Common mode leakage current suppression circuit and control method thereof

Abstract

The application discloses a common-mode leakage current suppression circuit and a control method thereof, and is suitable for non-isolated flexible interconnection equipment. The common-mode leakage current suppression circuit topological structure comprises a three-phase AC / DC converter, first and second DC / DC converters, first and second direct-current capacitors, first and second single-phase controllable inverter bridges and first and second single-phase filters. The filter capacitor in the first single-phase filter is connected in series with a positive direct-current bus, and the filter capacitor in the second single-phase filter is connected in series with a negative direct-current bus. The common-mode voltage in the capacitor voltage compensation system is controlled, so that the common-mode voltage in the non-isolated flexible interconnection device system is effectively reduced, and the common-mode leakage current is suppressed. The control method of the leakage current suppression circuit adopts a double-loop control strategy combining a current outer loop and a voltage inner loop, and the common-mode leakage current is suppressed in a closed loop, so that the common-mode leakage current can be effectively suppressed, and the safety and reliability of the non-isolated flexible interconnection equipment are improved.

Description

Technical Field

[0001] This invention belongs to the technical field of flexible interconnection equipment for power distribution networks, and specifically relates to a common-mode leakage current suppression circuit and its control method. Background Technology

[0002] The power distribution network is a crucial carrier for power transmission and distribution, as well as for absorbing distributed renewable energy sources, directly impacting local economic development and the quality of life for users. However, with the increasing DC loads such as electric vehicle charging stations and communication equipment, and the rising penetration rate of renewable energy sources like distributed photovoltaics, problems such as inconsistent power flow and uneven voltage distribution in the power distribution network feeders are becoming increasingly serious. To address these issues, the use of flexible interconnection equipment (FID) based on power electronics technology to interconnect and mutually supply multiple distribution areas with complementary spatiotemporal characteristics can effectively improve the load balancing and power flow optimization capabilities between distribution areas.

[0003] FID (Power Injection Transformer) is suitable for 10kV medium-voltage distribution networks and 380V low-voltage distribution networks. However, FIDs with power frequency isolation transformers are limited in application in distribution networks due to their large size and high losses. Therefore, eliminating the isolation transformer to improve the power density and efficiency of FIDs has become a research focus. However, for non-isolated FIDs, since the distribution network is directly grounded, the common-mode voltage injected by the modulation algorithm and the difference in grid operating conditions will cause the converter to generate significant common-mode leakage current to ground, affecting the power quality of the device. Furthermore, excessive leakage current can cause leakage protection devices to malfunction, threatening the safe and stable operation of the system.

[0004] To address the common-mode leakage current problem in non-isolated FIDs, existing technologies typically employ improved PWM modulation strategies (such as AZPWM, NSPWM, and CBPWM) to reduce the common-mode voltage amplitude. However, the optimization space for these modulation strategies is limited, and the calculation and control processes for achieving control by adjusting the carrier angle or peak position are quite complex. Especially in non-isolated FIDs, simultaneous control of the sending-end converter and the operating-end converter is required, further increasing the difficulty of real-time calculations. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a common-mode leakage current suppression circuit and its control method, applicable to non-isolated FIDs, which can effectively suppress common-mode leakage current caused by the direct grounding system in non-isolated FIDs.

[0006] The present invention adopts the following technical solution: a common-mode leakage current suppression circuit for non-isolated flexible interconnection equipment, the topology of which includes: a three-phase AC / DC converter, a first DC / DC converter, a first DC capacitor, a first single-phase controllable inverter bridge, a first single-phase filter, a second DC / DC converter, a second DC capacitor, a second single-phase controllable inverter bridge, and a second single-phase filter.

[0007] Specifically, the AC terminal of the three-phase AC / DC converter is connected to the three-phase power distribution network, converting the three-phase AC voltage provided by the three-phase power distribution network into DC voltage, and providing DC power to the input terminals of the first DC / DC converter and the second DC / DC converter.

[0008] The input terminals of the first DC / DC converter and the second DC / DC converter are connected in parallel to the DC terminal of the three-phase AC / DC converter.

[0009] The first DC capacitor is connected to the output terminal of the first DC / DC converter, and the voltage on the first DC capacitor is stabilized by the first DC / DC converter.

