Method for heating a high-voltage battery, high-voltage system, and vehicle

Abstract

The invention relates to a method for heating a high-voltage battery (2) of a high-voltage system (1) of an electrically operable vehicle, wherein: the high-voltage system (1) has an inverter (4) and at least one capacitor (C_X1, C_X2) associated with the inverter (4) in an intermediate circuit; the inverter (4) has two high-voltage potentials (P+, P-) as DC voltage connections, and three phase connections to which an electric machine (3) is connected; the inverter (4) has a plurality of semiconductor switches (S1 to S12); using the semiconductor switches (S1 to S12), the at least one capacitor (C_X1, C_X2) and the motor inductors (L1, L2, L3) of the electric machine (3), energy is transferred between the high-voltage battery (2) and the at least one capacitor (C_X1, C_X2); the inverter (4) is designed as a 3-level inverter; the intermediate circuit comprises a series connection of two capacitors (C_X1, C_X2) having a center tap (M) connected to the inverter (4); and, using the semiconductor switches (S1 to S12) of the inverter (4), energy is alternately transferred between the two capacitors (C_X1, C_X2) in order to cause a correspondingly reversing current flow between the high-voltage battery (2) and the capacitors (C_X1, C_X2), and thus heating of the high-voltage battery (2).

Description

[0001] Mercedes-Benz Group AG

[0002] Method for heating a high-voltage battery, high-voltage system and vehicle

[0003] The invention relates to a method for heating a high-voltage battery according to the preamble of claims 1 or 2, a high-voltage system according to the preamble of claim 6 and a vehicle according to the preamble of claim 7.

[0004] 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.

[0005] 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.

[0006] 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.

[0007] US 2023 / 0299374 A1 describes a battery heating device configured to connect to and heat a traction battery. The battery heating device comprises a heating module with a first branch, a second branch, and an energy storage element, as well as a control module configured to control the first and second branches to form a circuit through which the traction battery discharges into the energy storage element, and a circuit through which the energy storage element charges the traction battery, thus heating the traction battery during discharge and charging.

[0008] US 2023 / 0097027 A1 describes a device and method for processing battery energy and a vehicle that can charge batteries during self-heating.The battery energy processing device comprises: an energy exchange interface; a first circuit, wherein a first end of the first circuit is connected to the energy exchange interface and a second end of the first circuit is connected to a battery; a second circuit, wherein a first end of the second circuit is connected to the battery; an energy storage device connected to a second end of the second circuit; and a controller configured to: in a first preset state, control the second circuit to charge and discharge the battery, to heat the battery, and to control the first circuit to receive energy from the energy exchange interface and to output the energy to the battery to charge the battery.

[0009] From CN 1 16979859 A an electric drive system with a 3-level inverter for driving an electric motor is known, comprising a high-voltage battery with two partial batteries and a center tap, and an intermediate circuit with two capacitors associated with the inverter.

[0010] From DE 102024000322 A1 an electric drive system for a vehicle with two electric machines is known.

[0011] From CN 000218887319 U a battery heating circuit with a battery arrangement and an inverter circuit connected to the battery arrangement is known, which in turn is connected to a power grid.

[0012] From the publication by Z. Wang et al., “Design and Validation of A 250-kW All-Silicon Carbide High-Density Three-Level T-Type Inverter”, IEEE Journal of Emerging and Selected Topics in Power Electronics, Year: 2020, Volume: 8, Issue: 1, a 3-level T-type inverter with increased rated power and power density is known. The invention is based on the objective of providing a novel method for heating a high-voltage battery, a novel high-voltage system, and a novel vehicle.

[0013] The problem is solved according to the invention by a method for heating a high-voltage battery with the features of claims 1 or 2, a high-voltage system with the features of claim 6 and a vehicle with the features of claim 7.

[0014] Advantageous embodiments of the invention are the subject of the dependent claims.

[0015] 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 has an inverter and at least one capacitor associated with the inverter in an intermediate circuit, wherein the inverter has two high-voltage potentials as DC voltage terminals and three phase terminals to which an electric machine is connected, wherein the inverter has a plurality of semiconductor switches, wherein energy is transferred between the high-voltage battery and the at least one capacitor using the at least one capacitor and the motor inductances of the electric machine.

[0016] According to the invention, the inverter is designed as a 3-level inverter, wherein the intermediate circuit has a series connection of two capacitors with a central tap connected to the inverter, wherein energy is alternately transferred between the two capacitors using the semiconductor switch of the inverter in order to cause a correspondingly reversing current flow between the high-voltage battery and the capacitors and thus a heating of the high-voltage battery.

