Current source converter of hybrid controllable capacitor bank and direct current power transmission system

Abstract

The utility model provides a current source converter of a hybrid controllable capacitor bank and a direct current power transmission system. The converter comprises a plurality of converter transformers; a converter bridge circuit; the hybrid controllable capacitor bank comprises a first passive filter and a controllable capacitor bank which are electrically connected, the controllable capacitor bank comprises a plurality of fully-controlled devices and capacitors which are electrically connected, and each phase alternating current end of the converter bridge circuit is electrically connected with the first passive filter; the first ends of the filter reactors are electrically connected with the hybrid controllable capacitor bank and one phase alternating current end of the converter bridge circuit respectively, and the second ends of the filter reactors are electrically connected with the second ends of the corresponding converter transformers. According to the converter, the first passive filter is electrically connected with the controllable capacitor bank, so that the output alternating voltage of the controllable capacitor bank is reduced, and the number of sub-modules of the controllable capacitor bank is directly reduced under the condition that the voltage grade of a single sub-module is not changed, so that the cost and the loss are reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of direct current transmission, in particular to a hybrid controllable capacitor bank current source converter and a direct current transmission system. BACKGROUND

[0002] In the existing current source converter, a controllable current source converter is used as a main valve, and a controllable capacitor bank is used as a support valve. The existing support valve generally adopts a controllable capacitor bank scheme based on sub-module cascading. Since the controllable capacitor bank needs to provide reactive compensation for the main valve, the alternating current output voltage is high. Therefore, a large number of sub-modules need to be cascaded, resulting in increased cost and loss. SUMMARY

[0003] The main purpose of the present application is to provide a hybrid controllable capacitor bank current source converter and a direct current transmission system to at least solve the problem of high cost and loss of the existing current source converter.

[0004] In order to achieve the above purpose, according to one aspect of the present application, a hybrid controllable capacitor bank current source converter is provided, comprising: a plurality of converter transformers, a first end of the converter transformer being used for electrical connection with an alternating current load; a converter bridge circuit having a plurality of phase alternating current ends, a direct current end of the converter bridge circuit being used for connecting a direct current bus, the converter bridge circuit being used for active power transmission; a hybrid controllable capacitor bank comprising a first passive filter and a controllable capacitor bank electrically connected, the controllable capacitor bank comprising a plurality of fully controlled devices and a capacitor electrically connected, each phase alternating current end of the converter bridge circuit being electrically connected with the first passive filter, the hybrid controllable capacitor bank being used for reactive power support; a plurality of filter reactances, a first end of the filter reactance being electrically connected with the hybrid controllable capacitor bank and one phase alternating current end of the converter bridge circuit respectively, a second end of the filter reactance being electrically connected with a second end of the corresponding converter transformer.

[0005] Optionally, the first passive filter is connected in series or parallel with the controllable capacitor bank.

[0006] Optionally, the current source converter further comprises a second passive filter, wherein an input end of the first passive filter is electrically connected with a phase alternating current end of the converter bridge circuit and a first end of the second passive filter respectively, a second end of the second passive filter is electrically connected with an input end of the controllable capacitor bank, the first passive filter and the second passive filter have the same structure or different structures.

[0007] Optionally, the first passive filter comprises: a first capacitor module; a second capacitor module, a first end of the second capacitor module being electrically connected with a second end of the first capacitor module; a first inductor module, a first end of the first inductor module being electrically connected with a second end of the second capacitor module; a first resistor module, a first end of the first resistor module being electrically connected with the second end of the first capacitor module; wherein in the case that the first passive filter is connected in series with the controllable capacitor bank, the first end of the first capacitor module is electrically connected with the phase alternating current end of the converter bridge circuit, and the second end of the first inductor module and the second end of the first resistor module are both electrically connected with the input end of the controllable capacitor bank; in the case that the first passive filter is connected in parallel with the controllable capacitor bank, the first end of the first capacitor module is electrically connected with the phase alternating current end of the converter bridge circuit and the input end of the controllable capacitor bank.

[0008] Optionally, the first passive filter comprises: a third capacitor module; a second inductor module, a first end of the second inductor module being electrically connected with a second end of the third capacitor module; a third inductor module, a first end of the third inductor module being electrically connected with a second end of the second inductor module; a fourth capacitor module, a first end of the fourth capacitor module being electrically connected with the second end of the second inductor module and the first end of the third inductor module respectively, and a second end of the fourth capacitor module being electrically connected with a second end of the third inductor module; a second resistor module, a first end of the second resistor module being electrically connected with the second end of the third capacitor module; wherein in the case that the first passive filter is connected in series with the controllable capacitor bank, the first end of the third capacitor module is electrically connected with the phase alternating current end of the converter bridge circuit, and the second end of the third inductor module, the second end of the fourth capacitor module and the second end of the second resistor module are all electrically connected with the input end of the controllable capacitor bank; in the case that the first passive filter is connected in parallel with the controllable capacitor bank, the first end of the third capacitor module is electrically connected with the phase alternating current end of the converter bridge circuit and the input end of the controllable capacitor bank.

[0009] Optionally, the controllable capacitor bank comprises a plurality of connected sub-modules, and the connection mode of the plurality of sub-modules comprises any one of an angular chain connection and a star chain connection, wherein the sub-module comprises a sixth capacitor module and a first full-controlled device, a second full-controlled device, a third full-controlled device and a fourth full-controlled device connected in a full-bridge structure, a first end of the first full-controlled device is electrically connected with a second end of the second full-controlled device, a second end of the first full-controlled device is electrically connected with a second end of the third full-controlled device, a first end of the third full-controlled device is electrically connected with a second end of the fourth full-controlled device, a first end of the second full-controlled device is electrically connected with a first end of the fourth full-controlled device, a first end of the sixth capacitor module is electrically connected with the second end of the first full-controlled device and the second end of the third full-controlled device respectively, and a second end of the sixth capacitor module is electrically connected with the first end of the second full-controlled device and the first end of the fourth full-controlled device respectively; or the sub-module comprises a fifth full-controlled device and a sixth full-controlled device connected in a half-bridge structure, a first end of the fifth full-controlled device is electrically connected with a second end of the sixth full-controlled device, and a seventh capacitor module, a first end of the seventh capacitor module is electrically connected with a second end of the fifth full-controlled device, and a second end of the seventh capacitor module is electrically connected with a first end of the sixth full-controlled device.

[0010] Optionally, the current source converter further comprises an energy storage module connected in parallel with the sub-module.

[0011] Optionally, the converter bridge circuit comprises a DC reactor and a converter bridge arm, the converter bridge arm comprises a plurality of upper bridge arms and a plurality of lower bridge arms, a first end of the upper bridge arm is connected to a first DC end, a first end of the lower bridge arm is connected to a second DC end, a second end of one of the upper bridge arms and a second end of a corresponding one of the lower bridge arms are connected to a corresponding phase AC end, the first DC end is electrically connected to the DC bus through the DC reactor, and the second DC end is directly connected to the DC bus.

[0012] Optionally, the converter bridge circuit further comprises a saturation reactor, the second end of the upper bridge arm is electrically connected with the second end of the lower bridge arm through the saturation reactor, and / or the second end of the lower bridge arm is electrically connected with the second end of the upper bridge arm through the saturation reactor.

[0013] According to another aspect of the present application, a DC power transmission system is provided, comprising a sending end current source converter and a receiving end current source converter, at least one of the sending end current source converter and the receiving end current source converter is the current source converter of any one of the mixed controllable capacitor banks, and a DC end of the sending end current source converter is electrically connected with a DC end of the receiving end current source converter.

