Current source converter and direct current power transmission system

Abstract

The utility model provides a current source converter and a direct current transmission system, the converter comprises a plurality of single-phase full-bridge structures connected in series, and each bridge arm comprises at least one full-control device; the first ends of the primary coils of the phase change transformers are electrically connected with the first node of the single-phase full-bridge structure, the second ends of the primary coils of the phase change transformers are electrically connected with the second node of the single-phase full-bridge structure, and the first ends of the secondary coils of any two phase change transformers are electrically connected; the second end of the secondary coil of the phase change transformer is used for being electrically connected with an alternating current load, the first node is a node where a first upper bridge arm of the single-phase full-bridge structure is connected with a corresponding first lower bridge arm, and the second node is a node where a second upper bridge arm of the single-phase full-bridge structure is connected with a corresponding second lower bridge arm. According to the method, the turn-off capability of the full-control power semiconductor device and the cooperative work of the bridge arm transformer are adopted, so that the risk of commutation failure of the other two phases when the single-phase fault of the power grid occurs is reduced, and the operation reliability of the converter valve is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of converter, in particular to a current source converter and a DC power transmission system. BACKGROUND

[0002] Traditional grid commutated converters (LCC) based on thyristors have many challenges in high voltage DC power transmission. Firstly, a large number of series are needed to withstand high DC voltage, which leads to the fact that the commutation valve contains dozens or even hundreds of series thyristors, increasing the complexity and cost of the valve structure. Secondly, LCC relies on the AC power supply to provide commutation voltage for natural commutation, which is prone to commutation failure when the AC system fails or voltage drops. The strong coupling between the bridge arms / phases makes the LC fault influence range large, and a single-phase fault may affect the entire converter station or even the multi-fed DC system. In addition, due to the sharing of the same AC system and DC loop by each bridge arm, there is a lack of independence between valves, and a fault in one phase or one valve will interfere with the normal commutation of other bridge arms. In summary, the traditional LCC has technical bottlenecks in terms of a large number of thyristor series, high risk of commutation failure, and serious coupling between bridge arms, and it is necessary to find new topologies to improve its reliability. CONTENT OF THE UTILITY MODEL

[0003] The main purpose of the present application is to provide a current source converter and a DC power transmission system to at least solve the problem of high commutation failure risk of the traditional current source converter.

[0004] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a current source converter is provided, comprising: a plurality of single-phase full-bridge structures in series, each single-phase full-bridge structure comprising an upper bridge arm and a lower bridge arm, each bridge arm comprising at least one controllable device, the first single-phase full-bridge structure and the last single-phase full-bridge structure are both used for electrical connection with a DC bus; a plurality of phase-changing transformers, the first end of the primary coil of the phase-changing transformer is electrically connected with the first node of the single-phase full-bridge structure, the second end of the primary coil of the phase-changing transformer is electrically connected with the second node of the single-phase full-bridge structure, the first end of the secondary coil of any two phase-changing transformers is electrically connected, and the second end of the secondary coil of the phase-changing transformer is used for electrical connection with an AC load, the first node is the node connected by the first upper bridge arm and the corresponding first lower bridge arm of the single-phase full-bridge structure, the second node is the node connected by the second upper bridge arm and the corresponding second lower bridge arm of the single-phase full-bridge structure, and the phase-changing transformer corresponds to the single-phase full-bridge structure one by one.

[0005] Optionally, each of the commutation bridge arms comprises a plurality of series-connected controllable modules, and each controllable module comprises the controllable device and the voltage equalization circuit which are electrically connected.

[0006] Optionally, the single-phase full-bridge structure has three, the upper bridge arm has two, which are the first upper bridge arm and the second upper bridge arm, the lower bridge arm has two, which are the first lower bridge arm and the second lower bridge arm, the first end of the first upper bridge arm is electrically connected with the first end of the second upper bridge arm, the second end of the first upper bridge arm is electrically connected with the first end of the first lower bridge arm, the second end of the second upper bridge arm is electrically connected with the first end of the second lower bridge arm, and the second end of the first lower bridge arm is electrically connected with the second end of the second lower bridge arm, wherein the first end of the first upper bridge arm of the first single-phase full-bridge structure and the first end of the second upper bridge arm are electrically connected with the DC bus, the first upper bridge arm of the second single-phase full-bridge structure is electrically connected with the second end of the first lower bridge arm of the first single-phase full-bridge structure, the second upper bridge arm of the second single-phase full-bridge structure is electrically connected with the second end of the second lower bridge arm of the first single-phase full-bridge structure, the first upper bridge arm of the third single-phase full-bridge structure is electrically connected with the second end of the first lower bridge arm of the second single-phase full-bridge structure, the second upper bridge arm of the third single-phase full-bridge structure is electrically connected with the second end of the second lower bridge arm of the second single-phase full-bridge structure, and the second end of the first lower bridge arm of the third single-phase full-bridge structure and the second end of the second lower bridge arm are electrically connected with the DC bus.

[0007] Optionally, the full-controlled device is an IGCT device, and the voltage equalization circuit comprises a lightning arrester, a first diode, a first resistance module, and a first capacitance module, wherein the first end of the lightning arrester is electrically connected with the anode of the IGCT device, the second end of the lightning arrester is electrically connected with the cathode of the IGCT device, the anode of the first diode is electrically connected with the first end of the lightning arrester, the first end of the first resistance module is electrically connected with the anode of the first diode, the second end of the first resistance module is electrically connected with the cathode of the first diode, and the first pole of the first capacitance module is electrically connected with the second end of the first resistance module and the cathode of the first diode respectively, and the second pole of the first capacitance module is electrically connected with the second end of the lightning arrester.

[0008] Optionally, the full-controlled device is an IGCT device, and the voltage equalization circuit comprises a lightning arrester, a second resistance module, and a second capacitance module, wherein the first end of the lightning arrester is electrically connected with the anode of the IGCT device, the second end of the lightning arrester is electrically connected with the cathode of the IGCT device, the first end of the second resistance module is electrically connected with the anode of the IGCT device, the first pole of the second capacitance module is electrically connected with the second end of the second resistance module, and the second pole of the second capacitance module is electrically connected with the cathode of the IGCT device.

[0009] Optionally, the fully-controlled device is an IGBT device, and the voltage-sharing circuit comprises: a second diode, an anode of the second diode being electrically connected to a first pole of the IGBT device; a third resistance module, a first end of the third resistance module being electrically connected to the anode of the second diode, and a second end of the third resistance module being electrically connected to a cathode of the second diode; and a third capacitance module, a first pole of the third capacitance module being electrically connected to the second end of the third resistance module and the cathode of the second diode respectively, and a second pole of the third capacitance module being electrically connected to a second pole of the IGBT device.

