A Hybrid Series Single-Chain MMC for Flexible Interconnection and Its Control Method

Abstract

The present invention discloses a hybrid series single-chain MMC for flexible interconnection and its control method, which includes a DC side branch, a bridge arm branch and an AC side branch; the DC side branch contains a medium-high voltage DC port, a DC capacitor connected in parallel with the medium-high voltage DC port, and a group of bidirectional switches and disconnectors connected in series on any one of the positive and negative medium-high voltage DC ports. The bidirectional switch includes a pair of power switch devices connected in reverse series. The present invention uses a sub-module with DC fault clearing ability and adopts absorption of fault energy or voltage regulation operation control to cope with medium-high voltage DC short-circuit faults to achieve the function of fault ride-through. In addition, a corresponding starting control method is also proposed.

Description

Technical Field

[0001] The invention relates to a flexible interconnection-oriented hybrid series single-chain MMC and a control method thereof, belonging to the technical field of modular multi-level converters. Background Art

[0002] Building a new power system with new energy as the theme can effectively improve the ability to absorb and regulate new energy. The distribution network is the main body responsible for the distribution and absorption of electric energy. The flexible interconnection device using flexible interconnection technology has the advantages of flexible power regulation and rapid fault blocking, which can enable flexible energy transfer in space and realize flexible closed-loop operation of the distribution network. It is an important equipment for the development of distribution network towards flexible AC and DC interconnection. In particular, the addition of energy storage devices improves the time dimension of energy regulation and provides favorable guarantees for the reliable power supply of the system.

[0003] Power electronic converters based on modular structures are the protagonists in flexible interconnected devices. Although modular multilevel converters (MMC) are gradually becoming the main topology of medium-voltage DC distribution networks due to their excellent output characteristics, low switching frequency and modularity. However, the application of MMC in medium-voltage DC distribution networks also faces challenges such as more required power devices and lower power density. In order to solve the above problems, several improved MMC topologies have been proposed, which are mainly divided into parallel, series and hybrid structures. Among them, the topology represented by the series single chain (Series Single Chain-Link) MMC performs better in power density and equipment volume optimization. Compared with the traditional three-phase MMC topology, the SSC-MMC structure reduces the number of sub-modules (SM) by 2 / 3. Although the series single chain MMC is an improvement of MMC, it still needs to face the important challenge of DC short-circuit fault in the DC network. In addition, due to the different topologies of the series single chain MMC, its startup control is also an important aspect to ensure the stable operation of the device. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defects of the prior art and provide a hybrid series single-chain MMC for flexible interconnection and a control method thereof. The existing series single-chain MMC faces the challenge of DC short-circuit faults in the DC network for flexible interconnection and does not have the ability to handle DC short-circuit faults, which is disadvantageous for the safe operation of the equipment and the stable operation of the system. Two circuit combinations are used to realize the two fault self-crossing methods of absorbing fault energy by blocking method and flexibly transferring fault energy by voltage regulation operation. In order to make the system operate normally, corresponding startup control methods are proposed according to different power supplies.

[0005] Preferably, the present invention provides a hybrid series single-chain MMC for flexible interconnection, including a DC side branch, a bridge arm branch, and an AC side branch; the DC side branch includes a medium-high voltage DC port, a DC capacitor connected in parallel with the medium-high voltage DC port, and a set of bidirectional switches and disconnectors connected in series on either the positive or negative medium-high voltage DC port. The bidirectional switch includes a pair of power switch devices connected in reverse series.

[0006] Preferably, the bridge arm branch includes series-connected bridge arms ARM AC1 , bridge arm ARM AB , bridge arm ARM BC and bridge arm ARM AC2 , where bridge arm ARM AC1 and bridge arm ARM AC2 both include series-connected half-bridge sub-modules, single-capacitor sub-modules with DC fault clearing capabilities, or double-capacitor sub-modules with DC fault clearing capabilities. The number of half-bridge sub-modules in bridge arm ARM AC1 and bridge arm ARM AC2 is less than or equal to N / 4; the number of single-capacitor sub-modules in bridge arm ARM AC1 and bridge arm ARM AC2 is greater than or equal to N / 4, or the number of double-capacitor sub-modules in bridge arm ARM AC1 and bridge arm ARM AC2 is greater than or equal to N / 8; the total number of capacitors included in bridge arm ARM AC1 and bridge arm ARM AC2 is N / 2;

[0007] Bridge arm ARM AB and bridge arm ARM BC both include series-connected half-bridge sub-modules, single-capacitor sub-modules with DC fault clearing capabilities, or double-capacitor sub-modules with DC fault clearing capabilities. The number of half-bridge sub-modules in bridge arm ARM AB and bridge arm ARM BC is less than or equal to N / 4; the number of single-capacitor sub-modules in bridge arm ARM AB and bridge arm ARM BC is greater than or equal to N / 2, or the number of double-capacitor sub-modules in bridge arm ARM AB and bridge arm ARM BC is greater than or equal to N / 2; the total number of capacitors included in bridge arm ARM AB and bridge arm ARM BC is N. The series connection nodes between bridge arm ARM AC1 , bridge arm ARM AB , bridge arm ARM BC and bridge arm ARM AC2 are A', B', and C' respectively.