[0010] The DC terminal of the first single-phase controllable inverter bridge is connected to the first DC capacitor. The first single-phase controllable inverter bridge outputs the target AC voltage by controlling the opening and closing of the power switch in the inverter bridge.

[0011] The first single-phase filter is connected to the AC terminal of the first single-phase controllable inverter bridge. The first single-phase filter consists of a first filter inductor and a first filter capacitor. The first filter capacitor is connected in series with the positive bus of the common DC bus.

[0012] The second DC capacitor is connected to the output terminal of the second DC / DC converter, and the voltage on the second DC capacitor is stabilized by the second DC / DC converter.

[0013] The DC terminal of the second single-phase controllable inverter bridge is connected to the second DC capacitor. The second single-phase controllable inverter bridge outputs the target AC voltage by controlling the opening and closing of the power switch in the inverter bridge.

[0014] The second single-phase filter is connected to the AC terminal of the second single-phase controllable inverter bridge. The second single-phase filter consists of a second filter inductor and a second filter capacitor. The second filter capacitor is connected in series with the negative bus of the common DC bus.

[0015] Preferably, the three-phase AC / DC converter is a three-phase four-arm converter, comprising: a three-phase three-arm full-bridge rectifier and a fourth arm module;

[0016] The three-phase three-bridge full-bridge rectifier consists of a three-phase rectifier bridge composed of fully controlled switching devices and a three-phase LCL filter composed of three sets of filter inductors and capacitors. Each phase of the AC input terminal of the three-phase rectifier bridge is connected to the LCL filter, and the high-frequency harmonic components injected into the power grid by the filter circuit are filtered out.

[0017] The fourth bridge arm module consists of a fully controlled switching device, a neutral inductor, and a split capacitor. Both ends of the split capacitor and the fourth bridge arm are connected in parallel to the DC end of the three-phase three-bridge arm full-bridge rectifier. The two ends of the split capacitor are connected to the midpoint of the fourth bridge arm through the neutral inductor to reduce the high-frequency pulsation of the voltage at the midpoint of the split capacitor.

[0018] Preferably, the three-phase distribution network connected to the AC terminal of the three-phase AC / DC converter is also connected to the rectifier side or inverter side of the non-isolated flexible interconnection equipment.

[0019] Preferably, the first DC / DC converter and the second DC / DC converter have the same structure, both including: a power switching transistor, a high-frequency transformer, an anti-parallel diode, an auxiliary inductor, and a filter capacitor.

[0020] Preferably, the output terminal of the power switch in the first DC / DC converter is connected to the first DC capacitor, and the output terminal of the power switch in the second DC / DC converter is connected to the second DC capacitor.

[0021] Preferably, the first single-phase controllable inverter bridge and the second single-phase controllable inverter bridge have the same structure, both including upper and lower bridge arms, which are composed of power switching transistors and corresponding anti-parallel diodes.

[0022] Preferably, the filter capacitor of the first single-phase filter is connected in series with the positive bus of the common DC bus; the filter capacitor of the second single-phase filter is connected in series with the negative bus of the common DC bus; by controlling the voltage of the filter capacitor to compensate for the common-mode voltage in the system, the common-mode voltage inside the non-isolated flexible interconnect device system is reduced, thereby suppressing the common-mode leakage current.

[0023] Preferably, the non-isolated flexible interconnection equipment includes: a rectifier-side three-phase distribution network, a three-phase DC / AC rectifier, a three-phase AC / DC inverter, and an inverter-side three-phase distribution network;

[0024] The three-phase DC / AC rectifier and the three-phase AC / DC inverter are interconnected via positive and negative common DC buses. The AC side of the three-phase DC / AC rectifier and the AC side of the three-phase AC / DC inverter are respectively connected to the rectifier-side three-phase distribution network and the inverter-side three-phase distribution network. The rectifier-side three-phase distribution network and the inverter-side three-phase distribution network are grounded systems, and there is no isolation transformer in the system, which causes a common-mode leakage current to flow through the grounding network inside the non-isolated flexible interconnection equipment.