[0010] Optionally, the fully-controlled device is an IGBT device, and the voltage-sharing circuit comprises: a fourth resistance module, a first end of the fourth resistance module being electrically connected to a first pole of the IGBT device; and a fourth capacitance module, a first pole of the fourth capacitance module being electrically connected to a second end of the fourth resistance module, and a second pole of the fourth capacitance module being electrically connected to a second pole of the IGBT device.

[0011] Optionally, the fourth resistance module comprises a plurality of resistances in series and / or a plurality of resistances in parallel, and the fourth capacitance module comprises a plurality of capacitances in series and / or a plurality of capacitances in parallel.

[0012] Optionally, the current source converter further comprises: a direct-current side inductor, a first end of the direct-current side inductor being electrically connected to the single-phase full-bridge structure of the first stage, and a second end of the direct-current side inductor being configured to be electrically connected to a direct-current bus.

[0013] According to another aspect of the present application, a direct-current power transmission system is provided, comprising: any one of the current source converters.

[0014] By applying the technical solution of the present application, the current source converter comprises: a plurality of single-phase full-bridge structures connected in series, each bridge arm comprising at least one fully-controlled device; a plurality of phase-changing transformers, a first end of a primary coil of the phase-changing transformer being electrically connected to a first node of the single-phase full-bridge structure, a second end of the primary coil of the phase-changing transformer being electrically connected to a second node of the single-phase full-bridge structure, a first end of a secondary coil of any two phase-changing transformers being electrically connected, and a second end of the secondary coil of the phase-changing transformer being configured to be electrically connected to an alternating-current load, the first node being a node at which a first upper bridge arm and a corresponding first lower bridge arm of the single-phase full-bridge structure are connected, and the second node being a node at which a second upper bridge arm and a corresponding second lower bridge arm of the single-phase full-bridge structure are connected. By using the turn-off capability of the fully-controlled power semiconductor device and the cooperative work of the bridge arm transformer, the risk of commutation failure of the remaining two phases when the power grid is single-phase fault is reduced, the operation reliability of the converter valve is improved, and the problem of high risk of commutation failure of the traditional current source converter is solved. BRIEF DESCRIPTION OF DRAWINGS

[0015] The accompanying drawings, which form a part of this specification, are included to provide a further understanding of the application, and are incorporated in and constitute a part of this specification. The embodiments of the application, together with its

[0016] Figure 1 A structure diagram of a current source converter is shown according to an embodiment of the application;

[0017] Figure 2 A principle diagram of a current source converter in a non-fault state is shown according to an embodiment of the application;

[0018] Figure 3 A commutation principle diagram of a current source converter is shown according to an embodiment of the application;

[0019] Figure 4 A principle diagram of active shutdown of a current source converter in a phase A fault state is shown according to an embodiment of the application;

[0020] Figure 5 A structure diagram of a full-control module on one bridge arm of a single-phase full-bridge structure is shown according to an embodiment of the application;

[0021] Figure 6 A structure diagram of a full-control module is shown according to an embodiment of the application;

[0022] Figure 7 A structure diagram of another full-control module is shown according to an embodiment of the application;

[0023] Figure 8 A structure diagram of still another full-control module is shown according to an embodiment of the application;

[0024] Figure 9 A structure diagram of yet another full-control module is shown according to an embodiment of the application;

[0025] Figure 10 A structure diagram of a direct current power transmission system is shown according to an embodiment of the application.

[0026] Among the above drawings, the following reference signs are included:

[0027] 01, current source converter; 02, sending end converter; 10, single-phase full-bridge structure; 11, upper bridge arm; 12, lower bridge arm; 13, fully controlled module; 111, IGCT device; 112, lightning arrester; 113, IGBT device; 20, phase-change transformer; A, first node; B, second node; D1, first diode; D2, second diode; R1, first resistance module; R2, second resistance module; R3, third resistance module; R4, fourth resistance module; C1, first capacitor module; C2, second capacitor module; C3, third capacitor module; C4, fourth capacitor module; L dc , DC side inductance; L s , primary coil; L p , secondary coil. DETAILED DESCRIPTION

[0028] It should be noted that the embodiments and features of the embodiments in the present application can be combined with each other without conflict. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0029] In order for those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should be within the scope of protection of the present application.

[0030] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so that the embodiments of the present application described herein can be implemented. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device that includes a series of steps or units does not necessarily limit to those clearly listed steps or units, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0031] As introduced in the background, traditional thyristor-based line commutated converters (LCC) in high voltage direct current transmission have many challenges. Firstly, a large number of series are needed to withstand high DC voltage, which leads to the fact that the converter valve contains tens or even hundreds of series thyristors, increasing the complexity and cost of the valve structure. Secondly, LCC relies on the AC power supply to provide the commutation voltage for natural commutation, and commutation failure is prone to occur when the AC system fails or voltage drops. The strong coupling between the bridge arms / phases makes the LC fault impact range large, and a single-phase fault may affect the entire converter station or even the multi-fed DC system. In addition, due to the sharing of the same AC system and DC loop by each bridge arm, there is a lack of independence between the valves, and a fault in one phase or one valve will interfere with the normal commutation of other bridge arms. In summary, the traditional LCC has technical bottlenecks in terms of a large number of thyristor series, high risk of commutation failure, and serious coupling between bridge arms, and it is necessary to find a new topology to improve its reliability.

[0032] To solve the problem of high commutation failure risk of the traditional current source converter, the embodiment of the application provides a current source converter and a direct current transmission system.

[0033] The technical scheme in the embodiment of the application will be clearly and completely described in the following with reference to the drawings in the embodiment of the application.

[0034] Figure 1 is a structural schematic diagram of a current source converter according to the embodiment of the application. As shown in Figure 1 the current source converter comprises: a plurality of single-phase full-bridge structures 10 connected in series, the single-phase full-bridge structure 10 comprises an upper bridge arm 11 and a lower bridge arm 12, each bridge arm comprises at least one fully controlled device, the first single-phase full-bridge structure 10 and the last single-phase full-bridge structure 10 are both used for electrical connection with a DC bus; a plurality of phase-changing transformers 20, a first end of a primary coil Ls of the phase-changing transformer 20 is electrically connected with a first node A of the single-phase full-bridge structure 10, a second end of the primary coil Ls of the phase-changing transformer 20 is electrically connected with a second node B of the single-phase full-bridge structure 10, a first end of a secondary coil Lp of any two phase-changing transformers 20 is electrically connected, a second end of the secondary coil Lp of the phase-changing transformer 20 is used for electrical connection with an AC load, the first node A is a node connected by the first upper bridge arm 11 and the corresponding first lower bridge arm 12 of the single-phase full-bridge structure 10, the second node B is a node connected by the second upper bridge arm 11 and the corresponding second lower bridge arm 12 of the single-phase full-bridge structure 10, and the phase-changing transformer 20 corresponds to the single-phase full-bridge structure 10 one by one.

