Multi-stage inverter circuit for an electric drive system in motor vehicles and a method for its implementation

Abstract

The present disclosure provides a multi-stage inverter circuit (100) for a vehicle electric drive system (1000) which includes an electrical circuit assembly (130) electrically connected between a capacitor circuit (110) and a power circuit (120). The electrical circuit assembly (130) comprises a first circuit assembly (132) connected via a first DC link capacitor (C1) and a second circuit assembly (134) connected via a second DC link capacitor (C2).A control circuit (140) is electrically connected to the electrical circuit assembly (130) and is configured to perform active voltage equalization between the first and second DC link capacitors (C1, C2) and / or active discharge of the first and second DC link capacitors (C1, C2) and capacitor (C) during normal operation of the multi-level inverter circuit (100) by operating the first circuit assembly (132) and / or the second circuit assembly (134).

Description

TECHNICAL AREA

[0001] The present disclosure relates to the field of automobiles. In particular, the present disclosure provides a multi-stage inverter circuit for an electric vehicle drive system (E-drive) and a method for controlling the E-drive system. BACKGROUND

[0002] Currently, two-level inverters are primarily used for battery electric vehicles (BEVs) and hybrid vehicles (HVs). However, as the power requirements of drive systems increase, interest in three-level neutral point clamped (NPC) inverters as an alternative is growing. These three-level NPC inverters offer numerous advantages over their two-level counterparts, including higher power output, higher voltages, and lower harmonics. Despite these advantages, they also have some drawbacks. A significant disadvantage of three-level NPC inverters is the need for a capacitive voltage divider on the DC side, and maintaining balanced voltages across two capacitors in the divider circuit presents a challenging task.

[0003] Various pulse-width modulation (PWM) techniques have been developed to eliminate the neutral point current and ensure voltage balance, but these often overlook a parametric tolerance inherent in commercially available capacitors. Even capacitors with identical ratings can exhibit slight variations due to manufacturing tolerances, and their capacitance values ​​can diverge further with age. Consequently, achieving perfect balancing via voltage divider capacitors is difficult, even when the neutral point current is effectively eliminated in 3-level NPC inverters.

[0004] Many techniques have been developed to circumvent the aforementioned problems. For example, patent US2022 / 0037992A1 describes an intermediate circuit discharge unit for the intermediate circuit discharge of a multi-stage inverter, comprising a capacitor and a discharge circuit connected in parallel. The discharge circuit has an active discharge branch with at least one first discharge element and a passive discharge branch with at least one second discharge element. The active discharge branch includes a first control terminal, and the passive discharge branch includes a second control terminal. The active discharge branch is coupled to the passive discharge branch via the first control terminal in such a way that the active discharge branch is controlled by the passive discharge branch, in particular, that discharge via the active discharge branch can be activated or deactivated as needed.

[0005] Patent US2022 / 0393571A1 describes an active discharge circuit for an electric vehicle inverter. The active discharge circuit is connected in parallel to a DC link capacitor, which is connected between the positive and negative leads of a DC link. The circuit includes a dissipative current source, a switch connected in series with the current source between the DC leads, and a controller connected to the switch. The controller is configured to apply an activation signal in response to a control signal, which then opens the switch. The current source is configured to draw a discharge current and dissipate any energy stored in the DC link capacitor when the switch is in the conducting state.As long as the switch is closed by the activation signal, the power source draws a constant current and consumes power, and the voltage across the intermediate circuit capacitor decreases linearly.

[0006] Patent US2023 / 0216426A1 describes a three-stage inverter containing controllable switching components T1 through T6. Each controllable switching component comprises a parallel-connected junction capacitor and an antiparallel-connected diode. A first terminal of T1 is connected to a positive DC bus, a second terminal of T4 is connected to a negative DC bus, and a second terminal of T1 is connected to the first terminals of T2 and T5. A control device is configured to control, during a positive half-cycle, that T3 is switched on after T1 is switched on and that T3 is switched off before T1 is switched on again. During a negative half-cycle, it controls that T2 is switched on after T4 is switched on and that T2 is switched off before T4 is switched on again.The three-stage inverter can balance the voltages of the controllable switching components.

[0007] Although the cited documents reveal various techniques for balancing the voltages, they do not focus on providing a unified circuit that solves at least the problems mentioned above. SUBJECT OF THE PRESENT INVENTION

[0008] A general object of the present invention is to provide an efficient and reliable circuit that avoids the above-mentioned limitations of existing systems and methods and performs both active voltage balancing and active discharge of capacitors of an inverter in an electric drive system for vehicles.

[0009] The object of the present invention is to provide a multi-level inverter circuit which, during the normal operation of an inverter, actively balances the voltages at the direct current (DC) interconnection capacitors by operating power switching devices.

[0010] Another object of the present invention is to provide a multi-stage inverter circuit that performs an active discharge of DC link capacitors and a capacitor by operating first and second circuit assemblies based on an active discharge request.

[0011] Another object of the present invention is to provide a method for controlling a vehicle electric drive system by efficiently carrying out active balancing of the voltages at the DC link capacitors and active discharge of the DC link capacitors and a capacitor. SUMMARY

[0012] Aspects of the present disclosure relate to the field of automobiles. In particular, the present disclosure provides a multi-stage inverter circuit for an electric vehicle drive system (E-drive) and a method for controlling the E-drive system.