[0017] In one embodiment, while maintaining the total voltage of the series connection of the capacitors, the stored energy is varied by changing the voltage distribution between the capacitors over time.

[0018] According to the invention, the inverter is designed as a T-type inverter with three half-bridges, each consisting of a high-side branch and a low-side branch, wherein a T-branch consisting of two mutually anti-series connected semiconductor switches is connected between a center tap of each half-bridge and the center tap of the capacitors, wherein:

[0019] - the high-side branch of one or two of the half-bridges is switched on and the T-branch of one or two other half-bridges is switched on, so that a current discharges one capacitor via the stator windings, wherein when a predetermined upper limit of the current is reached, the switched-on high-side branch(es) is / are opened and magnetically stored energy in the stator windings drives a current to charge the other capacitor, - the low-side branch of one or two of the half-bridges is switched on and the T-branch of one or two other half-bridges is switched on, so that a current discharges the other capacitor via the stator windings, wherein when a predetermined upper limit of the current is reached, the switched-on low-side branch(es) is / are opened and magnetically stored energy in the stator windings drives a current to charge one capacitor.Changing the voltages across the capacitors allows for greater energy absorption as the voltage difference increases. In this case, this results in a current flowing from the high-voltage battery to the series connection of these capacitors. If the capacitor voltages approach each other, a current would flow from the series capacitor connection to the high-voltage battery.

[0020] Alternatively, according to the invention, the inverter is designed as an NPC inverter with three half-bridges, each consisting of a high-side branch and a low-side branch, each with a center tap to which one of the stator windings is connected, wherein the high-side branch is designed as a series connection of an outer semiconductor switch and an inner semiconductor switch, wherein the low-side branch is designed as a series connection of an inner semiconductor switch and an outer semiconductor switch, wherein a diode is connected between the outer semiconductor switch and the inner semiconductor switch on the one hand and the center tap of the capacitors on the other, in particular with the anode at the center tap for the high-side branches and with the cathode at the center tap for the low-side branches, wherein:

[0021] - the high-side branch of one or two of the half-bridges is switched on and the internal semiconductor switch of the low-side branch of one or two other half-bridges is switched on, so that a current discharges one capacitor through the stator windings, whereby when a predetermined upper limit of the current is reached, the switched-on high-side branch(es) is / are opened and magnetically stored energy in the stator windings drives a current to charge the other capacitor,

[0022] The two inner semiconductor switches of one or two of the half-bridges and the low-side branch of one or two of the other half-bridges are switched on, so that a current discharges the other capacitor through the stator windings. When a predetermined upper current limit is reached, the closed semiconductor switches of the low-side branches open, and magnetically stored energy in the stator windings drives a current to charge the first capacitor. As the voltages across the capacitors change, more energy can be absorbed if the voltage difference increases. In this case, this results in a current flowing from the high-voltage battery to the series connection of these capacitors. If the capacitor voltages approach each other, a current would flow from the series capacitor connection to the high-voltage battery.

[0023] It is also possible for the inverter to be configured as an AN PC inverter. The AN PC inverter is a variation of the N PC inverter. The principle of the switch positions can be transferred from the N PC inverter to the AN PC inverter.

[0024] In one embodiment, the semiconductor switches are each designed as an IGBT or MOSFET and each has a body diode or freewheeling diode.

[0025] In one embodiment, semiconductor switches through whose body diode or freewheeling diode a current flows in the forward direction are also switched on.

[0026] According to one aspect of the present invention, a high-voltage system for an electrically powered vehicle is proposed, comprising a high-voltage battery, an inverter, and at least one capacitor associated with the inverter in a DC link. The inverter has two high-voltage potentials as DC terminals and three phase terminals to which an electric machine is connected. The inverter includes a plurality of semiconductor switches. The inverter is configured as a three-level inverter, with the DC link comprising a series connection of two capacitors with a center tap connected to the inverter. According to the invention, the high-voltage system is configured to carry out the method described above.The inverter is designed as a T-type inverter with three half-bridges, each consisting of a high-side branch and a low-side branch, with a T-branch consisting of two mutually anti-series connected semiconductor switches being connected between a center tap of each half-bridge and the center tap of the capacitors.configured as an NPC inverter, with three half-bridges, each consisting of a high-side branch and a low-side branch, each with a center tap to which one of the stator windings is connected, wherein the high-side branch is configured as a series connection of an outer semiconductor switch and an inner semiconductor switch, wherein the low-side branch is configured as a series connection of an inner semiconductor switch and an outer semiconductor switch, wherein a diode is connected between the outer semiconductor switch and the inner semiconductor switch and the center tap of the capacitors, in particular for the high-side branches with the anode at the center tap and for the low-side branches with the cathode at the center tap.