[0025] The present invention also provides: a control method for a common-mode leakage current suppression circuit, applied to any of the above-mentioned common-mode leakage current suppression circuits, comprising the following steps:

[0026] S1, Collect positive bus current i p Negative bus current i nThe voltage u of the filter capacitor of the first single-phase filter c1 The voltage u of the filter capacitor of the second single-phase filter c2 ;

[0027] S2. Based on the positive and negative DC bus currents collected in step S1, calculate the magnitude i of the common-mode leakage current to ground of the non-isolated flexible interconnection equipment. cir ;

[0028] S3. Using the common-mode leakage current as the outer loop, a closed-loop controller G is employed. i1 With G i3 The common-mode leakage current i to ground of the non-isolated flexible interconnect equipment obtained in step S2 cir Perform closed-loop control;

[0029] The common-mode leakage current i cir With common-mode leakage current reference value i cir * The difference is calculated and passed through the outer current loop controller G. i1 With G i3 Then, the reference value of the output capacitor voltage u c * ;

[0030] S4, using the filter capacitor voltage u c1 u c2 For the inner loop, a closed-loop controller G is used. i2 With G i4 For the capacitor voltage reference value u obtained in step S3 C * Compared with the actual value u obtained in step S1 C1 u c2 The difference is used for closed-loop adjustment;

[0031] The voltage u of the filter capacitor c1 With capacitor voltage reference value u c * The difference is calculated and passed through the voltage inner loop controller G. i2 The voltage reference signal u of the first single-phase controllable inverter bridge is then output. O1 * ; the voltage u of the filter capacitor c2 With capacitor voltage reference value u c * The difference is calculated and passed through the voltage inner loop controller G. i2 The voltage reference signal u of the second single-phase controllable inverter bridge is then output. O2 * ;

[0032] S5. Based on the voltage reference signal u obtained in step S4 O1 *The drive signals for each power switch in the first single-phase controllable inverter bridge (6) are generated by a carrier modulation algorithm; based on the voltage reference signal u obtained in step S4... O2 * The drive signals for each switch in the second single-phase controllable inverter bridge are generated through a carrier modulation algorithm.

[0033] Preferably, the method for calculating the common-mode leakage current to ground of the non-isolated flexible interconnection equipment in step S2 is as follows:

[0034] i cir =i p +i n

[0035] Among them, i p i is the positive DC bus current. n It is the negative DC bus current.

[0036] Compared with the prior art, the present invention, employing the above technical solution, has the following technical effects:

[0037] 1. The common-mode leakage current suppression circuit and its control method proposed in this invention are applicable to non-isolated FIDs. By adjusting the capacitor voltage, the common-mode voltage source in the non-isolated FID system is compensated, thereby effectively reducing the common-mode voltage inside the non-isolated FID system, thus suppressing the common-mode leakage current and improving the safety and reliability of the device.

[0038] 2. The control method of the common-mode leakage current suppression circuit proposed in this invention adopts a dual closed-loop control strategy that combines the outer current loop and the inner voltage loop to suppress the common-mode leakage current in a closed loop, which can effectively suppress the common-mode leakage current caused by the direct grounding system in non-isolated FID. Attached Figure Description

[0039] Figure 1 This is a topology diagram of the common-mode leakage current suppression circuit of the present invention;

[0040] Figure 2 This is a control flow diagram of the common-mode leakage current suppression circuit control method of the present invention;

[0041] Figure 3 This is a schematic diagram of the non-isolated flexible interconnection equipment system structure after injecting an equivalent common-mode voltage source according to an embodiment of the present invention;

[0042] Figure 4 This is a simulation result of a single-phase short-circuit fault occurring in the right-side power grid of the non-isolated FID according to an embodiment of the present invention. Detailed Implementation

[0043] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] The terms "first," "second," etc., in the claims, description, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, systems, products, or apparatus.

[0045] In one embodiment of the present invention, a common-mode leakage current suppression circuit is proposed to address the common-mode leakage current problem to ground formed by the ground wire in flexible interconnection equipment without isolation transformers. The topology is as follows: Figure 1 As shown, it includes: a three-phase AC / DC converter 1, a first DC / DC converter 2, a first DC capacitor 4, a first single-phase controllable inverter bridge 6, a first single-phase filter 8, a second DC / DC converter 3, a second DC capacitor 5, a second single-phase controllable inverter bridge 7, and a second single-phase filter 9.

[0046] The three-phase power distribution network G1 is connected to the AC terminal of the three-phase AC / DC converter 1. The three-phase AC / DC converter 1 converts the three-phase AC voltage provided by the three-phase power distribution network G1 into DC voltage, thereby providing a stable DC power supply to the input terminals of the first DC / DC converter 2 and the second DC / DC converter 3.