[0035] The series single-phase full-bridge structure is a single-phase converter valve bridge arm part in the proposed converter valve topology, which is composed of four commutation bridge arms, each of which is composed of N full-controlled power semiconductor devices in series, as the main commutation path and blocking structure of the single-phase converter valve. The four bridge arms use full-bridge connection method, and the two bridge arms diagonally opposite to each other (the first upper bridge arm and the second lower bridge arm, the first lower bridge arm and the second upper bridge arm) are simultaneously turned on or turned off, and the bridge arms on the same side are alternately turned on (the first upper bridge arm and the first lower bridge arm, the second upper bridge arm and the second lower bridge arm). Similarly, each single-phase full-bridge structure has the same structure, and the bridge arm of each phase is composed of a plurality of devices in series, which is determined by the voltage level of the converter, and the higher the voltage level, the more the number of series.

[0036] The phase-change transformer includes a single-phase AC transformer secondary side coil (primary coil) and a primary side coil (secondary coil), wherein the transformer secondary side tap is connected to the midpoint of two bridge arms of the single-phase full-bridge structure, and the transformer primary side tap is connected to the AC power grid.

[0037] The above embodiment adopts the form of multiple power semiconductor devices in series in each phase, and uses the phase voltage of the AC power grid to realize natural commutation of each bridge arm, so that each sub-module can independently complete commutation. Specifically, each phase is composed of a plurality of full-controlled power semiconductor devices in series, which are connected in series at different taps of the converter transformer secondary winding. Since the bridge arm cascade structure is adopted, each sub-module only bears part of the voltage, which can reduce the series number of devices under the premise of meeting the bridge arm withstand voltage level, and realize independent adjustment of the trigger angle of each bridge arm. This means that the turn-on and turn-off time of each bridge arm can be controlled respectively, and it is no longer fixed to commutate in phase sequence like traditional LCC, thereby giving the converter greater control freedom and flexibility in topology. At the same time, since the phase voltage of the AC power grid is used as the commutation voltage, in the event of single-phase ground fault of the AC power grid, the remaining two phases can be independently controlled and commutated normally.

[0038] The series single-phase full-bridge structure allows the converter to withstand high voltage, and each single-phase full-bridge bears part of the voltage, reducing the voltage stress that a single full-controlled device needs to withstand. The use of phase-changing transformers realizes further distribution of the voltage, and through the connection of the original coils and the nodes of different single-phase full-bridge structures, the voltage is evenly distributed among the modules, improving the overall voltage equalization capability of the converter. Under normal operating conditions, the commutation of the device occurs at the zero-crossing point of the AC phase voltage and the full-bridge output voltage, which makes the commutation process a zero-voltage transition, reduces switching loss and electromagnetic interference, and improves the operating efficiency and reliability of the converter. By dispersing the commutation function to multiple series single-phase full-bridge structures, even if one or several modules fail, the remaining modules can still maintain the commutation function, improving the redundancy and fault tolerance of the converter. Each single-phase full-bridge structure can be independently controlled, which allows the converter to adjust its operating state under different operating conditions, improving its adaptability and flexibility to various grid conditions.

[0039] The current source converter of the present application comprises: a plurality of series single-phase full-bridge structures, each bridge arm comprising at least one full-controlled device; a plurality of phase-changing transformers, the first end of the original coil of the phase-changing transformer being electrically connected to the first node of the single-phase full-bridge structure, the second end of the original coil of the phase-changing transformer being electrically connected to the second node of the single-phase full-bridge structure, the first end of the secondary coil of any two phase-changing transformers being electrically connected, and the second end of the secondary coil of the phase-changing transformer being used for electrical connection with an AC load. The first node is the node connected by the first upper bridge arm and the corresponding first lower bridge arm of the single-phase full-bridge structure, and the second node is the node connected by the second upper bridge arm and the corresponding second lower bridge arm of the single-phase full-bridge structure. This method reduces the risk of failure of the remaining two-phase commutation when the power grid single-phase fails, improves the operation reliability of the converter, and solves the problem of high risk of commutation failure of traditional current source converters.

[0040] The traditional LCC converter needs a large number of devices in series to withstand hundreds of thousands of volts of DC voltage due to the limited voltage resistance of thyristors. The multi-bridge arm series topology distributes the total voltage to multiple modules through bridge arm voltage division, significantly reducing the number of series elements in a single valve. The traditional LCC relies on AC line voltage for natural commutation, and when a single-phase ground fault occurs in the power grid, causing voltage drop or phase abnormality, the device may not be able to turn off on time, resulting in commutation failure. The above embodiment avoids the risk of failure of the remaining two-phase commutation when the power grid single-phase fails by using the turn-off capability of full-controlled power semiconductor devices and the cooperative work of bridge arm transformers, improving the operation reliability of the converter.

[0041] Taking phase A as an example, the current path is as follows during normal operation Figure 2As shown, the complementary conduction mode is adopted for the full-controlled devices in the same bridge arm in the single-phase full-bridge structure, and the phase-changing transformer is used to establish the commutation voltage for the single-phase full-bridge structure, thereby supporting the current commutation. Since the upper and lower bridge arms of the three single-phase full-bridge structures are in the conducting state at any time, the circuit interruption does not occur in the series connection of the full-bridge strings in the conventional operation, and the commutation principle is as shown in Figure 3 As shown, the output voltages of the three single-phase full-bridge strings are superimposed to form the DC voltage through the 50Hz phase control mode of the AC power grid, i.e., the valve controller determines the time of issuing the trigger pulse by monitoring the AC power grid phase voltage, and determines the device combination of issuing the trigger pulse at this time according to the positive and negative relationship of the three-phase voltages, thereby ensuring that the AC power grid phase voltage and the output voltage of the full-bridge converter are zero at the same time and are complementarily conducted on each phase. At this time, since the devices are commutated in the natural turn-off mode, the zero-voltage conduction condition is achieved for the full-bridge series devices of each phase, and the overall converter valve achieves the soft switching effect.