[0027] According to another aspect of the present invention, an electrically operated vehicle is equipped with a high-voltage system designed as described above.

[0028] The present invention relates to a high-voltage system of an electrically powered vehicle comprising a high-voltage battery, a drive inverter with an associated electric motor, and a T-type inverter with a series connection of two capacitors whose neutral point is coupled to the T-branches of the inverter. It is proposed to use the inverter and / or the associated switching elements and inductors to alternately charge and discharge energy between the two capacitors, thereby causing a correspondingly reversed current flow through the battery and the capacitors and thus heating the high-voltage battery. Using the proposed topology, an impedance heating method can be implemented with a small number of additional components, thus representing a cost-effective method for battery heating.

[0029] According to the present invention, a 3-level inverter (T-type inverter or (A)NPC inverter) is used to vary the stored energy while maintaining the total voltage of the series connection of the two X-capacitors. For this purpose, the voltage distribution between the two X-capacitors is changed over time (balancing and unbalancing). The variation in the total energy stored in the two capacitors results in a balancing current in the battery, which is used to heat the battery.

[0030] No further measures are necessary inside the vehicle.

[0031] Exemplary embodiments of the invention are explained in more detail below with reference to drawings.

[0032] This shows:

[0033] Fig. 1 shows a schematic view of a high-voltage electrical system for an electrically powered vehicle.

[0034] Fig. 2 shows a schematic view of the high-voltage system during the charging of a second capacitor and the discharging of a first capacitor to generate AC current.

[0035] Fig. 3 shows a schematic view of the high-voltage system during the discharge of the first capacitor and the charging of the second capacitor for AC current generation.

[0036] Fig. 4 shows a schematic view of another embodiment of the high-voltage system during the charging of the second capacitor and the discharging of the first capacitor for AC current generation.

[0037] Fig. 5 shows a schematic view of the high-voltage system from Figure 4 during the charging of the second capacitor and the discharging of the first capacitor for AC current generation during a further step of the process.

[0038] Fig. 6 shows a schematic view of the high-voltage system from Figure 4 during the discharge of the second capacitor and the charging of the first capacitor for AC current generation, and

[0039] Fig. 7 shows a schematic view of the high-voltage system from Figure 4 during the discharge of the second capacitor and charging of the first capacitor for AC current generation during a second step.

[0040] Corresponding parts are provided with the same reference numerals in all figures. Figure 1 is a schematic view of an electrical high-voltage system 1 for an electrically powered vehicle. The electrical high-voltage system 1 has at least one electrical energy storage device 2, in particular a high-voltage battery 2, and at least one electric machine 3 with three stator windings L1, L2, L3, which can be supplied with energy from the high-voltage battery 2 to power the vehicle via an inverter 4, which is designed as a 3-level inverter, in particular a T-type 3-level inverter.

[0041] The high-voltage battery 2 has a positive terminal and a negative terminal.

[0042] The vehicle may be at least partially electrically powered, such as a hybrid vehicle or electric vehicle, in particular a passenger car, a commercial vehicle or a bus.

[0043] The electric machine 3 for driving the vehicle can be designed as a three-phase electric machine. In particular, this three-phase electric machine is an electric motor. Specifically, the three-phase electric machine can be operated in motor mode and thus as an electric motor. To operate the three-phase electric machine in motor mode, it can be supplied with an alternating voltage, in particular a high-voltage alternating voltage, via its phases. The phases of the three-phase electric machine can, for example, be connected to each other via a common neutral point.

[0044] In order for the electric machine 3 to be supplied with an alternating voltage, the electrical high-voltage system 1, and thus the vehicle, has at least one high-voltage battery 2. The high-voltage battery 2 can supply the electric machine 3 and, if applicable, other vehicle components and / or vehicle systems and / or on-board electrical systems with electrical energy.

[0045] A battery voltage can be provided using the high-voltage battery 2.

