Flexible loop closing device power module topological structure

Abstract

The invention discloses a power module topological structure of a flexible loop closing device. The power module topological structure comprises a primary side high-voltage interface circuit, an isolation DCDC circuit and a secondary side high-voltage interface circuit, the primary side high-voltage interface circuit and the secondary side high-voltage interface circuit both adopt three-level topology based on active neutral clamping topology, and the isolation DCDC circuit adopts a topological structure based on carrier phase shift. According to the topological structure provided by the invention, the voltage level of the power module of the flexible loop closing device is effectively improved and the number of the power modules is reduced through a two-stage topological structure for accessing and isolating DCDC at the high-voltage ports at the two ends of the single power module.

Description

Technical Field

[0001] The invention belongs to the technical field of distribution network equipment, and in particular relates to a topological structure of a power module of a flexible loop closing device. Background Art

[0002] With the large-scale access of diversified sources and loads to the distribution system, the power load of the distribution network is uneven, the voltage problem is prominent, and the impact of faults is serious. Among them, with the large-scale access of new energy sources such as photovoltaics, there are differences in the temporal and spatial characteristics of sources and loads between different feeders. The distribution network grid lines are mainly radial, with few feeder segments, and the load division of the distribution network is unreasonable. The increasingly frequent natural disasters and man-made attacks are threatening the safe and reliable operation of the power system. Therefore, improving the resilience has become an inevitable requirement for the development of the power system. Resilience is the ability of the power system to cope with various disasters and damages, that is, when the system suffers from various impact events, it can prevent them beforehand, resist them in time during the event, and recover quickly afterwards. A resilient power grid is called a resilient power grid. When facing extreme events, it can predict, resist, adapt to, and respond to extreme events, and recover quickly from extreme events, which can effectively reduce the loss of system load. Traditional distribution networks use interconnection switches to adjust the grid and divide the regions. Due to the single state of traditional interconnection switches, it is difficult to cope with the power distribution constraints caused by the rapid uncertainty of distributed power sources and fluctuating loads. In addition, the on and off of traditional interconnection switches need to accept the dispatching instructions of the superior, which leads to the lack of accurate fault detection capabilities. When facing power outages, it will affect the power supply quality of local areas, and problems such as loop impact are also difficult to avoid. Based on the flexible interconnection equipment of the distribution network, the active reconstruction equipment of all-power electronics can be installed at the key nodes of the distribution network to replace the traditional interconnection switches, which can realize the flexible interconnection of different feeder power sources and the system reconstruction and regulation based on this. The interconnection and state switching of power electronic flexible loop devices can easily realize the active reconstruction of the distribution network, which is convenient for realizing fault-oriented resistance, isolation and rapid recovery. The current mainstream implementation method of the flexible loop device is based on modular cascading technology. The power modules are connected in series on the high-voltage side of both ends, and the isolation transformer is used in the middle for isolation to realize the energy transfer between the two ends of the interconnection. It can be seen that the power module needs to meet important tasks such as power conversion and port isolation. As the most important conversion unit of the flexible loop device, the power module directly affects the function and performance of the flexible loop device.

[0003] The Chinese invention patent (application number CN201710012054.3) proposed a two-stage power module topology structure, which realizes the access to the high-voltage AC grid through a full-bridge circuit. In the latter stage of the full-bridge circuit, DCDC is used to achieve isolation between the two AC ports, and in the third stage, the full-bridge circuit is used to realize the access to the high-voltage AC grid. This topology consists of two stages, but the overall transformation of this topology is based on two-level technology. In order to meet the demand for high-voltage 10kV access, a large number of power modules are required, which in turn affects the cost, volume, weight and other indicators of the entire equipment. Summary of the invention

[0004] The purpose of the present invention is to provide a power module topology structure of a flexible loop device, which effectively improves the voltage level of the power module of the flexible loop device and reduces the number of power modules by accessing the high-voltage ports at both ends of a single power module and isolating the two-stage topology structure of DCDC.