[0047] The input terminal of the first DC / DC converter 2 and the input terminal of the second DC / DC converter 3 are connected in parallel to the DC terminal of the three-phase AC / DC converter 1.

[0048] The first DC capacitor 4 is connected to the output terminal of the first DC / DC converter 2, and the voltage on the first DC capacitor 4 is stabilized by the first DC / DC converter 2.

[0049] The DC terminal of the first single-phase controllable inverter bridge 6 is connected to the first DC capacitor 4. By controlling the opening and closing of the power switch in the inverter bridge, the target AC voltage is output.

[0050] The first single-phase filter 8 is connected to the AC terminal of the first single-phase controllable inverter bridge 6. The filter consists of a filter inductor and a filter capacitor, wherein the filter capacitor is connected in series with the positive bus of the common DC bus.

[0051] The second DC capacitor 5 is connected to the output terminal of the second DC / DC converter 3, and the voltage on the second DC capacitor 5 is stabilized by the second DC / DC converter 3.

[0052] The DC terminal of the second single-phase controllable inverter bridge 7 is connected to the second DC capacitor 5. By controlling the opening and closing of the power switch in the inverter bridge, the target AC voltage is output.

[0053] The second single-phase filter 9 is connected to the AC terminal of the second single-phase controllable inverter bridge 7. The filter consists of a filter inductor and a filter capacitor, wherein the filter capacitor is connected in series with the negative bus of the common DC bus.

[0054] Preferably, in this embodiment, the three-phase AC / DC converter 1 is a three-phase four-arm converter, including: a three-phase three-arm full-bridge rectifier and a fourth arm module.

[0055] The three-phase three-bridge full-bridge rectifier consists of a three-phase rectifier bridge composed of six fully controlled switching devices and a three-phase LCL filter composed of three sets of filter inductors and capacitors. The control system adopts a dual closed-loop control structure with an inner current loop and an outer voltage loop. Each phase of the AC input terminal of the three-phase rectifier bridge is connected to the LCL filter, and the high-frequency harmonic components injected into the power grid by the filter circuit are filtered out.

[0056] The fourth bridge arm module consists of two fully controlled switching devices MOSFETs, a neutral inductor, and a split capacitor. The split capacitor and the fourth bridge arm are both connected in parallel to the DC terminal of the three-phase three-bridge full-bridge rectifier, and their midpoints are connected through an inductor to reduce the high-frequency ripple of the voltage at the midpoint of the split capacitor, thereby reducing the common-mode current to ground.

[0057] Preferably, in this embodiment, the distribution network connected to the AC terminal of the three-phase AC / DC converter 1 can be used to connect the rectifier side or the inverter side of the non-isolated FID.

[0058] Preferably, in this embodiment, both the first DC / DC converter 2 and the second DC / DC converter 3 are isolated bidirectional active full-bridge DC-DC converters, which are composed of two sets of IGBT full-bridge circuits, a high-frequency transformer and an auxiliary inductor; wherein, the high-frequency transformer is used for electrical isolation and voltage matching, and the auxiliary inductor is used to store instantaneous electrical energy.

[0059] Preferably, in this embodiment, the output terminal of the power switch in the first DC / DC converter 2 is connected to the first DC capacitor 4; and the output terminal of the power switch in the second DC / DC converter 3 is connected to the second DC capacitor 5.

[0060] Preferably, in this embodiment, the first single-phase controllable inverter bridge 6 and the second single-phase controllable inverter bridge 7 have the same structure, both including upper and lower bridge arms, which are composed of power switching transistors and their corresponding anti-parallel diodes.

[0061] Preferably, in this embodiment, the filter capacitor of the first single-phase filter 8 is connected in series with the positive bus of the common DC bus; the filter capacitor of the second single-phase filter 9 is connected in series with the negative bus of the common DC bus; the two filter capacitors are connected in series with the common DC bus, and the common-mode voltage in the system is compensated by controlling the voltage of the filter capacitors, thereby effectively reducing the common-mode voltage inside the non-isolated flexible interconnect device system and suppressing the common-mode leakage current.

