voltage battery 2, an inverter 3 and a DC link capacitor Cx associated with the inverter 3. The inverter 3 has three phase terminals to which an electric machine 5 is connected, which here is represented by three motor inductances L1, L2, L3, for example stator windings.

[0030] Inverter 3 comprises three half-bridges, each consisting of an upper semiconductor switch S1, S3, S5 and a lower semiconductor switch S2, S4, S6, which can each be configured, for example, as a MOSFET or IGBT. The half-bridges are connected in parallel to each other and to the DC link capacitor Cx between a positive high-voltage potential HV+ and a negative high-voltage potential HV-. The positive high-voltage potential HV+ can be connected to a positive battery terminal of the high-voltage battery 2 via a main contactor. The negative high-voltage potential HV- can be connected to a negative battery terminal of the high-voltage battery 2 via a main contactor.

[0031] The motor inductances L1, L2, L3 can form a star point 6.

[0032] The aim of the invention is to implement battery heating in the most cost-effective way possible. This is achieved by avoiding additional features such as a battery center tap or additional switching elements in the high-voltage battery 2, as well as additional components for creating a resonant circuit. Furthermore, it is an aim to prevent the currents generated during charging processes from increasing to twice the heating current (in some components such as the center tap). Finally, it is desirable to implement the battery heating using components already present in the vehicle.

[0033] In the impedance heating method according to the invention, a resonant circuit is actively excited by the switching operations of the inverter 3. The resonant circuit comprises the intermediate circuit capacitor Cx of the inverter 3 and a lead inductance L_cable of a high-voltage cable between the inverter 3 and the high-voltage battery 2. The lead inductance L_cable has an inductance value that depends on both the length of the high-voltage cable and the path between a forward and a return conductor in the high-voltage cable. As a first approximation, one can assume about 1 µH / m. For a rear drivetrain of a vehicle, in particular a passenger car, with the high-voltage connection of the high-voltage battery 2 simultaneously located at the rear, this results in a leakage inductance of about 3 µH to 5 µH. When using the front drivetrain, the lead inductance L_cable can be, for example, 5 µH to 10 µH.

[0034] The capacitance of the resonant circuit is formed by the intermediate circuit capacitor Cx of inverter 3. It has a capacitance value of approximately 500 µF to 1000 µF. Furthermore, existing ammeters A on the DC side and at the AC outputs of inverter 3 can be used. Additionally, a DC voltmeter can be present across the intermediate circuit capacitor Cx (not shown). The current state of the oscillation excitation can be monitored via the ammeters A and voltmeter (current in the supply line inductance L_cable, capacitor voltage U_Cx across the intermediate circuit capacitor Cx, and current in the electric machine 5), and the switching rate of inverter 3 can be controlled accordingly.

[0035] This resonant circuit is set into oscillation by time-coordinated switching operations of the inverter 3, in which a building-up and decreasing current is generated in the windings of the electrical machine 5, which leads to a voltage change at the intermediate circuit capacitor Cx and a current change in the supply line inductance L_cable.

[0036] An increasing current in the motor windings leads to a voltage reduction across the DC link capacitor Cx and simultaneously to an increase in the discharge current of the high-voltage battery 2 (which also flows through the supply line inductance L_cable). A decreasing current in the motor inductances L1, L2, L3 leads to a charging of the DC link capacitor Cx and simultaneously to a charging current in the high-voltage battery 2 (which also flows through the supply line inductance L_cable).

[0037] Fig. Figure 2 is a schematic view of the high-voltage system 1 during the build-up of current in the motor inductors L1, L2, L3.

[0038] In inverter 3, one or two of the upper semiconductor switches S1, S3, S5 (high-side semiconductor switches) are switched on (in Fig. 2 only S1). Simultaneously, the lower semiconductor switches S2, S4, S6 (lowside semiconductor switches) of the half-bridges are switched on, whose corresponding highside semiconductor switches S1, S3, S5 are open. This results in Fig. 2 examples shown in Fig. The equivalent circuit shown on the right (2) depicts two of the three motor inductances, L2 and L3, connected in parallel, with the third motor inductance, L1, connected in series. The resulting current in this system can be represented by two mesh currents, I1 and I2.