[0005] The technical solution adopted by the present invention is that the power module topology structure of the flexible loop device includes a primary high-voltage interface circuit, an isolated DCDC circuit and a secondary high-voltage interface circuit connected in sequence; the primary high-voltage interface circuit and the secondary high-voltage interface circuit both adopt a three-level topology based on an active neutral clamp topology, and the isolated DCDC circuit adopts a topology structure based on carrier phase shifting; the isolated DCDC circuit includes a primary side bridge arm, a high-frequency loop and a secondary side bridge arm connected in sequence; The primary side bridge arm adopts a series half-bridge topology, including a primary side upper half bridge arm and a primary side lower half bridge arm. The high-frequency circuit includes DC blocking capacitors C3 and C4, a high-frequency transformer TR2, and resonant inductors L1 and L2. One end of the resonant inductor L1 is connected to the upper half bridge arm, and the other end of the resonant inductor L1 is connected to the high-frequency transformer TR2. The other end of the high-frequency transformer TR2 is connected to the DC blocking capacitor C3, and the other end of the DC blocking capacitor C3 is connected to the lower half bridge arm. The secondary side bridge arm adopts a series half-bridge topology, including an upper half bridge arm and a lower half bridge arm. One end of the resonant inductor L2 is connected to the upper half bridge arm, and the other end of the resonant inductor L2 is connected to the high-frequency transformer TR2. The other end of the high-frequency transformer TR2 is connected to the DC blocking capacitor C4. The other end of the DC blocking capacitor C4 is connected to the lower half bridge arm.

[0006] The present invention is also characterized in that: The upper half bridge arm on the primary side includes capacitor C1 and two fully-controlled devices S13 and S14 connected in series. The resonant inductor L1 is connected to the connection point of the two fully-controlled devices S13 and S14 connected in series. The lower half bridge arm on the primary side includes capacitor C2 and two fully-controlled devices S15 and S16 connected in series. The other end of the DC-isolating capacitor C3 is connected to the connection point of the two fully-controlled devices S15 and S16 connected in series. The upper half bridge arm on the primary side and the lower half bridge arm on the primary side are connected in series. On the DC bus side, capacitor C1 and capacitor C2 are connected in series to form a DC bus. The output of the upper half bridge arm on the primary side and the output of the lower half bridge arm on the primary side constitute the overall output of the high-voltage side bridge arm.

[0007] The primary high-voltage interface circuit includes twelve fully-controlled semiconductor devices, namely S1-S4, S5-S8, S9-S10 and S11-S12. The eight fully-controlled semiconductor devices S1-S4 and S5-S8 are connected in series to the DC bus. The two fully-controlled semiconductor devices S9 and S10 are connected in series and are respectively connected to the connection point of the two fully-controlled semiconductors S1 and S2 and the connection point of the two fully-controlled semiconductors S3 and S4. The fully-controlled semiconductor devices S11 and S12 are connected in series and are respectively connected to the connection point of the fully-controlled semiconductors S5 and S6 and the connection point of the fully-controlled semiconductors S7 and S8. The connection points of the fully-controlled semiconductor devices S9 and S10 and the fully-controlled semiconductor devices S11 and S12 are connected to the midpoint of the DC bus capacitors C1 and C2.

[0008] The secondary side bridge arm adopts a series half-bridge topology, including an upper half bridge arm on the secondary side and a lower half bridge arm on the secondary side. The upper half bridge arm on the secondary side includes a capacitor C5 and two series fully-controlled devices S17 and S118. One end of the resonant inductor L2 is connected to the connection point of the two series fully-controlled devices S17 and S18. The lower half bridge arm on the secondary side includes a capacitor C6 and two series fully-controlled devices S19 and S20. The other end of the DC-isolating capacitor C4 is connected to the connection point of the two series fully-controlled devices S19 and S20. The upper half bridge arm on the secondary side and the lower half bridge arm on the secondary side are connected in series. On the DC bus side, capacitors C5 and C6 are connected in series to form a DC bus. The output of the upper half bridge arm on the secondary side and the output of the lower half bridge arm on the secondary side constitute the overall output of the high-voltage side bridge arm.