[0014] According to the technical scheme of the application, the current source converter of the mixed controllable capacitor bank in the above description comprises: a plurality of converter transformers, the first end of the converter transformer is used for electrical connection with an alternating current load; a converter bridge circuit, having a plurality of phase alternating current ends, the direct current end of the converter bridge circuit is used for connecting a direct current bus, and the converter bridge circuit is used for active power transmission; a mixed controllable capacitor bank, comprising a first passive filter and a controllable capacitor bank which are electrically connected, the controllable capacitor bank comprises a plurality of fully controlled devices and a capacitor which are electrically connected, each phase alternating current end of the converter bridge circuit is electrically connected with the first passive filter, and the mixed controllable capacitor bank is used for reactive power support; and a plurality of filter reactances, the first end of the filter reactance is electrically connected with the mixed controllable capacitor bank and one phase alternating current end of the converter bridge circuit respectively, and the second end of the filter reactance is electrically connected with the second end of the corresponding converter transformer. The converter reduces the output alternating current voltage of the controllable capacitor bank by electrically connecting the first passive filter with the controllable capacitor bank, directly reduces the number of sub-modules of the controllable capacitor bank in the case of unchanged voltage level of a single sub-module, and thus reduces the cost and loss. BRIEF DESCRIPTION OF DRAWINGS

[0015] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the application, and together with the description of the exemplary embodiments of the present application, serve to explain the present application, and do not constitute any improper limitation to the present application. In the drawings:

[0016] Figure 1 A structure schematic diagram of a current source converter of a mixed controllable capacitor bank in a first series connection is shown according to an embodiment provided by the present application;

[0017] Figure 2 A structure schematic diagram of a current source converter of a mixed controllable capacitor bank in a parallel connection is shown according to an embodiment provided by the present application;

[0018] Figure 3 A structure schematic diagram of a current source converter of a mixed controllable capacitor bank in a second series connection is shown according to an embodiment provided by the present application;

[0019] Figure 4 A structure schematic diagram of a current source converter of a mixed controllable capacitor bank in a third series connection is shown according to an embodiment provided by the present application;

[0020] Figure 5 A structure schematic diagram of a current source converter of a mixed controllable capacitor bank in a fourth series connection is shown according to an embodiment provided by the present application;

[0021] FIG. 6(a) shows a schematic diagram of an angle type chain connected controllable capacitor bank according to an embodiment provided by the present application;

[0022] Fig. 6(b) shows a schematic diagram of a star-type chain-link controllable capacitor bank provided in an embodiment of the present application;

[0023] Fig. 7(a) shows a schematic diagram of an IGBT full-bridge sub-module structure provided in an embodiment of the present application;

[0024] Fig. 7(b) shows a schematic diagram of an IGBT half-bridge sub-module structure provided in an embodiment of the present application;

[0025] Fig. 8(a) shows a schematic diagram of an IGCT full-bridge sub-module structure provided in an embodiment of the present application;

[0026] Fig. 8(b) shows a schematic diagram of an IGCT half-bridge sub-module structure provided in an embodiment of the present application;

[0027] Fig. 9(a) shows a schematic diagram of another IGBT full-bridge sub-module structure provided in an embodiment of the present application;

[0028] Fig. 9(b) shows a schematic diagram of another IGBT half-bridge sub-module structure provided in an embodiment of the present application;

[0029] Figure 10 Fig. 10 shows a schematic diagram of a current source converter of another hybrid controllable capacitor bank provided in an embodiment of the present application;

[0030] Figure 11 Fig. 11 shows a schematic diagram of a converter bridge arm provided in an embodiment of the present application;

[0031] Figure 12 Fig. 12 shows a schematic diagram of another converter bridge arm provided in an embodiment of the present application;

[0032] Figure 13 Fig. 13 shows a schematic diagram of still another converter bridge arm provided in an embodiment of the present application;

[0033] Figure 14 Fig. 14 shows a schematic diagram of yet another converter bridge arm provided in an embodiment of the present application;

[0034] Figure 15 Fig. 15 shows a schematic diagram of AC voltage waveforms of an HCC, a first passive filter and a controllable capacitor bank provided in an embodiment of the present application;

[0035] Figure 16 Fig. 16 shows a schematic diagram of a DC power transmission system provided in an embodiment of the present application.

[0036] In the above drawings, the following reference signs are used:

[0037] 01, sending end current source converter; 02, receiving end current source converter; 10, converter transformer; 20, converter bridge circuit; 21, upper bridge arm; 22, lower bridge arm; 30, hybrid controllable capacitor bank; 31, first passive filter; 32, controllable capacitor bank; 321, sub-module; 40, saturated reactance; 50, energy storage module; C1, first capacitor module; C2, second capacitor module; C3, third capacitor module; C4, fourth capacitor module; C5, fifth capacitor module; C6, sixth capacitor module; C7, seventh capacitor module; L1, filter reactance; L2, first inductor module; L3, second inductor module; L4, third inductor module; R1, first resistor module; R2, second resistor module; L dc DC reactor; Q1, first fully controlled device; Q2, second fully controlled device; Q3, third fully controlled device; Q4, fourth fully controlled device; Q5, fifth fully controlled device; Q6, sixth fully controlled device. DETAILED DESCRIPTION

[0038] It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other without conflict. The technical solutions in the embodiments of the present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0039] 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 and in combination with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. 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.

[0040] 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 describe 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 including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0041] For the convenience of description, the following describes some nouns or terms related to the embodiments of the present application:

[0042] Full-controllable Composite Converter, F3C for short.

[0043] As introduced in the background, the F3C in the prior art includes a controllable current source converter as a main valve and a controllable capacitor bank as a support valve, has the characteristics of large capacity and low loss, can completely resist commutation failure and can realize decoupling control and flexible adjustment of active and reactive power, and has good application prospects in the field of high-power electric energy transmission conversion such as DC power transmission. The existing support valve generally adopts a controllable capacitor bank scheme based on sub-module cascading. Since the controllable capacitor bank needs to provide reactive power compensation for the main valve, the AC output voltage is relatively high. Therefore, a large number of sub-modules need to be cascaded, resulting in increased cost and loss.

[0044] To solve the problem of high cost and loss of the current source converter in the prior art, embodiments of the present application provide a current source converter of a hybrid controllable capacitor bank and a DC power transmission system.

[0045] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the drawings in the embodiments of the present application.

[0046] Figure 1 is a structural schematic diagram of the current source converter of the hybrid controllable capacitor bank according to the embodiments of the present application. As shown in Figure 1 the current source converter of the hybrid controllable capacitor bank includes: a plurality of converter transformers 10, a first end of the converter transformer 10 is used for electrical connection with an AC load; a converter bridge circuit 20 having a plurality of phase AC ends, a DC end of the converter bridge circuit 20 is used for connecting a DC bus, and the converter bridge circuit 20 is used for active power transmission; a hybrid controllable capacitor bank 30 including a first passive filter 31 and a controllable capacitor bank 32 electrically connected, the controllable capacitor bank 32 including a plurality of fully controllable devices and a capacitor electrically connected, each phase AC end of the converter bridge circuit 20 is electrically connected with the first passive filter 31, and the hybrid controllable capacitor bank 30 is used for reactive power support; a plurality of filter reactances L1, a first end of the filter reactance L1 is respectively electrically connected with the hybrid controllable capacitor bank 30 and one phase AC end of the converter bridge circuit 20, and a second end of the filter reactance L1 is electrically connected with a second end of the corresponding converter transformer 10.