[0008] Preferably, the arm branch includes the series-connected arms ARM AC1 , arm ARM AB , arm ARM BC and arm ARM AC2 , where the arm ARM AC1 and the arm ARM AC2 both include series-connected half-bridge sub-modules, bidirectional single-capacitor sub-modules with DC fault ride-through capability, or bidirectional double-capacitor sub-modules with DC fault ride-through capability. The number of half-bridge sub-modules in the arm ARM AC1 and the arm ARM AC2 is less than or equal to N / 4; the number of bidirectional single-capacitor sub-modules in the arm ARM AC1 and the arm ARM AC2 is greater than or equal to N / 4, or the number of bidirectional double-capacitor sub-modules in the arm ARM AC1 and the arm ARM AC2 is greater than or equal to N / 8;

[0009] The total number of capacitors included in the arm ARM AC1 and the arm ARM AC2 is N / 2. The arm ARM AB and the arm ARM BC both include series-connected half-bridge sub-modules, single-capacitor sub-modules with DC fault ride-through capability, or double-capacitor sub-modules with DC fault ride-through capability. The total number of capacitors included in the arm ARM AB and the arm ARM BC is N. The number of half-bridge sub-modules in the arm ARM AB and the arm ARM BC is less than or equal to N / 2; the number of single-capacitor sub-modules in the arm ARM AB and the arm ARM BC is greater than or equal to N / 2, or the number of double-capacitor sub-modules in the arm ARM AB and the arm ARM BC is greater than or equal to N / 8; At the series connection nodes between the arm ARM AC1 , arm ARM AB , arm ARM BC and arm ARM AC2 are A', B' and C' respectively.

[0010] Preferably, the AC side branch includes a three-phase medium-voltage AC port A, a three-phase medium-voltage AC port B, and a three-phase medium-voltage AC port C. A first DC-blocking capacitor and a first coupling inductor are connected in series between the three-phase medium-voltage AC port A and the arm series node A'. A second coupling inductor is connected in series between the three-phase medium-voltage AC port B and the arm series node B'. A second DC-blocking capacitor and a third coupling inductor are connected in series between the three-phase medium-voltage AC port C and the arm series node C'.

[0011] Preferably, using a hybrid series single-chain MMC for flexible interconnection according to any one of the above, perform the following steps:

[0012] When a DC short-circuit fault occurs in the DC side branch, if the strategy of fault blocking and energy absorption is selected, all power switch control signals are blocked, all half-bridge sub-modules are bypassed, and the capacitors in all single-capacitor sub-modules or double-capacitor sub-modules with DC fault clearing capabilities absorb the DC short-circuit fault energy. The capacitor voltages in the single-capacitor sub-modules or double-capacitor sub-modules with DC fault clearing capabilities increase, and the fault is determined to be cleared when the DC short-circuit fault current is 0.

[0013] Determine whether the fault is a short-term fault or a permanent fault; if the DC short-circuit fault is a short-term fault, recharge the capacitor voltages in the half-bridge sub-modules, single-capacitors or double-capacitors with DC fault clearing capabilities to the rated voltage, and then convert the hybrid series single-chain MMC to normal operation; if the DC short-circuit fault is a permanent fault, then disconnect the bidirectional switch and the isolating switch on the medium-voltage DC side after the DC short-circuit fault is cleared to isolate the DC short-circuit fault.

[0014] A control method for a hybrid series single-chain MMC for flexible interconnection, using a hybrid series single-chain MMC for flexible interconnection according to any one of the above, perform the following steps:

[0015] When a DC short-circuit fault occurs in the DC side branch, if the strategy of fault ride-through and bidirectional mode is selected, all half-bridge sub-modules are bypassed, and all bidirectional single-capacitor or bidirectional double-capacitor sub-modules with DC fault ride-through capabilities adopt a bidirectional operation mode, that is, the bidirectional single-capacitor or bidirectional double-capacitor sub-module can output positive voltage, negative voltage, and 0 voltage. Arm ARM AC1 and arm ARM AC2 is equal to the AC two-phase line voltage, arm ARM AB is equal to the AB two-phase line voltage, arm ARM BCThe voltage of the BC two-phase line is equal, making the voltage of the medium-voltage DC port of the hybrid series single-chain MMC zero; when the DC short-circuit fault current is zero, it is determined that the DC short-circuit fault is cleared; it is judged whether the DC short-circuit fault is a short-term fault or a permanent fault. If the DC short-circuit fault is a short-term fault, the capacitor voltages of each sub-module are recharged to the rated voltage, and then the hybrid series single-chain MMC is switched to normal operation; if the DC short-circuit fault is a permanent fault, then after the fault is cleared, the bidirectional switch and the disconnector of the DC side branch are disconnected.

[0016] Preferably, when receiving the command to start charging, if the DC side branch provides charging for the hybrid series single-chain MMC, the medium-voltage AC port of the AC side branch is disconnected, the AC side branch has no control signal and is in an uncontrolled rectification state, and all sub-modules in the DC side branch, including the half-bridge sub-module in claim 2, the single-capacitor or double-capacitor sub-module with DC fault clearing ability, or the half-bridge sub-module in claim 3, the bidirectional single-capacitor or bidirectional double-capacitor sub-module with DC fault ride-through ability, are charged simultaneously, and the capacitor voltage of the sub-module increases; when the capacitor voltage no longer rises, half of the sub-modules bypassed by each arm continue to be uncontrollably charged to the rated voltage, and then the bypassed sub-modules that have been fully charged are bypassed, so that the bypassed half-bridge sub-modules are uncontrollably charged to the rated voltage. If there are individual sub-modules that are not charged to the rated voltage, then the bypassed half of the sub-modules are used so that the other half of the sub-modules can be charged to the rated voltage; the bidirectional switch and the disconnector of the DC side branch are both turned on, and the arm ARM AC1 and ARM AC2 provide and establish the AC two-phase line voltage, and the arm ARM AB provide and establish the AB two-phase line voltage, and the arm ARM BC provide and establish the BC two-phase line voltage.