[0009] The secondary side high-voltage interface circuit includes twelve fully-controlled semiconductor devices, namely S21-S24, S25-S28, S29-S30 and S31-S32. The eight fully-controlled semiconductor devices S21-S24 and S25-S28 are connected in series to the DC bus. The two fully-controlled semiconductor devices S29 and S30 are connected in series and are respectively connected to the connection point of the two fully-controlled semiconductors S21 and S22 and the connection point of the two fully-controlled semiconductors S23 and S24. The fully-controlled semiconductor devices S31 and S32 are connected in series and are respectively connected to the connection point of the fully-controlled semiconductors S25 and S26 and the connection point of the fully-controlled semiconductors S27 and S28. The connection points of the fully-controlled semiconductor devices S29 and S30 and the connection points of the fully-controlled semiconductor devices S31 and S32 are connected to the midpoint of the DC bus capacitors C5 and C6.

[0010] The DC blocking capacitors are film capacitors or ceramic capacitors.

[0011] The beneficial effects of the present invention are: (1) The power module topology of the flexible loop device of the present invention is a two-stage topology structure with high-voltage ports at both ends of a single module connected and isolated DCDC. The high-voltage port access adopts the ANPC topology structure, and then uses power devices with lower withstand voltage to achieve access to high bus voltage. The isolated DCDC circuit adopts a topology structure based on carrier shifting, and achieves high voltage access on the high-voltage side through the ANPC three-level topology cascade. It can effectively support the bidirectional flow of energy. It can effectively improve the voltage level of the power module of the flexible loop device, reduce the number of power modules, support the bidirectional flow of the flexible loop device, and at the same time support low cost, high frequency and lightweight equipment, thereby promoting the wider application of flexible loop devices in distribution network systems.

[0012] (2) The power module topology of the flexible loop device of the present invention improves the voltage level inside the module on the basis of existing commercial power devices, thereby reducing the number of power modules; the solution can effectively promote the high frequency of isolated DCDC, and provide strong support for reducing the cost and weight of equipment; at the same time, the solution is compatible with the bidirectional operation of the flexible loop device, which provides broad prospects for application in different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a schematic diagram of the topological structure of the power module of the flexible ring closing device of the present invention; Figure 2 It is a schematic diagram of the modulation strategy of the primary and secondary side high voltage interface circuit of the present invention; Figure 3 It is a schematic diagram of the modulation strategy of the isolated DCDC circuit of the present invention.

[0014] Figure 4It is a topological structure diagram of a conventional power electronic transformer based on two-level conversion in Example 6. DETAILED DESCRIPTION

[0015] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0016] Example 1 The present invention provides a flexible loop closing device power module topology structure, such as Figure 1 As shown, the primary side high voltage interface circuit, the isolated DCDC circuit and the secondary side high voltage interface circuit; For the primary and secondary high-voltage interface circuit, in order to support higher DC voltage, the high-voltage interface circuit adopts a three-level topology based on the active neutral clamp topology. Since the flexible loop device adopts cascade access and the output port is two-phase, it can be compatible with medium-voltage AC and medium-voltage DC access at the same time. In view of the application requirements of the bidirectional flow of the flexible loop device, this topology can effectively work in the inverter and rectification modes, and the output power can be arbitrarily adjusted through the implementation of the modulation strategy.