[0047] The core idea of the F3C topology based on the hybrid controllable capacitor group in the above embodiment (hybrid controlled capacitor-F3C, referred to as HCC-F3C) is to replace the controllable capacitor group of the F3C with a hybrid controllable capacitor group, which is composed of a controllable capacitor group in series with a passive capacitor at the three-phase AC outlet. By replacing part of the sub-modules of the controllable capacitor group with passive devices, the cost and loss are reduced. Under the premise of using the same voltage and current level devices in the sub-modules, the key to reducing the cost and loss of the controllable capacitor group is to reduce the number of sub-modules, and the specific implementation is to reduce the AC voltage output by the controllable capacitor group. The hybrid controllable capacitor group reduces the maximum output AC voltage requirement of the controllable capacitor group by connecting a low-cost first passive filter in series at the outlet of the controllable capacitor group to bear part of the AC voltage, thereby reducing the number of sub-modules used.

[0048] It should be noted that there are actually three first passive filters, i.e. the current source converter has three phases, and then there are three first passive filters, one first passive filter connected to each phase, and only one controllable capacitor group. The controllable capacitor group has three input terminals, corresponding to the three phases of the current source converter. Then, in the case of the first passive filter and the controllable capacitor group in series, the a-phase input terminal of the controllable capacitor group is connected to the first passive filter connected to the a-phase, the b-phase input terminal of the controllable capacitor group is connected to the first passive filter connected to the b-phase, and the c-phase input terminal of the controllable capacitor group is connected to the first passive filter connected to the c-phase. And in the case of the first passive filter and the controllable capacitor group in parallel, the a-phase input terminal of the controllable capacitor group is directly connected to the a-phase AC terminal of the converter bridge circuit, the b-phase input terminal of the controllable capacitor group is directly connected to the b-phase AC terminal of the converter bridge circuit, and the c-phase input terminal of the controllable capacitor group is directly connected to the c-phase AC terminal of the converter bridge circuit.

[0049] By electrically connecting the first passive filter and the controllable capacitor group, the output AC voltage of the controllable capacitor group is reduced, and in the case of unchanged voltage level of a single sub-module, the number of sub-modules of the controllable capacitor group is directly reduced, thereby realizing the reduction of cost and loss.

[0050] The current source converter of the above-mentioned hybrid controllable capacitor bank of the present application comprises: a plurality of converter transformers, the first end of the converter transformer being used for electrical connection with an alternating current load; a converter bridge circuit, having a plurality of phase alternating current ends, the direct current end of the converter bridge circuit being used for connection with a direct current bus, the converter bridge circuit being used for active power transmission; a hybrid controllable capacitor bank, comprising a first passive filter and a controllable capacitor bank connected in series, the controllable capacitor bank comprising a plurality of fully controlled devices and a capacitor connected in series, each phase alternating current end of the converter bridge circuit being electrically connected with the first passive filter, the hybrid controllable capacitor bank being used for reactive power support; and a plurality of filter reactances, the first end of the filter reactance being electrically connected with the hybrid controllable capacitor bank and one phase alternating current end of the converter bridge circuit respectively, the second end of the filter reactance being electrically connected with the second end of the corresponding converter transformer. The converter reduces the output alternating current voltage of the controllable capacitor bank by electrically connecting the first passive filter with the controllable capacitor bank, directly reduces the number of sub-modules of the controllable capacitor bank in the case of unchanged voltage level of a single sub-module, and thus realizes the reduction of cost and loss.

[0051] In some embodiments, the above-mentioned first passive filter is connected in series or in parallel with the above-mentioned controllable capacitor bank. Figure 1 A structure schematic diagram of the controllable capacitor bank connected in series with the first passive filter. Figure 2 A structure schematic diagram of the controllable capacitor bank connected in parallel with the first passive filter.

[0052] In the case of the first passive filter and the controllable capacitor bank being in series, the voltage of the controllable capacitor bank is reduced, thus reducing the output alternating voltage of the controllable capacitor bank, so that the number of sub-modules in the controllable capacitor bank can be reduced, thereby reducing the cost and loss. In the case of the first passive filter and the controllable capacitor bank being in parallel, the capacity of the capacitor in the controllable capacitor bank can be reduced. In addition, the first passive filter and the controllable capacitor bank are in parallel, the first passive filter is responsible for fast commutation and partial reactive power compensation, and the controllable capacitor bank undertakes partial reactive power compensation and filtering function. The cooperation of the first passive filter and the controllable capacitor bank in parallel can be used for the controllable capacitor bank with inductance, that is, when the switching-off of the main valve (main valve) is turned off, the first passive filter acts as a low inductance loop, which can ensure the switching-off of the main valve and will not produce overvoltage. Because the first passive filter acts as a low inductance loop, the controllable capacitor bank can have inductance, avoiding the problem of high fault current rise rate and difficult protection of the controllable capacitor bank due to the lack of inductance current limiting of the controllable capacitor bank. The number of cascade sub-modules, the capacity of the capacitor and the device current capacity demand are reduced, and the cost and loss are reduced. Finally, the scheme combines the advantages of low cost and high technical maturity of the first passive filter and the controllable capacitor bank, effectively improving the technical economy and reliability of the overall system. That is, the parallel scheme ensures the low inductance loop of the first passive filter during the commutation of the main valve, and the controllable capacitor bank is used to emit and absorb reactive power, and absorb excess harmonic current, while avoiding the risk of overcurrent caused by the controllable capacitor bank.

[0053] Specifically, the existing F3C generally uses a controllable capacitor bank as a support valve, which also undertakes the functions of fast commutation, reactive power compensation and filtering of the main valve. In order to realize the fast commutation of the main valve, the alternating current outlet of the controllable capacitor bank cannot be configured with an alternating current inductor or connected to the main valve through a step-up transformer, and must use a sub-module cascade topology, with high voltage directly connected to the alternating current port of the main valve. There are the following problems: (1) When the alternating current port of the controllable capacitor bank fails, the lack of inductance current limiting results in high fault current rise rate and high protection difficulty. (2) The controllable capacitor bank needs to be directly connected to the outlet of the main valve, and the number of cascade sub-modules is large, resulting in high cost and loss. (3) The controllable capacitor bank undertakes the functions of filtering and reactive power regulation, resulting in large capacity of sub-module capacitors and large current capacity of devices, which is relatively high in cost.

[0054] Therefore, the above embodiment replaces the controllable capacitor bank in the traditional F3C by the parallel connection of the first passive filter (including a parallel capacitor) and the controllable capacitor bank: the first passive filter is responsible for fast commutation and partial reactive power compensation, and the controllable capacitor bank undertakes partial reactive power compensation and filtering function.

[0055] Compared with the traditional F3C, the above-mentioned embodiments have obvious advantages. Specifically, the cooperation of the first passive filter and the controllable capacitor bank avoids the problem of high AC port fault current rise rate and difficult protection caused by the lack of inductance current limiting of the controllable capacitor bank; the number of cascaded sub-modules, the capacitance value and the device current capacity demand are reduced, and the cost and loss are reduced. Finally, the scheme combines the advantages of low cost and high technical maturity of the first passive filter and the controllable capacitor bank, effectively improving the technical economy and reliability of the overall system.

[0056] In some other embodiments, the current source converter further comprises a second passive filter, wherein the input ends of the first passive filter are respectively electrically connected with the phase AC ends of the converter bridge circuit and the first end of the second passive filter, the second end of the second passive filter is electrically connected with the input end of the controllable capacitor bank, and the first passive filter and the second passive filter are the same or different in structure.

[0057] Wherein, the first passive filter and the second passive filter can jointly act to enhance the filtering effect of harmonics in the output current of the converter bridge circuit. Even if the harmonic components output by the converter bridge circuit change under different operating conditions, the combination of the two filters can provide more comprehensive filtering effect. The double-filter structure can better match the impedance characteristics of the power grid, reduce the resonance points in the power system, and improve the stability of the entire DC power transmission system. At the same time, the addition of the second passive filter can further reduce the influence of the controllable capacitor bank on the power grid and reduce the overall electromagnetic interference of the system. The second passive filter can take on the task of filtering harmonics to some extent, which means that the controllable capacitor bank does not need to be designed too large to cope with the harmonics of the converter bridge circuit. This can reduce the size of the controllable capacitor bank, reduce the manufacturing cost, and improve the economy of the system.