[0017] Preferably, when a charging start command is received, if the AC side branch provides charging for the hybrid series single-chain MMC, the medium-voltage DC positive and negative ports of the DC side branch of the hybrid series single-chain MMC are disconnected. All sub-modules have no control signals and are in an uncontrolled rectification state. The half-bridge sub-modules in claim 2, the single-capacitor or double-capacitor sub-modules with DC fault clearing ability, or the half-bridge sub-modules in claim 3, the bidirectional single-capacitor or bidirectional double-capacitor sub-modules with DC fault ride-through ability are charged simultaneously, and the capacitor voltage rises. When the capacitor voltage no longer rises, the uncontrolled rectification state ends. All half-bridge sub-modules in each arm are bypassed. All single-capacitor or double-capacitor sub-modules with DC fault clearing ability in claim 2 or all bidirectional single-capacitor or bidirectional double-capacitor sub-modules with DC fault ride-through ability in claim 3 continue to be uncontrollably charged to the rated voltage, and then the fully charged sub-modules are bypassed to enable the previously bypassed half-bridge sub-modules to be uncontrollably charged to the rated voltage. During this period, if individual sub-modules are not charged to the rated voltage, then half of the sub-modules are bypassed to enable the other half of the sub-modules to be charged to the rated voltage. Bypassing the half-bridge sub-modules first or bypassing the single-capacitor or double-capacitor sub-modules with DC fault clearing ability or all bidirectional single-capacitor or bidirectional double-capacitor sub-modules can achieve the startup purpose.

[0018] After the uncontrolled rectification state ends, whether to charge all sub-modules simultaneously is selected by the closed-loop control method during normal operation.

[0019] Preferably, a current-limiting resistor needs to be connected in series in both the DC side branch and the AC side branch of the hybrid series single-chain MMC at startup to ensure that the inrush current at the beginning of charging does not exceed the specified current value, and the current-limiting resistor is bypassed during or after the charging process. The current-limiting resistor is bypassed during the charging process and the current-limiting resistor is bypassed after the charging process.

[0020] Preferably, the present invention provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the steps of the method according to any one of the first aspect are implemented.

[0021] Preferably, the present invention provides a computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method according to any one of the first aspect are implemented.

[0022] The beneficial effects achieved by the present invention:

[0023] The present invention discloses a hybrid series single - chain MMC for flexible interconnection and its control method. Aiming at the topological structure characteristics of the series single - chain MMC and the requirements for dealing with DC short - circuit faults, sub - modules with DC fault clearing capabilities are utilized, and absorption of fault energy or voltage regulation operation control is adopted to deal with medium - and high - voltage DC short - circuit faults to achieve the function of fault self - crossing, improving the safety of the system. The present invention proposes corresponding start - up control methods for different power supplies, meeting the requirements of normal operation of the equipment, with low control complexity and easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] To more clearly illustrate the technical solutions of the present application, the accompanying drawings required for the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 It is a topological structure diagram of a hybrid series single - chain MMC for flexible interconnection according to the present invention;

[0026] Figure 2 It is a flowchart of the control method of a hybrid series single - chain MMC for flexible interconnection according to the present invention;

[0027] Figure 3 For Figure 1 the module topological structure diagram shown;

[0028] Figure 4 For Figure 3 the replacement circuits available for each module of a hybrid series single - chain MMC for flexible interconnection other than; DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To facilitate the description of the technical solutions of the application, some concepts involved in the present application will be described first below. Embodiment

[0030] Referring to Figure 1 , the present application discloses a hybrid series single - chain MMC for flexible interconnection. The topological structure of the hybrid series single - chain MMC includes a DC - side branch, an arm branch, and an AC - side branch; the DC - side branch includes a medium - and high - voltage DC port, a DC capacitor connected in parallel with the medium - and high - voltage DC port, and a group of bidirectional switches and disconnectors connected in series on either the positive or negative port of the medium - and high - voltage DC. The bidirectional switch includes a pair of power switch devices connected in reverse series.

[0031] The arm branch includes serially connected arm ARM AC1 , arm ARM AB , arm ARM BC and arm ARMAC2 , where the arm ARM AC1 and the arm ARM AC2 both include series-connected half-bridge sub-modules, single-capacitor sub-modules with DC fault clearing capabilities, or double-capacitor sub-modules with DC fault clearing capabilities. The number of half-bridge sub-modules in the arm ARM AC1 and the arm ARM AC2 is less than or equal to N / 4. The number of single-capacitor sub-modules in the arm ARM AC1 and the arm ARM AC2 is greater than or equal to N / 4. The number of double-capacitor sub-modules in the arm ARM AC1 and the arm ARM AC2 is greater than or equal to N / 8. The total number of capacitors included in the arm ARM AC1 and the arm ARM AC2 is N / 2. The arm ARM AB and the arm ARM BC both include series-connected half-bridge sub-modules, single-capacitor sub-modules with DC fault clearing capabilities, or double-capacitor sub-modules with DC fault clearing capabilities. The number of half-bridge sub-modules in the arm ARM AB and the arm ARM BC is less than or equal to N / 4. The number of single-capacitor sub-modules in the arm ARM AB and the arm ARM BC is greater than or equal to N / 2. The number of double-capacitor sub-modules in the arm ARM AB and the arm ARM BC is greater than or equal to N / 2. The total number of capacitors included in the arm ARM AB and the arm ARM BC is N. The series nodes between the arm ARM AC1 , the arm ARM AB , the arm ARM BC and the arm ARM AC2 are A', B' and C' respectively. These three nodes are respectively connected to the AC side branches. Among them, the half-bridge sub-module (Half bridge sub-module, HBSM), the DC fault clearing sub-module (Fault clearing sub-module, FCSM), and the full-bridge sub-module (Full bridge sub-module, FBSM) are all single-capacitor sub-modules. Among them, the half-bridge sub-module has no fault clearing ability, and the full-bridge sub-module and the DC fault clearing sub-module have fault clearing abilities. As Figure 3As shown, the half-bridge sub-module HBSM includes a first power supply, a first NPN transistor, a first diode, a second NPN transistor, and a second diode. The first NPN transistor and the first diode are connected in series, and the second NPN transistor and the second diode are connected in series. The positive pole of the first power supply is connected to the C pole of the first NPN transistor, the negative pole of the first power supply is connected to the E pole of the second NPN transistor, and the E pole of the first NPN transistor is connected to the C pole of the second NPN transistor.

