DC three-level flying capacitor pre-charging system

Abstract

The invention provides a DC three-level flying capacitor pre-charging system which comprises a first power supply module, a second power supply module, a power conversion module, a flying capacitor, a pre-charging switch module, an output filtering module, an upper bus capacitor, a lower bus capacitor and a rechargeable battery. The first power supply module and the second power supply module are connected with the power conversion module after being connected with the upper bus capacitor and the lower bus capacitor, and the power conversion module is sequentially connected with the flying capacitor, the pre-charging switch module, the second power supply module and the positive electrode of the upper bus capacitor to form a pre-charging loop. The problem that the pre-charging voltage of the flying capacitor is too high or too low during pre-charging is solved, the risk in the system starting process is reduced, the voltage stress of a switching device in the starting process is balanced, the damage risk is reduced, and the stability of the system can be effectively improved.

Description

Technical Field

[0001] The present invention relates to the technical field of precharging, and in particular to a DC three-level flying capacitor precharging system. Background Art

[0002] As the new energy market has become more and more prosperous in the past two years, the market demand for high-voltage battery charging and discharging has increased. In the face of high-voltage battery packs, traditional two-level DC converters can no longer meet current needs. More and more devices use flying capacitor three-level DC topology solutions to solve the problem of high voltage levels. In the flying capacitor three-level circuit, the voltage across the flying capacitor determines the voltage stress of each switching device. In order to protect the system switching devices, the flying capacitor must be pre-charged before the circuit is started. In order to make each switching device bear the same voltage stress, it is most appropriate to charge the flying capacitor voltage to half the bus voltage.

[0003] The pre-charging methods in the prior art all use the bus voltage to directly charge the flying capacitor, and control whether the pre-charging is completed by sampling the flying capacitor voltage. Since the entire pre-charging process takes a very short time, in the actual circuit, due to problems such as sampling and control loop delays, the flying capacitor voltage will be too high. In addition, when it comes to high-voltage systems, there will be problems such as difficulty in device selection and increased costs. It will also cause the switching devices to bear uneven voltage stress during system operation, and in severe cases, the switching devices will be damaged. Summary of the invention

[0004] In view of the deficiencies of the prior art, the present invention proposes a DC three-level flying capacitor pre-charging system, which can solve the problem of high or low pre-charging voltage of the flying capacitor and ensure that the pre-charging reaches the desired voltage value.

[0005] To implement the above technical solution, the present invention provides a DC three-level flying capacitor precharging system, which specifically includes: a first power supply module, a second power supply module, a power conversion module, a flying capacitor, a precharging switch module, an output filter module, an upper bus capacitor, a lower bus capacitor and a rechargeable battery, wherein the first power supply module and the second power supply module are connected in series, the upper bus capacitor and the lower bus capacitor are connected in series, one end of the first power supply module is connected to the upper port of the power conversion module, the other end of the first power supply module 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 first power supply module and the upper port of the power conversion module, and the upper bus The other end of the capacitor is connected to the lower bus capacitor, the other end of the lower bus capacitor is connected to the line connecting the second power supply module and the lower port of the power conversion module, one end of the pre-charging 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-charging switch module is connected to the third port of the power conversion module, one end of the flying capacitor is connected to the connection line between the pre-charging 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 electrode of the rechargeable battery, and the lower port of the power conversion module is connected to the negative electrode of the rechargeable battery.

[0006] Preferably, the DC three-level flying capacitor pre-charging system also includes resistors R1 and R2, one end of the resistor R1 is connected to the line connecting the upper bus capacitor and the upper port of the power conversion module, the other end of the resistor R1 is connected to the resistor R2, and the other end of the 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, 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 respectively connected to the second power supply module and the negative electrode of the rechargeable battery, one end of the flying capacitor is connected to the connecting line between T1 and T2, and the other end of the flying capacitor is connected to the connecting line between T3 and T4.

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

[0009] Preferably, the output filter 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 connecting line between T2 and T3, and the other end of the main power inductor L is connected to the positive electrode of the rechargeable battery, one end of the filter capacitor C3 is connected to the connecting line between the main power inductor L and the positive electrode of the rechargeable battery, and the other end of the filter capacitor C3 is connected to the connecting line between T4 and the negative electrode of the rechargeable battery.