[0058] In addition, since the converter bridge circuit has three-phase output, each phase corresponds to a passive filter, i.e. there are three,

[0059] In some embodiments, as shown in Figure 3 The first passive filter comprises: a first capacitor module C1; a second capacitor module C2, the first end of the second capacitor module C2 is electrically connected with the second end of the first capacitor module C1; a first inductor module L2, the first end of the first inductor module L2 is electrically connected with the second end of the second capacitor module C2; and a first resistor module R1, the first end of the first resistor module R1 is electrically connected with the second end of the first capacitor module C1.

[0060] Wherein, Figure 3 As shown in the structure schematic diagram of the current source converter of the hybrid controllable capacitor bank when the first passive filter and the controllable capacitor bank are connected in series,Figure 3 As shown, in the case of the first passive filter being connected in series with the controllable capacitor bank 32, the first end of the first capacitor module C1 is electrically connected to the phase AC end of the converter bridge circuit 20, and the second end of the first inductor module L2 and the second end of the first resistor module R1 are both electrically connected to the input end of the controllable capacitor bank 32.

[0061] In some other embodiments, in the case of the first passive filter being connected in parallel with the controllable capacitor bank, the first end of the first capacitor module is electrically connected to the phase AC end of the converter bridge circuit and the input end of the controllable capacitor bank.

[0062] In this embodiment, the first passive filter is designed to include a first capacitor module, a second capacitor module, a first inductor module, and a first resistor module, which are connected in series to form a series circuit. The first end of the first capacitor module is connected to the phase AC end of the converter bridge circuit, while the second end of the second capacitor module is connected to the first end of the first inductor module and ultimately to the controllable capacitor bank. The first end of the first resistor module is also connected to the second end of the first capacitor module, and its second end is connected to the controllable capacitor bank. This specific structure of the first passive filter in series with the controllable capacitor bank effectively reduces the AC voltage output of the controllable capacitor bank in the HCC-F3C topology, reduces the number of required sub-modules, and significantly reduces the cost and loss while maintaining the same voltage and current levels of the device. In addition, due to the addition of the first passive filter, the overall filtering effect is improved, further meeting the strict requirements of F3C converters for filtering and reactive power compensation, thereby ensuring the efficiency and stability of power transmission.

[0063] Among them, the LC filter network composed of the first capacitor module C1 and the first inductor module L2 can effectively filter out high-frequency harmonics. Inductors exhibit high impedance to high-frequency signals, while capacitors exhibit low impedance to high-frequency signals. The combination of the two can effectively attenuate harmonics and improve the purity of the output current. By introducing an RC filter network (i.e., the second capacitor module C2 and the first resistor module R1), the dynamic response characteristics of the system can be improved. The RC network helps to smooth voltage fluctuations and quickly respond to load changes, ensuring the stability and response speed of the system during transient processes. The inductors and capacitors in the first passive filter generally have good temperature and frequency stability, ensuring the consistency of the filtering effect under different environmental conditions.

[0064] In some embodiments, as shown in FIG. 4, the first passive filter is connected in parallel with the controllable capacitor bank 32. In this case, the first end of the first capacitor module C1 is electrically connected to the phase AC end of the converter bridge circuit 20 and the input end of the controllable capacitor bank 32. Figure 4As shown, the first passive filter includes a third capacitor module C3, a second inductor module L3, a first end of the second inductor module L3 being electrically connected to a second end of the third capacitor module C3, a third inductor module L4, a first end of the third inductor module L4 being electrically connected to a second end of the second inductor module L3, a fourth capacitor module C4, a first end of the fourth capacitor module C4 being electrically connected to the second end of the second inductor module L3 and the first end of the third inductor module L4 respectively, and a second end of the fourth capacitor module C4 being electrically connected to a second end of the third inductor module L4, and a second resistor module R2, a first end of the second resistor module R2 being electrically connected to the second end of the third capacitor module C3.

[0065] wherein, Figure 4 As shown, the first passive filter includes a third capacitor module C3, a second inductor module L3, a first end of the second inductor module L3 being electrically connected to a second end of the third capacitor module C3, a third inductor module L4, a first end of the third inductor module L4 being electrically connected to a second end of the second inductor module L3, a fourth capacitor module C4, a first end of the fourth capacitor module C4 being electrically connected to the second end of the second inductor module L3 and the first end of the third inductor module L4 respectively, and a second end of the fourth capacitor module C4 being electrically connected to a second end of the third inductor module L4, and a second resistor module R2, a first end of the second resistor module R2 being electrically connected to the second end of the third capacitor module C3. Figure 4 As shown, in the case of the first passive filter and the controllable capacitor bank 32 being connected in series, a first end of the third capacitor module C3 is electrically connected to the phase AC end of the converter bridge circuit 20, and a second end of the third inductor module L4, a second end of the fourth capacitor module C4, and a second end of the second resistor module R2 are all electrically connected to the input end of the controllable capacitor bank 32.

[0066] In other embodiments, in the case of the first passive filter and the controllable capacitor bank being connected in parallel, a first end of the third capacitor module is electrically connected to the phase AC end of the converter bridge circuit and the input end of the controllable capacitor bank.

[0067] In this embodiment, the design of the first passive filter further optimizes the performance of the HCC-F3C. The third capacitor module is directly connected to the phase AC end of the converter bridge circuit, the fourth capacitor module is connected to the second end of the second inductor module and the first end of the third inductor module respectively, and finally forms an electrical connection with the controllable capacitor bank, and the second resistor module is connected in series between the third capacitor module and the controllable capacitor bank. This configuration aims to reduce system cost and loss through the synergistic effect of the first passive filter and the controllable capacitor bank, while meeting the demand for high filtering quality and reactive power compensation. The first passive filter utilizes its inherent capacitor and inductor components to cooperate with the controllable capacitor bank, effectively reducing the burden on the controllable capacitor bank and reducing the number of necessary sub-modules, thereby reducing cost and loss while maintaining the same voltage and current level devices. At the same time, through precise electrical parameter design, the filter can provide additional filtering effect and reactive power compensation, ensuring the stability and efficiency of the system during operation. This design not only embodies the innovation of the system structure, but also improves the economy and reliability of the HCC-F3C in power transmission and conversion applications.

[0068] The LC filter network composed of the third capacitor module C3 and the second inductor module L3 effectively suppresses high-order harmonics, especially high-frequency noise generated by the switching operation of the commutator bridge circuit. The third capacitor module C3 presents low impedance to high-frequency signals, absorbing these frequency components, while the second inductor module L3 presents high impedance to these frequencies, preventing them from entering the load. The third inductor module L4 and the fourth capacitor module C4 further form another LC filter network to handle secondary harmonics, especially lower-frequency harmonics common in power systems, such as the 3rd and 5th harmonics. This combination can deeply filter out harmonics of specific frequencies, improving the purity of the output current. The connection between the second resistor module R2 and the third capacitor module C3 or the fourth capacitor module C4 can form an RC filter network. This network helps improve the dynamic response characteristics of the system and assists in power factor correction. The RC network can smooth voltage ripples and respond quickly to load changes, ensuring the stability of the system during transient processes. By using the first passive filter to handle most of the static filtering tasks, the design pressure of the controllable capacitor bank 32 can be reduced, thereby reducing the number of submodules required. This not only reduces the manufacturing cost of HCC-F3C, but also improves system efficiency because the first passive filter itself has low energy loss.