[0032] The DC fault clearing sub-module FCSM includes a second power supply, a third NPN transistor, a third diode, a fourth NPN transistor, a fourth diode, a fifth NPN transistor, a fifth diode, and a sixth diode. The third NPN transistor and the third diode are connected in series, and the fourth NPN transistor and the fourth diode are connected in series. The positive pole of the second power supply is connected to the C pole of the third NPN transistor, the negative pole of the second power supply is connected to the E pole of the fourth NPN transistor, and the E pole of the third NPN transistor is connected to the C pole of the fourth NPN transistor. The fifth NPN transistor and the fifth diode are connected in series, and the C pole of the fifth NPN transistor is connected to the positive pole of the second power supply after being connected in series with the sixth diode, and the E pole of the fifth NPN transistor is connected to the negative pole of the second power supply.

[0033] The full-bridge sub-module FBSM includes a third power supply, a sixth NPN transistor, a seventh diode, a seventh NPN transistor, an eighth diode, an eighth NPN transistor, a ninth diode, a twelfth diode, and a ninth NPN transistor. The sixth NPN transistor and the seventh diode are connected in series, and the seventh NPN transistor and the eighth diode are connected in series. The positive pole of the third power supply is connected to the C pole of the sixth NPN transistor, the negative pole of the third power supply is connected to the E pole of the seventh NPN transistor, and the E pole of the sixth NPN transistor is connected to the C pole of the seventh NPN transistor. The eighth NPN transistor and the ninth diode are connected in series, and the twelfth diode and the ninth NPN transistor are connected in series and then connected to the positive pole of the third power supply, and the E pole of the eighth NPN transistor is connected to the negative pole of the third power supply.

[0034] The AC side branch includes a three-phase medium-voltage AC port A, a three-phase medium-voltage AC port B, and a three-phase medium-voltage AC port C. A DC-blocking capacitor and a coupling inductor are connected in series between the three-phase medium-voltage AC port A and the bridge arm series node A', a coupling inductor is connected in series between the three-phase medium-voltage AC port B and the bridge arm series node B', and a DC-blocking capacitor and a coupling inductor are connected in series between the three-phase medium-voltage AC port C and the bridge arm series node C'.

[0035] In the embodiment of the present application, during normal operation, all single-capacitor or bidirectional-capacitor sub-modules with DC fault clearing capabilities are equivalent to one or two half-bridge sub-modules for operation. The hybrid series single-chain MMC is applicable to all modulation and control methods of the existing series single-chain MMC. The bidirectional switches and disconnector switches on the DC side branch are all turned on, and the bridge arm ARMAC1 and ARM AC2 Provide and establish the AC two-phase line voltage, bridge arm ARM AB Provide and establish the AB two-phase line voltage, bridge arm ARM BC Provide and establish the BC two-phase line voltage.

[0036] In the embodiment of the present application, when a DC short-circuit fault occurs in the DC side branch, if the strategy of fault blocking and energy absorption is selected, all power switch control signals are blocked, all half-bridge sub-modules are bypassed, and the capacitors in all single-capacitor sub-modules or bidirectional capacitor sub-modules with DC fault clearing capabilities absorb the DC short-circuit fault energy. The capacitor voltage in the single-capacitor sub-module or bidirectional capacitor sub-module with DC fault clearing capabilities increases, and the DC short-circuit fault current is determined to be cleared when it is 0;

[0037] Determine whether the fault is a short-term fault or a permanent fault; if the DC short-circuit fault is a short-term fault, recharge the capacitor voltage in the half-bridge sub-module, single-capacitor or double-capacitor sub-module with DC fault clearing capabilities to the rated voltage, and then convert the hybrid series single-chain MMC to normal operation; if the DC short-circuit fault is a permanent fault, then after the DC short-circuit fault is cleared, disconnect the bidirectional switch and the disconnector on the medium-high voltage DC side to isolate the DC short-circuit fault.

[0038] In the embodiment of the present application, when receiving the command to start charging, if the DC side branch provides charging for the hybrid series single-chain MMC, disconnect the medium-high voltage AC port of the AC side branch. The AC side branch has no control signal and is in an uncontrolled rectification state. All sub-modules in the DC side branch, including half-bridge sub-modules, single-capacitor or bidirectional capacitor sub-modules, and bidirectional single-capacitor or bidirectional double-capacitor sub-modules, are charged simultaneously, and the capacitor voltage of the sub-modules increases; when the capacitor voltage no longer rises, half of the sub-modules bypassed in each bridge arm, and the other half of the sub-modules continue to be uncontrollably charged to the rated voltage, and then bypass the fully charged sub-modules to make the bypassed half-bridge sub-modules be uncontrollably charged to the rated voltage; during this period, if there are individual sub-modules that are not charged to the rated voltage, then use half of the bypassed sub-modules to enable the other half of the sub-modules to be charged to the rated voltage.

