Converter and power transmission system

Abstract

The utility model provides a converter and a power transmission system, the converter comprises a converter bridge circuit, the direct current end of the converter bridge circuit is used for being electrically connected with a direct current bus, the converter bridge circuit comprises a plurality of converter bridge arms, each converter bridge arm comprises a commutation voltage providing module and a plurality of switch modules, the commutation voltage providing module is used for providing commutation voltage for the converter, the commutation voltage providing module is connected with all the switch modules in series, and all the switch modules are connected in series; the first end of each first inductance module is connected with one phase alternating current end of the converter bridge circuit, and the second end of each first inductance module is used for being connected with an alternating current load. The converter actively generates or compensates the voltage required by commutation through the commutation voltage providing module, ensures that enough commutation voltage can still be provided for the thyristor under the condition of weak power grid or fault, and avoids commutation failure caused by insufficient AC side voltage.

Description

TECHNICAL FIELD

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

[0002] High voltage direct current (HVDC) is the core technology for long-distance and large-capacity power transmission, and commutation failure is one of the key challenges. Commutation failure refers to the failure of the valve arm to normally turn off due to voltage drop, trigger delay or insufficient current during thyristor commutation, resulting in discontinuous DC current or system short circuit. In an ultra-high voltage system, the operating environment of high voltage and large current exacerbates the risk of commutation failure, especially when the receiving end AC system fails, the voltage may drop and continuous commutation failure may occur, threatening the stability of the power grid.

[0003] With the increase of renewable energy grid-connected proportion, the strength of the power grid decreases, and the commutation failure problem is prone to occur when the commutation area is insufficient due to AC fault of the converter. CONTENT OF THE UTILITY MODEL

[0004] The main purpose of the present application is to provide a converter and a power transmission system to at least solve the problem that the existing converter is prone to commutation failure when an AC fault occurs.

[0005] In order to achieve the above-mentioned purpose, according to one aspect of the present application, a converter is provided, comprising: a converter bridge circuit, a DC end of the converter bridge circuit being used for electrical connection with a DC bus, the converter bridge circuit comprising a plurality of converter bridge arms, one of the converter bridge arms comprising one commutation voltage providing module and a plurality of switching modules, the commutation voltage providing module being used for providing commutation voltage for the converter, the commutation voltage providing module and all the switching modules being connected in series on one of the converter bridge arms, all the switching modules being connected in series; a plurality of first inductor modules, a first end of one of the first inductor modules being connected to an AC end of one of the converter bridge circuits, and second ends of the first inductor modules being respectively used for connecting an AC load.

[0006] Optionally, the commutation voltage providing module comprises: a transformer, a primary side of the transformer being connected in series with the plurality of switching modules; a voltage submodule, the voltage submodule being electrically connected with a secondary side of the transformer, the voltage submodule being used for providing initial commutation voltage for the converter, a ratio of the commutation voltage of the converter to the initial commutation voltage being a ratio of the number of turns of the primary side of the transformer to the number of turns of the secondary side.

[0007] Optionally, the voltage sub-module comprises: a filter circuit, a first end of the filter circuit being electrically connected with a first end of the secondary side of the transformer, and a second end of the filter circuit being electrically connected with a second end of the secondary side of the transformer; a bridge circuit, a first end of the bridge circuit being electrically connected with a third end of the filter circuit, and a second end of the bridge circuit being electrically connected with a fourth end of the filter circuit.

[0008] Optionally, the bridge circuit comprises: a first switch assembly, a second switch assembly, a third switch assembly and a fourth switch assembly connected in a full-bridge structure, a first end of the first switch assembly being electrically connected with a second end of the second switch assembly and a third end of the filter circuit respectively, a second end of the first switch assembly being electrically connected with a second end of the third switch assembly, a first end of the third switch assembly being electrically connected with a second end of the fourth switch assembly and a fourth end of the filter circuit respectively, and a first end of the second switch assembly being electrically connected with a first end of the fourth switch assembly; a first capacitor module, a first end of the first capacitor module being electrically connected with the second end of the first switch assembly and the second end of the third switch assembly respectively, and a second end of the first capacitor module being electrically connected with the first end of the second switch assembly and the first end of the fourth switch assembly respectively.

[0009] Optionally, the bridge circuit comprises: a fifth switch assembly and a sixth switch assembly connected in a half-bridge structure, a first end of the fifth switch assembly being electrically connected with a second end of the sixth switch assembly and a third end of the filter circuit respectively; a second capacitor module, a first end of the second capacitor module being electrically connected with a second end of the fifth switch assembly, and a second end of the second capacitor module being grounded; and a third capacitor module, a first end of the third capacitor module being grounded, and a second end of the third capacitor module being electrically connected with a first end of the sixth switch assembly.

[0010] Optionally, the switch assembly comprises an IGBT device and a diode connected in parallel with the IGBT, a positive electrode of the diode being electrically connected with a source electrode of the IGBT device, and a negative electrode of the diode being electrically connected with a drain electrode of the IGBT device.

[0011] Optionally, the filter circuit comprises: a second inductor module, a first end of the second inductor module being electrically connected with a first end of the bridge circuit; and a fourth capacitor module, a first end of the fourth capacitor module being electrically connected with a second end of the second inductor module, and a second end of the fourth capacitor module being electrically connected with a second end of the bridge circuit.