[0069] In some embodiments, such as Figure 5 As shown, the first passive filter includes a fifth capacitor module C5, the first end of which is electrically connected to the phase AC terminal of the converter bridge circuit 20, and the second end of which is electrically connected to the controllable capacitor bank 32.

[0070] In this embodiment, the first passive filter includes a capacitor unit. The first end of this module is directly connected to the phase AC terminal of the converter bridge circuit, while the second end is connected to the controllable capacitor bank. This structural design effectively distributes the AC voltage load on the controllable capacitor bank, enabling it to operate with a lower AC output voltage. This significantly reduces the number of submodules in the controllable capacitor bank while maintaining the same voltage level and current capacity. By connecting the first passive filter in series with the controllable capacitor bank, not only is the overall cost and operating losses of the HCC-F3C reduced, but the basic requirements of the F3C converter for filtering and reactive power compensation are also maintained. In this configuration, the first passive filter handles a portion of the AC voltage and optimizes the system's filtering effect, achieving efficient suppression of grid harmonics and improving the stability and power quality of the power system. The collaborative work of the capacitor unit and the controllable capacitor bank ensures that the HCC-F3C can still provide reliable converter and power transmission performance while reducing system cost and losses.

[0071] The fifth capacitor module C5 is connected in series with the controllable capacitor bank and can bear a part of the alternating voltage, thereby reducing the peak value of the alternating voltage that the controllable capacitor bank needs to output. This means that the number of sub-modules of the controllable capacitor bank can be reduced, because each sub-module does not need to bear such a high voltage, thereby reducing the system cost and operating loss. The first passive filter (such as the fifth capacitor module C5) can usually effectively filter out harmonics of a specific frequency, improving the quality of the output current. In combination with the controllable capacitor bank, a wider-band filtering effect can be formed, and the controllable capacitor bank can dynamically adjust the reactive power, so that the entire system can maintain good filtering and reactive power compensation capability under different operating conditions. The capacitor in the first passive filter can be offset by the inductive load in the system, improving the overall power factor of the system. In the HCC-F3C, the first passive filter works in cooperation with the controllable capacitor bank, which not only can correct the power factor, but also can adjust the reactive power of the system by controlling the controllable capacitor bank, realizing more flexible power factor control. The addition of the first passive filter can increase the damping of the system, helping to suppress voltage and current fluctuations caused by switching operations, thereby enhancing the stability of the entire HCC-F3C system. Through cooperation with the first passive filter, the control strategy of the controllable capacitor bank can more centrally handle dynamic reactive power compensation and voltage support, while the first passive filter naturally handles static filtering tasks. This division of labor can simplify the control algorithm of the system and improve control efficiency.

[0072] It should be noted that the structures of the first passive filter and the second passive filter are not limited to the above three structures, and various different combinations can also be used as long as the functions of the passive filter can be met.

[0073] In some embodiments, as shown in FIGS. 6(a) and 6(b), the controllable capacitor bank includes a plurality of connected sub-modules 321, the sub-module 321 includes a plurality of fully controlled devices and a capacitor connected in series, and the connection mode of the plurality of sub-modules 321 includes any one of an angular chain connection and a star chain connection.

[0074] In FIG. 6(a), the angular chain connection is shown, and in FIG. 6(b), the star chain connection is shown. In FIGS. 6(a) and 6(b), u sa is an a-phase input end connected to an a-phase alternating current end, sb is a b-phase input end connected to a b-phase alternating current end, sc is a c-phase input end connected to a c-phase alternating current end.

[0075] Through the cascading of sub-modules (either angular or star chain connection), the controllable capacitor bank can achieve high-voltage level output. Each sub-module bears part of the voltage, and the total output voltage is equal to the superposition of the voltages of all sub-modules, which is particularly important in high-voltage direct current transmission systems (HVDC) and can meet the application requirements of high voltage and large capacity. The controllable capacitor bank can dynamically adjust its output reactive power by controlling the switching state of full-controlled devices (such as IGBT, IGCT, etc.). This ability is crucial for maintaining power system stability, improving power factor, and controlling voltage level, especially in cases of rapid load changes or unstable power grids. Since the controllable capacitor bank adopts a modular design, the system can easily add or remove sub-modules to adapt to changes in load or upgrade the system. In addition, the modular structure also facilitates daily inspection and maintenance, allowing for targeted replacement of faulty sub-modules rather than the entire system, reducing maintenance costs and downtime. Angular chain connection can reduce DC bus voltage, but may increase the voltage stress of switching devices; while star chain connection can better balance the voltage and current levels of switching devices, reducing losses. By choosing the appropriate connection method, the best balance between cost and efficiency can be found. The independent packaging of sub-modules and chain connection facilitates heat dissipation management and voltage balancing control. Each sub-module can be equipped with its own cooling system to ensure that the devices operate within a safe temperature range; at the same time, through advanced control strategies, voltage sharing among sub-modules can be achieved to avoid local overload and ensure long-term stable operation of the system.

[0076] In this embodiment, the controllable capacitor bank is composed of multiple connected sub-modules, each containing multiple full-controlled devices and capacitors connected electrically. The connection method between sub-modules can choose either angular chain connection or star chain connection, and this flexible configuration makes HCC-F3C adaptable to different application scenarios and requirements. By optimizing the layout and connection method of sub-modules, not only the operating efficiency of the entire system can be improved, but also the control precision can be enhanced, thereby achieving effective management of AC voltage and accurate supply of reactive power compensation. This design not only reduces the maximum output AC voltage required by the controllable capacitor bank, but also significantly reduces the number of sub-modules while maintaining the same voltage and current levels, thereby effectively reducing manufacturing costs and operating losses and improving the economic efficiency and reliability of the full-controlled composite converter. Of course, the specific configuration and connection method of sub-modules can be adjusted according to actual working conditions and system parameters to achieve the best operating state and economic benefits. In some embodiments, the above full-controlled devices are IGBT devices or IGCT devices.

[0077] Among them, both IGBT and IGCT have very fast switching performance, they can respond to control signals in a very short time, and conduct and turn off operation. This makes the controllable capacitor bank can realize fast voltage regulation and reactive power compensation, enhance the dynamic response ability of the system, can quickly adjust when the power system load changes or power grid fluctuation, maintain the stability of the power grid. IGCT devices are particularly suitable for high-voltage and high-current power systems. Compared with IGBT, IGCT can carry higher voltage level and current density, which is a significant advantage in high-voltage direct current transmission (HVDC) or other high-power conversion applications. The control logic of IGBT and IGCT devices is relatively simple, which can be seamlessly integrated with modern power electronic control strategies (such as PWM, NLM, etc.), to realize accurate voltage and reactive power regulation. Due to the fast switching characteristics of IGBT and IGCT, they are usually integrated with electromagnetic compatibility (EMC) measures, such as snubber circuits, to reduce electromagnetic interference generated during switching operation.

[0078] In some embodiments, as shown in FIG. 7(a), the above-mentioned sub-module includes a sixth capacitor module and a first full-controlled device Q1, a second full-controlled device Q2, a third full-controlled device Q3 and a fourth full-controlled device Q4 connected in a full-bridge structure, the first end of the first full-controlled device Q1 is electrically connected with the second end of the second full-controlled device Q2, the second end of the first full-controlled device Q1 is electrically connected with the second end of the third full-controlled device Q3, the first end of the third full-controlled device Q3 is electrically connected with the second end of the fourth full-controlled device Q4, the first end of the second full-controlled device Q2 is electrically connected with the first end of the fourth full-controlled device Q4, the first end of the sixth capacitor module C6 is respectively electrically connected with the second end of the first full-controlled device Q1 and the second end of the third full-controlled device Q3, and the second end of the sixth capacitor module C6 is respectively electrically connected with the first end of the second full-controlled device Q2 and the first end of the fourth full-controlled device Q4; or, as shown in FIG. 7(b), the above-mentioned sub-module includes a fifth full-controlled device Q5 and a sixth full-controlled device Q6 connected in a half-bridge structure, the first end of the fifth full-controlled device Q5 is electrically connected with the second end of the sixth full-controlled device Q6; a seventh capacitor module C7, the first end of the seventh capacitor module C7 is electrically connected with the second end of the fifth full-controlled device Q5, and the second end of the seventh capacitor module C7 is electrically connected with the first end of the sixth full-controlled device Q6.