[0039] The mesh current I2 discharges the intermediate circuit capacitor Cx through the switch positions of the semiconductor switches S1 to S6 via the motor inductances L1, L2, L3. Fig. 2. The mesh current I2 flows from the DC link capacitor Cx via the upper semiconductor switch S1, the motor inductor L1, the star point 6, in parallel through the motor inductors L2, L3 and the lower semiconductor switches S4, S6 back to the DC link capacitor Cx. The mesh current I2 builds up in the motor inductors L1, L2, L3. This results in energy W being stored in these motor inductors L1, L2, L3 (W = ½ L * I2). 2 ). In this process, the capacitor voltage U_Cx across the intermediate circuit capacitor Cx is reduced by the removal of charge.

[0040] The mesh current I1, starting from the high-voltage battery 2, recharges the intermediate circuit capacitor Cx via the supply line inductance L_cable. This also results in energy W being stored in the supply line inductance L_cable.

[0041] Fig. Figure 3 is a schematic view of the high-voltage system 1 during free-running current.

[0042] When a predetermined threshold value of the mesh current I2 is reached in the motor inductors L1, L2, L3 (for example, 200 A or 400 A), the previously closed semiconductor switches S1 to S6 of inverter 3 (in this example, semiconductor switches S1, S2, and S4) open. The mesh current I2 impressed in the motor inductors L1, L2, L3 commutates via the body diodes or the freewheeling diodes of the other semiconductor switches S1 to S6 (in this example, S3, S5, and S2). To protect against overheating, the corresponding semiconductor switches S3, S5, and S2 can be switched on as soon as the mesh current I2 flows through the body diode or freewheeling diode. This mesh current I2 charges the DC link capacitor Cx, whereby the mesh current I2 decreases and the capacitor voltage U_Cx across the DC link capacitor Cx increases.

[0043] Due to the voltage increase across the intermediate circuit capacitor Cx, the mesh current I1 charges the high-voltage battery 2 via the supply line inductance L_cable.

[0044] Fig. Figure 4 is a schematic view of a simulation setup of the high-voltage system 1.

[0045] In the simulation setup, the situation is depicted when using a drive very close to the terminals. The supply line inductance L_cable is 5 µF; this corresponds to approximately 2.5 m of cable length for the outgoing and return conductors. A maximum current value of 266 A is set for the motor inductances L1, L2, L3, for example. The switching frequency of inverter 3 can be varied (for example, up to a maximum of 10 kHz as a typical value) and has been set to 1 kHz here. The motor inductances L1, L2, L3 are L_EM = 300 µH in this example. With the method described here, the main inductance of the electric machine 5 can be used, unlike methods with a star point tap, where only the leakage inductance is effective (approximately 1% of the main inductance).

[0046] The upper semiconductor switch S1, along with the lower semiconductor switches S4 and S6, is switched on as soon as the mesh current I2 through the motor inductors L1, L2, L3 of the electric machine 5 falls below 1 A. The semiconductor switches S1, S4, S6 are opened again as soon as a mesh current I2 of 266 A is reached. The switching of the semiconductor switches S2, S3, S5 with a current-carrying body diode is not shown here. The AC resistance Ri of the high-voltage battery 2 was assumed to be 30 mΩ. The resistance R2 of the intermediate circuit capacitor Cx and the line resistance R3 of the supply line were each assumed to be 10 mΩ.

[0047] Fig. Figure 5 is a schematic diagram of the simulation results.

[0048] The following values ​​can be seen: - the mesh current I1 through the high-voltage battery 2: This mesh current I1 fluctuates between approximately +340 A and -294 A after a short settling-in phase. - a control signal Gate_S1 of the gate of the semiconductor switch S1, which is also used to control the gates of the semiconductor switches S4 and S6. - the capacitor voltage U_Cx across the intermediate circuit capacitor Cx. The fluctuations here are significantly higher than the voltage fluctuations at the battery terminals. This shows that the resonant circuit was excited by the supply line inductance L_cable and the intermediate circuit capacitor Cx. - the capacitor current I_Cx flowing through the DC link capacitor Cx. A positive value corresponds to a capacitor current I_Cx that leads to a voltage increase (load system). It can be seen that when the semiconductor switches S1, S4, and S6 open, the capacitor current I_Cx immediately rises to a very high value, which means that the freewheeling current (mesh current I2) of the motor inductors L1, L2, and L3 flows into the DC link capacitor Cx. - A choke voltage U_L_cable across the supply line inductance L_cable. Here, the difference between the voltage at the battery terminals and the capacitor voltage U_Cx drops across the intermediate circuit capacitor Cx. - the cable current I_L_cable through the supply line inductance L_cable. This is identical to the mesh current I1 through the high-voltage battery 2. - the motor current I_L1 through the motor inductance L1. It fluctuates between the values ​​1 A and 266 A. - The battery voltage Vm1 across the battery terminals. The AC voltage is only about + / - 10 V, while the voltage fluctuation across the DC link capacitor Cx is about + / - 35 V. The voltage difference is absorbed by the supply line inductance L_cable. Due to the low AC component across the battery terminals, the operation of other high-voltage components is possible without restrictions or special measures.