[0012] Optionally, the converter bridge circuit comprises converter bridge arms, the converter bridge arms comprise upper bridge arms and lower bridge arms, first ends of the upper bridge arms are connected respectively and form a common end as a first DC end, first ends of the lower bridge arms are connected respectively and form a common end as a second DC end, second ends of one of the upper bridge arms are connected to second ends of one of the lower bridge arms respectively, and a common end formed thereby is a phase AC end, and the first DC end and the second DC end are electrically connected to the DC bus.

[0013] Optionally, the switching module comprises semiconductor devices and voltage equalization circuits electrically connected, different semiconductor devices correspond to different voltage equalization circuits, and the semiconductor devices are one of thyristors, IGCT devices and IGBT devices.

[0014] According to another aspect of the present application, a power transmission system is provided, comprising any of the converter.

[0015] According to the technical solution of the present application, the converter comprises a converter bridge circuit, a DC end of the converter bridge circuit is electrically connected to a DC bus, the converter bridge circuit comprises a plurality of converter bridge arms, one of the converter bridge arms comprises one phase-voltage providing module and a plurality of switching modules, the phase-voltage providing module is used to provide a phase-voltage for the converter, the phase-voltage providing module and all the switching modules are connected in series, and all the switching modules are connected in series; a plurality of first inductor modules, a first end of one of the first inductor modules is connected to one phase AC end of the converter bridge circuit, and second ends of the first inductor modules are used to connect AC loads respectively. During commutation of current rise and fall of the converter in normal operation, positive and negative voltages are generated, thereby charging the phase-voltage providing module, when voltage drop of the converter occurs, i.e. in the case of insufficient external phase-voltage, the phase-voltage providing module provides pre-stored electric energy to the converter as a phase-voltage, thereby ensuring that sufficient phase-voltage is provided for the converter under weak grid or fault conditions, avoiding phase failure caused by insufficient AC side voltage, and solving the problem that the existing converter is prone to phase failure when AC fault occurs. BRIEF DESCRIPTION OF DRAWINGS

[0016] The drawings accompanying the specification of the present application form a part thereof, serve to provide further understanding of the present application, and together with the specification explain the present application, and do not constitute an inappropriate limitation to the present application. In the drawings:

[0017] Figure 1 A structure schematic diagram of a converter provided in an embodiment of the present application is shown;

[0018] Figure 2 A structure schematic diagram of another converter provided in an embodiment of the present application is shown;

[0019] Figure 3 A waveform diagram of bridge wall current and capacitor voltage is shown according to an embodiment of the present application;

[0020] Figure 4 A specific structure schematic diagram of a bridge circuit is shown according to an embodiment of the present application;

[0021] Figure 5 A specific structure schematic diagram of another bridge circuit is shown according to an embodiment of the present application;

[0022] Figure 6 A waveform schematic diagram of current and voltage of an IGCT is shown according to an embodiment of the present application;

[0023] Figure 7 A structure schematic diagram of a thyristor and its voltage equalization circuit is shown according to an embodiment of the present application;

[0024] Figure 8 A structure schematic diagram of an IGCT device and its voltage equalization circuit is shown according to an embodiment of the present application;

[0025] Figure 9 A structure schematic diagram of an IGBT device and its voltage equalization circuit is shown according to an embodiment of the present application;

[0026] Figure 10 A structure schematic diagram of still another inverter is shown according to an embodiment of the present application.

[0027] Among the above drawings, the following reference signs are included:

[0028] 10, commutation voltage providing module; 11, transformer; 12, voltage submodule; 121, filter circuit; 122, bridge circuit; 20, switch module; 30, AC load; 40, bypass switch; L1, first inductor module; L2, second inductor module; Q1, first switch component; Q2, second switch component; Q3, third switch component; Q4, fourth switch component; Q5, fifth switch component; Q6, sixth switch component; C1, first capacitor module; C2, second capacitor module; C3, third capacitor module; C4, fourth capacitor module. DETAILED DESCRIPTION

[0029] It should be noted that the embodiments and features 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.

[0030] In the following, the technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application, so that those skilled in the art can better understand the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments of the present application. 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.

[0031] It should be noted that the terms "first", "second", and the like in the description, claims, and drawings of the present application 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 including a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to the process, method, product, or device.

[0032] For ease of description, the following describes some nouns or terms related to the embodiments of the present application:

[0033] IGCT (Integrated Gate-commutated Thyristor) is a power electronic device that combines the high-power processing capability of a thyristor and the fast gate control turn-off characteristics of an IGBT (Insulated Gate Bipolar Transistor), suitable for high-voltage and high-power power conversion systems.

[0034] As introduced in the background, the commutation technology in the prior art relying on power grid support is difficult to support commutator commutation under weak power grid conditions. To solve the problem that the existing commutator is prone to commutation failure when an AC fault occurs, the embodiments of the present application provide a commutator and a power transmission system.

[0035] The technical solutions in the embodiments of the present application will be described clearly and completely in conjunction with the drawings in the embodiments of the present application.