[0017] The active neutral clamp three-level topology is composed entirely of fully controlled semiconductor devices, wherein the fully controlled semiconductor devices may be silicon-based IGBTs and MOSFETs, or IGBTs and MOSFETs based on silicon carbide or gallium nitride materials. The circuit is divided into two bridge arms to ensure the output of the two-phase system, wherein the primary high-voltage interface circuit includes eight fully controlled semiconductor devices S1-S4 and S5-S8 connected in series to the power module DC bus, four fully controlled semiconductor devices S9 and S10 connected in series to the connection points of S1 and S2 and the connection points of S3 and S4 fully controlled semiconductors, S11 and S12 fully controlled semiconductor devices connected in series and connected to the connection points of S5 and S6 fully controlled semiconductors and the connection points of S7 and S8 fully controlled semiconductors, and the connection points of S9 and S10 fully controlled semiconductor devices and S11 and S12 fully controlled semiconductor devices connected to the midpoints of DC bus capacitors C1 and C2 to achieve active neutral clamping. The voltage withstand level of the power devices in this circuit is based on half of the DC bus voltage. The DC bus voltage level of the module can be improved while using devices with common voltage withstand levels in the industry.

[0018] Among them, the secondary side high-voltage interface circuit includes twelve fully-controlled semiconductor devices, namely S21-S24, S25-S28, S29-S30 and S31-S32. The eight fully-controlled semiconductor devices S21-S24 and S25-S28 are connected in series to the DC bus. The two fully-controlled semiconductor devices S29 and S30 are connected in series and are respectively connected to the connection points of the two fully-controlled semiconductors S21 and S22 and the connection points of the two fully-controlled semiconductors S23 and S24. The fully-controlled semiconductor devices S31 and S32 are connected in series and are respectively connected to the connection points of the fully-controlled semiconductors S25 and S26 and the connection points of the fully-controlled semiconductors S27 and S28. The connection points of the fully-controlled semiconductor devices S29 and S30 and the connection points of the fully-controlled semiconductor devices S31 and S32 are connected to the midpoint of the DC bus capacitors C5 and C6.

[0019] Example 2 On the basis of Example 1, the isolated DCDC circuit as a whole includes three parts: a primary side bridge arm, a high-frequency loop and a secondary side bridge arm.

[0020] For the primary side bridge arm, a series half-bridge topology is adopted, in which the upper half bridge arm of the primary side includes capacitor C1 and two series fully controlled devices S13-S14, and the lower half bridge arm of the primary side includes capacitor C2 and two series fully controlled devices S15-S16. The upper half bridge arm of the primary side and the lower half bridge arm of the primary side are connected in series. On the DC bus side, capacitors C1 and C2 are connected in series to form a DC bus. On the output side of the bridge arm, the output of the upper half bridge arm of the primary side and the output of the lower half bridge arm of the primary side constitute the overall output of the high-voltage side bridge arm. Since the half-bridge form is used in series connection, each device uses half of the bus voltage as a reference for withstand voltage, and the DC bus voltage level of the module can be improved under the premise of using common withstand voltage level devices in the industry. At the same time, the commutation circuit of the power device only includes two devices, the overall commutation circuit is very simple, and the parasitic inductance in the commutation circuit is small. Therefore, the loss during the opening and closing process is lower than that of the traditional clamped topology, which can support a higher switching frequency, thereby promoting the miniaturization, lightweight and high efficiency of the device.

[0021] Example 3 On the basis of Example 2, the high-frequency circuit includes DC blocking capacitors C3 and C4, a high-frequency transformer TR2, and resonant inductors L1 and L2, wherein the DC blocking capacitor is used to isolate the DC component of the high-voltage side bridge arm output, thereby satisfying the transmission of the AC quantity in the high-frequency isolation transformer, and the DC blocking capacitor can be selected from a film capacitor or a ceramic capacitor, etc.; the high-frequency transformer is used to realize AC energy transfer and electrical isolation, which is beneficial to the isolation of the DCDC circuit in the circuit to operate in a high-frequency state. The isolation transformer has a smaller volume and weight than the traditional industrial frequency transformer, thereby promoting the lightweight and miniaturization of the equipment of the flexible loop device; the resonant inductor is used to suppress the slope of the current in the high-frequency circuit. In practical applications, the inductor can be configured separately or the leakage inductance inside the transformer can be reused.