[0042] When the single-phase fault of the AC power grid occurs, the voltage of a certain phase will drop, causing the commutation voltage to be insufficient and resulting in the commutation failure of the valve. Taking the voltage drop of the A phase as an example. The single-phase ground fault causes the input voltage of the secondary winding of the transformer to drop, resulting in the output voltage of the primary winding to drop, and the insufficient commutation voltage causes the devices to fail to turn off, and the devices of one side of the bridge arm in the single-phase full-bridge structure are simultaneously conducted. At this time, the upper bridge arm in the first single-phase full-bridge structure is simultaneously conducted, and it can be seen that the single-phase full-bridge structure has a commutation failure, but does not cause the circuit interruption of the series connection. The second single-phase full-bridge structure and the third single-phase full-bridge structure can still operate normally. At the same time, when the A phase has a commutation failure fault, the forced commutation can be performed in combination with the active turn-off capability of the full-controlled device IGCT in the example circuit to avoid the short circuit of the bridge arm, at this time, the valve controller adopts the active turn-off to operate the valve, wherein the single-phase full-bridge structure of the A phase is the circuit that actively turns off due to the local commutation failure fault. When the fault occurs, the first upper bridge arm and the second lower bridge arm of the single-phase full-bridge structure of the A phase trigger the active turn-off action, and the bridge arm current is forced to commutate to the second upper bridge arm and the first lower bridge arm, and the remaining two phases maintain normal operation. At this time, the current path is as shown in Figure 4 .

[0043] In some embodiments, the single-phase full-bridge structure has three, the upper bridge arms include two, which are the first upper bridge arm and the second upper bridge arm, the lower bridge arms include two, which are the first lower bridge arm and the second lower bridge arm, the first end of the first upper bridge arm is electrically connected to the first end of the second upper bridge arm, the second end of the first upper bridge arm is electrically connected to the first end of the first lower bridge arm, the second end of the second upper bridge arm is electrically connected to the first end of the second lower bridge arm, and the second end of the first lower bridge arm is electrically connected to the second end of the second lower bridge arm, wherein the first end of the first upper bridge arm and the first end of the second upper bridge arm of the first single-phase full-bridge structure are electrically connected to the DC bus, the first upper bridge arm of the second single-phase full-bridge structure is electrically connected to the second end of the first lower bridge arm of the first single-phase full-bridge structure, the second upper bridge arm of the second single-phase full-bridge structure is electrically connected to the second end of the second lower bridge arm of the first single-phase full-bridge structure, the first upper bridge arm of the third single-phase full-bridge structure is electrically connected to the second end of the first lower bridge arm of the second single-phase full-bridge structure, the second upper bridge arm of the third single-phase full-bridge structure is electrically connected to the second end of the second lower bridge arm of the second single-phase full-bridge structure, and the second end of the first lower bridge arm and the second end of the second lower bridge arm of the third single-phase full-bridge structure are electrically connected to the DC bus.

[0044] When a certain bridge arm fails, the impact of the failure can be effectively limited to the faulty bridge arm without affecting other bridge arms due to the independent connection between the bridge arms (e.g., no direct electrical connection between the first upper bridge arm and the first lower bridge arm, and no direct electrical connection between the second upper bridge arm and the second lower bridge arm). This isolation mechanism helps to maintain system operation to some extent, reduces the impact of the failure, and improves the fault tolerance and reliability of the entire system. The special design of the bridge arm connection structure allows the converter control system to independently control each upper bridge arm and lower bridge arm, which means that the converter can achieve more precise current regulation and voltage control by adjusting the turn-on and turn-off of different bridge arms. This flexibility is particularly important in dealing with grid voltage fluctuations, fault recovery, and other situations. By controlling the turn-on and turn-off times of the bridge arms, the converter can achieve soft switching during commutation, reduce device switching losses, prolong device life, and reduce electromagnetic interference and noise generated by the system. In some embodiments, as shown in FIG. 13, each bridge arm includes a plurality of series-connected full-controlled modules 13, and each full-controlled module 13 includes a full-controlled device and a voltage balancing circuit. Figure 5

[0045] ​Since the full-control module includes multiple full-control devices in series, each device only needs to withstand a fraction of the total voltage, greatly reducing the voltage stress on individual devices. This is particularly important for high-voltage direct current transmission systems, as the voltage withstand capability of the devices directly affects the reliability and cost of the converter. The voltage equalization circuit integrated within the full-control module is responsible for distributing the voltage more evenly among the series-connected full-control devices. This avoids overheating and potential failure of devices due to voltage imbalance, improving the operational stability and lifespan of the converter. The series-connected full-control modules increase the redundancy of the converter. If a module or device fails, the converter can still operate through other functional modules, reducing the risk of system failure due to single-point failure. Each full-control module can be independently controlled, which gives the converter more precise regulation capabilities. During commutation, specific modules can be precisely triggered or turned off as needed to optimize the current path and voltage waveform, improving the efficiency and quality of the commutation.

[0046] In this embodiment, each bridge arm includes multiple full-control modules in series, which are composed of electrically connected full-control devices and voltage equalization circuits. This design allows the bridge arm to withstand higher voltages while ensuring even voltage distribution among the series-connected devices through the voltage equalization circuit, effectively preventing device damage due to uneven voltage. The addition of the voltage equalization circuit not only extends the lifespan of the devices but also optimizes the voltage characteristics during commutation, allowing the converter to more stably control the voltage stress on each bridge arm during operation. In addition, by independently adjusting the trigger angle of each bridge arm, the converter is given greater control freedom, ensuring the normal operation of other bridge arms even in the case of single-phase failure of the AC power grid, thereby avoiding the impact of commutation failure on the entire system. This technical solution significantly improves the reliability, operational efficiency, and economy of the series-connected current source converter by reducing the series level of individual full-control devices and increasing the independent control capability between bridge arms. Of course, in other embodiments, the specific implementation of the voltage equalization circuit can be adjusted according to the actual voltage level and device characteristics to meet the needs of different scenarios. By flexibly configuring the voltage equalization circuit, this embodiment can further enhance the stability and voltage control precision of the converter.

[0047] In some embodiments, a configurable current-limiting inductor is included in the full-control device series bridge arm to limit the high di / dt (voltage rate of change) when the full-control device turns on, as well as to limit the fault current size when an AC-DC fault occurs. The value of the current-limiting inductor is negatively related to the di / dt (voltage rate of change) tolerance of the full-control device and the fault current limit value.

[0048] Wherein, the di / dt tolerance capability analysis of the controllable device, firstly, according to the selected IGCT or IGBT device specification, the maximum di / dt change rate that the controllable device can withstand is determined, for example, the di / dt tolerance capability of IGCT can be 100A / μs, and the di / dt tolerance capability of IGBT can be 200A / μs. The fault current limit value determination includes: analyzing the maximum fault current value that the converter system can generate under the most serious fault condition (such as AC side short circuit fault). This usually requires detailed electrical simulation analysis of the entire DC power transmission system or power grid to determine the peak value of the current under fault condition.

[0049] In some embodiments, the current limiting inductor can be an inductor with a rated current of 15kA and an inductance value of 100 micro henries, which is connected in series between the controllable devices of each bridge arm.