[0013] One aspect of the present disclosure relates to a multi-level inverter circuit for a vehicle electric drive system. The multi-level inverter circuit comprises a capacitor circuit with a capacitor and at least one first DC link capacitor and a second DC link capacitor, which are connected in series on a DC bus connection on one side of the multi-level inverter circuit. The multi-level inverter circuit includes a power circuit with a plurality of power switching devices configured to convert an input DC voltage into an output AC voltage. The multi-level inverter includes an electrical circuit arrangement that is electrically connected between the capacitor circuit and the power circuit.The electrical circuit assembly comprises a first circuit assembly connected via the first DC link capacitor and a second circuit assembly connected via the second DC link capacitor. The multi-level inverter circuit includes a control circuit that is electrically connected to the electrical circuit assembly and configured to perform active voltage equalization between the first and second DC link capacitors and / or active discharge of the first and second DC link capacitors or capacitors during normal operation of the multi-level inverter circuit by operating the first circuit assembly and / or the second circuit assembly.

[0014] In one embodiment, the first circuit arrangement can include a first controllable switching element connected in series with a second controllable switching element, wherein one end of the series connection of the controllable switching elements can be connected to a positive DC supply line. The first circuit arrangement can include a first inductor, wherein a first end of the first inductor is electrically connected to the other end of the series connection of the controllable switching elements, and a second end of the first inductor can be electrically connected to a midpoint of the series connection of the first and second DC link capacitors. The first circuit arrangement can include a first resistor connected across the second controllable switching element.

[0015] In one embodiment, the second circuit arrangement can include a third controllable switching element connected in series with a fourth controllable switching element, wherein one end of the series connection of the controllable switching elements can be connected to a negative DC supply line. The second circuit arrangement can include a second inductor, wherein a first end of the second inductor can be electrically connected to the other end of the series connection of the controllable switching elements, and a second end of the second inductor can be electrically connected to a midpoint of the series connection of the first and second DC link capacitors. The second circuit arrangement can include a second resistor connected via the fourth controllable switching element.

[0016] In one embodiment, the electrical circuit arrangement can comprise a first diode and a second diode. A negative terminal of the first diode can be connected to a midpoint between the first end of the first coil and the other end of the series connection of the controllable switching elements, and a positive terminal of the first diode can be connected to a negative DC supply line. Furthermore, a positive terminal of the second diode can be connected to a midpoint between the second end of the second coil and the other end of the series connection of the controllable switching elements, and a negative terminal of the second diode can be connected to a positive DC supply line.

[0017] In one embodiment, the control circuit can be configured to control controllable switching elements in the first and second circuit assemblies during the active balancing of the voltages at the first and second DC link capacitors, such that energy in the first DC link capacitor is discharged to a first inductor and energy in the first inductor is transferred to the second DC link capacitor to charge the second DC link capacitor when the voltage at the first DC link capacitor is greater than the voltage at the second DC link capacitor.Furthermore, the control circuit can be configured to control controllable switching elements in the first and second circuit assemblies so that energy in the second DC link capacitor is discharged to the second inductor and energy in the second inductor can be transferred to the first DC link capacitor to charge the first DC link capacitor when the voltage across the first DC link capacitor is lower than the voltage across the second DC link capacitor during normal operation of the multi-stage inverter circuit.

[0018] In one embodiment, the control circuit can be configured to switch on the first and second controllable switching elements in the first circuit assembly when the voltage across the first DC link capacitor is greater than the voltage across the second DC link capacitor, thus enabling the first DC link capacitor to transfer the energy to the first inductor via the first and second controllable switching elements. Furthermore, the control circuit can be configured to switch off the third controllable switching element and switch on the fourth controllable switching element in the second circuit assembly, transferring the energy stored in the first inductor to the second DC link capacitor to charge it.

[0019] In one embodiment, the control circuit can be configured to switch on the third and fourth controllable switching elements in the second circuit assembly when the voltage across the first DC link capacitor is lower than the voltage across the second DC link capacitor, thus enabling the second DC link capacitor to transfer energy to the second inductor. Furthermore, the control circuit can be configured to switch off the first controllable switching element and switch on the second controllable switching element in the first circuit assembly, transferring the energy stored in the second inductor to charge the first DC link capacitor.

[0020] In one embodiment, the control circuit can be configured to perform the active discharge of the first and second intermediate circuit capacitors or the capacitor based on an active discharge request.

[0021] In one embodiment, the control circuit can be configured during the active discharge of the first DC link capacitor such that it switches on the first controllable switching element and switches off the second controllable switching element in the first circuit assembly, enabling the first DC link capacitor to discharge the energy via the first inductor and the first resistor switched via the second controllable switching element.

[0022] In one embodiment, the control circuit can be configured during the active discharge of the second DC link capacitor such that, in the second circuit arrangement, it switches on the third controllable switching element and switches off the fourth controllable switching element, enabling the second DC link capacitor to discharge the energy via the second inductor and the second resistor, which is connected via the fourth controllable switching element.

[0023] In one embodiment, the control circuit can be configured during the active discharge of the capacitor to switch on a first and a third controllable switching element and to switch off a second and a fourth controllable switching element, enabling the capacitor to discharge the energy via the first coil, the first resistor, the second coil and the second resistor, respectively.

[0024] In one embodiment, the multi-stage inverter can be a diode-clamped multi-stage inverter, a multi-stage inverter with flying capacitors, or a cascaded H-bridge multi-stage inverter.

