A dc three-level flying capacitor pre-charge system

Abstract

The application provides a DC three-level flying capacitor pre-charging system, comprising a first power supply module, a second power supply module, a power conversion module, a flying capacitor, a pre-charging switch module, an output filter module, an upper bus capacitor, a lower bus capacitor and a charging battery, the first power supply module and the second power supply module are connected with the upper bus capacitor and the lower bus capacitor and then connected with the power conversion module, the power conversion module is connected with the flying capacitor, the pre-charging switch module, the second power supply module and the positive electrode of the upper bus capacitor in sequence and forms a pre-charging loop. The application solves the problem of high or low pre-charging voltage of the flying capacitor during pre-charging, reduces the risk of the system starting process, balances the voltage stress of the switching device during the starting process, reduces the damage risk, and can effectively increase the stability of the system.

Description

Technical Field

[0001] This invention relates to the field of pre-charging technology, and more specifically to a DC three-level flying capacitor pre-charging system. Background Technology

[0002] With the booming new energy market in the past two years, the demand for high-voltage battery charging and discharging has been increasing. Faced with high-voltage battery packs, traditional two-level DC-DC converters are no longer sufficient. More and more devices are adopting a flying capacitor three-level DC topology to address the high-voltage issue. In a flying capacitor three-level circuit, the voltage across the flying capacitor determines the voltage stress on each switching device. To protect the system switching devices, the flying capacitor must be pre-charged before the circuit starts. To ensure that each switching device experiences the same voltage stress, charging the flying capacitor to half the bus voltage is optimal.

[0003] Existing pre-charging methods all use the bus voltage to directly charge the flying capacitor, and control the completion of pre-charging by sampling the flying capacitor voltage. Since the entire pre-charging process takes a very short time, in actual circuits, due to issues such as sampling and control loop delays, the flying capacitor voltage may be too high. Furthermore, for high-voltage systems, this can lead to difficulties in component selection and increased costs. It can also cause uneven voltage stress on switching devices during system operation, which in severe cases can damage the switching devices. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention proposes a DC three-level flying capacitor pre-charge system, which can solve the problem of flying capacitor pre-charge voltage being too high or too low, while ensuring that the pre-charge reaches the desired voltage value.

[0005] To achieve the above technical solution, this invention provides a DC three-level flying capacitor pre-charge system, specifically including: a first power supply module, a second power supply module, a power conversion module, a flying capacitor, a pre-charge switch module, an output filter module, an upper bus capacitor, a lower bus capacitor, and a rechargeable battery. The first and second power supply modules are connected in series, as are the upper and lower bus capacitors. One end of the first power supply module is connected to the upper port of the power conversion module, and the other end is connected to the second power supply module. The other end of the second power supply module is connected to the lower port of the power conversion module. One end of the upper bus capacitor is connected to the line connecting the upper ports of the first power supply module and the power conversion module. The other end of the capacitor is connected to the lower bus capacitor, and the other end of the lower bus capacitor is connected to the line connecting the lower ports of the second power supply module and the power conversion module. One end of the pre-charge switch module is connected to the line connecting the first power supply module and the second power supply module, and the other end of the pre-charge switch module is connected to the third port of the power conversion module. One end of the flying capacitor is connected to the line connecting the pre-charge switch module and the third port of the power conversion module, and the other end of the flying capacitor is connected to the fourth port of the power conversion module. One end of the output filter module is connected to the fifth port of the power conversion module, and the other end of the output filter module is connected to the positive terminal of the rechargeable battery. The lower port of the power conversion module is connected to the negative terminal of the rechargeable battery.

[0006] Preferably, the DC three-level flying capacitor pre-charge system further includes resistors R1 and R2. One end of resistor R1 is connected to the line connecting the upper bus capacitor and the upper port of the power conversion module, and the other end of resistor R1 is connected to resistor R2. The other end of resistor R2 is connected to the line connecting the lower bus capacitor and the lower port of the power conversion module.