[0050] Wherein, a switching device can also be connected in parallel across the current limiting inductor, and when the switching device is turned on, the current limiting inductor is short-circuited, and when the switching device is turned off, the current limiting inductor is connected to the circuit. For example: when the current limiting inductor fails, the switching device can be turned on to short-circuit the inductor. The switching device can be a mechanical switch such as a relay, or a switching device with a control terminal such as a mos tube or an IGBT.

[0051] In addition, in a controllable module, the parallel connection of controllable devices can achieve soft switching, improve current carrying capacity, and reduce the requirements on the voltage sharing circuit.

[0052] In some embodiments, the above controllable device is one of an IGCT device and an IGBT device.

[0053] In this embodiment, IGCT or IGBT devices are selected as the core components of the series-type current source converter. This choice allows the converter to fully utilize the fast response characteristics and high efficiency of the devices to achieve precise control of voltage and current. IGCT (Integrated Gate Commutated Thyristor) and IGBT (Insulated Gate Bipolar Transistor) are ideal choices for building high-efficiency converters due to their excellent switching performance and low switching losses. Using these fully controlled devices, the converter can achieve natural commutation in coordination with the AC phase voltage, i.e., triggering the device to turn on or off at the voltage zero-crossing point, reducing losses and improving the smoothness of the commutation process. Furthermore, the inherent turn-off characteristics of these devices provide the converter with active turn-off capability, enabling forced commutation during grid faults, preventing commutation failures, and enhancing the system's fault tolerance and robustness. Overall, the series-type current source converter using IGCT or IGBT devices not only optimizes the commutation mechanism and reduces manufacturing costs, but also improves the system's stability and reliability, providing strong technical support for high-voltage direct current transmission. Of course, in other embodiments, the fully controlled device can also be other types of high-power semiconductor devices, as long as they can meet the converter's requirements for fast switching and high voltage withstand capability.

[0054] In some embodiments, such as Figure 6 As shown, the aforementioned fully controlled device is an IGCT device 111, and the aforementioned voltage equalization circuit includes: a surge arrester 112, the first terminal of which is electrically connected to the anode of the IGCT device 111, and the second terminal of which is electrically connected to the cathode of the IGCT device 111; a first diode D1, the anode of which is electrically connected to the first terminal of the surge arrester 112; a first resistor module R1, the first terminal of which is electrically connected to the anode of the first diode D1, and the second terminal of which is electrically connected to the cathode of the first diode D1; and a first capacitor module C1, the first terminal of which is electrically connected to the second terminal of the first resistor module R1 and the cathode of the first diode D1, respectively, and the second terminal of which is electrically connected to the second terminal of the surge arrester 112.

[0055] Specifically, the lightning arrester is connected in parallel with the anode and cathode of the IGCT device, which absorbs transient overvoltage and protects the IGCT device from voltage spikes. Meanwhile, the nonlinear characteristics of the lightning arrester help to achieve voltage equalization, ensuring uniform distribution of device voltage in series configuration and avoiding damage to individual devices due to excessive voltage. The first capacitor module C1 is connected in parallel with the IGCT device, forming a snubber circuit. During the IGCT device turn-off process, the capacitor can store the residual energy of the device and then release it at a lower voltage and current slope, achieving zero voltage switching (ZVS) or near zero voltage switching, effectively reducing switching loss and improving overall converter efficiency. The first resistor module R1 is connected in series with the capacitor C1, together forming an overvoltage clamping circuit for the IGCT device. In the device turn-off moment, if the voltage rise rate is too fast, the resistor and capacitor can jointly limit the voltage rise rate and absorb excess charge, preventing the device from being impacted by overvoltage and ensuring its safe operation. The role of the first diode D1 is to provide a bypass during the reverse recovery of the IGCT device, allowing the reverse recovery current to flow through the diode instead of the main IGCT device, reducing the reverse recovery energy and thus reducing the temperature rise and loss of the device during high-frequency switching. In the entire full-control module, the lightning arrester, the first diode D1, the first resistor module R1, and the first capacitor module C1 together form an effective fault isolation circuit. Once the IGCT device fails, these passive elements can quickly respond to limit the fault range and prevent the fault current from affecting adjacent modules or other parts of the system.

[0056] In this embodiment, the full-control module integrates IGCT devices, lightning arresters, first diodes, first resistor modules, and first capacitor modules. The core of this design is to build a complete protection and voltage equalization circuit around the IGCT device. The lightning arrester is directly connected to the anode and cathode of the IGCT device to absorb overvoltage and protect the power device from voltage spikes. The first diode and the first resistor module are connected in series to form a current limiting and voltage stabilizing branch, which is connected in parallel with the lightning arrester to ensure safe operation of the circuit under abnormal conditions. The first capacitor module is further connected in parallel across the IGCT device for voltage equalization and energy storage, making the voltage stress of the device more uniform during switching and improving the power conversion efficiency of the circuit. Overall, this full-control module design not only strengthens the protection of power devices but also effectively improves voltage distribution, reduces the risk of voltage stress concentration in series operation, and improves the stability and reliability of the converter. Through this series of carefully configured circuit elements, the full-control module can ensure the safety of the device while achieving efficient voltage equalization, providing more robust hardware support for the operation of the converter. In other embodiments, the number and configuration of the first capacitor module can be adjusted according to actual working conditions and requirements to meet the performance requirements of the circuit in different application scenarios.

[0057] In some embodiments, as shown in FIG. 1 1, the all-controlling device is an IGCT device 111, and the voltage equalization circuit includes: a lightning arrester 112, a first end of the lightning arrester 112 being electrically connected to an anode of the IGCT device 111, and a second end of the lightning arrester 112 being electrically connected to a cathode of the IGCT device 111; a second resistance module R2, a first end of the second resistance module R2 being electrically connected to the anode of the IGCT device 111; and a second capacitance module C2, a first pole of the second capacitance module C2 being electrically connected to a second end of the second resistance module R2, and a second pole of the second capacitance module C2 being electrically connected to the cathode of the IGCT device 111. Figure 7

[0058] The lightning arrester is directly connected across the anode and cathode of the IGCT device, used to absorb and clamp sudden rising voltage such as overvoltage caused by lightning strike or system transients. This protects the IGCT device from potential voltage peak impact, prevents device damage, and improves system anti-interference ability and reliability. The second capacitance module is connected in parallel with the IGCT device, capable of storing and releasing energy, especially during the switching transient process of the device. This helps to achieve soft switching, i.e. zero voltage switching (ZVS), when the IGCT device is turned off, thereby reducing switching loss and thermal stress, and improving the efficiency of the converter and the service life of the device. The second resistance module R2 is connected in series with the second capacitance module C2, forming an RC snubber circuit, used to clamp the voltage rise rate and avoid the IGCT device bearing excessive voltage gradient during reverse recovery. It can absorb reverse recovery energy, reduce the switching loss of the IGCT device, and optimize its switching performance. The combination of the lightning arrester and the RC snubber circuit provides a failsafe mechanism, capable of responding quickly when the device suddenly fails, protecting the entire module from chain reaction, limiting the scope of failure, and improving the survivability of the converter under abnormal conditions.