[0079] That is, the above-mentioned sub-module refers to a full-bridge sub-module or a half-bridge sub-module using IGBT as a controllable switching device, the specific structure is shown in FIG. 7(a) and FIG. 7(b), or the sub-module can also be a full-bridge sub-module or a half-bridge sub-module using IGCT as a controllable switching device, the specific structure is shown in FIG. 8(a) and FIG. 8(b), and the specific type of sub-module is selected in combination with the actual scene.

[0080] In some embodiments, as shown in FIG. 9(a) and FIG. 9(b), the above-mentioned current source converter further includes an energy storage module 50 connected in parallel with the above-mentioned sub-module.

[0081] By integrating the energy storage module into the support valve and injecting energy into the sub-module of the support valve, the problem that the traditional F3C cannot independently black start is solved, the support valve independently black starts and assists the main valve to start, this improvement enables the system to quickly start without external power supply, and breaks through the limitation of relying on external energy.

[0082] At the same time, the support valve integrated with the energy storage module significantly enhances the active power sending and absorbing capacity, adjusts the grid active power by cooperating with the main valve, solves the technical problems of weak F3C grid support capacity and insufficient flexibility, enables the grid to operate more stably during load fluctuation, and improves the support response speed and adjustment range.

[0083] In addition, the energy storage module can provide independent voltage stabilization function for the sub-module capacitor voltage, and solves the problem of difficult capacitor voltage balance control of F3C in different scenes. This function reduces the complexity of the control algorithm, and also makes the voltage fluctuation amplitude smaller.

[0084] By integrating the energy storage unit into the support valve, the black start, grid support capacity and sub-module capacitor voltage balance control are obviously improved compared with F3C. In terms of black start, the energy storage unit injects energy into the sub-module of the support valve, which can realize the independent black start of the support valve, and then assist the main valve to start. In terms of grid support capacity, the active power sending and absorbing capacity of the support valve of ES-F3C is significantly enhanced, and by cooperating with the main valve to send or absorb active power to the grid, the grid support capacity and flexibility are significantly improved. In terms of sub-module capacitor voltage balance control, the energy storage unit realizes independent voltage stabilization of the capacitor voltage, and reduces the difficulty of capacitor voltage balance control in different scenes.

[0085] In some embodiments, as shown in FIG. 10(a) and FIG. 10(b), the above-mentioned current source converter further includes an energy storage module 50 connected in parallel with the above-mentioned sub-module. Figure 10 dc ​and the converter bridge arms, the converter bridge arms including a plurality of upper bridge arms 21 and a plurality of lower bridge arms 22, first ends of the upper bridge arms 21 being connected to the first DC end, first ends of the lower bridge arms 22 being connected to the second DC end, second ends of one of the upper bridge arms 21 and one of the lower bridge arms 22 being connected to one of the phase AC ends, the first DC end being connected to the DC bus through the DC reactor L dc The second DC end is directly connected to the DC bus.

[0086] The main function of the DC reactor is to smooth the DC current. In a DC power transmission system, current fluctuations can affect the stability and efficiency of the system. By providing the function of storing and releasing energy, it can effectively reduce the ripple in the DC current, making the current more stable, which is crucial for devices that require stable DC power. In the event of a short circuit fault in the system, the DC reactor can limit the rising rate of short circuit current, avoiding excessive current impact on the device, reducing the impact of the fault on the system, and enhancing the safety of the system. The DC reactor can also suppress the harmonics generated by the switching operation of the converter bridge arm. Since the switching action of IGBT or IGCT devices will generate certain high-frequency noise, the DC reactor can filter out these noises through its inductive effect, improving the quality of the output power. The DC reactor can temporarily store energy, and when there is a transient power imbalance in the power system (such as sudden load changes), the DC reactor can buffer this part of the energy, preventing large fluctuations in the DC voltage, thereby improving the dynamic response capability and overall stability of the power system. By adding a DC reactor to the converter bridge circuit, the control performance of the controllable capacitor bank can be improved. The DC reactor helps to stabilize the DC side voltage, providing a more stable reference point for the control algorithm of the controllable capacitor bank, enhancing the accuracy of reactive power regulation. The addition of the DC reactor improves the reliability of the system, as it can reduce the damage to the device caused by current fluctuations and short circuit faults.

[0087] In this embodiment, the converter bridge circuit includes a DC reactor and a converter bridge arm, which is composed of multiple upper bridge arms and lower bridge arms. The first end of the upper bridge arm is connected to the first DC end, and the first end of the lower bridge arm is connected to the second DC end. The second end of each pair of upper bridge arm and lower bridge arm is connected to a phase AC end. This design enables the main valve to efficiently perform current source commutation. The first DC end is connected to the DC bus through the DC reactor, and the second DC end is directly connected to the DC bus. This connection helps to stabilize the voltage on the DC side while reducing energy loss in the circuit. The structural design of the converter bridge arm realizes efficient conversion of DC voltage and AC voltage. By controlling the switching devices in the upper bridge arm and the lower bridge arm, the voltage output to the phase AC end can be accurately adjusted, thereby optimizing the operating performance of the entire F3C converter. This configuration of the converter bridge circuit not only improves the stability and controllability of the system, but also realizes efficient conversion of DC and AC electric energy, reducing energy consumption and cost in the process of high-power electric energy transmission and conversion.

[0088] In some embodiments, as shown in FIG. 1, Figure 11 The converter bridge arm includes a first current path and a second current path connected in anti-parallel. The first current path includes any one of a first branch formed by a plurality of reverse blocking IGCT devices connected in series, a second branch formed by a plurality of IGBT devices connected in series, and a third branch formed by at least one asymmetric IGCT device and at least one IGBT device connected in series. The second current path includes any one of a first branch formed by a plurality of reverse blocking IGCT devices connected in series, a second branch formed by a plurality of IGBT devices connected in series, a fourth branch formed by a plurality of diodes connected in series, and a fifth branch formed by a plurality of thyristors connected in series.

[0089] In this embodiment, the first current path includes any combination of a first branch formed by reverse blocking IGCT devices connected in series, a second branch formed by IGBT devices connected in series, and a third branch formed by asymmetric IGCT devices and IGBT devices connected in series. The second current path includes any one of a first branch formed by reverse blocking IGCT devices connected in series, a second branch formed by IGBT devices connected in series, a fourth branch formed by diodes connected in series, and a fifth branch formed by thyristors connected in series. This design not only enriches the structural diversity of the converter bridge arm, but also allows for flexible adjustment of control strategies and performance indicators according to different application scenarios. By introducing combinations of multiple devices, the converter bridge arm can ensure high efficiency and reliability while achieving fine control of current and voltage, thereby optimizing the working state of the entire F3C converter and improving its adaptability and stability in complex power system environments.