[0007] Preferably, the power conversion module is composed of four IGBT modules T1, T2, T3 and T4 connected in series. The upper port of T1 is connected to the first power supply module, and the other end of T1 is connected to T2. T2, T3 and T4 are connected in series in sequence. The lower port of T4 is connected to the second power supply module and the negative terminal of the rechargeable battery, respectively. One end of the flying capacitor is connected to the connection line between T1 and T2, and the other end of the flying capacitor is connected to the connection line between T3 and T4.

[0008] Preferably, the pre-charge switch module includes contactor switches S1 and S2 and a current-limiting resistor R3. One end of contactor switch S1 is connected to the line connecting the first power supply module and the second power supply module, and the other end of contactor switch S1 is connected to the current-limiting resistor R3. The other end of the current-limiting resistor R3 is connected to the line connecting the flying capacitor and the third port of the power conversion module. One end of contactor switch S2 is connected to the line connecting the first power supply module and the second power supply module, and the other end of contactor switch S2 is connected to the line connecting the flying capacitor and the third port of the power conversion module.

[0009] Preferably, the output filtering module includes a main power inductor L and a filter capacitor C3, wherein one end of the main power inductor L is connected to the connection line between T2 and T3, and the other end of the main power inductor L is connected to the positive terminal of the rechargeable battery; one end of the filter capacitor C3 is connected to the connection line between the main power inductor L and the positive terminal of the rechargeable battery, and the other end of the filter capacitor C3 is connected to the connection line between T4 and the negative terminal of the rechargeable battery.

[0010] Preferably, the system is controlled in the following manner:

[0011] S1. Start the first power supply module and the second power supply module, and charge the upper bus capacitor and the lower bus capacitor through the first power supply module and the second power supply module;

[0012] S2 and switch S1 are closed, and at the same time IGBT module T4 is turned on to form the first stage of pre-charge circuit;

[0013] S3, switch S1 is open, T4 remains open, switch S2 is closed to perform the second stage of pre-charging. When the voltage of the flying capacitor is detected to be half of the bus voltage, T4 is turned off and then S2 is opened to complete the pre-charging.

[0014] S4. After pre-charging is completed, the system starts to work normally. After the system starts running, the stability of the output voltage and the flying capacitor voltage is controlled by adjusting the conduction time of T1 and T2 through the loop.

[0015] The beneficial effects of the DC three-level flying capacitor pre-charge system provided by this invention are as follows:

[0016] (1) This invention solves the problem of high or low pre-charge voltage of flying capacitor during pre-charge by using the midpoint potential of series bus, reduces the risk of system startup, balances voltage stress of switching devices during startup, reduces the risk of damage, and can effectively increase system stability.

[0017] (2) This invention introduces the control of the flying capacitor voltage into the control system and decouples it from the output voltage. The voltage of the flying capacitor is controlled in real time so that its voltage is always stable near the given value. This keeps the voltage stress of the IGBT within a limited range during system operation, reducing the risk of IGBT damage and effectively reducing R&D risk.

[0018] (3) The present invention reduces the voltage withstand requirement of the tubes by using a three-level structure. Compared with the traditional two-level structure, the use of tubes with lower voltage withstand in high-voltage scenarios allows the switching frequency of the system to be higher, effectively reducing the overall size of the system and lowering the cost. Attached Figure Description

[0019] Figure 1 These are the constituent units of the system of the present invention;

[0020] Figure 2 The system topology and pre-charging circuit of this invention are shown below;

[0021] Figure 3 This is the first stage pre-charging circuit of the system of the present invention;

[0022] Figure 4 This is the second stage pre-charging circuit of the system of the present invention;

[0023] Figure 5 This is a block diagram of the control strategy structure of the system of the present invention;

[0024] Figure 6 This is a flowchart of the system of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0026] Example: A DC three-level flying capacitor pre-charge system.