[0036] In the present embodiment, a commutator is provided, such as Figure 1As shown, the converter includes: a converter bridge circuit, a direct current end of the converter bridge circuit is used for electrical connection with a direct current bus, the converter bridge circuit includes a plurality of converter bridge arms, one of the converter bridge arms includes a commutation voltage providing module 10 and a plurality of switch modules 20, the commutation voltage providing module 10 is used for providing a commutation voltage for the converter, on one of the converter bridge arms, the commutation voltage providing module 10 and all the switch modules 20 are connected in series, and all the switch modules 20 are connected in series; a plurality of first inductance modules L1, a first end of one of the first inductance modules L1 is connected to a phase alternating current end of the converter bridge circuit, and second ends of the first inductance modules L1 are respectively used for connecting an alternating current load 30.

[0037] It should be pointed out that the type of the converter bridge circuit is not unique, and can be a six-pulse converter bridge circuit or other types of converter bridge circuits, and is not limited in particular. The first inductance module can be a plurality of inductances connected in series or parallel, and the first inductance module is actually a filter reactance. The number of the first inductance module is not unique, and will be different according to the type of the converter bridge circuit, as long as each phase alternating current end of the converter bridge circuit is connected to one first inductance module. In an embodiment, taking a six-pulse converter bridge circuit as an example, the current source converter should include three first inductance modules connected to three phase alternating current ends of the six-pulse converter bridge circuit. In the scheme of the embodiment, the first inductance module can suppress the output current harmonics of the converter bridge circuit, and can also prevent direct current interruption. Moreover, the first inductance module can effectively filter high-frequency current harmonics generated in the commutation process, smooth the current waveform, reduce electromagnetic interference, and optimize the electromagnetic compatibility of the equipment.

[0038] The main function of the commutation voltage providing module is to provide additional or auxiliary commutation voltage for the main circuit during commutation. In the traditional converter, the commutation voltage completely depends on the alternating current source, but under certain conditions (such as grid failure or weak grid environment), the commutation voltage provided by the alternating current source may not be sufficient for the switch module to reliably commutate. Therefore, the commutation voltage providing module can compensate for this part of voltage loss, ensuring that commutation can be completed under any condition.

[0039] The commutation voltage providing module generates or compensates the voltage required for commutation, ensures that the thyristor can still provide sufficient commutation voltage under weak grid or fault conditions, avoids commutation failure caused by insufficient voltage on the alternating current side, and enhances the commutation reliability. By providing stable commutation voltage, even under adverse grid conditions, the normal commutation of the switch module can be ensured, the commutation failure can be prevented, and the operation stability and system reliability of the converter can be improved. When the grid strength is weakened or there is a fault, the commutation voltage providing module can actively intervene to provide necessary voltage support, so that the converter can maintain efficient and stable operation under various grid environments.

[0040] And, when the receiving end grid has a low short circuit ratio (SCR) or there is harmonic interference, the commutation voltage providing module can dynamically adjust the amplitude and phase of the commutation voltage to suppress the risk of continuous commutation failure. The short circuit ratio (SCR) of the receiving end grid is an indicator of the strength of the grid, which is defined as the ratio of the peak short circuit current of the grid to the rated DC current of the converter. In a weak grid (i.e., in the case of a low SCR), the voltage and current support capability of the AC power source is poor, which means that during the commutation process, the AC power source may not be able to provide enough voltage to ensure that the thyristor (or other switching module) is effectively turned off at the commutation point. This lack of voltage can increase the risk of commutation failure, i.e., the device cannot be turned off at the expected time, causing the current to flow abnormally between the bridge arms, thereby affecting the stability and efficiency of the entire DC system. Harmonic interference refers to voltage or current fluctuations at frequencies other than the fundamental frequency (50Hz or 60Hz) in the grid. These harmonics can be generated by power electronic devices, nonlinear loads, etc., which can interfere with the voltage waveform during the commutation process, causing deviations in the phase and amplitude of the commutation voltage. This deviation can also increase the probability of commutation failure, especially when the harmonics overlap with the key frequencies during the commutation process, which can seriously interfere with the normal operation of the device.

[0041] The commutation voltage providing module can cooperate with the control system through power electronic converters (such as full-bridge or half-bridge circuits composed of IGBTs) to monitor the waveforms of the AC side voltage and current in real time. Once it detects that the amplitude of the voltage is too low or the phase is not matched, the auxiliary circuit immediately intervenes to generate or adjust the commutation voltage to compensate for or improve this defect. In this way, even in the case of a weak grid or harmonic interference, the stability and accuracy of the commutation voltage can be ensured to meet the commutation requirements. Once commutation failure occurs, it can trigger a chain reaction, leading to continuous commutation failure, which can seriously affect system stability and power quality. The voltage regulation capability of the commutation voltage providing module responds immediately when the initial commutation failure occurs, actively provides or adjusts the commutation voltage to quickly restore the commutation conditions, avoiding the occurrence of continuous commutation failure, and enhancing the resistance of the HVDC system to commutation failure.