[0059] ​In this embodiment, the full control module uses an IGCT device as its core, combined with a surge arrester, a second resistor module, and a second capacitor module to form a highly efficient voltage equalization and protection circuit. A precise electrical connection is established between the IGCT device, the surge arrester, the resistor module, and the capacitor module. The first end of the surge arrester is connected to the anode of the IGCT, and the second end is connected to the cathode of the IGCT, forming an effective overvoltage protection path. Simultaneously, the first end of the second resistor module is also connected to the anode of the IGCT, while its second end is electrically connected to the cathode of the IGCT through the second capacitor module, constructing a voltage equalization circuit to ensure a balanced voltage distribution during IGCT operation. This design not only enhances the voltage withstand capability of the power semiconductor device but also effectively improves the stability and reliability of the entire converter valve through the reasonable configuration of the surge arrester and voltage equalization circuit. This allows the converter to operate more safely and efficiently in high-voltage direct current transmission scenarios, responding quickly and smoothly even in the event of fluctuations or faults in the AC power grid, avoiding damage to critical components and enhancing the overall performance and durability of the power system. In other embodiments not shown, this structure can also be optimized by adjusting circuit parameters or replacing other types of fully controlled devices to further improve its adaptability and flexibility and meet the needs of different operating conditions.

[0060] In some embodiments, such as Figure 8 As shown, the aforementioned fully controlled device is an IGBT device 113. The aforementioned voltage equalization circuit includes: a second diode D2, the anode of which is electrically connected to the first terminal of the IGBT device 113; a third resistor module R3, the first terminal of which is electrically connected to the anode of the second diode D2, and the second terminal of which is electrically connected to the cathode of the second diode D2; and a third capacitor module C3, the first terminal of which is electrically connected to the second terminal of the third resistor module R3 and the cathode of the second diode D2, respectively, and the second terminal of which is electrically connected to the second terminal of the IGBT device 113.

[0061] In this embodiment, the full-control module adopts a combination of IGBT devices, the second diode, the third resistance module, and the third capacitor module. The first pole of the IGBT device is connected to the anode of the second diode, which is connected to the first end of the third resistance module, while the second end of the third resistance module is connected to the cathode of the second diode and the first pole of the third capacitor module. The second pole of the third capacitor module is connected to the second pole of the IGBT device. This design not only ensures the electrical connection between devices, but also provides necessary voltage clamping protection and energy buffering for the IGBT device, making the application of the full-control module in the high-voltage direct current transmission system more secure and reliable. During the operation of the converter, the IGBT device is responsible for the on-off control of the current, while the diode, resistance, and capacitor modules cooperate to form a protection circuit that can provide voltage clamping during device shutdown to avoid high reverse voltage damaging the IGBT. At the same time, based on the voltage sharing mechanism of the capacitor, the voltage balance between the series devices is ensured, improving the operational stability of the entire converter. This modular full-control device design not only simplifies the structure of the converter, but also optimizes the working conditions of the devices, improving the overall performance of the high-voltage direct current transmission system.

[0062] In this embodiment, the full-control module adopts a combination of IGBT devices, the second diode, the third resistance module, and the third capacitor module. The first pole of the IGBT device is connected to the anode of the second diode, which is connected to the first end of the third resistance module, while the second end of the third resistance module is connected to the cathode of the second diode and the first pole of the third capacitor module. The second pole of the third capacitor module is connected to the second pole of the IGBT device. This design not only ensures the electrical connection between devices, but also provides necessary voltage clamping protection and energy buffering for the IGBT device, making the application of the full-control module in the high-voltage direct current transmission system more secure and reliable. During the operation of the converter, the IGBT device is responsible for the on-off control of the current, while the diode, resistance, and capacitor modules cooperate to form a protection circuit that can provide voltage clamping during device shutdown to avoid high reverse voltage damaging the IGBT. At the same time, based on the voltage sharing mechanism of the capacitor, the voltage balance between the series devices is ensured, improving the operational stability of the entire converter. This modular full-control device design not only simplifies the structure of the converter, but also optimizes the working conditions of the devices, improving the overall performance of the high-voltage direct current transmission system.

[0063] Some embodiments, such as Figure 9As shown, the above-mentioned all-controlling device is an IGBT device 113, and the above-mentioned voltage equalization circuit comprises: the IGBT device 113; a fourth resistance module R4, a first end of the fourth resistance module R4 being electrically connected with a first pole of the IGBT device 113; a fourth capacitance module C4, a first pole of the fourth capacitance module C4 being electrically connected with a second end of the fourth resistance module R4, and a second pole of the fourth capacitance module C4 being electrically connected with a second pole of the IGBT device 113.

[0064] The fourth capacitance module C4 is connected in parallel with the IGBT device, which can provide a bypass for the current through the device at the moment of IGBT device turn-off, store energy and delay voltage rise, so that the IGBT can turn off under near-zero voltage condition, realize zero-voltage turn-off (ZVS) or near-soft switching, significantly reduce switching loss and improve inverter efficiency. When the IGBT changes from on-state to off-state, the internal parasitic diode will experience a reverse recovery process, generating a reverse recovery current. The RC circuit formed by the fourth resistance module R4 and the capacitance C4 can absorb and dissipate this part of reverse recovery energy, protect the IGBT from overvoltage or overheating damage caused by reverse recovery current, and prolong the service life of the device. The combination of the fourth capacitance module C4 and the fourth resistance module R4 helps to clamp the voltage across the IGBT, especially during the off process. This ensures the stable operation of the IGBT in a high-voltage environment, reducing the risk of switching loss and device damage caused by voltage spikes. The presence of the RC circuit provides a certain degree of fault protection. If the IGBT device fails, such as overvoltage or overcurrent, the RC circuit can absorb the excess energy instantaneously, reducing the impact on the entire module and system, providing a fault isolation mechanism to limit the scope of the failure.

[0065] In this embodiment, the all-controlling module comprises an IGBT device and a fourth resistance module and a fourth capacitance module connected in series with the IGBT device. The first pole of the IGBT device is connected with the first end of the fourth resistance module, and the second end of the fourth resistance module is connected with the first pole of the fourth capacitance module, and the second pole of the fourth capacitance module is connected with the second pole of the IGBT device. This structure design realizes the protection and control of the IGBT device, and the fourth resistance module and the fourth capacitance module together constitute a buffer circuit of the IGBT device, which can effectively absorb the instantaneous energy in the switching process of the device, suppress overvoltage, reduce switching loss, and improve the stability and efficiency of the entire inverter. Through the controllability of the IGBT device combined with the protection of the buffer circuit, this embodiment can realize the active turn-off of the inverter under fault conditions, avoid bridge arm short circuit, and thus improve the fault tolerance and operation reliability of the inverter. In other embodiments not shown, the specific parameters and structure of the buffer circuit can also be adjusted according to actual needs to adapt to inverter applications under different voltage levels and working conditions.