[0039] In the embodiment of the present application, when a charging start command is received, if the AC side branch is used to charge the hybrid series single-chain MMC, the medium-high voltage DC positive and negative ports of the DC side branch of the hybrid series single-chain MMC are disconnected. All DC side branches have no control signals and are in an uncontrolled rectification state. Sub-modules including half-bridge sub-modules, single-capacitor or bidirectional-capacitor sub-modules, and bidirectional single-capacitor or bidirectional double-capacitor sub-modules are charged simultaneously, and the capacitor voltage increases. When the capacitor voltage no longer rises, all half-bridge sub-modules, all single-capacitor sub-modules or double-capacitor sub-modules with DC fault clearing capabilities, and all single-capacitor or bidirectional-capacitor sub-modules in each bypass continue to be uncontrollably charged to the rated voltage, and then the fully charged sub-modules are bypassed to enable the previously bypassed half-bridge sub-modules to be uncontrollably charged to the rated voltage. During this period, if individual sub-modules are not charged to the rated voltage, then half of the sub-modules can be bypassed again so that the other half of the sub-modules can be charged to the rated voltage. Whether it is the half-bridge sub-modules bypassed first or the single-capacitor or bidirectional-capacitor sub-modules with DC fault clearing capabilities, as well as the bidirectional single-capacitor or bidirectional double-capacitor sub-modules, the startup purpose can be achieved.

[0040] In the embodiment of the present application, a current-limiting resistor needs to be connected in series in both the DC side branch and the AC side branch of the hybrid series single-chain MMC during startup to ensure that the inrush current at the beginning of charging does not exceed the specified current value, and the current-limiting resistor is bypassed during or after the charging process. Bypassing the current-limiting resistor during the charging process helps to accelerate the charging process, and bypassing the current-limiting resistor after the charging process ensures that the hybrid series single-chain MMC can enter the normal operating state.

[0041] Such as Figure 4As shown, the clamp double submodule (CDSM), series-connected double submodule (SDSM), T-type full-bridge submodule (TFBSM), and cross-connected double submodule (CCDSM) are all double-capacitor submodules. Among them, the clamp double submodule (CDSM) and series-connected double submodule (SDSM) are not bi-directional submodules, while the T-type full-bridge submodule (TFBSM) and cross-connected double submodule (CCDSM) are bi-directional submodules (Bi-direction sub-module, BDSM).

[0042] The clamp double submodule (CDSM) includes transistors T1, T2, T3, T4, T5, diodes D1, D2, D3, D4, D5, D6, D7, capacitor C1, and capacitor C2. Transistor T1 and diode D1 are connected in series, transistor T2 and diode D2 are connected in series. The E electrode of transistor T1 is connected to the C electrode of transistor T2. The C electrode of transistor T1 is connected to the positive electrode of capacitor C1 and diode D6. Diode D6 is connected to the C electrode of transistor T5, the positive electrode of capacitor C2, and the C electrode of transistor T4.

[0043] The E electrode of transistor T2 is connected to the negative electrode of capacitor C1, the E electrode of transistor T5, and diode D7. Diode D7 is connected to the negative electrode of capacitor C2 and the E electrode of transistor T3. Transistor T4 and diode D4 are connected in series, and transistor T3 and diode D3 are connected in series.

[0044] The series-connected double submodule (SDSM) includes transistor T1, transistor T2, transistor T3, transistor T4, transistor T5, diode D1, diode D2, diode D3, diode D4, diode D5, diode D6, capacitor C1 and capacitor C2. Transistor T1 and diode D1 are connected in series, transistor T2 and diode D2 are connected in series, transistor T3 and diode D3 are connected in series, transistor T4 and diode D4 are connected in series. The C pole of transistor T1 is connected to the positive pole of capacitor C1 and diode D6. The E pole of transistor T2 is connected to the negative pole of capacitor C1 and the E pole of diode D5. The positive pole of capacitor C2 is connected to the C pole of diode D5. The negative pole of capacitor C2 is connected to diode D6. The positive pole of capacitor C2 is connected to the C pole of transistor T4. The negative pole of capacitor C2 is connected to the E pole of transistor T3. The E pole of transistor T4 is connected to the C pole of transistor T3. The E pole of transistor T1 is connected to the C pole of transistor T2.

[0045] Both the series-connected double submodule (SDSM) and the T-type full-bridge submodule (TFBSM) include transistor T1, transistor T2, transistor T3, transistor T4, transistor T5, transistor T6, transistor T7, transistor T8, diode D1, diode D2, diode D3, diode D4, capacitor C1, capacitor C2. Transistor T1 and diode D1 are connected in series, transistor T2 and diode D2 are connected in series, transistor T3 and diode D3 are connected in series, transistor T4 and diode D4 are connected in series. The E pole of transistor T1 is connected to the C pole of transistor T2. The C pole of transistor T1 is connected to the C pole of transistor T4. The E pole of transistor T2 is connected to the E pole of transistor T3. The C pole of transistor T3 is connected to the E pole of transistor T4. The E pole of transistor T5 is connected to the C pole of transistor T6. The E pole of transistor T6 is connected to the C pole of transistor T5. The E pole of transistor T5 is connected to the E pole of transistor T1. The C pole of transistor T5 is connected to the negative pole of capacitor C1 and the positive pole of capacitor C2. The E pole of transistor T7 is connected to the C pole of transistor T8. The E pole of transistor T8 is connected to the C pole of transistor T7. The E pole of transistor T8 is connected to the E pole of transistor T4. The C pole of transistor T8 is connected to the negative pole of capacitor C1 and the positive pole of capacitor C2. The E pole of transistor T4 is connected to the C pole of transistor T3.