[0042] The above-mentioned converter of the present application comprises: a converter bridge circuit, a DC end of the converter bridge circuit being used for electrical connection with a DC bus, the converter bridge circuit comprising a plurality of converter bridge arms, one converter bridge arm comprising one commutation voltage providing module and a plurality of switching modules, the commutation voltage providing module being used for providing a commutation voltage for the converter, the commutation voltage providing module and all the switching modules being connected in series, and all the switching modules being connected in series; a plurality of first inductor modules, a first end of one first inductor module being connected with one phase AC end of the converter bridge circuit, and second ends of the first inductor modules being respectively used for connecting AC loads. During the commutation period of current rise and fall of the converter in normal operation, positive and negative voltages are generated, thereby charging the commutation voltage providing module. When voltage drop of the converter occurs, i.e. in the case of insufficient external commutation voltage, the commutation voltage providing module provides the pre-stored electric energy to the converter as the commutation voltage, thereby ensuring that sufficient commutation voltage can be provided for the converter under weak grid or fault conditions, avoiding commutation failure caused by insufficient AC side voltage, and solving the problem that the existing converter is prone to commutation failure when AC fault occurs.

[0043] In some embodiments, as shown in Figure 1 and Figure 2 The above-mentioned commutation voltage providing module 10 comprises: a transformer 11, a primary side of the above-mentioned transformer 11 being connected in series with a plurality of the above-mentioned switching modules 20; a voltage submodule 12, the above-mentioned voltage submodule 12 being electrically connected with a secondary side of the above-mentioned transformer 11, the above-mentioned voltage submodule 12 being used for providing an initial commutation voltage for the above-mentioned converter, and a ratio of the commutation voltage of the above-mentioned converter to the above-mentioned initial commutation voltage being a ratio of the number of turns of the primary side of the above-mentioned transformer 11 to the number of turns of the secondary side.

[0044] During normal operation of the converter valve, the bridge arm current is a trapezoidal wave, and during the commutation period of current rise and fall, the bridge arm transformer will generate positive and negative voltages, which can be transformed to the energy storage module (generally a capacitor) in the voltage submodule to charge. The specific current-voltage principle diagram is shown in Figure 3 , i.e. during the change of the bridge wall current I, the energy storage module (i.e. capacitor) in the voltage submodule is charged, and the capacitor voltage changes to U.

[0045] The primary function of a transformer is to boost or buck the initial commutation voltage generated by the voltage submodule to meet the voltage demands of the converter arm circuit. By changing the transformer's turns ratio, the output voltage can be increased to a preset multiple, ensuring that the commutation voltage meets the switching module's commutation requirements under various operating conditions. The transformer also provides electrical isolation, protecting the DC and AC sides of the converter from mutual electrical interference. Especially during grid faults, it prevents fault currents from directly affecting the DC side, protecting the DC system from damage. As a medium for energy transfer, the transformer transmits the energy stored in the voltage submodule to the arm circuit, providing the necessary energy support for the commutation process.

[0046] The voltage submodule is responsible for providing the initial commutation voltage during the commutation process. This voltage provides necessary support for normal commutation of the switching module when the grid voltage is insufficient or harmonic interference is present. When used in conjunction with a transformer, the initial commutation voltage output by the voltage submodule can be adjusted to a preset multiple, allowing the commutation voltage to adaptively adjust according to changes in converter operating conditions, ensuring stable and reliable operation of the converter under various operating environments. The voltage submodule typically contains energy storage elements (such as capacitors), which can be charged through the grid or auxiliary circuits during normal operation. When needed, the energy stored in the capacitors can be rapidly released to form the required commutation voltage, enhancing the converter's commutation capability.

[0047] The commutation voltage supply module, through the coordinated operation of the transformer and voltage submodule, can dynamically adjust the amplitude and phase of the commutation voltage when the short-circuit ratio (SCR) of the receiving-end grid is low or harmonic interference is present, ensuring reliable commutation of the switching module. This mechanism significantly enhances the converter's adaptability to grid changes, reduces the probability of commutation failure, and improves the overall operational stability and efficiency of the DC system. Especially in weak grid environments, the supply of auxiliary commutation voltage can prevent continuous commutation failures and maintain the continuity of DC current.

[0048] In some embodiments, such as Figure 2 As shown, the voltage submodule 12 includes: a filter circuit 121, the first end of which is electrically connected to the first end of the secondary side of the transformer 11, and the second end of which is electrically connected to the second end of the secondary side of the transformer 11; and a bridge circuit 122, the first end of which is electrically connected to the third end of the filter circuit 121, and the second end of which is electrically connected to the fourth end of the filter circuit 121.

[0049] The filtering circuit is primarily used to remove high-frequency noise and harmonic components from the voltage submodule output to obtain a clean, compliant commutation voltage waveform. This step is crucial for ensuring stable commutation of switching modules (such as IGBTs), as noise and harmonics can lead to device malfunctions or damage. The filtering circuit uses an inductor-capacitor assembly (LC filter) to convert the irregular, fluctuating voltage into a smoother waveform. This positively impacts the quality of the commutation voltage, reduces electromagnetic interference, and ensures the system's electromagnetic compatibility (EMC).