[0046] In particular, the vehicle can be a battery-powered vehicle with a voltage of 800 volts. The battery voltage can provide a voltage of essentially 800 volts. The electric machine 3 requires an alternating voltage to operate. This alternating voltage can be provided by the inverter 4. This process converts the battery voltage into an alternating voltage. Specifically, the provision of the alternating voltage for the electric machine 3 is achieved through a primary function of the inverter 4.

[0047] For example, the inverter 4 can be connected or arranged between the high-voltage battery 2 and the electric machine 3.

[0048] A series circuit consisting of a first capacitor C_X1 and a second capacitor C_X2 is connected between a positive high-voltage potential P+ and a negative high-voltage potential P- of inverter 4. With respect to the electrical energy storage device 2, this series circuit is located at the input of inverter 4. Specifically, the positive potential of the first capacitor C_X1 is connected to the positive high-voltage potential P+ of inverter 4. The negative potential of the first capacitor C_X1 is connected to the positive potential of the second capacitor C_X2. Consequently, the negative potential of the second capacitor C_X2 is connected to the negative high-voltage potential P- of inverter 4. A center tap M is located between the first capacitor C_X1 and the second capacitor C_X2.

[0049] For example, inverter 4 can be configured as a three-level T-type inverter. Inverter 4 can have three half-bridges, each consisting of a high-side branch HS1 to HS3 with a semiconductor switch S1 to S3 and a low-side branch LS1 to LS3 with a semiconductor switch S4 to S6. A center tap M1 to M3 is provided between the high-side branch HS1 to HS3 and the low-side branch LS to LS3 of each half-bridge. One of the stator windings L1 to L3 is connected to the center tap M1 to M3 of each half-bridge. Furthermore, a T-branch BDS1 to BDS3 or a bidirectional switch BDS1 to BDS3 consisting of two semiconductor switches S7 to S12 connected in anti-series is connected between the center tap M1 to M3 of each half-bridge and the center tap M of the capacitors C_X1 and C_X2.

[0050] Each of the semiconductor switches S1 to S12 can, for example, be configured as an IGBT or MOSFET. For example, the capacitors C_X1 and C_X2, together with the center tap M, form an intermediate circuit of the inverter 4. According to the present invention, an impedance heating process of the high-voltage battery 2 is to be carried out using the high-voltage system 1 by generating AC current. In this process, energy is transferred from the high-voltage battery 2 to another energy storage device, for example, another battery, a charging station, or an electrical storage device such as a capacitor or inductor. In this process, with a 3-level inverter (for example, a T-type inverter), the stored energy is varied while maintaining the total voltage of the series connection of capacitors C_X1 and C_X2 by changing the voltage distribution between capacitors C_X1 and C_X2 over time (balancing and unbalancing).

[0051] A minimum amount of electrical energy is stored in the combined voltage of both capacitors C_X1 and C_X2 when both capacitor voltages are equal (for example, 400V with a battery voltage of 800V). The storable energy is at its maximum when one of the two capacitors C_X1 and C_X2 is fully charged (800V) and the other capacitor C_X1 and C_X2 is completely discharged. In a typical implementation of the 3-level inverter, such an extreme unbalance (800V and 0V) is not practical, as this would require the horizontally arranged semiconductor switches in the T-branch BDS1 to BDS3 and the capacitors C_X1 and C_X2 to be designed for an 800V operating voltage, which would entail additional costs or an increase in the size of the capacitors C_X1 and C_X2. Typically, however, these components are designed for operation up to 500V.Nevertheless, the voltage in the capacitors C_X1, C_X2 can be varied from 300V to 500V to generate an AC current in the high-voltage battery 2.

[0052] Calculation of the energy Win of the two capacitors C_X1, C_X2:

[0053]

[0054] with:

[0055] C Capacitance Cxi Capacitance of capacitor C_X1 0x2 Capacitance of capacitor C_X2 U VoltageUsatt Battery voltage Uxi Voltage across capacitor C_X1 Ux2 Voltage across capacitor C_X2 AU Voltage difference

[0056] This shows that the energy W in the capacitors C_X1 , C_X2 is minimal when the voltage is equal (AU = OV) and the energy difference when an asymmetry of AU is created has the value AW = C AU 2 This assumes a symmetrical voltage distribution. First, the operating principle of a T-type inverter will be discussed.