[0049] Fig. Figure 6 is a schematic view of the high-voltage system 1 during the build-up of current in the motor inductors L1, L2, L3 of the electric machine 5 in an alternative embodiment of the method.

[0050] If it is advantageous for selecting the resonant frequency to increase the resulting inductance during the discharge and charging of the DC link capacitor Cx, it is also possible to switch only one semiconductor switch S1 to S6 of the upper and lower switch rows (here S1 and S6) at a time. In the equivalent circuit diagram, this results in a series connection of two motor inductors L1 and L3, which corresponds to a slightly higher inductance value than in the previous example. The excitation of the resonant circuit is carried out according to the same principle.

[0051] The loop current I2 discharges the intermediate circuit capacitor Cx through the switch positions of the semiconductor switches S1 to S6 (here S1 and S6) via the motor inductors L1, L3. During this process, the loop current I2 builds up in the motor inductors L1, L3, and energy is stored in these motor inductors L1, L3 (W = ½ L * I2). 2). In this process, the capacitor voltage U_Cx across the intermediate circuit capacitor Cx is reduced by the removal of charge.

[0052] The mesh current I1, starting from the high-voltage battery 2, recharges the intermediate circuit capacitor Cx via the supply line inductance L_cable. This also results in energy being stored in the supply line inductance L_cable.

[0053] Fig. Figure 7 is a schematic view of the high-voltage system 1 during free-running current.

[0054] During the freewheeling phase, the current also flows only through two semiconductor switches S2 and S5. Overall, this principle allows more energy to be stored in the two motor inductors L1 and L3, and thus the resonant circuit can be more strongly excited, even with the same maximum current value.

[0055] When a predetermined threshold value of the mesh current I2 is reached in the motor inductors L1 and L3 (for example, 200 A or 400 A), the previously closed semiconductor switches S1 to S6 of inverter 3 (in this example, semiconductor switches S1 and S6) are opened. The mesh current I2 impressed in the motor inductors L1 and L3 commutates via the body diodes or the freewheeling diodes of the other semiconductor switches S1 to S6 of the same half-bridges (in this example, S2 and S5). To protect against overheating, the respective semiconductor switches S2 and S3 can be switched on as soon as the mesh current I2 flows through the body diode or freewheeling diode. This mesh current I2 charges the intermediate circuit capacitor Cx, whereby the mesh current I2 decreases and the capacitor voltage U_Cx across the intermediate circuit capacitor Cx increases.

[0056] Due to the voltage increase across the intermediate circuit capacitor Cx, the mesh current I1 charges the high-voltage battery 2 via the supply line inductance L_cable.

[0057] Any topology is conceivable for Inverter 3. The examples shown depict a 2-level B6 inverter. However, 3-level topologies such as T-type, NPC, ANPC, or flying capacitor are also suitable.

[0058] The greater the inductance of the electric machine 5, the better suited the described method is for generating an AC current in the high-voltage battery 2. The same applies to the maximum current that can be allowed in the stator windings. Here, it can be helpful to utilize the thermal capacity of the electric machine 5 to enable higher currents for a short period of time.

[0059] The supply line inductance L_cable manifests its effect as an increase in the current amplitude compared to the current in the windings of the electrical machine 5. However, the method can also be implemented without the supply line inductance L_cable, for example, with very short supply lines. This was realized in the simulation setup by an ideal short circuit across the supply line inductance L_cable and its ohmic resistance R3.

[0060] Fig. Figure 8 is a schematic diagram of the simulation results for an ideal short circuit across the supply line inductance L_cable and its ohmic line resistance R3.