[0050] A bridge circuit typically refers to a full-bridge or half-bridge circuit, composed of multiple switching elements (such as IGBTs). Driven by control signals, the bridge circuit converts direct current (DC) to alternating current (AC), generating a commutation voltage that meets the frequency, amplitude, and phase requirements. It is the core component for dynamically adjusting the commutation voltage, capable of rapidly responding to the actual needs of the converter and providing the necessary support voltage. The bridge circuit performs an inverter function, converting DC from the voltage submodule into AC, a crucial step in constructing the auxiliary commutation voltage. The inverted voltage, after being adjusted by a transformer, compensates for insufficient AC side voltage, ensuring smooth commutation. By controlling the on and off states of the switching elements in the bridge circuit, the amplitude and phase of the output voltage can be adjusted to adapt to commutation requirements under different conditions. This flexibility enables the system to cope with grid fluctuations and faults, enhancing the robustness and adaptability of the converter. In some designs, bridge circuits can also support bidirectional power flow, meaning that they can not only provide auxiliary commutation voltage to the converter when needed, but also feed energy back to the storage unit during non-commutation phases, achieving efficient energy management and utilization.

[0051] In some embodiments, such as Figure 4 As shown, the bridge circuit 122 includes: a first switch assembly Q1, a second switch assembly Q2, a third switch assembly Q3, and a fourth switch assembly Q4 connected in a full-bridge structure. The first end of the first switch assembly Q1 is electrically connected to the second end of the second switch assembly Q2 and the third end of the filter circuit 121, the second end of the first switch assembly Q1 is electrically connected to the second end of the third switch assembly Q3, the first end of the third switch assembly Q3 is electrically connected to the second end of the fourth switch assembly Q4 and the fourth end of the filter circuit 121, and the first end of the second switch assembly Q2 is electrically connected to the first end of the fourth switch assembly Q4; and a first capacitor module C1, the first end of the first capacitor module C1 is electrically connected to the second end of the first switch assembly Q1 and the second end of the third switch assembly Q3, and the second end of the first capacitor module C1 is electrically connected to the first end of the second switch assembly Q2 and the first end of the fourth switch assembly Q4.

[0052] A full-bridge circuit efficiently converts direct current (DC) to alternating current (AC), providing the necessary commutation voltage for the commutation process. By controlling the on and off states of each switching component, the bridge circuit can generate an AC voltage with a specific frequency, phase, and amplitude based on a preset modulation wave. This dynamically generated voltage can compensate for or enhance the voltage of the external AC power supply, ensuring smooth commutation, especially under grid fault or weak grid conditions. Due to its nature, the full-bridge circuit can support bidirectional power flow. During commutation, when auxiliary voltage is required, the full-bridge circuit can output the energy stored in the first capacitor module C1 in AC form; when the system does not require additional commutation voltage support, the full-bridge circuit can convert the energy received from the AC side into DC energy and store it in capacitor C1. This energy regeneration and recycling improves system energy efficiency, reduces energy waste, and enhances system response speed and flexibility.

[0053] When a voltage drop occurs and the external commutation voltage is insufficient, the power electronic conversion module of each bridge arm, according to the control strategy, is instructed to complete the voltage inverter output according to the specified modulation wave. This voltage is then applied to each bridge arm through a transformer in series, thus completing the auxiliary voltage construction.

[0054] In some embodiments, such as Figure 5 As shown, the bridge circuit includes: a fifth switch assembly Q5 and a sixth switch assembly Q6 connected in a half-bridge structure, wherein the first end of the fifth switch assembly Q5 is electrically connected to the second end of the sixth switch assembly Q6 and the third end of the filter circuit 121; a second capacitor module C2, wherein the first end of the second capacitor module C2 is electrically connected to the second end of the fifth switch assembly Q5 and the second end of the second capacitor module C2 is grounded; and a third capacitor module C3, wherein the first end of the third capacitor module C3 is grounded and the second end of the third capacitor module C3 is electrically connected to the first end of the sixth switch assembly Q6.

[0055] The half-bridge circuit is composed of two controllable switches (such as IGBT or MOSFET) and two capacitors. Two switch components Q5 and Q6 control the connection of one end of capacitors C2 and C3 to other parts of the circuit, while the other end of the capacitors is grounded. This structure allows each capacitor to alternately act as a positive or negative power supply, generating an alternating voltage output. When the fifth switch component Q5 is turned on, the DC power supply (or energy storage capacitor C2) forms a path with one end of the load, while the other end is grounded through the parallel diode of the sixth switch component Q6 (when Q6 is off), thereby forming a forward voltage across the load. When Q5 is off and Q6 is on, the other end of the DC power supply (or energy storage capacitor C3) forms a path with the load, while the other end of the load is grounded through the parallel diode of Q5, forming a reverse voltage, i.e. a negative voltage across the load. By rapidly switching the state of Q5 and Q6, the half-bridge circuit can alternately generate positive and negative voltages across the load, thereby forming an alternating voltage output. Capacitors C2 and C3 act as energy storage and voltage smoothing in the circuit, ensuring the continuity of power supply and the stability of voltage during switching.

[0056] The two capacitor modules C2 and C3 also provide necessary voltage isolation to prevent the voltage across the load from directly affecting the DC power supply side. In addition, they can provide voltage support to the circuit during switching, prevent voltage drop, and ensure smooth and stable inverter process.

[0057] In some embodiments, as shown in FIGS. 1A and 1B, the switch component includes an IGBT device and a diode connected in parallel with the IGBT, the anode of the diode is electrically connected to the source of the IGBT device, and the cathode of the diode is electrically connected to the drain of the IGBT device. Figure 4 and Figure 5 The anode of the diode is electrically connected to the source of the IGBT device, and the cathode of the diode is electrically connected to the drain of the IGBT device.