[0025] One aspect of the present disclosure relates to a vehicle electric drive system comprising a motor and a multi-level inverter circuit electrically connected to the motor. The multi-level inverter circuit includes a capacitor circuit with a capacitor and at least one first DC link capacitor and a second DC link capacitor connected in series on a DC bus connection on one side of the multi-level inverter circuit. The multi-level inverter circuit includes a power circuit with a plurality of power switching devices configured to convert an input DC voltage into an output AC voltage. The multi-level inverter includes an electrical circuit arrangement electrically connected between the capacitor circuit and the power circuit.The electrical circuit assembly comprises a first circuit assembly connected via the first DC link capacitor and a second circuit assembly connected via the second DC link capacitor. The multi-level inverter circuit includes a control circuit that is electrically connected to the electrical circuit assembly and configured to perform active voltage equalization between the first and second DC link capacitors and / or active discharge of the first and second DC link capacitors or capacitors during normal operation of the multi-level inverter circuit by operating the first circuit assembly and / or the second circuit assembly.

[0026] One aspect of the present disclosure relates to a method for controlling a vehicle electric drive system. The method comprises determining a voltage across a first DC link capacitor and a voltage across a second DC link capacitor in a multi-level inverter circuit. The method includes controlling controllable switching elements in the multi-level inverter circuit to perform active balancing of the voltages across the first and second DC link capacitors based on this determination. Furthermore, the method comprises controlling the controllable switching elements and at least a first circuit assembly and a second circuit assembly to perform active discharge of the first and second DC link capacitors, or of a capacitor, during normal operation of the multi-level inverter circuit.

[0027] Various objects, features, aspects and advantages of the invention will become clearer from the following detailed description of preferred embodiments together with the accompanying drawings, in which the same numbers represent the same components. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The accompanying drawings serve to further understand the present disclosure and are an integral part of this description. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure. Fig. Figure 1A shows an exemplary block diagram of an electric drive system for vehicles (E-Drive) according to an embodiment of the present disclosure. Fig. Figure 1B shows a circuit diagram of a vehicle electric drive system according to an embodiment of the present disclosure. Fig. Figures 2A-2C show circuit diagrams illustrating the switching operations during active voltage equalization across the DC capacitors in accordance with an embodiment of the present disclosure. Fig. Figure 2D shows a flowchart for the implementation of an example method for performing active voltage equalization via DC link capacitors in accordance with embodiments of the present disclosure. Fig. 2E and Fig. Figure 2F shows graphical representations of active equalization processes of voltages at intermediate circuit capacitors in accordance with embodiments of the present disclosure. Fig. Figure 3A shows a circuit diagram illustrating the switching operations during an active discharge of intermediate circuit capacitors and a capacitor according to an embodiment of the present disclosure. Fig. Figure 3B shows a flowchart for the implementation of an example method for performing an active discharge of intermediate circuit capacitors and a capacitor according to an embodiment of the present disclosure. Fig. 3C and Fig. 3D shows graphical representations of active discharge processes of intermediate circuit capacitors and a capacitor according to the embodiments of the present disclosure. Fig. Figure 4 shows a flowchart for the implementation of an example method for controlling an electric drive system of a vehicle in accordance with embodiments of the present disclosure. DETAILED DESCRIPTION

[0029] A detailed description of embodiments of the disclosure, illustrated in the accompanying drawings, follows. The embodiments are described in sufficient detail to clarify the disclosure. However, this level of detail is not intended to limit foreseeable variations of embodiments; on the contrary, it is intended to cover all modifications, equivalents, and alternatives that fall within the spirit and scope of the present disclosure as defined by the accompanying claims.

[0030] The embodiments described herein relate to the field of motor vehicles. In particular, the present disclosure provides a multi-stage inverter circuit for an electric vehicle drive system (E-drive) and a method for controlling the E-drive system. Various embodiments of the present disclosure are described with reference to the Fig. 1A-3D.

[0031] Fig. Figure 1A shows an example block diagram of an electric drive system for vehicles and Fig. Figure 1B shows a circuit diagram of the electric drive system for vehicles according to an embodiment of the present disclosure.

[0032] With reference to the Fig. 1A and Fig. 1B can comprise, for example, but not exclusively, the electric drive system of a vehicle (here interchangeably referred to as System 1000) of a multi-level inverter circuit 100 implemented in a vehicle. The vehicle can be, for example, a battery electric vehicle (BEV) or a hybrid vehicle (HV), but is not limited to either. The multi-level inverter circuit 100 can be, for example, but not exclusively, a 3-level inverter, a 3-level NPC (Neutral Point Clamped) inverter, or a 4-level inverter. In a preferred embodiment, the multi-level inverter circuit can be a 3-level inverter.

[0033] Referring to Fig. 1A and Fig. 1B The vehicle electric drive system 1000 can include, among other things, a motor 200 and the multi-stage inverter circuit 100, which is electrically connected to the motor 200. In one embodiment, the multi-stage inverter circuit 100 can include a capacitor circuit 110, a power circuit 120, an electrical circuit arrangement 130, and a control circuit 140.

[0034] In one embodiment, the capacitor circuit 110 can comprise a capacitor C and at least one first DC link capacitor C1 and a second DC link capacitor C2, which are connected in series in a DC link on a DC side of the multi-stage inverter circuit 100. In one embodiment, the power circuit 120 can comprise a plurality of power switching devices P1-P2. 12include those configured to convert an input DC voltage into an output AC voltage.

[0035] In one embodiment, the electrical circuit assembly 130 can be electrically connected between the capacitor circuit 110 and the power circuit 120. The electrical circuit assembly 130 can comprise a first circuit assembly 132, which is connected via the first intermediate circuit capacitor C1, and a second circuit assembly 134, which is connected via the second intermediate circuit capacitor C2.