[0090] Specifically, through the structure of reverse parallel, the converter bridge arm can realize the control of bidirectional power flow. This means that no matter the DC side or the AC side, the current can freely flow in and out, enhancing the flexibility of the power electronic device, suitable for a variety of occasions of inversion and rectification. Using the combination of IGCT devices and IGBT devices, especially the reverse blocking type IGCT device, the power handling capacity and voltage bearing capacity of the converter bridge arm can be effectively improved. IGCT devices are suitable for high-voltage and large-current environments, while IGBTs perform well at medium and low voltages, and the combination of the two can expand the application range of the power electronic device. The mixed use of asymmetric IGCT and IGBT, as well as the addition of diodes and thyristors, can find a balance point between cost and performance. Although IGCT has superior performance, the cost is relatively high; while the cost of IGBT, diode and thyristor is relatively low, through reasonable design, the overall cost can be reduced while ensuring system performance.

[0091] In some other embodiments, the first through-flow branch and the second through-flow branch can also be respectively configured with a buffer branch, that is, the buffer branch includes a first buffer branch and a second buffer branch, the first buffer branch is connected in parallel with the first through-flow branch, and the second buffer branch is connected in parallel with the second through-flow branch.

[0092] Specifically, the first buffer branch is used to equalize the voltage of the first through-flow branch when the first through-flow branch is turned on, and the second buffer branch is used to equalize the voltage of the second through-flow branch when the second through-flow branch is turned on. The structure of the buffer component of the first buffer branch and the buffer component of the second buffer branch can be the same, for example Figure 12 As shown, RCD dynamic voltage equalization circuit can be used; in other embodiments, the buffer component of the first buffer branch and the buffer component of the second buffer branch can also be one or more of static voltage equalization resistance, RC circuit, and circuit formed by parallel connection of RC and MOV. In some other embodiments, LC circuit can also be added to the first buffer branch and the second buffer branch, and the resonance characteristics of inductance and capacitance are used to further smooth the voltage change in the off process of the switching device, reduce the overvoltage phenomenon, and the inductance can also help the buffer branch to branch, reduce the loss of the buffer branch.

[0093] The structure of the first buffer branch and the second buffer branch can be different, for example Figure 13 As shown, the first buffer branch is built by using RCD dynamic voltage equalization circuit, and the second buffer branch is built by using RC circuit. In other embodiments, the first buffer branch and the second buffer branch can also be other combinations, which are not limited in particular.

[0094] It is understandable that, in practical scenarios, if the first and second buffer branches use circuits without polarity requirements, such as static equalizing resistors, RC circuits, or circuits formed by parallel RC and MOV circuits, they can simply be connected in parallel with the first and second current-carrying branches respectively. If the first or second buffer branch uses circuits with polarity requirements, such as RCD dynamic equalizing circuits, the first buffer branch must be connected in parallel with the first current-carrying branch in the same direction, and the second buffer branch must be connected in parallel with the second current-carrying branch in the same direction; that is, the first and second buffer branches must be connected in parallel in opposite directions.

[0095] In one embodiment, such as Figure 14 As shown, the converter bridge arm also includes energy-dissipating branches connected in parallel with the first and second current-carrying branches, respectively. Among them, as... Figure 14 As shown, the energy dissipation branch includes a surge arrester. In addition to the surge arrester, the energy dissipation branch can also use multiple metal oxide varistors (MOVs). These resistors have nonlinear volt-ampere characteristics, which can effectively limit high-voltage pulses, thereby protecting the switching devices. Alternatively, an RC circuit can be combined with the surge arrester MOV or other nonlinear components to form a composite buffer circuit. In the event of overvoltage, the surge arrester MOV triggers first, absorbing most of the overvoltage energy; when the voltage drops to a certain level, the RC circuit continues to perform voltage equalization and energy absorption, ensuring the safe turn-off of the switching devices. A capacitor can also be added to the energy dissipation branch to store and release a large amount of electrical energy during transient processes, helping to stabilize the DC bus voltage and absorb energy during turn-off.

[0096] Specifically, in this embodiment, the scheme is illustrated by using a first current-carrying branch constructed with a series-connected reverse-resistance IGCT, a second current-carrying branch constructed with a series-connected thyristor, a first buffer branch constructed with an RCD dynamic voltage equalization circuit, and a second buffer branch constructed with an RC circuit. Energy-dissipating branches are also connected in parallel at both ends of the converter bridge arm. The energy-dissipating branches serve two purposes: limiting overvoltage of the devices and equalizing voltage across multiple devices in series. It should be noted that the type of energy-dissipating branch is not unique; any circuit capable of achieving the above two functions is acceptable.

[0097] In some embodiments, such as Figure 10 As shown, the above-mentioned commutator bridge circuit 20 also includes a saturated reactance 40. The second end of the upper bridge arm 21 is electrically connected to the second end of the lower bridge arm 22 through the saturated reactance 40, and / or the second end of the lower bridge arm 22 is electrically connected to the second end of the upper bridge arm 21 through the saturated reactance 40.

[0098] In the embodiment, the converter bridge circuit further comprises a saturable reactor, the second end of the upper bridge arm is electrically connected to the second end of the lower bridge arm through the saturable reactor, and the second end of the lower bridge arm is also electrically connected to the second end of the upper bridge arm through the saturable reactor. This design effectively increases the impedance adjustment capability of the circuit. Through the characteristics of the saturable reactor, stable alternating voltage can be maintained in a large current range, and the stability of the system is improved. At the same time, the saturable reactor shows high impedance under light load conditions to avoid direct current short circuit, and automatically reduces impedance under heavy load conditions to ensure the continuity of the current. Such structure optimization not only enhances the operating performance of the controllable current source converter, but also further reduces the control difficulty of the hybrid controllable capacitor bank in dealing with complex working conditions, so that the system responds more quickly and stably in various working states, and the efficiency and reliability of the entire F3C topology are improved.

[0099] Specifically, the saturable reactor can automatically limit the current when the current increases sharply, because when the current increases to a certain extent, the magnetic core of the saturable reactor will enter a saturated state, and its reactance value will decrease significantly, thereby limiting the further growth of the current. This feature provides additional protection when power electronic devices suffer short circuits, overloads, and other faults, preventing equipment damage. The saturable reactor can provide a nonlinear reactance characteristic, which means that it exhibits different reactance values at different current levels. This nonlinear characteristic helps to filter out specific frequency harmonics in the power system, especially those secondary harmonics corresponding to the saturation point of the saturable reactor, thereby improving power quality. The saturable reactor can store magnetic field energy in the non-saturated region and release energy in the saturated region. This feature helps to balance the energy flow on both sides of the converter bridge arm, especially during the commutation process, which can smooth voltage fluctuations and improve the stability of the direct current voltage.

[0100] In some embodiments, the AC voltage waveform diagram of the HCC, the first passive filter and the controllable capacitor bank is as shown in Figure 15 .

[0101] Embodiments of the present application also provide a direct current transmission system, as shown in Figure 16 , comprising a sending end current source converter 01 and a receiving end current source converter 02, at least one of the sending end current source converter 01 and the receiving end current source converter 02 is any one of the above-mentioned hybrid controllable capacitor bank current source converter, and the direct current end of the sending end current source converter is electrically connected to the direct current end of the receiving end current source converter.

[0102] The application provides a direct current transmission system, which adopts at least one current source converter based on a hybrid controllable capacitor bank, wherein the hybrid controllable capacitor bank is composed of controllable capacitor banks and passive capacitors in series at an alternating current port. This design makes the current source converter effectively reduce the cost and loss of reactive power compensation, because under the condition of the same sub-module voltage and current level, part of the alternating current voltage is borne by the passive capacitors, and the number of sub-modules required for cascading the controllable capacitor bank is reduced. Therefore, the system not only maintains the advantages of the original F3C converter in large capacity and low loss, but also significantly improves the economy and filtering effect, and solves the problem of high cost and loss caused by the large number of sub-modules of the traditional F3C converter. The application of the improved converter in the current source converter at the sending end and the receiving end realizes more efficient and economical direct current power transmission.