[0057] Figure 2 is a schematic view of the high-voltage system 1 during the charging of capacitor C_X2 and the discharging of capacitor C_X1 for AC current generation. One or two of the high-side branches HS1 to HS3 are switched on. Simultaneously, at least one semiconductor switch S7 to S12 is switched on in the T-branches BDS1 to BDS3, so that a conductive path is established from the positive high-voltage potential P+ at capacitor C_X1, via one or two stator windings L1 to L3 of the electric machine 3, to the negative terminal of capacitor C_X1, i.e., the center tap M. In the example of Figure 2, the high-side branch HS3 is switched on. Likewise, the two lower T-branches BDS2 and BDS3 are conductive. This discharges capacitor C_X1, and an increasing current 11 flows through the stator windings L1 to L3.When switching on the high-side branch HS3, the upper T-branch BDS 1, which is connected to the same stator winding L1 as the high-side branch HS3, must not be switched on simultaneously, as otherwise the capacitor C_X1 would short-circuit across the semiconductors without current limiting and this would lead to the destruction of components (especially the semiconductors).

[0058] When an upper limit of the current 11 is reached (for example, 200 A), the high-side branches HS1 to HS3 are opened. However, the T-branches BDS2 and BDS3 remain conducting. In the example shown in Figure 2, the high-side branch HS3 opens, and the two lower T-branches BDS2 and BDS3 remain closed. The energy magnetically stored in the stator windings L1 to L3 causes a further current I2 to flow in these windings (inductor current freewheeling). This current I2 then charges the capacitor C_X2. The current I2 weakens as it does so. By changing the voltages Uxi and Ux2 across the capacitors C_X1 and C_X2, more energy can be absorbed as the voltage difference increases. In this case, this results in a current I3 flowing from the high-voltage battery 2 to the series connection of these capacitors C_X1, C_X2.If the capacitor voltages approach each other, a current I4 would flow from the series capacitor circuit to the high-voltage battery 2.

[0059] Figure 3 is a schematic view of the high-voltage system 1 during the discharge of capacitor C_X2 and the charging of capacitor C_X1 to generate AC current.

[0060] One or two of the low-side branches LS1 to LS3 are switched on. Simultaneously, at least one of the T-branches BDS1 to BDS3 is switched on, so that a conductive path is established from the positive terminal of capacitor C_X2, i.e., the center tap M, via one or two stator windings L1 to L3 of the electric machine 3 to the negative terminal of capacitor C_X2, i.e., the negative high-voltage potential P-. In the example of Figure 3, the low-side branch LS3 switches on. Likewise, the two lower T-branches BDS2 and BDS3 are conductive. This discharges capacitor C_X2 and increases a current 11 in the stator windings L1 to L3.When switching on the low-side branch LS3, the upper T-branch BDS1, which is connected to the same stator winding L1 as the low-side branch LS3, must not be switched on simultaneously, as otherwise the capacitor C_X2 would short-circuit across the semiconductors without current limiting and this would lead to the destruction of components (especially the semiconductors).

[0061] When an upper limit of the current 11 is reached (for example, 200 A), the low-side branches LS1 to LS3 are opened. However, the T-branches BDS2 and BDS3 remain conducting. In the example shown in Figure 3, the low-side branch LS3 opens, and the two lower T-branches BDS2 and BDS3 remain closed. The energy magnetically stored in the stator windings L1 to L3 causes a weakening current I2 in the stator windings L1 to L3 (inductance freewheeling). This current I2 then charges the capacitor C_X1. The current I2 weakens as it does so. Due to the change in the voltages across the capacitors C_X1 and C_X2, more energy can be absorbed if the voltage difference increases. In this case, this results in a current I3 from the high-voltage battery 2 to the series connection of capacitors C_X1 and C_X2.If the capacitor voltages approach each other, a current I4 would flow from the series capacitor circuit to the high-voltage battery 2.

[0062] Figure 4 is a schematic view of an embodiment of the high-voltage system 1 during the charging of capacitor C_X2 and the discharging of capacitor C_X1 for AC current generation. In this embodiment, the inverter 4 is configured as a 3-level inverter (for example, an NPC inverter).

[0063] Inverter 4 can have three half-bridges, each consisting of a high-side branch HS1 to HS3 connected in series with an outer semiconductor switch S1 to S3 and an inner semiconductor switch S4 to S6, and a low-side branch LS1 to LS3 connected in series with an inner semiconductor switch S7 to S9 and an outer semiconductor switch S10 to S12, each with a center tap M1 to M3 between the high-side branch HS1 to HS3 and the low-side branch LS1 to LS3. One of the stator windings L1 to L3 is connected to the center tap M1 to M3 of each half-bridge. Furthermore, a diode D1 to D6 is connected between the outer semiconductor switches S1 to S3, S10 to S12 and the inner semiconductor switches S4 to S9 and the center tap M of the capacitors C_X1, C_X2, namely with the anode at the center tap M for the high-side branches HS1 to HS3 and with the cathode at the center tap M for the low-side branches LS1 to LS3.