[0036] In one embodiment, the first circuit arrangement 132 can include a first controllable switching element S1 connected in series with a second controllable switching element S2. One end of the series connection of the controllable switching elements S1, S2 can be connected to a positive DC supply line. The first circuit arrangement 132 can include a first induction coil L1, wherein a first end of the first induction coil L1 can be electrically connected to the other end of the series connection of the controllable switching elements S1, S2, and a second end of the first induction coil L1 can be electrically connected to a midpoint of the series connection of the first and second DC link capacitors C1, C2. Furthermore, the first circuit arrangement 132 can include a first resistor R1 connected via the second controllable switching element S2.

[0037] In one embodiment, the second circuit arrangement 134 can include a third controllable switching element S3, which is connected in series with a fourth controllable switching element S4. One end of the series connection of the controllable switching elements S3, S4 can be connected to a negative DC supply line. The second circuit arrangement 134 can include a second induction coil L2, wherein a first end of the second induction coil L2 can be electrically connected to the other end of the series connection of the controllable switching elements S3, S4, and a second end of the second induction coil L2 can be electrically connected to a midpoint of the series connection of the first and second DC link capacitors C1, C2. Furthermore, the second circuit arrangement 134 can include a second resistor R2, which is connected via the fourth controllable switching element S4.

[0038] In one embodiment, the electrical circuit arrangement 130 can include a first diode D1 and a second diode D2. A negative terminal of the first diode D1 can be connected to a midpoint between the first end of the first inductor L1 and the other end of the series connection of the controllable switching elements S1, S2. A positive terminal of the first diode D1 can be connected to the negative DC supply line. A positive terminal of the second diode D2 can be connected to a midpoint between the second end of the second inductor L2 and the other end of the series connection of the controllable switching elements S3, S4, and a negative terminal of the second diode D2 can be connected to the positive DC supply line.

[0039] In one embodiment, the control circuit 140 can be electrically connected to the electrical circuit arrangement 130. In another embodiment, the control circuit 140 can be configured to actively equalize the voltages across the first and second DC link capacitors C1 and C2. In yet another embodiment, the control circuit 140 can be configured to actively discharge the first and second DC link capacitors C1 and C2 and capacitor C. The control circuit 140 can be configured to perform the active discharge by operating the first circuit assembly 132 and / or the second circuit assembly 134 during normal operation of the multi-stage inverter circuit 100. The control circuit 140 can be configured to perform the active discharge based on an active discharge request.

[0040] In one embodiment, the control circuit 140 can be configured during the active balancing of the voltages at the first and second DC link capacitors C1, C2 such that it controls controllable switching elements S1-S4 in the first and second circuit assemblies 132, 134 such that energy stored in the first DC link capacitor C1 can be discharged into the first inductor L1, and energy stored in the first inductor L1 can be transferred to the second DC link capacitor C2 to charge the second DC link capacitor C2, when the voltage at the first DC link capacitor C1 is greater than the voltage at the second DC link capacitor C2.

[0041] In one embodiment, the control circuit 140 can be configured during the active balancing of the voltages across the first and second DC link capacitors C1, C2 such that it controls controllable switching elements S1-S4 in the first and second circuit assemblies 132, 134 so that energy in the second DC link capacitor C2 can be discharged to the second inductor L2, and energy in the second inductor L2 can be transferred to the first DC link capacitor C1 to charge the first DC link capacitor C1 when the voltage across the first DC link capacitor C1 is lower than the voltage across the second DC link capacitor C2 during the normal operation of the multi-stage inverter circuit 100.

[0042] The Fig. Circuit diagrams 200A-200C show the circuit processes during the active balancing of the voltages at the first and second intermediate circuit capacitors C1, C2, according to an embodiment of the present disclosure.

[0043] Fig. Figure 2A shows the circuit diagram 200A of the capacitor circuit 110 and the electrical circuit arrangement 130 in the multi-stage inverter circuit 100 when the voltages across the first DC link capacitor C1 and the second DC link capacitor C2 are balanced. For example, the voltages across the first DC link capacitor C1 and the second DC link capacitor C2 can be balanced by a voltage balancing circuit. When the voltages across the first DC link capacitor C1 and the second DC link capacitor C2 are balanced, the multi-stage inverter circuit 100 can produce a more symmetrical output voltage waveform, resulting in lower total harmonic distortion (THD) and improved power quality.When the voltages across the first DC link capacitor C1 and the second DC link capacitor C2 are balanced, the controllable switching elements S1-S4 can be switched off and subjected to a lower voltage load, thereby increasing their reliability and service life. Furthermore, symmetrical DC link voltages can improve the overall efficiency of the multi-stage inverter circuit 100. This can be attributed to the minimization of power losses associated with asymmetrical voltages.

[0044] Fig. Figure 2B shows the circuit diagram 200B of the capacitor circuit 110 and the electrical circuit arrangement 130 in the multi-stage inverter circuit 100 when the voltage at the first intermediate circuit capacitor C1 is greater than the voltage at the second intermediate circuit capacitor C2.

[0045] With reference to Fig. In one embodiment of 2B, if the voltage across the first DC link capacitor C1 is greater than the voltage across the second DC link capacitor C2, the first DC link capacitor C1 smooths the voltage supplied to the multi-stage inverter circuit 100. During operation, the first DC link capacitor C1 can charge up to a peak voltage of a DC power source (e.g., a battery or a rectified AC line). When the multi-stage inverter circuit 100 switches on to generate an AC output, the first DC link capacitor C1 can discharge its stored energy into the first inductor L1.This discharge of energy from the first intermediate circuit capacitor C1 into the first inductor L1 can maintain a relatively constant DC voltage at the input terminals of the multi-stage inverter circuit 100 and simultaneously supply the necessary energy to generate the AC output. The first inductor L1 can filter the current flowing through the multi-stage inverter circuit 100, thereby smoothing out fluctuations caused by switching operations of the multi-stage inverter circuit 100 and thus ensuring stable and efficient operation of the multi-stage inverter circuit 100.