[0103] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, all possible combinations of the technical features in the above-described embodiments are not described, but as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present application.

[0104] 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 "including a" does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0105] From the above description, it can be seen that the above-described embodiments of the application achieve the following technical effects:

[0106] 1) The current source converter of the above-mentioned hybrid controllable capacitor bank of the present application comprises: a plurality of converter transformers, the first end of the converter transformer being used for electrical connection with an AC load; a converter bridge circuit, having a plurality of phase AC terminals, the DC terminal of the converter bridge circuit being used for connection with a DC bus, the converter bridge circuit being used for active power transmission; a hybrid controllable capacitor bank, comprising a first passive filter and a controllable capacitor bank electrically connected, the controllable capacitor bank comprising a plurality of fully controlled devices and a capacitor electrically connected, each phase AC terminal of the converter bridge circuit being electrically connected with the first passive filter, the hybrid controllable capacitor bank being used for reactive power support; a plurality of filter reactances, the first end of the filter reactance being electrically connected with the hybrid controllable capacitor bank and one phase AC terminal of the converter bridge circuit respectively, the second end of the filter reactance being electrically connected with the second end of the corresponding converter transformer. The converter reduces the output AC voltage of the controllable capacitor bank by electrically connecting the first passive filter with the controllable capacitor bank, directly reduces the number of sub-modules of the controllable capacitor bank under the condition that the voltage level of a single sub-module is unchanged, thereby realizing the reduction of cost and loss.

[0107] 2) The present application provides a DC power transmission system, which adopts at least one current source converter based on a hybrid controllable capacitor bank, wherein the hybrid controllable capacitor bank is composed of a controllable capacitor bank and a passive capacitor electrically connected at an AC port. This design enables the current source converter to effectively reduce the cost and loss of reactive power compensation, because under the condition of the same sub-module voltage and current level, the passive capacitor bears part of the AC voltage, reducing the number of sub-modules required for cascading of the controllable capacitor bank. Therefore, the system not only maintains the advantages of the original F3C converter in terms of large capacity and low loss, but also significantly improves the economy and filtering effect, solving the problem of high cost and loss caused by the large number of sub-modules of the traditional F3C converter. The application of this improved converter in the current source converter of the sending end and the receiving end realizes more efficient and economical DC power transmission.

[0108] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Those skilled in the art can make various modifications and changes to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A current source converter for a hybrid controllable capacitor bank, characterized by Comprise: a plurality of converter transformers, a first end of the converter transformers being configured to be electrically connected to an AC load; a converter bridge circuit having a plurality of phase AC terminals, a DC terminal of the converter bridge circuit being configured to be connected to a DC bus, the converter bridge circuit being configured for active power transmission; a hybrid controllable capacitor bank comprising a first passive filter and a controllable capacitor bank electrically connected, the controllable capacitor bank comprising a plurality of fully controlled devices and a capacitor electrically connected, each phase AC terminal of the converter bridge circuit being electrically connected to the first passive filter, the hybrid controllable capacitor bank being configured for reactive power support; a plurality of filter reactances, a first end of the filter reactances being electrically connected to the hybrid controllable capacitor bank and one of the phase AC terminals of the converter bridge circuit respectively, a second end of the filter reactances being electrically connected to a second end of the corresponding converter transformer.

2. The current source converter of claim 1, wherein, The first passive filter is connected in series or in parallel with the controllable capacitor bank.

3. The current source converter of claim 1, wherein, The current source converter further comprises a second passive filter, wherein an input end of the first passive filter is electrically connected to a phase AC terminal of the converter bridge circuit and a first end of the second passive filter respectively, a second end of the second passive filter is electrically connected to an input end of the controllable capacitor bank, the first passive filter and the second passive filter have the same structure or different structures.

4. The current source converter of claim 1, wherein, The first passive filter comprises: a first capacitor module; a second capacitor module, a first end of the second capacitor module being electrically connected to a second end of the first capacitor module; a first inductor module, a first end of the first inductor module being electrically connected to a second end of the second capacitor module; a first resistor module, a first end of the first resistor module being electrically connected to a second end of the first capacitor module; wherein, in the case that the first passive filter is connected in series with the controllable capacitor bank, the first end of the first capacitor module is electrically connected to the phase AC terminal of the converter bridge circuit, the second end of the first inductor module and the second end of the first resistor module are electrically connected to the input end of the controllable capacitor bank, in the case that the first passive filter is connected in parallel with the controllable capacitor bank, the first end of the first capacitor module is electrically connected to the phase AC terminal of the converter bridge circuit and the input end of the controllable capacitor bank.

5. The current source converter of claim 1, wherein, The first passive filter comprises: a third capacitor module; a second inductor module, a first end of the second inductor module being electrically connected to a second end of the third capacitor module; a third inductor module, a first end of the third inductor module being electrically connected to a second end of the second inductor module; a fourth capacitor module, a first end of the fourth capacitor module being electrically connected to the second end of the second inductor module and the first end of the third inductor module respectively, a second end of the fourth capacitor module being electrically connected to a second end of the third inductor module; a second resistor module, a first end of the second resistor module being electrically connected to a second end of the third capacitor module; In the case of the first passive filter being connected in series with the controllable capacitor bank, the first end of the third capacitor module is electrically connected to the phase alternating current end of the converter bridge circuit, and the second end of the third inductor module, the second end of the fourth capacitor module and the second end of the second resistor module are all electrically connected to the input end of the controllable capacitor bank. In the case of the first passive filter being connected in parallel with the controllable capacitor bank, the first end of the third capacitor module is electrically connected to the phase alternating current end of the converter bridge circuit and the input end of the controllable capacitor bank.

6. The current source converter of claim 1, wherein, The controllable capacitor bank comprises: A plurality of connected sub-modules, the connection mode of the plurality of sub-modules comprising any one of an angular chain connection and a star chain connection, In the case of the first passive filter being connected in series with the controllable capacitor bank, the first end of the third capacitor module is electrically connected to the phase alternating current end of the converter bridge circuit, and the second end of the third inductor module, the second end of the fourth capacitor module and the second end of the second resistor module are all electrically connected to the input end of the controllable capacitor bank. In the case of the first passive filter being connected in parallel with the controllable capacitor bank, the first end of the third capacitor module is electrically connected to the phase alternating current end of the converter bridge circuit and the input end of the controllable capacitor bank.

7. The current source converter of claim 6, wherein, The current source converter further comprises an energy storage module connected in parallel with the sub-module.

8. The current source converter of claim 1, wherein, The converter bridge circuit comprises a direct current reactor and a converter bridge arm, the converter bridge arm comprising a plurality of upper bridge arms and a plurality of lower bridge arms, the first end of the upper bridge arm being connected to a first direct current end, the first end of the lower bridge arm being connected to a second direct current end, the second end of one of the upper bridge arms and the second end of a corresponding one of the lower bridge arms being connected to a corresponding phase alternating current end, the first direct current end being electrically connected to the direct current bus through the direct current reactor, and the second direct current end being directly connected to the direct current bus.

9. The current source converter of claim 8, wherein, The converter bridge circuit further comprises a saturation reactor, the second end of the upper bridge arm being electrically connected to the second end of the lower bridge arm through the saturation reactor, and / or the second end of the lower bridge arm being electrically connected to the second end of the upper bridge arm through the saturation reactor.

10. A direct current power transmission system, characterized by Comprise: A sending current source converter and a receiving current source converter, at least one of the sending current source converter and the receiving current source converter being a current source converter of the hybrid controllable capacitor bank according to any one of claims 1 to 9, the DC terminals of the sending current source converter and the receiving current source converter being electrically connected.

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