Method and device for operating an inverter of an electric vehicle

Abstract

The invention relates to a method and a device for operating a T-type NPC inverter and an associated switching arrangement for two battery banks (B1, B2) of a battery system, wherein the switching arrangement consists of two switching elements (S1, S2) which can connect the battery banks (B1, B2) both in series and in parallel. Three different operating modes are realized by the switching of the power controllers (L1 / L1', L2 and L3) and the switching elements (S1 and S2). In a first operating mode (M1), with the switching element (S1) closed and the switch (S2) open, driving is carried out with both battery banks (B1 and B2) connected in series. In the second operating mode (M2), with the power controllers (L1 / L1', L2 and L3) open and non-conductive, both battery banks (B1 and B2) are charged.B2) is connected in series with the summed voltage of the battery banks (B1+B2) and in a third operating mode (M3) the first switching element (S1) is open and the second switching element (S2) is closed, whereby the first power controllers (L1 / L1') and the second power controller (L2) are still switched to conduct, so that when the third power controller (L3) is open (not switched to conduct), both battery banks (B1, B2) are connected in parallel with respect to a DC charging system connected to the positive (DC+) and negative DC bus (DC-) and can be charged simultaneously in parallel with a voltage level that corresponds to the voltage level of one of the battery banks (B1, B2).

Description

[0001] The present invention relates to a method and a device for operating an inverter in charging and driving mode for an electric vehicle using a T-Type NPC inverter. State of the art

[0002] European patent EP 3 224 075 B1 discloses a battery system comprising a hybrid battery and an inverter connected to the battery input. The hybrid battery consists of a first energy storage source with multiple first energy storage cells and a second energy storage source with multiple second energy storage cells connected in series. The inverter is a neutral-point clamped diode multilevel inverter (NPC) with at least three voltage levels. The document describes a method for operating the inverter and a vehicle equipped with the described battery system and an electric motor. The electric motor can be operated in various modes to meet torque and speed requirements in different operating ranges.Depending on the operating mode, the energy storage sources are used individually or connected in series to provide the energy for operating the drive motor. Different configurations for charging at various voltage levels are not described.

[0003] German patent application DE 10 2018 124 789 A1 discloses a device for charging the battery of a motor vehicle equipped with an electric drive motor, as well as an electric drive system with such a charging device. The charging device comprises an inductor and an inverter, which converts the battery's DC voltage for the motor during drive operation. During charging operation, the inductor, together with the inverter, acts as a boost converter to charge the battery. The application also describes an adjustment of the voltage levels between the charging device and the battery using boost converters. For this purpose, a switching unit is used, which enables direct charging or, alternatively, charging via the motor's inductor and the inverter.

[0004] A battery system with two battery packs is known from WO 2021 / 165 655 A1. Each battery pack has its own inverter. The two inverters are arranged on opposite sides of the motor inductors. The respective battery packs can be connected to the motor inductors via the inverters' switching elements (dual-inverter open winding arrangement). One of the battery packs has two subpacks, which can be connected in parallel and in series for charging and discharging, respectively, via further switching elements.

[0005] WO 2016 / 065 012 A1 discloses a T-type NPC inverter for controlling a three-phase electric motor, as also used in the device according to the invention. The neutral conductor branches off between two battery modules and leads to the coils of the electric motor for each of the three phases via first switching elements. Each coil can be connected to the positive and negative DC buses via second and third switching elements. The arrangement is described here in full for a three-phase electric machine. The disclosure of the publication is explicitly included here to describe the NPC topology.

[0006] German patent DE 10 2021 208 773 B1 discloses a traction network with a T-type NPC inverter in which two battery blocks supplying the inverter with DC voltage can be reconfigured. During driving and charging, the battery blocks are connected in series at 800V and in parallel at 400V during charging. A switch connected in series with one of the batteries is required for the parallel connection of the two batteries during charging. This switch must be designed as a reversing switch.