[0010] Preferably, the system is regulated by:

[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, switch S1 is closed, and IGBT module T4 is turned on to form the first stage pre-charging circuit;

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

[0014] S4. After the pre-charging is completed, the system starts to work normally. When 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 a DC three-level flying capacitor pre-charging system provided by the present invention are:

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

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

[0018] (3) The present invention reduces the system's requirements on the voltage resistance of the tube through a three-level structure. Compared with the traditional two-level structure, tubes with lower voltage resistance are used in high-voltage scenarios, and the switching frequency of the system can also be made higher, effectively reducing the overall volume of the system and reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a component unit of the system of the present invention;

[0020] Figure 2 A topological diagram and a pre-charging circuit of the system of the present invention;

[0021] Figure 3 Pre-charging the first stage loop of the system of the present invention;

[0022] Figure 4 Pre-charging the second stage loop of the system of the present invention;

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

[0024] Figure 6 The figure is a flowchart of the system of the present invention. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary persons in the art without creative work are within the scope of protection of the present invention.

[0026] Embodiment: A DC three-level flying capacitor pre-charging 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, with reference to Figure 1As shown, 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, one end of the first power supply module 1 is connected to the upper port of the power conversion module 3, 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 first power supply module 1 and the upper port of the power conversion module 3, the other end of the upper bus capacitor 7 is connected to the lower bus capacitor 8, and the other end of the lower bus capacitor 8 is connected to the second power supply module 2 and the lower port of the power conversion module 3 On the connected line, one end of the pre-charging switch module 5 is connected to the line connecting the first power supply module 1 and the second power supply module 2, the other end of the pre-charging 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 connection line between the pre-charging switch module 5 and the third port of the power conversion module 3, 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, the other end of the output filter module 6 is connected to the positive pole of the rechargeable battery 9, and the lower port of the power conversion module 3 is connected to the negative pole 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 to the flying capacitor 4, the pre-charging switch module 5, the second power supply module 2 and the positive electrode of the upper bus capacitor 7 in sequence to form a pre-charging circuit.

[0029] Reference Figure 2 As shown, the DC three-level flying capacitor pre-charging system also includes resistors R1 and R2, one end of the 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 the resistor R1 is connected to the resistor R2, and the other end of the resistor R2 is connected to the line connecting the lower bus capacitor C2 and the lower port of the power conversion module 3. During actual operation, the upper bus capacitor C1 and the lower bus capacitor C2 are connected in parallel with the two series resistors R1 and R2 for 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, 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 electrode of the rechargeable battery 9 respectively, one end of the flying capacitor 4 is connected to the connecting line between T1 and T2, and the other end of the flying capacitor 4 is connected to the connecting line between T3 and T4.

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

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

[0033] Reference Figures 2 to 4 As shown, the working process of the DC three-level flying capacitor pre-charging 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] S2, switch S1 is closed, and IGBT module T4 is turned on to form the first stage pre-charging circuit, such as Figure 3 As shown;

[0036] S3, switch S1 is disconnected, T4 remains on, and switch S2 is closed. Figure 4 As shown, the second stage of pre-charging is performed. When it is detected that the voltage of the flying capacitor is half of the bus bar, T4 is turned off, and then S2 is disconnected, and the pre-charging is completed;

[0037] S4. After the pre-charging is completed, the system starts to work normally. When 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 the present invention is as follows:

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

[0040] (2) When the system starts, the control loop starts to work, the voltage loop starts to calculate, and the calculation result is used as the given value of the current loop to participate in the calculation of the current loop. The calculation result of the current loop is subtracted from the calculation result of the flying capacitor voltage loop, and the difference result is compared with the triangular carrier to generate the PWM signal of the T1 tube. The triangular carrier is phase-shifted by 180°, the calculation result of the current loop is added to the calculation result of the flying capacitor voltage loop, and the result is compared with the phase-shifted triangular carrier to generate the PWM signal of the T2 tube.