[0027] Reference Figures 1 to 6 As shown, a DC three-level flying capacitor pre-charging system specifically includes: a first power supply module 1, a second power supply module 2, a power conversion module 3, a flying capacitor 4, a pre-charging switch module 5, an output filter module 6, an upper bus capacitor 7, a lower bus capacitor 8, and a rechargeable battery 9, wherein, referring to... Figure 1As shown, the first power supply module 1 and the second power supply module 2 are connected in series, and the upper bus capacitor 7 and the lower bus capacitor 8 are connected in series. One end of the first power supply module 1 is connected to the upper port of the power conversion module 3, and the other end of the first power supply module 1 is connected to the second power supply module 2. The other end of the second power supply module 2 is connected to the lower port of the power conversion module 3. One end of the upper bus capacitor 7 is connected to the line connecting the upper port of the first power supply module 1 and the upper port of the power conversion module 3, and the other end of the upper bus capacitor 7 is connected to the lower bus capacitor 8. The other end of the lower bus capacitor 8 is connected to the lower port of the second power supply module 2 and the lower port of the power conversion module 3. On the connected lines, one end of the pre-charge switch module 5 is connected to the line connecting the first power supply module 1 and the second power supply module 2, and the other end of the pre-charge switch module 5 is connected to the third port of the power conversion module 3. One end of the flying capacitor 4 is connected to the line connecting the pre-charge switch module 5 and the third port of the power conversion module 3, and the other end of the flying capacitor 4 is connected to the fourth port of the power conversion module 3. One end of the output filter module 6 is connected to the fifth port of the power conversion module 3, and the other end of the output filter module 6 is connected to the positive terminal of the rechargeable battery 9. The lower port of the power conversion module 3 is connected to the negative terminal of the rechargeable battery 9.

[0028] In the above technical solution, the first power supply module 1 and the second power supply module 2 are connected in series, the upper bus capacitor 7 and the lower bus capacitor 8 are connected in series, and the first power supply module 1 and the second power supply module 2 are connected to the upper bus capacitor 7 and the lower bus capacitor 8 and then connected to the power conversion module 3, which is used to transmit the power supply voltage provided by the first power supply module 1 and the second power supply module 2 to the upper bus capacitor 7, the lower bus capacitor 8 and the power conversion module 3; the power conversion module 3 is connected in sequence with the flying capacitor 4, the pre-charge switch module 5 and the positive terminal of the second power supply module 2 and the upper bus capacitor 7 to form a pre-charge circuit.

[0029] Reference Figure 2 As shown, the DC three-level flying capacitor pre-charge system also includes resistors R1 and R2. One end of resistor R1 is connected to the line connecting the upper bus capacitor C1 and the upper port of the power conversion module 3. The other end of resistor R1 is connected to resistor R2. The other end of resistor R2 is connected to the line connecting the lower bus capacitor C2 and the lower port of the power conversion module 3. In actual operation, the upper bus capacitor C1 and the lower bus capacitor C2 are connected in parallel with the two series-connected resistors R1 and R2 to perform voltage division.

[0030] Reference Figure 2As shown, the power conversion module 3 is composed of four IGBT modules T1, T2, T3 and T4 connected in series. The upper port of T1 is connected to the first power supply module 1, and the other end of T1 is connected to T2. T2, T3 and T4 are connected in series in sequence. The lower port of T4 is connected to the second power supply module 2 and the negative terminal of the rechargeable battery 9 respectively. One end of the flying capacitor 4 is connected to the connection line between T1 and T2, and the other end of the flying capacitor 4 is connected to the connection line between T3 and T4.

[0031] Reference Figure 2 As shown, the pre-charge switch module 5 includes contactor switches S1 and S2 and a current-limiting resistor R3. One end of contactor switch S1 is connected to the line connecting the first power supply module 1 and the second power supply module 2, and the other end of contactor switch S1 is connected to the current-limiting resistor R3. The other end of the current-limiting resistor R3 is connected to the line connecting the flying capacitor 4 and the third port of the power conversion module 3. One end of contactor switch S2 is connected to the line connecting the first power supply module 1 and the second power supply module 2, and the other end of contactor switch S2 is connected to the line connecting the flying capacitor 4 and the third port of the power conversion module 3.