[0022] One end of the resonant inductor L1 is connected to the connection point of the two fully-controlled semiconductors S13 and S14, and the other end of the resonant inductor L1 is connected to the high-frequency transformer TR2, and the other end of the high-frequency transformer TR2 is connected to the DC blocking capacitor C3, and the other end of the DC blocking capacitor C3 is connected to the connection point of the two fully-controlled semiconductors S15 and S16; one end of the resonant inductor L2 is connected to the secondary side bridge arm, and the other end of the resonant inductor L2 is connected to the high-frequency transformer TR2, and the other end of the high-frequency transformer TR2 is connected to the DC blocking capacitor C4, and the other end of the DC blocking capacitor C4 is connected to the secondary side bridge arm.

[0023] Example 4 On the basis of Example 3, the secondary side bridge arm adopts a series half-bridge topology, including an upper half bridge arm on the secondary side and a lower half bridge arm on the secondary side. The upper half bridge arm on the secondary side includes a capacitor C5 and two series fully-controlled devices S17 and S118, and the lower half bridge arm on the secondary side includes a capacitor C6 and two series fully-controlled devices S19 and S20. One end of the resonant inductor L2 is connected to the connection point of the two fully-controlled semiconductors S17 and S18, and the other end of the DC blocking capacitor C4 is connected to the connection point of the two fully-controlled semiconductors S19 and S20; the upper half bridge arm on the secondary side and the lower half bridge arm on the secondary side are connected in series, and the capacitors C5 and C6 on the DC bus side are connected in series to form a DC bus. The output of the upper half bridge arm on the secondary side and the output of the lower half bridge arm on the secondary side constitute the overall output of the high-voltage side bridge arm.

[0024] Example 5 like Figure 2 As shown, the modulation method of the primary-secondary high-voltage interface circuit of the present invention is used to control the power devices in the high-voltage interface circuit. The circuit can realize the modulation of DC and AC circuits. This embodiment is introduced by taking AC system modulation as an example.

[0025] Specifically, the modulation signal sends corresponding modulation signals according to the left and right bridge arms of the circuit. In order to achieve a higher working voltage, the modulation signals between the left and right bridge arms are mutually inverted to form modulation signal 1 and modulation signal 2. Modulation signal 1 and modulation signal 2 are compared with the carrier signal respectively. The carrier signal includes the upper half carrier signal 1 and the lower half carrier signal 2. The carrier signal 1 modulates the one and three transistors of the half bridge arm device, corresponding to Figure 3 S1 and S3 of the left half bridge arm and S5 and S6 of the right half bridge arm are discussed with the left half bridge arm as an example. Carrier signal 1 is compared with the modulation signal to generate a corresponding signal wave and a waveform after the signal wave is inverted, which are provided to S1 and S3 respectively. Carrier signal 2 is compared with the modulation signal to generate a corresponding signal wave and a waveform after the signal wave is inverted, which are provided to S2 and S4 respectively. For S9 and S10, the same modulation strategy as S3 and S2 can be adopted to optimize the loss distribution of the bridge arm, reduce the temperature of the switch tube, and thus extend the life of the power device. For the right half bridge arm, the corresponding modulation method is the same.

[0026] Through the above modulation strategy, the control of the active clamp circuit can be realized to adapt to the AC system and the DC system. More generally, the modulation signals 1, 2 and the carrier signals 1, 2 can be phase-adjusted; the carrier signal can adopt other waveforms such as sawtooth wave, trapezoidal wave, etc., which also belong to the protection scope of the present invention.

[0027] like Figure 3 As shown, the modulation mode of the isolated DCDC circuit of the present invention is adopted. For the application of the present invention, the modulation strategy of mutual shifting of the primary and secondary sides is adopted. The secondary side carrier can be phase-shifted when the primary side carrier remains unchanged, or the primary side carrier can be phase-shifted when the secondary side carrier remains unchanged. The following is an introduction taking the primary side carrier unchanged and the secondary side carrier shifted as an example.