[0066] In some embodiments, the fourth resistance module includes multiple resistors in series and / or multiple resistors in parallel, and the fourth capacitance module includes multiple capacitors in series and / or multiple capacitors in parallel. Similarly, the first resistance module, the second resistance module, and the third resistance module can each include multiple resistors in series and / or multiple resistors in parallel, and the first capacitance module, the second capacitance module, and the third capacitance module can each include multiple capacitors in series and / or multiple capacitors in parallel.

[0067] In the present embodiment, the fourth resistance module and the fourth capacitance module employ a combination of multiple resistors in series and / or in parallel, and multiple capacitors in series and / or in parallel. This design allows the converter to exhibit higher adaptability and efficiency when facing different voltage and current demands. The series and parallel structure not only enhances the voltage withstand and capacity of the module, but also provides voltage and current equalization effects, ensuring that each device bears more balanced pressure and current, thereby prolonging the device life and improving the system reliability. In addition, by flexibly adjusting the number and combination of resistors and capacitors in the module, the dynamic response of the converter can be optimized, better matching the energy conversion between the alternating current grid and the direct current load. This not only simplifies the design of the converter and reduces costs, but also improves its performance and fault handling capability in high-voltage direct current transmission scenarios. In summary, the combination of the fourth resistance module and the fourth capacitance module greatly enhances the functionality of the converter, making it perform well in various working conditions, and is an important component in the present embodiment.

[0068] In some embodiments, as shown in FIG. 1, the current source converter further includes a DC side inductor Ldc, a first end of the DC side inductor Ldc being electrically connected to the first-stage single-phase full-bridge structure 10, and a second end of the DC side inductor Ldc being configured to be electrically connected to a DC bus. Figure 1

[0069] ​In this embodiment, the first end of the DC side inductor is electrically connected with the first single-phase full-bridge structure, and the second end is used to be electrically connected with the DC bus. The DC side inductor plays a key role in current smoothing and fault protection here. In the normal operation state of the converter, the DC side inductor can effectively suppress the fluctuation of the DC side current, ensure the smoothness of the DC voltage output, and thus improve the power quality and transmission efficiency of the entire DC power transmission system. When a single-phase ground fault or other abnormal conditions occur in the AC power grid, the DC side inductor can store energy in a short time to provide continuous current support for the converter, prevent the sudden drop of the DC voltage, and play a buffering and protection role. In addition, the DC side inductor can also coordinate the energy balance of the converter during the fault period, avoid greater impact on the system caused by the fault current, and thus improve the operation reliability of the converter and the stability of the system. This design not only optimizes the overall performance of the current source converter, but also enhances its ability to cope with power grid faults, making the series bridge converter topology more robust in practical applications.

[0070] The embodiments of the present application also provide a DC power transmission system, which comprises the current source converter 01. Figure 10 As shown in the figure, the DC power transmission system comprises the current source converter 01. The DC power transmission system further comprises a sending-end converter 02, wherein the current source converter 01 is a receiving-end converter.

[0071] The present application provides a DC power transmission system, which comprises the current source converter. The converter adopts a topology structure constructed by series connection of multi-phase full-bridge circuits, each bridge arm is composed of series connection of fully controlled power semiconductor devices, and natural commutation is realized by using the phase voltage of the AC power grid, which effectively reduces the series number of the devices, simplifies the design of the converter valve, and reduces the manufacturing cost. During normal operation, the power semiconductor devices perform commutation at the zero-crossing point of the phase voltage, realize zero-voltage turn-on, reduce switching loss, and improve the operation efficiency of the converter. When a single-phase fault occurs in the AC power grid, the present embodiment can limit the influence of commutation failure to the local bridge arm of the fault phase, and the unaffected bridge arm can operate normally, avoiding the risk of through of the entire converter station caused by commutation failure of the traditional converter, and significantly improving the operation reliability and fault tolerance of the DC system. In summary, the technical solution of the present application has significant technical effects in reducing the number of series devices and improving the fault tolerance performance, and is particularly suitable for use in high-voltage DC power transmission systems to enhance the stability and economy thereof.

[0072] In addition, in the DC power transmission system, if the sending end adopts the traditional LCC converter and the receiving end adopts the proposed series bridge converter topology, the complementary advantages of both can be fully utilized. The LCC at the sending end has mature and reliable high-power rectification capability, which is suitable for high-voltage and high-power DC transmission. The topology at the receiving end has significant advantages in voltage stress, device utilization rate and fault tolerance performance. The fewer series devices reduce the complexity and cost of the converter valve, and improve the voltage sharing characteristics, making it easier to achieve voltage equalization. In the case of AC system fault or commutation failure, the topology can limit the impact to the local module, thereby maintaining the stable transmission of part of the DC power and significantly improving the reliability and operation flexibility of the DC system. In addition, the topology has soft switching characteristics, which can effectively reduce the converter loss and harmonic content and improve the power quality at the receiving end. Therefore, the combination of the LCC at the sending end and the series bridge converter at the receiving end not only ensures the high-power DC transmission capability, but also improves the stability and economy of the system, which is suitable for application in long-distance and large-capacity DC projects.

[0073] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present disclosure.

[0074] It should also be noted that the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that processes, methods, articles, or devices including a series of elements not only include those elements, but also include other elements not explicitly listed, or inherent to such processes, methods, articles, or devices. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or device including the element.

[0075] From the above description, it can be seen that the above-described embodiments of the present application achieve the following technical effects:

[0076] 1) The above-mentioned current source converter of the application comprises: a plurality of single-phase full-bridge structures connected in series, each bridge arm comprising at least one fully controlled device; a plurality of phase-changing transformers, the first end of the primary coil of the phase-changing transformer being electrically connected to the first node of the single-phase full-bridge structure, the second end of the primary coil of the phase-changing transformer being electrically connected to the second node of the single-phase full-bridge structure, the first end of the secondary coil of any two phase-changing transformers being electrically connected, and the second end of the secondary coil of the phase-changing transformer being used for electrical connection with the alternating current load. The first node is the node connected by the first upper bridge arm and the corresponding first lower bridge arm of the single-phase full-bridge structure, and the second node is the node connected by the second upper bridge arm and the corresponding second lower bridge arm of the single-phase full-bridge structure. By using the turn-off capability of the fully controlled power semiconductor device and the cooperative work of the bridge transformer, the risk of commutation failure of the remaining two phases when the power grid single-phase fault occurs is reduced, the operation reliability of the converter is improved, and the problem of high risk of commutation failure of the traditional current source converter is solved.