[0058] IGBT is a power electronic device that can switch quickly, combining the high-speed switching characteristics of MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and the high current carrying capacity of bipolar transistor. In the bridge circuit of the inverter, the fast switching of IGBT can accurately control the frequency, phase and amplitude of the output power, thereby efficiently generating the required commutation voltage.

[0059] The diode connected in parallel between the source and drain of the IGBT provides a free-wheeling path for the current in the circuit when the IGBT is off. This means that when the IGBT is off and there is still residual current in the circuit, the current can flow back to the power supply or load side through the diode, preventing voltage spikes when the current is suddenly interrupted, protecting the IGBT and other circuit components.

[0060] In a bridge circuit, when the IGBT is turned off, a reverse voltage present in the circuit can cause the IGBT to break down. The parallel diode can prevent this from happening because its forward conduction characteristic allows the reverse voltage to be shorted by the diode, thus avoiding the IGBT from being subjected to the reverse voltage, prolonging the service life of the IGBT, and improving the reliability of the system.

[0061] Through the combined use of IGBT and parallel diode, the switching assembly can achieve fast and reliable switching action while protecting the circuit from reverse voltage and current spikes, ensuring smooth and efficient commutation process in high voltage direct current (HVDC) systems. This not only enhances the stability of the system, but also improves its ability to cope with grid fluctuations and faults.

[0062] Some embodiments, as shown in Figure 2 The filter circuit 121 includes a second inductor module L2, the first end of the second inductor module L2 is electrically connected to the first end of the bridge circuit 122; a fourth capacitor module C4, the first end of the fourth capacitor module C4 is electrically connected to the second end of the second inductor module L2, and the second end of the fourth capacitor module C4 is electrically connected to the second end of the bridge circuit 122.

[0063] Specifically, the use of LC filter can significantly improve the electromagnetic compatibility of the system. It reduces the electromagnetic interference (EMI) generated by the device, while also reducing the impact of external electromagnetic interference on the internal circuit, which is crucial for the stability of power electronic devices in actual application environment, especially in high voltage direct current transmission systems, good EMC performance helps to reduce the interference to the surrounding equipment and improve the anti-interference ability of itself. LC filter can protect the subsequent circuit from the influence of transient voltage and current from the output of the bridge circuit. These transient phenomena can cause damage to sensitive electronic devices, and by filtering them out, the normal operation of the subsequent circuit can be ensured.

[0064] In summary, the filter circuit 121, through the combined use of the second inductor module L2 and the fourth capacitor module C4, can achieve multiple effects such as smoothing of output voltage, filtering of high-frequency harmonics, improvement of electromagnetic compatibility, and protection of subsequent circuits. Through the precise design and optimization of the LC filter, the voltage ripple and electromagnetic interference can be minimized, so that the commutation voltage supply module can stably output high-quality commutation auxiliary voltage under various grid conditions, including weak grid and harmonic environment, ensuring the normal commutation and continuous operation of the HVDC converter.

[0065] Specifically, the existing related solutions to resist commutation failure are mostly from the aspects of predictive control and topology modification, which have problems of complex logic and high modification difficulty. The above embodiments construct a circuit through a commutation voltage providing module without modifying the original bridge arm series structure and replacing the bridge arm elements, only adding a series transformer and a secondary side power electronic conversion energy storage module. Not only is the control method simple, but the energy storage link is uncontrolled rectification, and the inverter strategy is only used when the auxiliary commutation voltage is constructed, without affecting normal operation. That is, the above converter is mainly used to actively construct commutation voltage when the commutation area is insufficient due to AC fault of the converter, the purpose is to improve the operation reliability of the converter and the ability to resist commutation failure.

[0066] In some embodiments, as shown in Figure 1 The above converter bridge circuit includes: a converter bridge arm, the converter bridge arm includes an upper bridge arm and a lower bridge arm, the first end of each upper bridge arm is connected respectively and forms a common end as a first DC end, the first end of each lower bridge arm is connected respectively and forms a common end as a second DC end, the second end of one upper bridge arm is connected to the second end of one lower bridge arm respectively, and the common end formed is an AC end of one phase, and the first DC end and the second DC end are electrically connected to the DC bus.

[0067] Wherein, the types and quantities of upper bridge arms and lower bridge arms are consistent, and the specific quantity will be different according to the type of converter bridge circuit. In one embodiment, the converter bridge circuit is a six-pulse converter bridge circuit, and accordingly, it includes six bridge arms, including three upper bridge arms and three lower bridge arms.

[0068] The converter bridge circuit can provide voltage support and current smoothing between the DC side and the AC side through the cooperation of the upper bridge arm and the lower bridge arm. On the DC side, the converter bridge circuit can use the voltage on the DC bus to provide stable AC voltage to the AC side through the control of the switching device. On the AC side, the converter bridge circuit can adjust the waveform of the output current by controlling the switching state of the bridge arm, reduce the harmonic component in the current, and improve the quality of the output electric energy. The three-phase output of the converter bridge circuit matches the three-phase input of the power grid, and by controlling the switching state of each bridge arm in the converter bridge circuit, seamless connection with the power grid can be achieved. This design ensures that the converter can adapt to the voltage and frequency changes of the power grid, and also improves the energy transmission efficiency between the converter and the power grid.