[0007] The object of the present invention is to provide a method and a device for carrying out the method which enables the high-performance driving operation of an electric vehicle with low current flow using only one inverter and furthermore provides a possibility to charge a battery system with two battery banks, wherein DC charging systems of different voltage levels can be used.

[0008] Advantageously, a method for operating a T-type NPC inverter and an associated switching arrangement is described, which can be used for a battery system with two battery banks. The switching arrangement has two switching elements that can connect the battery banks in series and in parallel. According to the topology of an NPC inverter, a neutral conductor (N) branches off for each phase of an electric machine (EM) between the positive terminal of the first battery bank and the negative terminal of the second battery bank. This conductor is connected to each of the coils of an electric machine via the first power controller. The neutral conductor is further connected, in a known manner, at its coil-side end to the positive DC bus via a second power controller and to the negative DC bus via a third power controller.Advantageously, according to the invention, three different operating modes can be switched in a simple manner using an inverter by means of the circuitry of the power controllers and switching elements. In a first operating mode, with the first switching element closed and the second switching element open, the two battery banks are connected in series, and the sum of the voltage of the two battery banks can be controlled by the inverter's power controllers for the operation of the electric motor. Advantageously, according to the invention, with the same position of the switching elements and the inverter's open (non-conductive) power controllers, direct DC charging is achieved by connecting a DC charging system to the positive and negative DC bus. This allows both battery banks to be connected in series and charged by the DC charging system at a voltage level corresponding to the sum of the battery banks' voltages.In a third operating mode, the first switching element is opened and the second switching element is closed. According to the invention, a parallel connection of the battery banks is established using the power controllers in the T-type NPC topology and the switching elements. By opening the first switching element between the battery banks and closing the second switching element, the negative terminals of the two battery banks are connected. Furthermore, the first power controller in the neutral conductor and the second power controller leading to the positive DC bus are switched to conduction, so that when the third power controller is open (not switched to conduction), the positive terminal of the first battery bank is connected to the positive DC bus and thus to the positive terminal of the second battery bank.Both battery banks are connected in parallel to a DC charging system connected to the positive and negative DC voltage buses and can be charged simultaneously at a voltage level corresponding to the voltage level of one of the battery banks. Advantageously, according to the invention, current flow via the inverter's power controllers is used to implement the third operating mode, allowing the battery banks to be charged at two different voltage levels, once in series and once in parallel, by means of two additional switching elements, utilizing the inverter's power controllers.

[0009] Further advantageous embodiments of the present invention and a description of the effects achieved can be found in the following exemplary embodiment and in the dependent patent claims.

[0010] Fig. Figure 1 shows the device according to the invention in a schematic diagram for one phase of a T-type NPC inverter, as known for controlling an electric motor Em in electric vehicles. For a complete three-phase version of the inverter, reference is made, for example, to WO 2016 / 065 012 A1. The device has two battery banks (B1, B2) of a battery system, which in this exemplary embodiment each have a nominal voltage of 400 V. The battery banks are of the same battery type and have the same nominal voltage. The device further has a switching arrangement consisting of two switching elements S1 and S2. A first switching element S1 is arranged between the positive terminal of a first battery bank B1 and the negative terminal of a second battery bank B2. The switching element S1 is shown here in the open state.A neutral conductor N branches off between the positive terminal of the first battery bank B1 and the first switching element S1. Only one phase of the three-phase system is shown here. In a complete diagram, the neutral conductor is present in three branches, each leading to one of the inverter's bridge branches or one of the electric machine's coils Em. The device also includes a second switching element S2, which branches off between the first switching element S1 and the negative terminal of the second battery bank B2, connecting this point to the negative terminal of the first battery bank B1. The negative terminal of the first battery bank B1 forms the negative DC bus DC-, and the positive terminal of the second battery bank B2 forms the positive DC bus DC+.The neutral conductor N, which begins between the positive terminal of the first battery bank B1 and the negative terminal of the second battery bank B2, leads via the first power controllers L1 / L1' to one of the bridge branches of the inverter or one of the coils of an electric machine Em. The neutral conductor N is further connected via a second power controller L2 to the positive DC bus DC+ and via a third power controller L3 to the negative DC bus DC.