[0046] In one embodiment, the control circuit 140 can be configured such that, when the voltage across the first DC link capacitor C1 is greater than the voltage across the second DC link capacitor C2, it switches on the first and second controllable switching elements S1 and S2 in the first circuit assembly 132, enabling the first DC link capacitor C1 to transfer energy to the first inductor L1 via the first and second controllable switching elements S1 and S2. Furthermore, the control circuit 140 can be configured in the second circuit assembly 134 such that it switches off the third controllable switching element S3 and switches on the fourth controllable switching element S4, transferring the energy stored in the first inductor L1 to the second DC link capacitor C2 to charge it.Therefore, the second intermediate circuit capacitor C2 can be charged by storing energy in the form of an electric field across its plates. This charging process allows the voltage across the second intermediate circuit capacitor C2 to be regulated, thus ensuring a stable DC voltage level for the operation of the multi-stage inverter circuit 100.

[0047] Conversely, it shows Fig. 2C the circuit diagram 200C of the capacitor circuit 110 and the electrical circuit assembly 130, when the voltage across the first intermediate circuit capacitor C1 is lower than the voltage across the second intermediate circuit capacitor C2. In one embodiment, the second intermediate circuit capacitor C2 can discharge its stored energy into the second inductor L2 when the voltage across the first intermediate circuit capacitor C1 is lower than the voltage across the second intermediate circuit capacitor C2, and the first intermediate circuit capacitor C1 can be charged with the energy transferred by the second inductor L2.

[0048] In one embodiment, the control circuit 140 can be configured such that, when the voltage across the first DC link capacitor C1 is lower than the voltage across the second DC link capacitor C2, it switches on the third and fourth controllable switching elements S3 and S4 in the second circuit assembly 134, enabling the second DC link capacitor C2 to discharge energy to the second inductor L2. In the first circuit arrangement 132, the control circuit 140 can be configured to switch off the first controllable switching element S1 and switch on the second controllable switching element S2, transferring the energy stored in the second inductor L2 to charge the first DC link capacitor C1. This can help stabilize the DC voltage and facilitate the conversion of DC to AC in the multi-stage inverter circuit 100.

[0049] Fig. Figure 2D shows a flowchart of an example method 200D for carrying out the active balancing of the voltages on the intermediate circuit capacitors C1, C2, in accordance with embodiments of the present disclosure.

[0050] With reference to Fig. 2D, the control circuit 140 at 202 can be configured during the normal operation of the multi-stage inverter circuit 100 to determine whether the voltage at the first intermediate circuit capacitor C1 is equal to the voltage at the second intermediate circuit capacitor C2.

[0051] At 204, when the voltage across the first intermediate circuit capacitor C1 is equal to the voltage across the second intermediate circuit capacitor C2, the first controllable switching element S1 and the second controllable switching element S2 can be switched off.

[0052] At 206, if the voltage across the first intermediate circuit capacitor C1 is not equal to the voltage across the second intermediate circuit capacitor C2, the control circuit 140 can be configured to determine whether the voltage across the first intermediate circuit capacitor C1 is greater than the voltage across the second intermediate circuit capacitor C2.

[0053] At 208, when the voltage across the first intermediate circuit capacitor C1 is greater than the voltage across the second intermediate circuit capacitor C2, the control circuit 140 can be configured to activate the first controllable switching element S1 to receive a pulse width modulation (PWM) signal and to turn off the second controllable switching element S2.

[0054] At 210, the control circuit 140 can be configured to determine, in response to the receipt of the PWM signal, whether the first controllable switching element S1 is switched on.

[0055] At 212, when the first controllable switching element S1 is switched on, the control circuit 140 can be configured to activate the first intermediate circuit capacitor C1 to discharge the energy to the first inductor L1, and to charge the first inductor L1 connected to the first intermediate circuit capacitor C1.

[0056] At 214, when the first controllable switching element S1 is switched off, the control circuit 140 can be configured to activate the first inductor L1 to discharge the energy and charge the second intermediate circuit capacitor C2 via the first diode D1 to perform the active balancing of the voltages on the first and second intermediate circuit capacitors C1, C2.

[0057] At 216, when the voltage across the first intermediate circuit capacitor C1 is smaller than the voltage across the second intermediate circuit capacitor C2, the control circuit 140 can be configured to switch off the first controllable switching element S1 and enable the second controllable switching element S2 to receive the PWM signal.

[0058] At 218, the control circuit 140 can be configured to determine whether the second controllable switching element S2 is switched on with respect to receiving the PWM signal.

[0059] At 220, when the second controllable switching element S2 is switched on, the control circuit 140 can be configured to activate the second DC link capacitor C2 to discharge the energy and charge the second inductor L2, which is connected to the second DC link capacitor C2, using the discharged energy of the second DC link capacitor C2.

[0060] At 222, when the second controllable switching element S2 is switched off, the control circuit 140 can be configured to discharge the second inductor L2 and charge the first intermediate circuit capacitor C1 via the second diode D2 to perform the active balancing of the voltages on the first and second intermediate circuit capacitors C1, C2.

[0061] Fig. Figure 2E shows a graphical representation 200E in which the voltages at the first and second intermediate circuit capacitors C1, C2 are shown according to the embodiments of the present disclosure.