[0062] It should be noted that, in this embodiment, the non-isolated FID structure includes: a three-phase distribution network G2 on the rectifier side, a three-phase DC / AC rectifier, a three-phase AC / DC inverter, and a three-phase distribution network G3 on the inverter side.

[0063] The three-phase DC / AC rectifier and the three-phase AC / DC inverter are interconnected through positive and negative common DC buses. Since the three-phase power distribution network connected to the AC side of the three-phase DC / AC rectifier and the AC side of the three-phase AC / DC inverter is generally a grounded system and there is no isolation transformer in the system, a significant common-mode leakage current is generated inside the non-isolated FID and flows through the grounded network.

[0064] In this embodiment, for ease of description, the inverter composed of the first single-phase controllable inverter bridge 6 and the first single-phase filter 8 is referred to as the first inverter, and the inverter composed of the second single-phase controllable inverter bridge 7 and the second single-phase filter 9 is referred to as the second inverter.

[0065] Furthermore, this embodiment provides a control method for a leakage current suppression circuit, which is achieved through the coordinated operation of a first inverter and a second inverter, and its control structure is as follows: Figure 2 As shown.

[0066] This embodiment describes the control method for the common-mode leakage current suppression circuit, focusing on each step and in conjunction with the accompanying drawings and tables. The control method for the first inverter includes the following steps:

[0067] 1) The controller collects the positive bus current i p Negative bus current i n The voltage u of the filter capacitor of the first single-phase filter 8 C1The voltage u of the filter capacitor of the second single-phase filter 9 C2 .

[0068] 2) Based on the positive and negative DC bus currents collected in step 1), calculate the common-mode leakage current i to ground for the non-isolated FID. cir The calculation method is as follows:

[0069] i cir =i p +i n (1)

[0070] Among them, i p For positive bus current, i n This is the negative bus current.

[0071] 3) Using the common-mode leakage current as the outer loop, a closed-loop controller G is employed. i1 Reference value for common-mode leakage current i cir * Compared with the actual value i obtained in step 2), cir The difference is used for closed-loop adjustment to generate a capacitor voltage reference value u. C * .

[0072] Among them, the common-mode leakage current reference value i for non-isolated flexible interconnect equipment cir * Set to 0, closed-loop controller G i1 It can be a proportional-integral controller.

[0073] 4) Using the capacitor voltage as the inner loop, a closed-loop controller G is employed. i2 The capacitor voltage reference value u obtained in step 3) C * Compared with the actual value u obtained in step 1), C1 The difference is used for closed-loop regulation to generate a voltage reference signal u for the single-phase controllable inverter bridge. O1 * Among them, the closed-loop controller G i2 It can be a proportional-integral controller.

[0074] 5) The voltage reference signal u of the single-phase controllable inverter bridge obtained in step 4) O1 * The input is sent to the carrier modulation algorithm module to generate the drive signals for each power switch in the first single-phase controllable inverter bridge (6).

[0075] The control method for the second inverter is similar to that for the first inverter, including the following steps:

[0076] 6) Using the common-mode leakage current as the outer loop, a closed-loop controller G is employed. i3 Reference value for common-mode leakage current icir * Compared with the actual value i obtained in step 2), cir The difference is used for closed-loop adjustment to generate a capacitor voltage reference value u. C * Among them, the common-mode leakage current reference value i for non-isolated FIDs. cir * Set to 0, closed-loop controller G i3 The parameters and the closed-loop controller G in step 3) i1 same.

[0077] It should be noted that, in order to keep the voltage across capacitor C1 and capacitor C2 consistent, the capacitor voltage reference value u generated in step 6) is... C * Compared with the capacitor voltage reference value u generated by the controller in step 3), C * Therefore, for convenience, the capacitor voltage reference values ​​generated in steps 3) and 6) are not distinguished and are both denoted as u. C * .

[0078] 7) Using the capacitor voltage as the inner loop, a closed-loop controller G is employed. i4 The capacitor voltage reference value u obtained in step 6) C * Compared with the actual value u obtained in step 1), C2 The difference is used for closed-loop regulation to generate a voltage reference signal u for the single-phase controllable inverter bridge. O2 * Among them, the closed-loop controller G i4 The parameters and the closed-loop controller G in step 4) i2 same.