[0046] The cross - series twin module CCDSM includes triode T1, triode T2, triode T3, triode T4, triode T5, triode T6, diode D1, diode D2, diode D3, diode D4, diode D5, diode D6, diode D7, capacitor C1 and capacitor C2. Triode T1 and diode D1 are in series, triode T2 and diode D2 are in series. The E - pole of triode T1 is connected to the C - pole of triode T2. The C - pole of triode T1 is connected to the positive pole of capacitor C1, diode D6. Diode D6 is connected to the C - pole of triode T5, the positive pole of capacitor C2, the C - pole of triode T4.

[0047] The E - pole of triode T2 is connected to the negative pole of capacitor C1, the E - pole of triode T5, diode D7. Diode D7 is connected to the negative pole of capacitor C2, the E - pole of triode T3. Triode T4 and diode D4 are in series, triode T3 and diode D3 are in series.

[0048] The series twin module SDSM includes triode T1, triode T2, triode T3, triode T4, triode T5, diode D1, diode D2, diode D3, diode D4, diode D5, diode D6, capacitor C1 and capacitor C2. Triode T1 and diode D1 are in series, triode T6 is in parallel with diode D6. Triode T2 and diode D2 are in series, triode T3 and diode D3 are in series, triode T4 and diode D4 are in series. The C - pole of triode T1 is connected to the positive pole of capacitor C1, diode D6. The E - pole of triode T2 is connected to the negative pole of capacitor C1, the E - pole of diode D5. The positive pole of capacitor C2 is connected to the C - pole of diode D5. The negative pole of capacitor C2 is connected to diode D6. The positive pole of capacitor C2 is connected to the C - pole of triode T4. The negative pole of capacitor C2 is connected to the E - pole of triode T3. The E - pole of triode T4 is connected to the C - pole of triode T3. The E - pole of triode T1 is connected to the C - pole of triode T2. In the embodiments of the present application, the present invention provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, the steps of the method described in any one of the above are implemented.

[0049] In the embodiments of the present application, the present invention provides a computer - readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, the steps of the method described in any one of the above are implemented. Embodiment

[0050] Different from Embodiment 1, in this embodiment, the bridge - arm branch includes series - connected bridge - arm ARM AC1 , bridge - arm ARM AB , bridge - arm ARM BC and bridge - arm ARM AC2 , where bridge - arm ARM AC1And arm ARM AC2 Both include series-connected half-bridge sub-modules, bidirectional single-capacitor sub-modules with DC fault ride-through capability, or bidirectional double-capacitor sub-modules with DC fault ride-through capability. The arm ARM AC1 And arm ARM AC2 The number of half-bridge sub-modules in is less than or equal to N / 4. The arm ARM AC1 And arm ARM AC2 The number of bidirectional single-capacitor sub-modules in is greater than or equal to N / 4. The arm ARM AC1 And arm ARM AC2 The number of bidirectional double-capacitor sub-modules in is greater than or equal to N / 8;

[0051] Arm ARM AC1 And arm ARM AC2 The total number of capacitors included is N / 2. The arm ARM AB And arm ARM BC Both include series-connected half-bridge sub-modules, single-capacitor sub-modules with DC fault ride-through capability, or double-capacitor sub-modules with DC fault ride-through capability. The arm ARM AB And arm ARM BC The total number of capacitors included is N. The arm ARM AB And arm ARM BC The number of half-bridge sub-modules in is less than or equal to N / 2. The arm ARM AB And arm ARM BC The number of single-capacitor sub-modules in is greater than or equal to N / 2. The arm ARM AB And arm ARM BC The number of double-capacitor sub-modules in is greater than or equal to N / 8. At the arm ARM AC1 Arm ARM AB Arm ARM BC And arm ARM AC2 The series nodes between are A', B' and C' respectively.

[0052] In the embodiment of the present application, when a DC short-circuit fault occurs in the DC side branch, if the strategy of fault ride-through and bidirectional mode is selected, all half-bridge sub-modules are bypassed, and all bidirectional single-capacitor or bidirectional double-capacitor sub-modules with DC fault ride-through capability adopt the bidirectional operation mode, that is, the bidirectional single-capacitor or bidirectional double-capacitor sub-module can output positive voltage, negative voltage and 0 voltage. The arm ARM AC1 And arm ARM AC2 Is equal to the AC two-phase line voltage. The arm ARM AB Is equal to the AB two-phase line voltage. The arm ARM BC Is equal to the BC two-phase line voltage, so that the medium-high voltage DC port voltage of the hybrid series single-chain MMC is 0;

[0053] Determine whether the DC short-circuit fault is a short-term fault or a permanent fault. If the DC short-circuit fault is a short-term fault, recharge the capacitor voltages of each sub-module to the rated voltage again, and then convert the hybrid series single-chain MMC to normal operation. If the DC short-circuit fault is a permanent fault, then after the fault is cleared, disconnect the bidirectional switch and the disconnector on the DC side branch to isolate the DC short-circuit fault.

[0054] Each embodiment in this specification is described in a progressive manner. For the same or similar parts among the embodiments, reference can be made to each other. The key point of each embodiment is to illustrate the differences from other embodiments.

[0055] After considering the specification and practicing the invention herein, those skilled in the art will readily conceive of other embodiments of the present invention. This application is intended to cover any variations, uses, or adaptations of the present invention, which follow the general principles of the present invention and include the common general knowledge or conventional technical means in the technical field not invented by the present invention. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present invention are pointed out by the following claims.