[0032] Reference Figure 2 As shown, the output filtering module 6 includes a main power inductor L and a filter capacitor C3. One end of the main power inductor L is connected to the connection line between T2 and T3, and the other end of the main power inductor L is connected to the positive terminal of the rechargeable battery 9. One end of the filter capacitor C3 is connected to the connection line between the main power inductor L and the positive terminal of the rechargeable battery 9, and the other end of the filter capacitor C3 is connected to the connection line between T4 and the negative terminal of the rechargeable battery 9.

[0033] Reference Figures 2 to 4 As shown, the working process of this DC three-level flying capacitor pre-charge system is as follows:

[0034] S1. Start the first power supply module and the second power supply module, and charge the upper bus capacitor and the lower bus capacitor through the first power supply module and the second power supply module;

[0035] When switches S2 and S1 are closed, and IGBT module T4 is simultaneously turned on, the first stage of the pre-charge circuit is formed. Figure 3 As shown;

[0036] S3, switch S1 is open, T4 remains open, close switch S2, as follows Figure 4 As shown, the second stage of pre-charging is performed. When the voltage of the flying capacitor is detected to be half of the bus voltage, T4 is turned off and S2 is then disconnected, and the pre-charging is completed.

[0037] S4. After pre-charging is completed, the system starts to work normally. After the system starts running, the stability of the output voltage and the flying capacitor voltage is controlled by adjusting the conduction time of T1 and T2 through the loop.

[0038] Reference Figure 5 and Figure 6 As shown, the working principle of this invention is as follows:

[0039] (1) The present invention stabilizes the voltage of the Pequa capacitor at half the bus voltage through a pre-charging circuit.

[0040] (2) Upon system startup, the control loop begins operation. The voltage loop starts calculations and uses the result as the setpoint for the current loop. The result of the current loop calculation is subtracted from the result of the flying capacitor voltage loop calculation, and the difference is compared with the triangular carrier wave to generate the PWM signal for transistor T1. The triangular carrier wave is phase-shifted by 180°, and the result of the current loop calculation is added to the result of the flying capacitor voltage loop calculation. The result is then compared with the phase-shifted triangular carrier wave to generate the PWM signal for transistor T2.

[0041] (3) When the voltage across the flying capacitor is too high, the control loop will decrease the duty cycle of the PWM signal of transistor T1 and increase the duty cycle of transistor T2. The discharge time of the flying capacitor will be longer than the charging time, and the voltage across the flying capacitor will decrease. When the voltage across the flying capacitor is too low, the duty cycle of the PWM signal of transistor T1 will increase, the duty cycle of transistor T2 will decrease, the discharge time of the flying capacitor will be shorter than the charging time, and the voltage across the flying capacitor will increase. Simultaneously, it can be seen from the control structure that the output voltage and the flying capacitor voltage are completely decoupled; therefore, adjusting the flying capacitor voltage will not affect the output voltage. Ultimately, the loop adjustment will ensure stable system operation.

[0042] This invention solves the problem of excessively high or low pre-charge voltage of the flying capacitor during pre-charging, reducing the risk during system startup and ensuring balanced voltage stress on switching devices during startup, thus reducing the risk of damage and effectively increasing system stability. This invention incorporates flying capacitor voltage control into the entire system's control loop, performing real-time control to keep the voltage of the flying capacitor stable near a given value. This keeps the voltage stress on the IGBT within a defined range during system operation, reducing the risk of IGBT damage and effectively mitigating development risks. Furthermore, this invention uses a three-level structure to reduce the voltage withstand requirements of the transistors. Compared to the traditional two-level structure, using lower voltage-rated transistors in high-voltage scenarios allows for higher switching frequencies, effectively reducing the overall system size and cost.

[0043] The above description is only a preferred embodiment of the present invention, but the present invention should not be limited to the content disclosed in the embodiments and drawings. Therefore, any equivalent or modified embodiments made without departing from the spirit of the present invention shall fall within the protection scope of the present invention.