[0079] 8) The voltage reference signal u of the single-phase controllable inverter bridge obtained in step 7) O2 * The input is sent to the carrier modulation algorithm module to generate the drive signals for each power switch in the second single-phase controllable inverter bridge (7).

[0080] Furthermore, this embodiment is based on the obtained capacitor voltage feedback value u of the first inverter. C1 Feedback value u of the capacitor voltage of the second inverter C2 A common-mode voltage u is injected into a non-isolated FID system by connecting two capacitors in series with the positive and negative common DC buses, respectively. cm-c u cm-c The calculation method is as follows:

[0081]

[0082] In addition to the common-mode leakage current i given in step 2), cir In addition to the calculation method, the ground common-mode leakage current i in a non-isolated FID system after injecting the equivalent common-mode voltage can also be calculated using the following formula (3). cir The calculation method is as follows:

[0083]

[0084] Among them, u cm-c The equivalent common-mode voltage injected into a non-isolated FID system by the common-mode leakage current suppression circuit, u cm-total Z represents the original common-mode voltage within a non-isolated FID system. cm-eq This represents the total equivalent common-mode impedance in a non-isolated FID system. cm-total The common-mode voltage is derived from the modulation algorithm and the difference in grid operating conditions. As shown in equation (3), by controlling u... cm-c The size can be i cir Suppressed to 0.

[0085] In this embodiment, the u in the non-isolated flexible interconnection equipment system cm-total The calculation method is as follows:

[0086] u cm-total =u cmg-1 +u cm-1 +u cm-2 +u cmg-2 (4)

[0087] Among them, u cmg-1 The common-mode voltage u is generated by the unbalanced operating conditions of the rectifier-side power grid. cm-1 The common-mode voltage injected into the modulation algorithm on the rectifier side, u cm-2 The common-mode voltage injected into the inverter-side modulation algorithm, u cmg-2 This refers to the common-mode voltage generated by unbalanced grid conditions on the inverter side. The structure of a non-isolated FID system after injecting an equivalent common-mode voltage source is as follows: Figure 3 As shown.

[0088] In this embodiment, the control parameters of each closed-loop controller are designed in the frequency domain according to the desired dynamic and steady-state response performance.

[0089] Table 1 shows the key parameters of the common-mode leakage current suppression circuit applicable to non-isolated FID.

[0090] Table 1

[0091]

[0092] Furthermore, in this embodiment, the simulation results of a single-phase short-circuit fault occurring in the right-side power grid of the non-isolated FID are as follows: Figure 4As shown. Figure 4 In the figure, (a) and (b) represent the voltage waveforms of the distribution networks connected to both sides of the flexible interconnection equipment under the simulated operating condition. Figure 4 As shown in (c), when no suppression measures are taken for the common-mode leakage current to ground in the non-isolated FID, the common-mode leakage current contains both low-frequency harmonics and high-frequency oscillations, with an amplitude of nearly 100A. Figure 4 Figure (d) shows the common-mode leakage current waveform to ground in the non-isolated FID after the common-mode leakage current suppression circuit is connected to the system. It can be seen that the common-mode leakage current in the system is quickly suppressed to below 3A, which shows that the control method in this embodiment effectively suppresses the common-mode leakage current to ground in the non-isolated flexible interconnect equipment.

[0093] Furthermore, in one embodiment of the present invention, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the method described in the present invention, which will not be repeated here.

[0094] Furthermore, in one embodiment of the present invention, an electronic device is also provided, comprising: a memory, a processor, and a computer program stored in the memory and executable on the processor.

[0095] It should be noted that the processing flow of the computer-readable storage medium or electronic device mentioned in the above embodiments corresponds to the specific steps of the method provided in the embodiments of the present invention, and has the corresponding functional modules and beneficial effects for executing the method. Technical details not described in detail in this embodiment can be found in the method provided in the embodiments of the present invention.

[0096] The program code used to implement the methods of this application may be written in any combination of one or more programming languages. This program code may be provided to a processor or controller of a general-purpose computer, special-purpose computer, or other programmable data processing device, such that when executed by the processor or controller, the functions / operations specified in the flowcharts and / or block diagrams are implemented. The program code may be executed entirely on a machine, partially on a machine, as a standalone software package partially on a machine and partially on a remote machine, or entirely on a remote machine or server.