[0056] The above specific implementation manners further elaborate on the purpose, technical solution, and beneficial effects of this application. It should be understood that the above are only the specific implementation manners of this application and are not used to limit the protection scope of this application. Any modifications, equivalent replacements, improvements, etc. made on the basis of the technical solution of this application shall be included in the protection scope of this application.

Claims

1. A hybrid series single-chain MMC for flexible interconnection, characterized in that: It includes a DC side branch, a bridge arm branch and an AC side branch; the DC side branch includes a medium-high voltage DC port, a DC capacitor connected in parallel with the medium-high voltage DC port, and a group of bidirectional switches and isolating switches connected in series on any one of the medium-high voltage DC positive and negative ports, and the bidirectional switch includes a pair of power switch devices connected in reverse series; The bridge arm branch includes bridge arms ARM connected in series AC1 、Bridge arm ARM AB 、Bridge arm ARM BC and bridge arm ARM AC2 , where bridge arm ARM AC1 and bridge arm ARM AC2 Each includes a half-bridge submodule connected in series, a single capacitor submodule with DC fault clearing capability, or a dual capacitor submodule with DC fault clearing capability, and the bridge arm ARM AC1 and bridge arm ARM AC2 The number of half-bridge submodules in the bridge is less than or equal to N / 4; bridge arm ARM AC1 and bridge arm ARM AC2 The number of single capacitor submodules in the bridge arm is greater than or equal to N / 4, or the bridge arm ARM AC1 and bridge arm ARM AC2 The number of dual capacitor submodules in the bridge arm ARM is greater than or equal to N / 8; AC1 and bridge arm ARM AC2 The total number of capacitors included is N / 2; Bridge arm ARM AB and bridge arm ARM BC Each includes a half-bridge submodule connected in series, a single capacitor submodule with DC fault clearing capability, or a dual capacitor submodule with DC fault clearing capability, and the bridge arm ARM AC1 and bridge arm ARM AC2 The number of half-bridge submodules in the bridge is less than or equal to N / 4, and the bridge arm ARM AC1 and bridge arm ARM AC2 The number of single capacitor submodules in the bridge arm is greater than or equal to N / 2, or the bridge arm ARM AC1 and bridge arm ARM AC2 The number of dual capacitor submodules in the bridge arm is greater than or equal to N / 2. AB and bridge arm ARM BC The total number of capacitors included is N, in the bridge arm ARM AC1 、Bridge arm ARM AB 、Bridge arm ARM BC and bridge arm ARM AC2 The series nodes between them are A', B' and C'.

2. A hybrid series single-chain MMC for flexible interconnection according to claim 1, characterized in that: The bridge arm branch includes bridge arms ARM connected in series AC1 、Bridge arm ARM AB 、Bridge arm ARM BC and bridge arm ARM AC2 , where bridge arm ARM AC1 and bridge arm ARM AC2 Each includes a half-bridge submodule connected in series, a bidirectional single capacitor submodule with DC fault ride-through capability, or a bidirectional dual capacitor submodule with DC fault ride-through capability, and the bridge arm ARM AC1 and bridge arm ARM AC2 The number of half-bridge submodules in the bridge is less than or equal to N / 4; bridge arm ARM AC1 and bridge arm ARM AC2 The number of bidirectional single capacitor submodules in the bridge arm is greater than or equal to N / 4, or the bridge arm ARM AC1 and bridge arm ARM AC2 The number of bidirectional dual-capacitor submodules is greater than or equal to N / 8; Bridge arm ARM AC1 and bridge arm ARM AC2 The total number of capacitors included is N / 2, bridge arm ARM AB and bridge arm ARM BC Each includes a half-bridge submodule connected in series, a single capacitor submodule with DC fault ride-through capability, or a dual capacitor submodule with DC fault ride-through capability, and the bridge arm ARM AB and bridge arm ARM BC The total number of capacitors included is N, and the bridge arm ARM AC1 and bridge arm ARM AC2 The number of half-bridge submodules in the bridge is less than or equal to N / 2; bridge arm ARM AC1 and bridge arm ARM AC2 The number of single capacitor submodules in the bridge arm is greater than or equal to N / 2, or the bridge arm ARM AC1 and bridge arm ARM AC2 The number of dual capacitor submodules in the bridge arm ARM is greater than or equal to N / 8; AC1 、Bridge arm ARM AB 、Bridge arm ARM BC and bridge arm ARM AC2 The series nodes between them are A', B' and C'.

3. The hybrid series single-chain MMC for flexible interconnection according to claim 1, characterized in that: The AC side branch includes a three-phase medium-high voltage AC port A, a three-phase medium-high voltage AC port B and a three-phase medium-high voltage AC port C. A first DC blocking capacitor and a first coupling inductor are connected in series between the three-phase medium-high voltage AC port A and the bridge arm series node A', a second coupling inductor is connected in series between the three-phase medium-high voltage AC port B and the bridge arm series node B', and a second DC blocking capacitor and a third coupling inductor are connected in series between the three-phase medium-high voltage AC port C and the bridge arm series node C'.