[0064] Each of the semiconductor switches S1 to S12 can, for example, be designed as an IGBT or MOSFET. For example, the capacitors C_X1 and C_X2, together with the center tap M, form an intermediate circuit of inverter 4.

[0065] The discharge of capacitor C_X1 and the charging of capacitor C_X2 are illustrated in two figures. First, the discharge of capacitor C_X1 is shown.

[0066] In one or two half-bridges, the semiconductor switches S1 to S6 of the high-side branches HS1, HS2, HS3 are switched on. In the example shown in Figure 4, this applies to the high-side branch HS1. Additionally, in the other half-bridges, whose high-side branches HS2, HS3 are not switched on, the inner semiconductor switches S8, S9 of the low-side branches LS2, LS3 are switched on. Thus, a current 11 flows from capacitor C_X1 (positive high-voltage potential P+) through the stator windings L1, L2, L3 of the electric machine 3 and back to capacitor C_X1 (center tap M). The capacitor C_X1 is thereby discharged, and the current 11 in the stator windings L1 to L3 increases. The change in charge of the series connection of capacitors C_X1 and C_X2 causes a current I3 to charge and / or a current I4 to discharge in the high-voltage battery 2 (same principle as with the T-type inverter in figures 1 to 3).

[0067] Figure 5 is a schematic view of the high-voltage system 1 from Figure 4 during the charging of capacitor C_X2 and the discharging of capacitor C_X1 for AC current generation during a further step of the process.

[0068] When the current 11 reaches a predetermined current value in the stator windings L1 to L3, the previously closed semiconductor switches S1, S4 of the high-side branch HS1 of the half-bridge are opened. The energy magnetically stored in the stator windings L1 to L3 drives the current I2 further (freewheeling current), which now discharges into the capacitor C_X2. This process also leads to a change in the total energy in the capacitors C_X1, C_X2, thus generating a current I3 for charging and / or a current I4 for discharging in the high-voltage battery 2 (same principle as the T-type inverter in Figures 1 to 3).

[0069] Figure 6 is a schematic view of the high-voltage system 1 from Figure 4 during the discharge of capacitor C_X2 and the charging of capacitor C_X1 to generate AC current. This process is also shown in two figures. First, the discharge of capacitor C_X2 is shown.

[0070] In one or two half-bridges, the two inner semiconductor switches S4 to S9 are switched on. In the example shown in Figure 6, these are semiconductor switches S4 and S7. Additionally, in the other half-bridges, the two low-side branches LS2 and LS3 are switched on. Thus, a current 11 flows from capacitor C_X2 (center tap M) through the stator windings L1 to L3 of the electric machine 3 and back to capacitor C_X2 (negative high-voltage potential P-). Capacitor C_X2 is thereby discharged, and simultaneously, an increasing current 11 builds up in the stator windings L1 to L3. The change in charge of the series connection of capacitors C_X1 and C_X2 induces a current I3 for charging and / or a current I4 for discharging in the high-voltage battery 2. Figure 7 is a schematic view of the high-voltage system 1 from Figure 4 during the discharge of capacitor C_X2 and the charging of capacitor C_X1 for AC current generation during a second step.

[0071] When the current 11 reaches a predetermined value in the stator windings L1 to L3, all closed semiconductor switches S7 to S12 of the low-side branches LS1 to LS3 are opened. The energy magnetically stored in the stator windings L1, L2, L3 drives a current I2 (freewheeling current), which then discharges into capacitor C_X1. This process also leads to a change in the total energy in capacitors C_X1 and C_X2, thereby generating a current I3 and / or I4 to or from the high-voltage battery 2.

[0072] An ANPC inverter can also be used instead of an NPC inverter. The ANPC inverter is a variation of the NPC inverter. The principle of the switch positions can be transferred from the NPC inverter to the ANPC inverter.