[0077] 2) The application provides a direct current transmission system, which comprises the above-mentioned current source converter. The converter adopts a topology structure constructed by connecting a plurality of single-phase full-bridge circuits in series, each bridge arm is composed of fully controlled power semiconductor devices connected in series, and natural commutation is realized by using the alternating current grid phase voltage, thereby effectively reducing the number of series devices, simplifying the design of the converter, and reducing the manufacturing cost. During normal operation, the power semiconductor devices perform commutation at the zero-crossing point of the phase voltage, zero-voltage conduction is realized, switching loss is reduced, and the operation efficiency of the converter is improved. When a single-phase fault occurs in the alternating current grid, the application can limit the influence of commutation failure to the local bridge arm of the fault phase, and the unaffected bridge arm can operate normally, thereby avoiding the risk of direct through of the entire converter station caused by commutation failure of the traditional converter, and significantly improving the operation reliability and fault tolerance capability of the direct current system. In summary, the technical solution of the application has significant technical effects in reducing the number of series devices and improving the fault tolerance performance, and is particularly suitable for use in a high-voltage direct current transmission system to enhance its stability and economy.

[0078] The above-mentioned only for the preferred embodiments of the application, and not for limiting the application, for those skilled in the art, the application can have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A current source converter, characterized in that, include: Multiple single-phase full-bridge structures connected in series, each single-phase full-bridge structure including an upper bridge arm and a lower bridge arm, each bridge arm including at least one fully controlled device, the first single-phase full-bridge structure and the last single-phase full-bridge structure are both used for electrical connection to the DC bus; Multiple phase change transformers are provided. The first end of the primary coil of each phase change transformer is electrically connected to the first node of the single-phase full-bridge structure, and the second end of the primary coil of each phase change transformer is electrically connected to the second node of the single-phase full-bridge structure. The first ends of the secondary coils of any two phase change transformers are electrically connected, and the second end of the secondary coil of each phase change transformer is used to connect to an AC load. The first node is the node connecting the first upper bridge arm and the corresponding first lower bridge arm of the single-phase full-bridge structure, and the second node is the node connecting the second upper bridge arm and the corresponding second lower bridge arm of the single-phase full-bridge structure. Each phase change transformer corresponds one-to-one with the single-phase full-bridge structure.

2. The current source converter according to claim 1, characterized in that, Each of the bridge arms includes multiple series-connected full control modules, and each full control module includes the full control device and the voltage equalization circuit that are electrically connected.

3. The current source converter according to claim 1, characterized in that, The single-phase full-bridge structure has three parts: two upper bridge arms (first upper bridge arm and second upper bridge arm) and two lower bridge arms (first lower bridge arm and second lower bridge arm). The first end of the first upper bridge arm is electrically connected to the first end of the second upper bridge arm, and the second end of the first upper bridge arm is electrically connected to the first end of the first lower bridge arm. The second end of the second upper bridge arm is electrically connected to the first end of the second lower bridge arm, and the second end of the first lower bridge arm is electrically connected to the second lower bridge arm. In the first single-phase full-bridge structure, the first ends of both the first upper bridge arm and the second upper bridge arm are electrically connected to the DC bus. In the second single-phase full-bridge structure... The first upper bridge arm of the structure is electrically connected to the second end of the first lower bridge arm of the first single-phase full-bridge structure; the second upper bridge arm of the second single-phase full-bridge structure is electrically connected to the second end of the second lower bridge arm of the first single-phase full-bridge structure; the first upper bridge arm of the third single-phase full-bridge structure is electrically connected to the second end of the first lower bridge arm of the second single-phase full-bridge structure; the second upper bridge arm of the third single-phase full-bridge structure is electrically connected to the second end of the second lower bridge arm of the second single-phase full-bridge structure; and the second ends of the first lower bridge arm and the second lower bridge arm of the third single-phase full-bridge structure are both electrically connected to the DC bus.

4. The current source converter according to claim 2, characterized in that, The fully controlled device is an IGCT device, and the voltage equalization circuit includes: A surge arrester, wherein the first end of the surge arrester is electrically connected to the anode of the IGCT device, and the second end of the surge arrester is electrically connected to the cathode of the IGCT device; A first diode, the anode of which is electrically connected to the first terminal of the surge arrester; A first resistor module, wherein a first end of the first resistor module is electrically connected to the anode of the first diode, and a second end of the first resistor module is electrically connected to the cathode of the first diode; The first capacitor module has its first terminal electrically connected to the second terminal of the first resistor module and the cathode of the first diode, respectively, and its second terminal electrically connected to the second terminal of the surge arrester.

5. The current source converter according to claim 2, characterized in that, The fully controlled device is an IGCT device, and the voltage equalization circuit includes: A surge arrester, wherein the first end of the surge arrester is electrically connected to the anode of the IGCT device, and the second end of the surge arrester is electrically connected to the cathode of the IGCT device; The second resistor module has its first terminal electrically connected to the anode of the IGCT device. The second capacitor module has its first terminal electrically connected to the second terminal of the second resistor module, and its second terminal electrically connected to the cathode of the IGCT device.

6. The current source converter according to claim 2, characterized in that, The fully controlled device is an IGBT device, and the voltage equalization circuit includes: The second diode, the anode of which is electrically connected to the first electrode of the IGBT device; The third resistor module has its first end electrically connected to the anode of the second diode and its second end electrically connected to the cathode of the second diode. The third capacitor module has its first terminal electrically connected to the second terminal of the third resistor module and the cathode of the second diode, and its second terminal electrically connected to the second terminal of the IGBT device.

7. The current source converter according to claim 2, characterized in that, The fully controlled device is an IGBT device, and the voltage equalization circuit includes: The fourth resistor module, wherein the first terminal of the fourth resistor module is electrically connected to the first electrode of the IGBT device; The fourth capacitor module has its first terminal electrically connected to the second terminal of the fourth resistor module, and its second terminal electrically connected to the second terminal of the IGBT device.

8. The current source converter according to claim 7, characterized in that, The fourth resistor module includes multiple resistors connected in series and / or multiple resistors connected in parallel, and the fourth capacitor module includes multiple capacitors connected in series and / or multiple capacitors connected in parallel.

9. The current source converter according to claim 1, characterized in that, Also includes: A DC-side inductor, wherein the first end of the DC-side inductor is electrically connected to the first-stage single-phase full-bridge structure, and the second end of the DC-side inductor is used to be electrically connected to the DC bus.

10. A DC transmission system, characterized in that, include: The current source converter according to any one of claims 1 to 9.

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