[0028] For the circuit modulation on the primary side, the carrier signal is compared with the modulation signal to generate the PWM signals of S1-S4, where the amplitude of the modulation signal is half of the amplitude of the carrier signal, thereby ensuring that the PWM signal has a 50% duty cycle. In the comparison results, the S1 and S4 signals are the same, the S2 and S3 signals are the same and opposite to the S1 and S4 signals.

[0029] For the modulation of the secondary circuit, the carrier signal is phase-shifted relative to the primary side. If power needs to be transferred from the primary side to the secondary side, the secondary side phase lags behind the primary side. If power needs to be transferred from the secondary side to the primary side, the secondary side phase leads the primary side. The secondary side carrier signal is also compared with the modulation signal to generate a 50% duty cycle PWM signal, where the signals of S5 and S8 are the same, and the signals of S6 and S7 are the same and opposite to the signals of S5 and S8.

[0030] Example 6 like Figure 4As shown in the figure, it is a traditional two-level flexible closing device power module. The power module includes a high-voltage interface circuit at both ends and an isolated DCDC circuit. The high-voltage interface circuit is connected to the distribution network system of 10kV and above, and is connected to the outside through the series connection between modules. The high-voltage interface circuit often adopts a full-bridge circuit topology. The isolated DCDC circuit realizes the electrical isolation and power transmission between the high-voltage side and the low-voltage side of the module. Since the flexible closing device is based on a high-frequency isolation circuit, the isolated DCDC circuit converts DC power into high-frequency AC power through a switch network. In the high-frequency path, due to the inconsistency of the parasitic parameters and switch timing of the switch network, a DC isolation capacitor is often connected. At the same time, a certain amount of inductance needs to be added to the switch network to suppress excessive current. In implementation, it can often be realized by externally connecting a resonant inductor or using the leakage inductance in a high-frequency transformer. In the switch network, since the output voltage only includes the positive and negative bus voltages, the number of levels is only two, and this technical route is a two-level technical route. Inside the power module, the voltage withstand level of the device limits the voltage level of the DC bus. Therefore, more power modules are required under the traditional solution to ensure the connection of the high-voltage bus.

[0031] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. The power module topology of the flexible loop closing device is characterized by: It includes a primary high-voltage interface circuit, an isolated DCDC circuit and a secondary high-voltage interface circuit connected in sequence; the primary high-voltage interface circuit and the secondary high-voltage interface circuit both adopt a three-level topology based on an active neutral clamp topology, and the isolated DCDC circuit adopts a topology structure based on carrier phase shifting; the isolated DCDC circuit includes a primary side bridge arm, a high-frequency loop and a secondary side bridge arm connected in sequence; The primary side bridge arm adopts a series half-bridge topology, including a primary side upper half bridge arm and a primary side lower half bridge arm, the high-frequency circuit includes DC blocking capacitors C3 and C4, a high-frequency transformer TR2, and resonant inductors L1 and L2, one end of the resonant inductor L1 is connected to the upper half bridge arm, the other end of the resonant inductor L1 is connected to the high-frequency transformer TR2, the other end of the high-frequency transformer TR2 is connected to the DC blocking capacitor C3, and the other end of the DC blocking capacitor C3 is connected to the lower half bridge arm; The secondary side bridge arm adopts a series half-bridge topology, including an upper half bridge arm on the secondary side and a lower half bridge arm on the secondary side. One end of the resonant inductor L2 is connected to the upper half bridge arm on the secondary side, and the other end of the resonant inductor L2 is connected to the high-frequency transformer TR2. The other end of the high-frequency transformer TR2 is connected to the DC blocking capacitor C4, and the other end of the DC blocking capacitor C4 is connected to the lower half bridge arm on the secondary side.