[0073] In all embodiments, a semiconductor switch through which current flows in the direction of its body diode or freewheeling diode can also be switched on to reduce conduction losses and to protect the semiconductor switch from thermal overheating. Reference numeral list

[0074] 1 High-voltage system

[0075] 2 Energy storage devices, high-voltage battery 3 Electric machine

[0076] 4 Inverter

[0077] BDS1, BDS2, BDS3 T-branch, bidirectional switch C_X1, C_X2 capacitor

[0078] D1 to D6 Diode

[0079] HS1, HS2, HS3 High-Side Branch

[0080] 11 to I4 electricity

[0081] L1, L2, L3 Stator winding

[0082] LS1, LS2, LS3 Low-Side Branch

[0083] M Center tap

[0084] M1 to M3 center tap

[0085] P+ positive high-voltage potential

[0086] P- negative high-voltage potential S1 to S12 semiconductor switches

[0087] Ußatt battery voltage

[0088] Uxi, Ux2 voltage

Claims

Mercedes-Benz Group AG Patent claims 1. 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 (4) and at least one capacitor (C_X1, C_X2) associated with the inverter (4) in an intermediate circuit, wherein the inverter (4) has two high-voltage potentials (P+, P-) as DC terminals and three phase terminals to which an electric machine (3) is connected, wherein the inverter (4) has a plurality of semiconductor switches (S1 to S12), wherein energy is transferred between the high-voltage battery (2) and the at least one capacitor (C_X1, C_X2) using the semiconductor switches (S1 to S12), the at least one capacitor (C_X1, C_X2) and the motor inductances (L1, L2, L3) of the electric machine (3), wherein the inverter (4) is configured as a 3-level inverter, wherein the Intermediate circuit: a series connection of two capacitors (C_X1,C_X2) with a center tap (M) connected to the inverter (4), and wherein energy is alternately transferred between the two capacitors (C_X1, C_X2) using the semiconductor switches (S1 to S12) of the inverter (4) in order to cause a correspondingly reversing current flow between the high-voltage battery (2) and the capacitors (C_X1, C_X2) and thus to heat the high-voltage battery (2), characterized in that the inverter (4) is designed as a T-type inverter with three half-bridges, each consisting of a high-side branch (HS1 to HS3) and a low-side branch (LS1 to LS3), wherein a T-branch (BDS1 to BDS3) consisting of two mutually anti-series connected semiconductor switches (S7 to S12) is connected between a center tap (M1 to M3) of each half-bridge and the center tap (M) of the capacitors (C_X1, C_X2). S12) is connected, wherein:, - the high-side branch (HS1 to HS3) of one or two of the half-bridges is switched on and the T-branch (BDS1 to BDS3) of one or two other half-bridges is switched on, so that a current (11) discharges one capacitor (C_X1) via the stator windings (L1 to L3), wherein when a predetermined upper limit of the current (11) is reached, the switched-on high-side branch(es) (HS1 to HS3) is / are opened and magnetically stored energy in the stator windings (L1 to L3) drives a current (I2) to charge the other capacitor (C_X2), - the low-side branch (LS1 to LS3) of one or two of the half-bridges is switched on and the T-branch (BDS1 to BDS3) of one or two other of the half-bridges is switched on, so that a current (11) discharges the other capacitor (C_X2) via the stator windings (L1 to L3), whereby when a predetermined upper limit of the current (11) is reached, the switched-on low-side branch(es) (LS1 to LS3) is / are opened and magnetically stored energy in the stator windings (L1 to L3) drives a current (I2) to charge one of the capacitors (C_X1).