4. A control method for a flexible interconnected hybrid series single-chain MMC, characterized in that: Using the hybrid series single-chain MMC for flexible interconnection as described in claim 1 or 3, the following steps are performed: When a DC short circuit fault occurs in the DC side branch, if the fault blocking and energy absorption strategy is selected, all power switch control signals are blocked, all half-bridge sub-modules are bypassed, and the capacitors in all single capacitor sub-modules or dual capacitor sub-modules with DC fault clearing capabilities absorb the DC short circuit fault energy. The capacitor voltage in the single capacitor sub-module or dual capacitor sub-module with DC fault clearing capabilities increases, and the fault is determined to be cleared when the DC short circuit fault current is 0; Determine whether the fault is a short-term fault or a permanent fault; If the DC short circuit fault is a short-term fault, the capacitor voltage in the half-bridge sub-module, the single capacitor or the dual capacitor sub-module with DC fault clearing capability is recharged to the rated voltage, and then the hybrid series single-chain MMC is switched to normal operation; if the DC short circuit fault is a permanent fault, then after the DC short circuit fault is cleared, the bidirectional switch and the isolating switch on the medium and high voltage DC side need to be disconnected to isolate the DC short circuit fault.

5. A control method for a flexible interconnected hybrid series single-chain MMC, characterized in that: Using the hybrid series single-chain MMC for flexible interconnection as described in any one of claims 1, 2 and 3, the following steps are performed: When a DC short circuit fault occurs in the DC side branch, if the fault ride-through and bidirectional mode strategies are selected, all half-bridge sub-modules are bypassed, and all bidirectional single capacitor or bidirectional dual capacitor sub-modules with DC fault ride-through capability adopt bidirectional operation mode, that is, the bidirectional single capacitor or bidirectional dual capacitor sub-module can output positive voltage, negative voltage and 0 voltage, and the bridge arm ARM AC1 and bridge arm ARM AC2 Equal to the AC two-phase line voltage, bridge arm ARM AB The voltage of the two-phase line AB is equal to that of the bridge arm ARM. BC The voltage of the two-phase line of BC is equal to that of the medium and high voltage DC port of the hybrid series single-chain MMC is 0; when the DC short-circuit fault current is 0, the DC short-circuit fault is determined to be cleared; it is determined whether the DC short-circuit fault is a short-term fault or a permanent fault. If the DC short-circuit fault is a short-term fault, the capacitor voltage of each sub-module is recharged to the rated voltage, and then the hybrid series single-chain MMC is switched to normal operation; if the DC short-circuit fault is a permanent fault, the bidirectional switch and the isolating switch of the DC side branch are disconnected after the fault is cleared.

6. A control method for a flexible interconnected hybrid series single-chain MMC according to claim 4 or 5, characterized in that: When receiving a command to start charging, if the DC side branch provides charging for the hybrid series single-chain MMC, the medium and high voltage AC port of the AC side branch is disconnected, the AC side branch has no control signal and is in an uncontrolled rectification state, and all submodules in the DC side branch, including the half-bridge submodule in claim 2, the single capacitor or dual capacitor submodule with DC fault clearing capability, or the half-bridge submodule in claim 3, the bidirectional single capacitor or bidirectional dual capacitor submodule with DC fault ride-through capability, are charged at the same time, and the capacitor voltage of the submodule increases; when the capacitor voltage no longer increases, half of the submodules in each bridge arm are bypassed, and the other half of the submodules continue to be charged uncontrolled to the rated voltage, and then the fully charged submodules are bypassed, so that the bypassed half-bridge submodules are charged uncontrolled to the rated voltage. If individual submodules are not charged to the rated voltage, then half of the bypassed submodules are used to enable the other half of the submodules to be charged to the rated voltage; The bidirectional switch and isolating switch of the DC side branch are both turned on, and the bridge arm ARM AC1 and ARM AC2 Provide and establish AC two-phase line voltage, bridge arm ARM AB Provide and establish AB two-phase line voltage, bridge arm ARM BC Provide and establish BC two-phase line voltage.

7. A control method for a flexible interconnected hybrid series single-chain MMC according to claim 4 or 5, characterized in that: When receiving a command to start charging, if the AC side branch provides charging for the hybrid series single-chain MMC, the medium and high voltage DC positive and negative ports of the DC side branch of the hybrid series single-chain MMC are disconnected, and all sub-modules have no control signals and are in an uncontrolled rectification state, including the half-bridge sub-module in claim 2, the single capacitor or dual capacitor sub-module with DC fault clearing capability or the half-bridge sub-module in claim 3, the bidirectional single capacitor or bidirectional dual capacitor sub-module with DC fault riding capability are charged at the same time, and the capacitor voltage increases; when the capacitor voltage no longer increases, the uncontrolled rectification state ends, each bridge arm bypasses all half-bridge sub-modules, and claim 2 All the single capacitor or dual capacitor submodules with DC fault clearing capability or all the bidirectional single capacitor or dual capacitor submodules with DC fault ride-through capability in claim 3 continue to be uncontrolled charged to the rated voltage, and then bypass the charged submodules, so that the previously bypassed half-bridge submodules are uncontrolled charged to the rated voltage; during this period, if individual submodules are not charged to the rated voltage, then bypass half of the submodules so that the other half of the submodules can be charged to the rated voltage; whether to bypass the half-bridge submodule first or bypass the single capacitor or dual capacitor submodule with DC fault clearing capability or all the bidirectional single capacitor or bidirectional dual capacitor submodules can achieve the startup purpose; After the uncontrolled rectification state ends, whether to charge all submodules simultaneously is selected through the closed-loop control method during normal operation.

8. A control method for a flexible interconnected hybrid series single-chain MMC according to claim 4 or 5, characterized in that: In the DC side branch and AC side branch of the hybrid series single-chain MMC, current limiting resistors must be connected in series at startup to ensure that the impact current at the beginning of charging does not exceed the limited current value, and the current limiting resistors are bypassed during or after charging.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the program, the steps of the method according to any one of claims 4 to 8 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 4 to 8 are implemented.

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