[0062] In a scenario where active voltage balancing between the first and second DC link capacitors C1 and C2 is not performed, or where the voltage balancing circuit in the multi-stage inverter circuit 100 is deactivated, and the voltage across the first DC link capacitor C1 is 5500 µF and the voltage across the second DC link capacitor C2 is 4500 µF, the DC link voltage can be 750 V during normal operation of the multi-stage inverter circuit 100.

[0063] Fig. Figure 2F shows a graphical representation 200F in which the voltages at the first and second intermediate circuit capacitors C1, C2 are shown according to the embodiments of the present disclosure.

[0064] With reference to Fig. Section 2F considers a scenario where the voltage equalization circuit in the multi-stage inverter circuit 100 is activated. If the voltage across the first DC link capacitor C1 is 5500 µF and the voltage across the second DC link capacitor C2 is 4500 µF, the DC link voltage during normal operation of the multi-stage inverter circuit 100 can be 750 V.

[0065] Fig. Figure 3A shows a circuit diagram 300A, which illustrates the switching operations during an active discharge of the first and second intermediate circuit capacitors C1, C2 and capacitor C according to an embodiment of the present disclosure.

[0066] With reference to Fig. In one embodiment, the control circuit 140 can be configured to perform the active discharge of the first and second DC link capacitors C1 and C2, and capacitor C, by operating the first circuit assembly 132 and / or the second circuit assembly 134 by permanently opening the third controllable switching element S3 and the fourth controllable switching element S4 based on the active discharge request. Alternatively, the control circuit 140 can be configured to perform the active discharge of the first and second DC link capacitors C1 and C2, and capacitor C, by permanently closing the first controllable switching element S1 and the second controllable switching element S2 based on the active discharge request. During the active discharge process, the first DC link capacitor C1 can discharge through the first resistor R1 and the first inductor L1.Similarly, the second intermediate circuit capacitor C2 can discharge through the second resistor R2 and the second inductor L2. Furthermore, the capacitor C can discharge through the first resistor R1, the first inductor L1, the second resistor R2, and the second inductor L2, as shown in [reference]. Fig. 3A is shown.

[0067] Furthermore, the first and second resistors R1 and R2 can only be operated during the active discharge process. During the active discharge process, the multi-stage inverter circuit 100 can become an RLC circuit with pre-charged capacitors. The values ​​of the first and second resistors R1 and R2 can be selected so that the RLC circuit becomes a critically damped or overdamped circuit. Because the RLC circuit becomes an overdamped or critically damped circuit, a steady-state voltage of zero across the first and second DC link capacitors C1 and C2 can be ensured, and current and voltage oscillations across these capacitors can be prevented. Additionally, smooth switching is possible for all controllable switching elements S1–S4 that are operating during the active discharge process.

[0068] Fig. Figure 3B shows a flowchart of an example method 300B for carrying out the active discharge of the first and second intermediate circuit capacitors C1, C2 and capacitor C according to an embodiment of the present disclosure.

[0069] With reference to Fig. 3B, the control circuit 140 at 302 can be configured to perform the active discharge of the first and second intermediate circuit capacitors C1, C2 and capacitor C based on the active discharge requirement.

[0070] At 304, when the active discharge requirement is active, the control circuit 140 can be configured to turn on the first controllable switching element S1 and the third controllable switching element S3 and turn off the second controllable switching element S2 and the fourth controllable switching element S4 in order to perform the active discharge of the first and second intermediate circuit capacitors C1, C2 and capacitor C, as shown in Fig. Figure 3A illustrates this. During the active discharge process, the first intermediate circuit capacitor C1 can discharge through the first resistor R1 and the first inductor L1. Similarly, the second intermediate circuit capacitor C2 can discharge through the second resistor R2 and the second inductor L2. Furthermore, capacitor C can discharge through the first resistor R1, the first inductor L1, the second resistor R2, and the second inductor L2.

[0071] At 306, when the active discharge request is inactive, the control circuit 140 can be configured to perform the active balancing of the voltages at the first and second DC link capacitors C1, C2 by switching on the third controllable switching element S3 and the fourth controllable switching element S4, as shown in the Fig. 2B and Fig. 2C is shown.

[0072] Fig. 3C and Fig. 3D graphic representations 300C and 300D show active discharge processes of the first and second intermediate circuit capacitors C1, C2 and capacitor C according to the embodiments of the present disclosure.

[0073] The discharge behavior of the first intermediate circuit capacitor C1 can look like this, for example: Fig. 3C can be illustrated by considering that the active discharge resistances of the first and second resistors R1, R2 are 50Ω, the values ​​of the first and second inductances L1, L2 are 1 mH, the voltage across the first intermediate circuit capacitor C1 is 5500 µF, the voltage across the second intermediate circuit capacitor C2 is 4500 µF, and an initial voltage across the first intermediate circuit capacitor C1 is 400 V.

[0074] The discharge behavior of the second intermediate circuit capacitor C2 can be described, for example, as in Fig. 3D representation is possible when considering that the active discharge resistances of the first and second resistors R1, R2 are 50Ω, the values ​​of the first and second inductances L1, L2 are 1mH, the voltage across the first intermediate circuit capacitor C1 is 5500 µF, the voltage across the second intermediate circuit capacitor C2 is 4500 µF, and an initial voltage across the second intermediate circuit capacitor C2 is 400 V.

[0075] Fig. Figure 4 shows a flowchart for the implementation of an example method (400) for controlling the electric drive system (1000) of a vehicle according to the embodiments of the present disclosure.