[0011] Fig. Figure 2 shows the first operating mode M1 of the method according to the invention. The switching element S1 is, in comparison to the Fig. 1. The circuit is closed. Battery banks B1 and B2 are connected in series. The power controllers L1 / L1', L2, and L3 are controlled in a known manner to generate a corresponding torque for the electric machine Em via the current flow through its coils. The electric machine Em can be operated with the sum of the voltage values ​​of both battery banks B1 and B2 (here 800 V), thus requiring a lower current flow compared to operation with only one of the battery banks B1 or B2.

[0012] Fig. Figure 3 shows an identical wiring configuration as in Fig. 2, based on the Fig. Section 3 explains the second operating mode, M2. The thickened lines illustrate the current flow in the second operating mode, M2, which involves charging with high DC voltage. These thickened lines and the arrows, starting from DC+, then to the second battery bank B2, via the closed switching element S1 to the first battery bank B1, and from there to DC-, symbolize the current flow during DC charging. For this purpose, the positive DC+ and negative DC- bus are connected to a DC charging system (not shown), which charges the two series-connected battery banks B1 and B2. In this operating mode, M2, the power controllers L1 / L1', L2, and L3 are non-conductive, i.e., switched off. No current flows through them during charging. An 800-volt charging system is required for the two series-connected battery banks B1 and B2, each with a voltage of 400 V.Both battery banks B1 and B2 can thus be charged simultaneously at a high voltage level. The advantage of the invention, namely that the battery banks B1 and B2 can also be charged with a less efficient charging system of, for example, 400 volts, becomes... Fig. 4 described.

[0013] Fig.Figure 4 shows the third operating mode M3, in which the first switching element S1 is open, thus disconnecting the positive terminal of the first battery bank B1 from the negative terminal of the second battery bank B2. Closing the second switching element S2 connects the negative terminal of the second battery bank B2 to the negative terminal of the first battery bank B1. Furthermore, the first power controllers L1 / L1' and the second power controller L2 are switched to conduction, so that when the third power controller L3 is open (but not switched to conduction), the positive terminal of the first battery bank B1 is connected to the positive terminal of the positive DC bus DC+ and thus also to the positive terminal of the second battery bank B2. Therefore, both battery banks B1 and B2 are connected in parallel with respect to a DC charging system (not shown) connected to the positive and negative DC buses.Both battery banks B1 and B2 can be charged simultaneously at a lower voltage level than in the second operating mode M2. In this example, both battery banks can be charged simultaneously using a 400 V DC charging system.