Claims

1. A DC three-level flying capacitor pre-charge system, characterized in that... include: The system comprises a first power supply module, a second power supply module, a power conversion module, a flying capacitor, a pre-charge switch module, an output filter module, an upper bus capacitor, a lower bus capacitor, and a rechargeable battery. The first and second power supply modules are connected in series, as are the upper and lower bus capacitors. The series connection point of the first and second power supply modules is connected to the series connection point of the upper and lower bus capacitors. One end of the first power supply module is connected to the upper port of the power conversion module, and the other end is connected to the second power supply module. The other end of the second power supply module is connected to the lower port of the power conversion module. One end of the upper bus capacitor is connected to the line connecting the upper ports of the first power supply module and the power conversion module. The other end of the bus capacitor is connected to the lower bus capacitor, and the other end of the lower bus capacitor is connected to the line connecting the lower port of the second power supply module and the power conversion module. One end of the pre-charge switch module is connected to the line connecting the first power supply module and the second power supply module. The other end of the pre-charge switch module is connected to the third port of the power conversion module. One end of the flying capacitor is connected to the line connecting the pre-charge switch module and the third port of the power conversion module. The other end of the flying capacitor is connected to the fourth port of the power conversion module. One end of the output filter module is connected to the fifth port of the power conversion module. The other end of the output filter module is connected to the positive terminal of the rechargeable battery. The lower port of the power conversion module is connected to the negative terminal of the rechargeable battery. The pre-charge switch module includes contactor switches S1 and S2 and a current-limiting resistor R3. One end of contactor switch S1 is connected to the line connecting the first power supply module and the second power supply module, and the other end of contactor switch S1 is connected to the current-limiting resistor R3. The other end of the current-limiting resistor R3 is connected to the line connecting the flying capacitor and the third port of the power conversion module. One end of contactor switch S2 is connected to the line connecting the first power supply module and the second power supply module, and the other end of contactor switch S2 is connected to the line connecting the flying capacitor and the third port of the power conversion module.

2. The DC three-level flying capacitor pre-charge system as described in claim 1, characterized in that: It also includes resistors R1 and R2. One end of resistor R1 is connected to the line connecting the upper bus capacitor and the upper port of the power conversion module, and the other end of resistor R1 is connected to resistor R2. The other end of resistor R2 is connected to the line connecting the lower bus capacitor and the lower port of the power conversion module.

3. The DC three-level flying capacitor pre-charge system as described in claim 1, characterized in that: The power conversion module consists of four IGBT modules T1, T2, T3 and T4 connected in series. The upper port of T1 is connected to the first power supply module, and the other end of T1 is connected to T2. T2, T3 and T4 are connected in series in sequence. The lower port of T4 is connected to the second power supply module and the negative terminal of the rechargeable battery, respectively. One end of the flying capacitor is connected to the connection line between T1 and T2, and the other end of the flying capacitor is connected to the connection line between T3 and T4.

4. The DC three-level flying capacitor pre-charge system as described in claim 1, characterized in that: The output filtering module includes a main power inductor L and a filter capacitor C3. One end of the main power inductor L is connected to the connection line between T2 and T3, and the other end of the main power inductor L is connected to the positive terminal of the rechargeable battery. One end of the filter capacitor C3 is connected to the connection line between the main power inductor L and the positive terminal of the rechargeable battery, and the other end of the filter capacitor C3 is connected to the connection line between T4 and the negative terminal of the rechargeable battery.

5. The DC three-level flying capacitor pre-charge system as described in claim 4, characterized in that... The system is controlled in the following manner: S1. Start the first power supply module and the second power supply module, and charge the upper bus capacitor and the lower bus capacitor through the first power supply module and the second power supply module; S2 and switch S1 are closed, and at the same time IGBT module T4 is turned on to form the first stage of pre-charge circuit; S3, switch S1 is open, T4 remains open, switch S2 is closed to perform the second stage of pre-charging. When the voltage of the flying capacitor is detected to be half of the bus voltage, T4 is turned off and then S2 is opened to complete the pre-charging. S4. After pre-charging is completed, the system starts to work normally. After the system starts running, the stability of the output voltage and the flying capacitor voltage is achieved by adjusting the conduction time of T1 and T2 through the controller.

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