[0069] In addition, the current and voltage waveform diagram of the IGCT on the bridge arm is as shown in Figure 6 For the IGCT series structure shown in Figure 6 , it works at a switching frequency of 50Hz, and alternately turns on and off.

[0070] The switch module includes electrically connected semiconductor devices and voltage equalization circuits, different semiconductor devices correspond to different voltage equalization circuits, and the semiconductor devices are one of thyristors, IGCT devices, and IGBT devices. Figure 7 、 Figure 8 and Figure 9 . Figure 7 is a structural schematic diagram of a thyristor and a voltage equalization circuit thereof, including resistors R1, R2, a capacitor C5, and a thyristor, wherein the capacitor C5 and the resistor R2 are connected in series, a branch formed by the capacitor C5 and the resistor R2 is connected in parallel on both sides of the thyristor, and the resistor R1 is also connected in parallel on both sides of the thyristor. Figure 8 is a structural schematic diagram of an IGCT device and a voltage equalization circuit thereof, including a lightning arrester MOV, resistors R3, R4, a capacitor C6, and an IGCT device, wherein the capacitor C6 and the resistor R4 are connected in series, a branch formed by the capacitor C6 and the resistor R4 is connected in parallel on both sides of the IGCT device, and the resistor R3 and the lightning arrester MOV are also connected in parallel on both sides of the IGCT device. Figure 9 is a structural schematic diagram of an IGBT device and a voltage equalization circuit thereof, including resistors R5, R6, R7, capacitors C7, C8, diodes D1, D2, and an IGBT device, wherein a first end of the resistor R7 is electrically connected to a control end of the IGBT device, a first end of the IGBT device is electrically connected to a positive electrode of the diode D2, a second end of the IGBT device is electrically connected to a negative electrode of the diode D2, a second end of the resistor R7 is electrically connected to a negative electrode of the diode D1, a positive electrode of the diode D1 is electrically connected to the resistors R5, R6, the capacitors C7, C8, respectively, the resistor R5 is connected in parallel with the capacitor C7, and the resistor R6 is connected in parallel with the capacitor C7.

[0071] The converter of the present application can also accurately determine whether there is a voltage deficiency in the commutation process by monitoring the current commutation parameters of the converter in real time, such as the inversion angle. If the AC side voltage drops, resulting in insufficient commutation voltage to support the commutation process, the system automatically generates a compensation commutation voltage to ensure the smooth progress of the commutation process. This greatly reduces the probability of commutation failure and improves the reliability of the converter operation.

[0072] When the power grid fails, such as voltage sag or harmonic interference, the traditional converter may fail to commutate smoothly due to insufficient commutation voltage, and even may cause commutation failure and system shutdown. The converter in the embodiment generates forward and reverse voltages during current rise and fall commutation in normal operation, thereby charging the commutation voltage providing module. When the converter experiences voltage drop, i.e. insufficient external commutation voltage, the commutation voltage providing module provides the pre-stored electrical energy to the converter as the commutation voltage, thereby ensuring that sufficient commutation voltage is provided for the converter under weak grid or fault conditions, avoiding commutation failure due to insufficient AC side voltage, and solving the problem of commutation failure of the existing converter when AC fault occurs. Since the converter can generate the required commutation voltage itself, even in poor grid quality conditions, the converter can ensure smooth commutation through self-regulation. This reduces the dependence of the converter on grid stability and quality, allowing the converter to maintain high performance and high reliability under a wider range of grid operating conditions.

[0073] In summary, the above-mentioned converter can achieve a more stable and reliable commutation process, and can maintain high efficiency even in grid fault or weak grid environment, which not only improves the overall performance of the power system, but also enhances its ability to cope with grid abnormalities, providing strong technical support for high voltage direct current (HVDC) systems, and helping to improve the safety and economy of power transmission.

[0074] Among them, as shown in Figure 8 , the relationship between the compensation voltage output by the inverter and the capacitor voltage after passing through the series transformer is: , is the voltage of the primary side of the transformer (i.e. the maximum voltage compensation voltage value), is the voltage of the secondary side of the transformer, n is the transformer ratio, and m is the upper limit of the modulation ratio of the system, is the DC side voltage of the commutation voltage providing module (i.e. the capacitor voltage). Therefore, the transformer ratio can be calculated according to the upper limit of the modulation ratio of the device, the DC voltage value and the maximum voltage compensation voltage value.

[0075] In other embodiments, as shown in Figure 10 , the converter further includes a bypass switch 40, which can be a mechanical switch such as a relay, or a switching device with a control terminal such as a MOS tube. The bypass switch is used to conduct when the converter is being repaired or the commutation voltage providing module fails, to isolate the commutation voltage providing module.

[0076] Any technical features in the above-described embodiments can be combined in any manner, and for the sake of brevity, not all possible combinations are described, but it is understood that the application encompasses all such possible combinations.

[0077] It should also be noted that the terms "comprising", "containing", or any other similar term are intended to encompass non-exclusive inclusions, such that a process, method, article, or apparatus that comprises a list of elements does not include those elements solely, but can also include other elements not expressly listed, or also include elements inherent in such process, method, article, or apparatus. Without more limitations, an element defined by the phrase "comprising a" does not exclude the existence of additional identical elements in the process, method, article, or apparatus that includes the element.