Claims

[1] Method for operating a T-type NPC inverter and an associated switching arrangement for two battery banks (B1, B2) of a battery system, wherein the switching arrangement consists of two switching elements (S1, S2), wherein a first switching element (S1) is arranged between the positive terminal of a first battery bank (B1) and the negative terminal of a second battery bank (B2) and connects them conductively in a series circuit when closed, wherein furthermore, for each of the 3 phases of an electric motor, the neutral point of the T-type inverter is contacted between the positive terminal of the first battery bank (B1) and the negative terminal of the second battery bank (B2), and the switching arrangement has a second switching element (S2) that branches off between the first switching element (S1) and the negative terminal of the second battery bank (B2) and connects it switchably to the negative terminal of the first battery bank (B1),wherein the negative terminal of the first battery bank (B1) forms the negative DC bus (DC-) and the positive terminal of the second battery bank (B2) forms the positive DC bus (DC+), between which for each phase of an electric machine (Em) a neutral conductor (N) is connected, starting from between the positive terminal of the first battery bank (B1) and the negative terminal of the second battery bank (B2) and connected via first power controllers (L1 / L1') to each of the coils of an electric machine (Em), wherein the neutral conductor (N) is further connected via a second power controller (L2) to the positive DC bus (DC+) and via a third power controller (L3) to the negative DC bus (DC-), so that the respective coil of the electric machine (Em) is supplied with current starting from the connection point of the first power controllers (L1 / L1') with the second (L2) and the third power controllers (L3), wherein by the circuit of the power controllers (L1 / L1',Three different operating modes are selected using the switching elements (S1 and S2) (L2 and L3). In the first operating mode (M1), with the switching element (S1) closed, the positive terminal of the first battery bank (B1) is connected to the negative terminal of the second battery bank (B2). With the switch (S2) open, the two battery banks (B1 and B2) are connected in series, and the sum of the voltages of the two battery banks (B1 and B2) can be switched between the positive DC bus (DC+) and the negative DC bus (DC-) via the inverter's power controllers (L1 / L1', L2, and L3) to the coils of the electric motor (Em). This allows for operation with a maximum voltage of the sum of the battery banks (B1 and B2). In the second operating mode (M2), with the same switch positions as in the first operating mode (M1), but with the non-conductive power controllers open, the system operates in the same way. (L1 / L1',L2 and L3) the positive DC bus (DC+) and the negative DC bus (DC-) can be connected to the corresponding poles of a DC charging system, thus allowing both battery banks (B1 and B2) to be connected in series and charged with the sum of the battery banks (B1+B2), and in a third operating mode (M3) the first switching element (S1) is opened, so that the connection between the positive terminal of the first battery bank (B1) and the negative terminal of the second battery bank (B2) is broken, and by closing the second switching element (S2) the negative terminal of the second battery bank (B2) is connected to the negative terminal of the first battery bank (B1), whereby the first power controllers (L1 / L1') and the second power controller (L2) are also switched to conduction.so that when the third power controller (L3) is open (not conductive), the positive terminal of the first battery bank (B1) is connected to the positive DC bus and thus to the positive terminal of the second battery bank (B2), so that both battery banks (B1, B2) are connected in parallel with respect to a DC charging system connected to the positive (DC+) and negative DC bus (DC-) and can be charged simultaneously at a voltage level that corresponds to the voltage level of one of the battery banks (B1, B2). [2] Device characterized bythat this includes a control system implementing a method according to claim 1, wherein the device comprises a three-phase T-type NPC inverter with power controllers (L1, L1', L2 and L3) and a switching arrangement for two battery banks (B1, B2) of a battery system, wherein the switching arrangement consists of two switching elements (S1, S2) and a first switching element (S1) is arranged between the positive terminal of a first battery bank (B1) and the negative terminal of a second battery bank (B2) and connects them conductively in a series circuit when closed, wherein furthermore, for each of the 3 phases of an electric motor, the neutral point of the T-type inverter is contacted between the positive terminal of the first battery bank (B1) and the negative terminal of the second battery bank (B2), wherein furthermore, the switching arrangement comprises a second switching element (S2),which branches off between the first switching element (S1) and the negative terminal of the second battery bank (B2) and connects this point switchably to the negative terminal of the first battery bank (B1), wherein the negative terminal of the first battery bank (B1) forms the negative DC bus (DC-) and the positive terminal of the second battery bank (B2) forms the positive DC bus (DC+), between which, for each of the 3 phases of an electric motor, a neutral conductor (N) is connected, starting from between the positive terminal of the first battery bank (B1) and the negative terminal of the second battery bank (B2), via the first power controller (L1 / L1') to one of the coils of an electric machine (EM), wherein each of the neutral conductors (N) is further connected via a second power controller (L2) to the positive DC bus (DC+) and via a third power controller (L3) to the negative DC bus (DC-). [3] Device according to claim 2, characterized bythat the first battery bank (B1) and the second battery bank (B2) have the same voltage levels. [4] Device according to claims 2 to 3, characterized by that the switching elements (S1 / S2) are relay or semiconductor switches and the power controllers (L1L1', L2 and L3) are semiconductor switches such as IGBTs, MOSFETs, SiC or GaN transistors.

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