[0097] In the context of this application, a computer-readable medium can be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, apparatus, or device. A machine-readable medium can be a machine-readable signal medium or a machine-readable storage medium. A computer-readable medium can be, but is not limited to, electronic, magnetic, optical, electromagnetic, infrared, or semiconductor systems, apparatus, or devices, or any suitable combination of the foregoing. More specific examples of machine-readable storage media include electrical connections based on one or more wires, portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination of the foregoing.

[0098] In summary, this invention proposes a common-mode leakage current suppression circuit and its control method. The leakage current suppression circuit compensates for the common-mode voltage source in the system by adjusting the capacitor voltage, thereby effectively reducing the common-mode voltage inside the non-isolated flexible interconnect device system and suppressing the common-mode leakage current. The control method of the leakage current suppression circuit adopts a dual closed-loop control strategy combining the outer current loop and the inner voltage loop to suppress the common-mode leakage current in a closed loop.

[0099] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0100] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A common-mode leakage current suppression circuit for non-isolated flexible interconnect equipment, characterized in that, The suppression circuit topology includes: a three-phase AC / DC converter (1), a first DC / DC converter (2), a first DC capacitor (4), a first single-phase controllable inverter bridge (6), a first single-phase filter (8), a second DC / DC converter (3), a second DC capacitor (5), a second single-phase controllable inverter bridge (7), and a second single-phase filter (9). The AC terminal of the three-phase AC / DC converter (1) is connected to the three-phase power distribution network, converting the three-phase AC voltage provided by the three-phase power distribution network into DC voltage, and providing DC power to the input terminals of the first DC / DC converter (2) and the second DC / DC converter (3). The input terminal of the first DC / DC converter (2) and the input terminal of the second DC / DC converter (3) are connected in parallel to the DC terminal of the three-phase AC / DC converter (1); The first DC capacitor (4) is connected to the output terminal of the first DC / DC converter (2), and the voltage on the first DC capacitor (4) is stabilized by the first DC / DC converter (2); The DC terminal of the first single-phase controllable inverter bridge (6) is connected to the first DC capacitor (4). The first single-phase controllable inverter bridge (6) outputs the target AC voltage by controlling the opening and closing of the power switch in the inverter bridge. The first single-phase filter (8) is connected to the AC terminal of the first single-phase controllable inverter bridge (6). The first single-phase filter (8) is composed of a first filter inductor and a first filter capacitor. The first filter capacitor is connected in series with the positive bus of the common DC bus. The second DC capacitor (5) is connected to the output terminal of the second DC / DC converter (3) to stabilize the voltage on the second DC capacitor (5) through the second DC / DC converter (3); The DC terminal of the second single-phase controllable inverter bridge (7) is connected to the second DC capacitor (5). The second single-phase controllable inverter bridge (7) outputs the target AC voltage by controlling the opening and closing of the power switch in the inverter bridge. The second single-phase filter (9) is connected to the AC terminal of the second single-phase controllable inverter bridge (7). The second single-phase filter (9) is composed of a second filter inductor and a second filter capacitor. The second filter capacitor is connected in series with the negative bus of the common DC bus.

2. The common-mode leakage current suppression circuit according to claim 1, characterized in that, The three-phase AC / DC converter (1) is a three-phase four-arm converter, including a three-phase three-arm full-bridge rectifier and a fourth arm module; The three-phase three-bridge full-bridge rectifier consists of a three-phase rectifier bridge composed of fully controlled switching devices and a three-phase LCL filter composed of three sets of filter inductors and capacitors. Each phase of the AC input terminal of the three-phase rectifier bridge is connected to the LCL filter, and the high-frequency harmonic components injected into the power grid by the filter circuit are filtered out. The fourth bridge arm module consists of a fully controlled switching device, a neutral inductor, and a split capacitor. Both ends of the split capacitor and the fourth bridge arm are connected in parallel to the DC end of the three-phase three-bridge arm full-bridge rectifier. The two ends of the split capacitor are connected to the midpoint of the fourth bridge arm through the neutral inductor to reduce the high-frequency pulsation of the voltage at the midpoint of the split capacitor.

3. The common-mode leakage current suppression circuit according to claim 1, characterized in that, The three-phase power distribution network is connected to the AC terminal of the three-phase AC / DC converter (1), and is also connected to the rectifier side or inverter side of the non-isolated flexible interconnection equipment.