[0076] With reference to Fig. 4 the method (400) at 402 can include the determination of the voltage across the first intermediate circuit capacitor (C1) and the voltage across the second intermediate circuit capacitor (C2) in the multi-level inverter circuit (100).

[0077] In 404, the method (400) can include the control of controllable switching elements (S1 - S4) in the multi-level inverter circuit (100) to perform the active balancing of the voltages on the first and second intermediate circuit capacitors (C1 , C2) based on the determination.

[0078] In 406, the method (400) can include the control of the controllable switching elements (S1-S4) and at least one of the first circuit assembly (132) and the second circuit assembly (134) to perform the active discharge of the first and second intermediate circuit capacitors (C1, C2) or the capacitor (C) during the normal operation of the multi-level inverter circuit (100).

[0079] Therefore, the present disclosure enables the multi-level inverter circuit 100 to actively balance the voltages across the DC link capacitors C1 and C2 by actuating the controllable switching elements S1-S4 during normal operation of the multi-level inverter circuit 100. Furthermore, the multi-level inverter circuit 100 can actively discharge the DC link capacitors C1 and C2 and capacitor C by operating the resistors R1 and R2 more efficiently based on the active discharge requirement.

[0080] While the foregoing describes various embodiments of the invention, other and further embodiments of the invention can be developed without deviating from the fundamental scope of the invention. The scope of the invention is defined by the following claims. The invention is not limited to the described embodiments, variants, or examples, provided that they are included to enable a person with ordinary technical knowledge to manufacture and use the invention when combined with information and knowledge available to such a person. BENEFITS OF THE PRESENT DISCLOSURE

[0081] The present disclosure describes active voltage balancing and active discharge of capacitors of a 3-level inverter in a vehicle electric drive (e-Drive) system.

[0082] The present disclosure provides a multi-level inverter circuit that performs active balancing of the voltages at the direct current (DC) interconnecting capacitors by operating controllable switching elements during the normal operation of the multi-level inverter circuit.

[0083] The present disclosure provides a multi-stage inverter circuit that performs active discharge of DC link capacitors by actuating active discharge resistors based on an active discharge request.

[0084] The present disclosure provides a method for controlling an electric drive system for vehicles (e-Drive) in which active balancing of the voltages on the DC link capacitors and active discharge of the DC link capacitors and a capacitor is efficiently carried out. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2022 / 0037992A1

[0004] US 2022 / 0393571A1

[0005] US 2023 / 0216426A1

[0006]