[0061] These are the same values ​​as in Fig. 5 shown.

[0062] Compared to the simulation results in Fig. 5 is in Fig. Figure 8 clearly shows that the waveform of the mesh current I1 through the high-voltage battery 2 no longer corresponds to a sine wave. The maximum and minimum current values ​​in the high-voltage battery 2 have been reduced. While in Fig. 5. Values ​​between approximately +340 A and -294 A were still reached, so in Fig. 8 Only values ​​between +239 A and -170 A are achievable. Reference symbol list 1 High-voltage system 2 high-voltage batteries 3 Inverter 5 electric machine 6 Star point A power meter Cx DC link capacitor, intermediate circuit capacitor Gate_S1 control signal HV+, HV High-voltage potential I_Cx Capacitor current I_L_Cable Cable power I_L1 Motor current I1 Mesh current I2 mesh current L_Cable supply line inductance L1, L2, L3 Motor inductance Ri AC resistance R2 resistance R3 line resistance S1 to S6 semiconductor switches U_Cx Capacitor voltage U_L_Cable Throttle voltage Vm1 Battery voltage

Claims

Method for heating a high-voltage battery (2) of a high-voltage system (1) of an electrically powered vehicle, wherein the high-voltage system (1) comprises an inverter (3) and an intermediate circuit capacitor (Cx) associated with the inverter (3), wherein the inverter (3) has two high-voltage potentials (HV+, HV-) as DC voltage terminals and three phase terminals to which an electric machine (5) is connected, wherein the inverter (3) has a plurality of semiconductor switches (S1 to S6), and wherein, using the semiconductor switches (S1 to S6), a resonant circuit comprising the intermediate circuit capacitor (Cx) and motor inductances (L1, L2, L3) of the electric machine (5) and / or inductances of the inverter (3) and / or a high-voltage cable between the high-voltage battery (2) and the inverter (3) is excited to transfer energy between the high-voltage battery (2) and the intermediate circuit capacitor. (Cx) to reload, characterized by,that the inverter (3) has three half-bridges, each with an upper semiconductor switch (S1, S3, S5) and a lower semiconductor switch (S2, S4, S6), wherein one or two upper semiconductor switches (S1, S3, S5) are switched on and simultaneously the lower semiconductor switches (S2, S4, S6) of those half-bridges whose associated upper semiconductor switch (S1, S3, S5) is open are switched on, wherein when a predetermined threshold value of a mesh current (I2) in the motor inductors (L1, L2, L3) of the electric machine (5) is reached, the previously closed semiconductor switches (S1 to S6) of the inverter (3) are opened, and wherein the mesh current (I2) impressed in the motor inductors (L1, L2, L3) is commutated via body diodes or freewheeling diodes of the other semiconductor switches (S1 to S6). Method according to claim 1, characterized in that the resonant circuit is set into oscillation by time-coordinated switching operations of the inverter (3), in which an alternately increasing and decreasing current is generated in the motor inductors (L1 to L3) of the electric machine (5), which leads to a voltage change at the intermediate circuit capacitor (Cx) and a current change in the high-voltage cable. Method according to claim 1 or 2, characterized in that a current at at least one of the DC voltage terminals and / or at least one of the phase terminals of the inverter (3) and / or a capacitor voltage (U_Cx) across the intermediate circuit capacitor (Cx) is measured and taken into account for controlling the switching operations of the inverter (3) for oscillation excitation. Method according to one of the preceding claims, characterized in that when the mesh current (I2) flows through the body diode or freewheeling diode, the respective associated semiconductor switch (S1 to S6) is closed. High-voltage system (1) for an electrically operated vehicle, wherein the high-voltage system (1) comprises an inverter (3) and an intermediate circuit capacitor (Cx) associated with the inverter (3), wherein the inverter (3) has two high-voltage potentials (HV+, HV-) as DC voltage terminals and three phase terminals to which an electric machine (5) is connected, wherein the inverter (3) has a plurality of semiconductor switches (S1 to S6), characterized in that the high-voltage system (1) is configured to carry out the method according to one of the preceding claims. High-voltage system (1) according to claim 5, characterized in that the inverter (3) is designed as a 2-level B6 inverter or as a 3-level inverter. High-voltage system (1) according to claim 6, characterized in that the 3-level inverter has the topology T-type, NPC, ANPC or flying capacitor.

Images