4. The common-mode leakage current suppression circuit according to claim 1, characterized in that, The first DC / DC converter (2) and the second DC / DC converter (3) have the same structure, both including: power switching transistor, high frequency transformer, anti-parallel diode, auxiliary inductor and filter capacitor.

5. The common-mode leakage current suppression circuit according to claim 4, characterized in that, The output terminal of the power switch in the first DC / DC converter (2) is connected to the first DC capacitor (4), and the output terminal of the power switch in the second DC / DC converter (3) is connected to the second DC capacitor (5).

6. The common-mode leakage current suppression circuit according to claim 1, characterized in that, The first single-phase controllable inverter bridge (6) and the second single-phase controllable inverter bridge (7) have the same structure, both including upper and lower bridge arms, which are composed of power switching transistors and corresponding anti-parallel diodes.

7. The common-mode leakage current suppression circuit according to claim 1, characterized in that, The filter capacitor of the first single-phase filter (8) is connected in series with the positive bus of the common DC bus; the filter capacitor of the second single-phase filter (9) is connected in series with the negative bus of the common DC bus; by controlling the voltage of the filter capacitor to compensate for the common mode voltage in the non-isolated flexible interconnection equipment system, the common mode voltage inside the non-isolated flexible interconnection device system is reduced, thereby suppressing the common mode leakage current.

8. The common-mode leakage current suppression circuit according to claim 1, characterized in that, The non-isolated flexible interconnection equipment includes: a rectifier-side three-phase distribution network, a three-phase DC / AC rectifier, a three-phase AC / DC inverter, and an inverter-side three-phase distribution network; The three-phase DC / AC rectifier and the three-phase AC / DC inverter are interconnected via positive and negative common DC buses. The AC side of the three-phase DC / AC rectifier and the AC side of the three-phase AC / DC inverter are respectively connected to the rectifier-side three-phase distribution network and the inverter-side three-phase distribution network. The rectifier-side three-phase distribution network and the inverter-side three-phase distribution network are grounded systems and have no internal isolation transformers, resulting in a common-mode leakage current flowing through the grounding network inside the non-isolated flexible interconnection equipment.

9. A control method for a common-mode leakage current suppression circuit, applied to the common-mode leakage current suppression circuit according to any one of claims 1 to 8, characterized in that, Includes the following steps: S1. Acquire positive bus current Negative bus current The voltage of the filter capacitor of the first single-phase filter (8) The voltage of the filter capacitor of the second single-phase filter (9) ; S2. Based on the positive and negative DC bus currents collected in step S1, calculate the magnitude of the common-mode leakage current to ground of the non-isolated flexible interconnection equipment. ; S3. Using the common-mode leakage current as the outer loop, a closed-loop controller G is employed. i1 With G i3 The common-mode leakage current to ground of the non-isolated flexible interconnect equipment obtained in step S2 Perform closed-loop control; Common-mode leakage current Reference value for common-mode leakage current The difference is calculated and passed through the outer current loop controller G. i1 With G i3 Then, the reference value of the output capacitor voltage. ; S4, using the voltage of the filter capacitor For the inner loop, a closed-loop controller G is used. i2 With G i4 For the capacitor voltage reference value obtained in step S3 Compared with the actual value obtained in step S1 The difference is used for closed-loop adjustment; The voltage u of the filter capacitor c1 With capacitor voltage reference value The difference is calculated and passed through the voltage inner loop controller G. i2 The voltage reference signal of the first single-phase controllable inverter bridge (6) is then output. ; The voltage u of the filter capacitor c2 With capacitor voltage reference value The difference is calculated and passed through the voltage inner loop controller G. i2 The voltage reference signal of the second single-phase controllable inverter bridge (7) is then output. ; S5. Based on the voltage reference signal obtained in step S4 The drive signals for each power switch in the first single-phase controllable inverter bridge (6) are generated by a carrier modulation algorithm; based on the voltage reference signal obtained in step S4... The drive signals for each switch in the second single-phase controllable inverter bridge (7) are generated by a carrier modulation algorithm.

10. The control method for the common-mode leakage current suppression circuit according to claim 9, characterized in that, The calculation method for the common-mode leakage current to ground of the non-isolated flexible interconnect equipment in step S2 is as follows: ； in, This is the positive DC bus current. It is the negative DC bus current.

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