2. The power module topology structure of the flexible loop closing device according to claim 1 is characterized in that: The upper half bridge arm on the primary side includes a capacitor C1 and two fully-controlled devices S13 and S14 connected in series, the resonant inductor L1 is connected to the connection point of the two fully-controlled devices S13 and S14 connected in series, the lower half bridge arm on the primary side includes a capacitor C2 and two fully-controlled devices S15 and S16 connected in series, the other end of the DC-isolating capacitor C3 is connected to the connection point of the two fully-controlled devices S15 and S16 connected in series, the upper half bridge arm on the primary side and the lower half bridge arm on the primary side are connected in series, and the capacitor C1 and the capacitor C2 on the DC bus side are connected in series to form a DC bus, and the output of the upper half bridge arm on the primary side and the output of the lower half bridge arm on the primary side constitute the overall output of the high-voltage side bridge arm.

3. The power module topology structure of the flexible loop closing device according to claim 2 is characterized in that: The primary high-voltage interface circuit includes twelve fully-controlled semiconductor devices, namely S1-S4, S5-S8, S9-S10 and S11-S12. The eight fully-controlled semiconductor devices S1-S4 and S5-S8 are connected in series to the DC bus. The two fully-controlled semiconductor devices S9 and S10 are connected in series and are respectively connected to the connection points of the two fully-controlled semiconductors S1 and S2 and the connection points of the two fully-controlled semiconductors S3 and S4. The fully-controlled semiconductor devices S11 and S12 are connected in series and are respectively connected to the connection points of the fully-controlled semiconductors S5 and S6 and the connection points of the fully-controlled semiconductors S7 and S8. The connection points of the fully-controlled semiconductor devices S9 and S10 and the fully-controlled semiconductor devices S11 and S12 are connected to the midpoints of the DC bus capacitors C1 and C2.

4. The power module topology structure of the flexible loop closing device according to claim 1 is characterized in that: The secondary side bridge arm adopts a series half-bridge topology, including a secondary side upper half bridge arm and a secondary side lower half bridge arm, the secondary side upper half bridge arm includes a capacitor C5 and two series fully-controlled devices S17 and S118, one end of the resonant inductor L2 is connected to the connection point of the two series fully-controlled devices S17 and S18, the secondary side lower half bridge arm includes a capacitor C6 and two series fully-controlled devices S19 and S20, the other end of the DC blocking capacitor C4 is connected to the connection point of the two series fully-controlled devices S19 and S20, the secondary side upper half bridge arm and the secondary side lower half bridge arm are connected in series, and the capacitors C5 and C6 on the DC bus side are connected in series to form a DC bus, and the output of the secondary side upper half bridge arm and the output of the secondary side lower half bridge arm constitute the overall output of the high-voltage side bridge arm.

5. The power module topology structure of the flexible loop closing device according to claim 4 is characterized in that: The secondary side high-voltage interface circuit includes twelve fully-controlled semiconductor devices, namely S21-S24, S25-S28, S29-S30 and S31-S32. The eight fully-controlled semiconductor devices S21-S24 and S25-S28 are connected in series to the DC bus. The two fully-controlled semiconductor devices S29 and S30 are connected in series and are respectively connected to the connection points of the two fully-controlled semiconductors S21 and S22 and the connection points of the two fully-controlled semiconductors S23 and S24. The fully-controlled semiconductor devices S31 and S32 are connected in series and are respectively connected to the connection points of the fully-controlled semiconductors S25 and S26 and the connection points of the fully-controlled semiconductors S27 and S28. The connection points of the fully-controlled semiconductor devices S29 and S30 and the fully-controlled semiconductor devices S31 and S32 are connected to the midpoint of the DC bus capacitors C5 and C6.

6. The power module topology structure of the flexible loop closing device according to claim 1, characterized in that: The DC blocking capacitor is a film capacitor or a ceramic capacitor.

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