[0041] (3) When the voltage of the flying capacitor is too high, the control loop will reduce the duty cycle of the PWM signal of tube T1, and the duty cycle of tube T2 will increase. The discharge time of the flying capacitor is greater than the charging time, and the voltage on the flying capacitor decreases. When the voltage of the flying capacitor is too low, the duty cycle of the PWM signal of tube T1 increases, and the duty cycle of tube T2 will decrease. The discharge time of the flying capacitor is less than the charging time, and the voltage on the flying capacitor increases. At the same time, it can be seen from the control structure that the output voltage is completely decoupled from the flying capacitor voltage, so adjusting the flying capacitor voltage will not affect the output voltage. Ultimately, the system will operate stably through loop regulation.

[0042] The present invention solves the problem of the flying capacitor pre-charge voltage being too high or too low during pre-charging, reduces the risk of the system startup process, balances the voltage stress of the switching device during the startup process, reduces the risk of damage, and can effectively increase the stability of the system. The present invention introduces the control of the flying capacitor voltage into the control loop of the entire system, and controls the voltage of the flying capacitor in real time, so that its voltage is always stable near a given value, so that the voltage stress of the IGBT during the operation of the system is always maintained within a limited range, reduces the risk of IGBT damage, and can effectively reduce the risk of research and development. The present invention reduces the system's requirements for the withstand voltage of the tube through a three-level structure. Compared with the traditional two-level structure, a tube with a lower withstand voltage is used in a high-voltage scenario, and the switching frequency of the system can also be made higher, effectively reducing the overall volume of the system and reducing costs.

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

Claims

1. A DC three-level flying capacitor pre-charging system, characterized in that include: 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 rechargeable battery, wherein the first power supply module and the second power supply module are connected in series, the upper bus capacitor and the lower bus capacitor are connected in series, one end of the first power supply module is connected to the upper port of the power conversion module, the other end of the first power supply module 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 first power supply module and the upper port of the power conversion module, the other end of the upper bus capacitor is connected to the lower bus capacitor, and the lower The other end of the bus capacitor is connected to the line connecting the second power supply module and the lower port of the power conversion module, one end of the pre-charging 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-charging switch module is connected to the third port of the power conversion module, one end of the flying capacitor is connected to the connection line between the pre-charging 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 electrode of the rechargeable battery, and the lower port of the power conversion module is connected to the negative electrode of the rechargeable battery.

2. The DC three-level flying capacitor pre-charging system according to claim 1, characterized in that: It also includes resistors R1 and R2, one end of the resistor R1 is connected to the line connecting the upper bus capacitor and the upper port of the power conversion module, the other end of the resistor R1 is connected to the resistor R2, and the other end of the 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-charging system according to claim 1, characterized in that: 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, 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 respectively connected to the second power supply module and the negative electrode of the rechargeable battery, one end of the flying capacitor is connected to the connecting line between T1 and T2, and the other end of the flying capacitor is connected to the connecting line between T3 and T4.

4. The DC three-level flying capacitor pre-charging system according to claim 3, characterized in that: The pre-charging switch module includes contactor switches S1, S2 and a current limiting resistor R3, wherein one end of the contactor switch S1 is connected to the line connecting the first power supply module and the second power supply module, the other end of the contactor switch S1 is connected to the current limiting resistor R3, the other end of the current limiting resistor R3 is connected to the connection line between the flying capacitor and the third port of the power conversion module, one end of the 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 the contactor switch S2 is connected to the connection line between the flying capacitor and the third port of the power conversion module.

5. The DC three-level flying capacitor pre-charging system according to claim 4, characterized in that: The output filter 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 electrode 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 electrode of the rechargeable battery, and the other end of the filter capacitor C3 is connected to the connection line between T4 and the negative electrode of the rechargeable battery.

6. The DC three-level flying capacitor pre-charging system as claimed in claim 5, characterized in that The system is regulated by: 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, switch S1 is closed, and IGBT module T4 is turned on to form the first stage pre-charging circuit; S3, switch S1 is disconnected, T4 remains open, and switch S2 is closed to perform the second stage of pre-charging. When it is detected that the voltage of the flying capacitor is half of the bus, T4 is turned off, and then S2 is disconnected, and the pre-charging is completed; S4. After the pre-charging is completed, the system starts to work normally. When the system starts running, the controller adjusts the on-time of T1 and T2 to control the stability of the output voltage and the flying capacitor voltage.

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