2. 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 (4) and at least one capacitor (C_X1, C_X2) associated with the inverter (4) in an intermediate circuit, wherein the inverter (4) has two high-voltage potentials (P+, P-) as DC voltage terminals and three phase terminals to which an electric machine (3) is connected, wherein the inverter (4) has a plurality of semiconductor switches (S1 to S12), wherein energy is transferred between the high-voltage battery (2) and the at least one capacitor (C_X1, C_X2) using the semiconductor switches (S1 to S12), the intermediate circuit a series connection of two capacitors (C_X1,C_X2) with a center tap (M) connected to the inverter (4), and wherein energy is alternately transferred between the two capacitors (C_X1, C_X2) using the semiconductor switches (S1 to S12) of the inverter (4) in order to cause a correspondingly reversing current flow between the high-voltage battery (2) and the capacitors (C_X1, C_X2) and thus to heat the high-voltage battery (2), characterized in that the inverter (4) is designed as an N PC inverter, with three half-bridges, each consisting of a high-side branch (HS1 to HS3) and a low-side branch (LS1 to LS3), each with a center tap (M1 to M3) to which one of the stator windings (L1 to L3) is connected, wherein the high-side branch (HS1 to HS3) is configured as a series connection of an outer semiconductor switch (S1 to S3) and an inner semiconductor switch (S4 to S6) is trainedwherein the low-side branch (LS1 to LS3) is configured as a series connection consisting of an inner semiconductor switch (S7 to S9) and an outer semiconductor switch (S10 to S12), wherein a diode (D1 to D6) is connected between the outer semiconductor switch (S1 to S3, S10 to S12) and the inner semiconductor switch (S4 to S9) and the center tap (M) of the capacitors (C_X1, C_X2), wherein: - the high-side branch (HS1 to HS3) of one or two of the half-bridges is switched on and the internal semiconductor switch (S7, S8, S9) of the low-side branch (LS1, LS2, LS3) of one or two other half-bridges is switched on, so that a current (11) discharges one capacitor (C_X1) through the stator windings (L1 to L3), wherein when a predetermined upper limit of the current (11) is reached, the switched-on high-side branch(es) (HS1 to HS3) is / are opened and magnetically stored energy in the stator windings (L1 to L3) drives a current (I2) to charge the other capacitor (C_X2), - the two inner semiconductor switches (S4 to S9) of one or two of the half-bridges and the low-side branch (LS1, LS2, LS3) of one or two of the other half-bridges are switched on, so that a current (11) discharges the other capacitor (C_X2) via the stator windings (L1 to L3), whereby when a predetermined upper limit of the current (11) is reached the closed semiconductor switches (S7 to S12) of the low-side branches (LS1 to LS3) are opened and magnetically stored energy in the stator windings (L1 to L3) drives a current (I2) to charge one capacitor (C_X1).

3. Method according to claim 1 or 2, characterized in that, while maintaining the total voltage of the series connection of the capacitors (C_X1, C_X2), the stored energy varies by changing the voltage distribution between the The capacitors (C_X1, C_X2) are changed over time.

4. Method according to one of the preceding claims, characterized in that the semiconductor switches (S1 to S12) are each designed as IGBT or MOSFET and each have a body diode or freewheeling diode.

5. Method according to claim 4, characterized in that the semiconductor switches (S1 to S12), through whose body diode or freewheeling diode a current flows, are also switched on.

6. High-voltage system (1) for an electrically powered vehicle, comprising a high-voltage battery (2), an inverter (4) and at least one capacitor (C_X1, C_X2) associated with the inverter (4) in an intermediate circuit, wherein the inverter (4) has two high-voltage potentials (P+, P-) as DC terminals and three phase terminals to which an electric machine (3) is connected, wherein the inverter (4) has a plurality of semiconductor switches (S1 to S12), wherein the inverter (4) is configured as a 3-level inverter, and wherein the intermediate circuit comprises a series connection of twocomprising capacitors (C_X1, C_X2) with a center tap (M) connected to the inverter (4), characterized in that the high-voltage system (1) is configured to carry out the method according to one of the preceding claims, and that the inverter (4) is designed as a T-type inverter with three half-bridges, each consisting of a high-side branch (HS1 to HS3) and a low-side branch (LS1 to LS3), wherein a T-branch (BDS1 to BDS3) consisting of two mutually anti-series connected semiconductor switches (S7 to S12) is connected between a center tap (M1 to M3) of each half-bridge and the center tap (M) of the capacitors (C_X1, C_X2), respectively.that the inverter (4) is configured as an NPC inverter, with three half-bridges, each consisting of a high-side branch (HS1 to HS3) and a low-side branch (LS1 to LS3), each with a center tap (M1 to M3) to which one of the stator windings (L1 to L3) is connected, wherein the high-side branch (HS1 to HS3) is configured as a series connection of an outer semiconductor switch (S1 to S3) and an inner semiconductor switch (S4 to S6), wherein the low-side branch (LS1 to LS3) is configured as a series connection of an inner semiconductor switch (S7 to S9) and an outer semiconductor switch (S10 to S12), wherein a diode is connected between the outer semiconductor switch (S1 to S3, S10 to S12) and the inner semiconductor switch (S4 to S9) and the center tap (M) of the capacitors (C_X1, C_X2). (D1 to D6) is connected.

7. Electrically powered vehicle with a high-voltage system (1), characterized in that the high-voltage system (1) is designed according to claim 6.

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