Claims

[1] Multi-stage inverter circuit (100) for a vehicle electric drive system (1000), wherein the multi-stage inverter circuit (100) comprises: a capacitor circuit (110) comprising a capacitor (C) and at least one first DC link capacitor (C1) and one second DC link capacitor (C2) connected in series on a DC bus connection at a DC side of the multi-level inverter circuit (100); a power circuit (120) comprising a plurality of power switching devices (P1 -P 12 ) includes devices configured to convert an input DC voltage into an output AC voltage; an electrical circuit arrangement (130) which is electrically connected between the capacitor circuit (110) and the power circuit (120), wherein the electrical circuit arrangement (130) comprises a first circuit arrangement (132) which is connected via the first DC intermediate circuit capacitor (C1), and a second circuit arrangement (134) which is connected via the second DC intermediate circuit capacitor (C2); and a control circuit (140) which is electrically connected to the electrical circuit arrangement (130), wherein the control circuit (140) is configured to perform at least one of the following functions: an active voltage equalization between the first and second intermediate circuit capacitors (C1, C2) and an active discharge of the first and second intermediate circuit capacitors (C1, C2) or the capacitor (C) by operating at least one of the first circuit assembly (132) and the second circuit assembly (134) during normal operation of the multi-level inverter circuit (100). [2] Multi-stage inverter circuit (100) according to claim 1, wherein the first circuit arrangement (132) comprises: a first controllable switching element (S1) connected in series with a second controllable switching element (S2), wherein one end of the series connection of the controllable switching elements (S1 , S2) is connected to a positive DC supply line; a first choke coil (L1), wherein a first end of the first choke coil (L1) is electrically connected to the other end of the series connection of the controllable switching elements (S1, S2), and a second end of the first choke coil (L1) is electrically connected to a midpoint of the series connection of the first and second intermediate circuit capacitors (C1, C2); and a first resistor (R1) which is connected to the second controllable switching element (S2). [3] Multi-stage inverter circuit (100) according to claim 1, wherein the second circuit arrangement (134) comprises: a third controllable switching element (S3) connected in series with a fourth controllable switching element (S4), wherein one end of the series connection of the controllable switching elements (S3, S4) is connected to a negative DC supply line; a second choke coil (L2), wherein a first end of the second choke coil (L2) is electrically connected to the other end of the series connection of the controllable switching elements (S3, S4) and a second end of the second choke coil (L2) is electrically connected to a midpoint of the series connection of the first and second intermediate circuit capacitors (C1, C2); and a second resistor (R2) which is connected to the fourth controllable switching element (S4). [4] Multi-stage inverter circuit (100) according to claim 2, wherein the electrical circuit arrangement (130) comprises a first diode (D1) and a second diode (D2), wherein a negative terminal of the first diode (D1) is connected to a midpoint between the first end of the first inductor (L1) and the other end of the series connection of the controllable switching elements (S1, S2), and a positive terminal of the first diode (D1) is connected to a negative DC supply line, and wherein a positive terminal of the second diode (D2) is connected to a midpoint between the second end of the second inductor (L2) and the other end of the series connection of the controllable switching elements (S3, S4), and a negative terminal of the second diode (D2) is connected to a positive DC supply line. [5] Multi-stage inverter circuit (100) according to claim 1, wherein during the active balancing of the voltages at the first and second intermediate circuit capacitors (C1 , C2) the control circuit (140) is configured such that it: controllable switching elements (S1 - S4) in the first and second circuit arrangements (132, 134) such that energy in the first intermediate circuit capacitor (C1) is discharged to a first inductor (L1), and energy in the first inductor (L1) is transferred to the second intermediate circuit capacitor (C2) to charge the second intermediate circuit capacitor (C2) when the voltage across the first intermediate circuit capacitor (C1) is greater than the voltage across the second intermediate circuit capacitor (C2); or controllable switching elements (S1 - S4) in the first and second circuit arrangements (132, 134) such that energy in the second DC link capacitor (C2) is discharged to a second inductor (L2), and energy in the second choke coil (L2) is transferred to the first DC link capacitor (C1) to charge the first DC link capacitor (C1) when the voltage across the first DC link capacitor (C1) is lower than the voltage across the second DC link capacitor (C2) during the normal operation of the multi-stage inverter circuit (100). [6] Multi-stage inverter circuit (100) according to claim 5, wherein the voltage across the first intermediate circuit capacitor (C1) is greater than the voltage across the second intermediate circuit capacitor (C2), the control circuit (140) is configured such that it switches on the first and second controllable switching elements (S1, S2) in the first circuit arrangement (132) and enables the first intermediate circuit capacitor (C1) to deliver the energy to the first induction coil (L1) via the first and second controllable switching elements (S1, S2), and the control circuit (140) is configured to switch off the third controllable switching element (S3) and switch on the fourth controllable switching element (S4) in the second circuit arrangement (134) and to transfer the energy stored in the first inductor (L1) to the second intermediate circuit capacitor (C2) in order to charge the second intermediate circuit capacitor (C2). [7] Multi-stage inverter circuit (100) according to claim 5, wherein the voltage across the first intermediate circuit capacitor (C1) is lower than the voltage across the second intermediate circuit capacitor (C2), the control circuit (140) is configured to switch on the third and fourth controllable switching element (S3, S4) in the second circuit arrangement (134) and to enable the second intermediate circuit capacitor (C2) to transfer the energy to the second inductor (L2), and the control circuit (140) is configured such that in the first circuit arrangement (132) it switches off the first controllable switching element (S1) and switches on the second controllable switching element (S2) and transfers the energy stored in the second inductor (L2) to the first intermediate circuit capacitor (C1) in order to charge the first intermediate circuit capacitor (C1). [8] Multi-stage inverter circuit (100) according to claim 1, wherein the control circuit (140) is configured to perform the active discharge of the first and second intermediate circuit capacitor (C1, C2) or of the capacitor (C) on the basis of an active discharge request, wherein during the active discharge of the first intermediate circuit capacitor (C1) the control circuit (140) is configured to switch on a first controllable switching element (S1) and switch off a second controllable switching element (S2) in the first circuit assembly (132) and enables the first intermediate circuit capacitor (C1) to discharge the energy via a first inductor (L1) and a first resistor (R1) which are switched via the second controllable switching element (S2); wherein, during the active discharge of the second intermediate circuit capacitor (C2), the control circuit (140) is configured to switch on a third controllable switching element (S3) and switch off a fourth controllable switching element (S4) in the second circuit assembly (134), enabling the second intermediate circuit capacitor (C2) to discharge the energy via a second inductor (L2) and a second resistor (R2) connected via the fourth controllable switching element (S4); and wherein during the active discharge of the capacitor (C) the control circuit (140) is configured to switch on a first and a third controllable switching element (S1 , S3) and to switch off a second and a fourth controllable switching element (S2, S4) and to allow the capacitor (C) to discharge the energy through a first inductor (L1), a first resistor (R1), a second inductor (L2) or a second resistor (R2). [9] Multistage inverter circuit (100) according to claim 1, wherein the multistage inverter circuit (100) is one of the following: a diode-clamped multistage inverter, a multistage inverter with flying capacitors and a cascaded H-bridge multistage inverter. [10] Electric drive system (1000) for a vehicle, comprising: an engine (200); and a multi-stage inverter circuit (100) which is electrically connected to the motor (200), wherein the multi-stage inverter circuit (100) comprises the following: a capacitor circuit (110) comprising a capacitor (C) and at least one first DC link capacitor (C1) and a second DC link capacitor (C2) connected in series on a DC bus connection at a DC side of the multi-level inverter circuit (100); a power circuit (120) comprising a plurality of power switching devices (P1 -P 12 ) includes devices configured to convert an input DC voltage into an output AC voltage; an electrical circuit arrangement (130) which is electrically connected between the capacitor circuit (110) and the power circuit (120), wherein the electrical circuit arrangement (130) comprises a first circuit arrangement (132) which is connected via the first DC intermediate circuit capacitor (C1), and a second circuit arrangement (134) which is connected via the second DC intermediate circuit capacitor (C2); and a control circuit (140) which is electrically connected to the electrical circuit arrangement (130), wherein the control circuit (140) is configured to perform at least one of the following functions: an active voltage equalization between the first and second intermediate circuit capacitors (C1 , C2) and an active discharge of the first and second intermediate circuit capacitors (C1 , C2) or the capacitor (C) by operating at least one of the first circuit assembly (132) and the second circuit assembly (134) during normal operation of the multi-level inverter circuit (100).

Images