[0078] From the above description, it can be seen that the above-described embodiments of the application achieve the following technical effects:

[0079] The above-described converter of the application comprises: a converter bridge circuit, a direct current end of the converter bridge circuit being used for electrical connection with a direct current bus, the converter bridge circuit comprising a plurality of converter bridge arms, one converter bridge arm comprising one commutation voltage providing module and a plurality of switching modules, the commutation voltage providing module being used for providing a commutation voltage for the converter, the commutation voltage providing module and all the switching modules being in series, and all the switching modules being in series; and a plurality of first inductor modules, a first end of one first inductor module being connected to one phase alternating current end of the converter bridge circuit, and second ends of the first inductor modules being respectively used for connecting alternating current loads. During commutation of current rise and fall of the converter in normal operation, positive and negative voltages are generated, so as to charge the commutation voltage providing module. When voltage drop of the converter occurs, i.e., in the case of insufficient external commutation voltage, the commutation voltage providing module provides the pre-stored electric energy to the converter as the commutation voltage, so as to ensure that sufficient commutation voltage is provided for the converter under weak power grid or fault condition, and commutation failure caused by insufficient alternating current side voltage is avoided, and the problem of commutation failure of the existing converter when alternating current fault occurs is solved.

[0080] The above only describes the preferred embodiments of the application and is not intended to limit the application. The application can have various modifications and changes for those skilled in the art. 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 converter, characterized by The application relates to a converter circuit, comprising: a converter bridge circuit, a direct current end of the converter bridge circuit being used for electrical connection with a direct current bus, the converter bridge circuit comprising a plurality of converter bridge arms, one of the converter bridge arms comprising one commutation voltage providing module and a plurality of switch modules, the commutation voltage providing module being used for providing a commutation voltage for a converter, the commutation voltage providing module and all the switch modules being connected in series on one of the converter bridge arms, all the switch modules being connected in series; a plurality of first inductance modules, a first end of one of the first inductance modules being connected with an alternating current end of one phase of the converter bridge circuit, second ends of the first inductance modules being respectively used for connecting with alternating current loads.

2. The converter of claim 1, characterized in that The commutation voltage providing module comprises: a transformer, a primary side of the transformer being connected in series with the plurality of switch modules; a voltage sub-module, the voltage sub-module being electrically connected with a secondary side of the transformer, the voltage sub-module being used for providing an initial commutation voltage for the converter, a ratio of the commutation voltage of the converter to the initial commutation voltage being a ratio of a primary side turn number of the transformer to a secondary side turn number.

3. The converter of claim 2, wherein, The voltage sub-module comprises: a filter circuit, a first end of the filter circuit being electrically connected with a first end of the secondary side of the transformer, a second end of the filter circuit being electrically connected with a second end of the secondary side of the transformer; a bridge circuit, a first end of the bridge circuit being electrically connected with a third end of the filter circuit, a second end of the bridge circuit being electrically connected with a fourth end of the filter circuit.

4. The converter of claim 3, wherein, The bridge circuit comprises: a first switch assembly, a second switch assembly, a third switch assembly and a fourth switch assembly connected in a full-bridge structure, a first end of the first switch assembly being electrically connected with a second end of the second switch assembly and a third end of the filter circuit respectively, a second end of the first switch assembly being electrically connected with a second end of the third switch assembly, a first end of the third switch assembly being electrically connected with a second end of the fourth switch assembly and a fourth end of the filter circuit respectively, a first end of the second switch assembly being electrically connected with a first end of the fourth switch assembly; a first capacitance module, a first end of the first capacitance module being electrically connected with the second end of the first switch assembly and the second end of the third switch assembly respectively, a second end of the first capacitance module being electrically connected with the first end of the second switch assembly and the first end of the fourth switch assembly respectively.

5. The converter of claim 3, wherein, The bridge circuit comprises: a fifth switch assembly and a sixth switch assembly connected in a half-bridge structure, a first end of the fifth switch assembly being electrically connected with a second end of the sixth switch assembly and a third end of the filter circuit respectively; a second capacitance module, a first end of the second capacitance module being electrically connected with a second end of the fifth switch assembly, a second end of the second capacitance module being grounded; a third capacitance module, a first end of the third capacitance module being grounded, a second end of the third capacitance module being electrically connected with a first end of the sixth switch assembly.

6. The converter according to claim 4 or 5, characterized in that The switch assembly comprises an IGBT device and a diode connected in parallel with the IGBT, a positive electrode of the diode being electrically connected with a source electrode of the IGBT device, a negative electrode of the diode being electrically connected with a drain electrode of the IGBT device.

7. The converter of claim 3, wherein, The filter circuit comprises: A second inductor module, a first end of the second inductor module being electrically connected with a first end of the bridge circuit; A fourth capacitor module, a first end of the fourth capacitor module being electrically connected with a second end of the second inductor module, and a second end of the fourth capacitor module being electrically connected with a second end of the bridge circuit.

8. The converter of claim 1, wherein, The converter bridge circuit comprises: A converter bridge arm, each of the upper bridge arms having a first end connected and forming a common end as a first DC end, each of the lower bridge arms having a first end connected and forming a common end as a second DC end, a second end of one of the upper bridge arms being connected with a second end of one of the lower bridge arms, and a common end formed thereby being as a phase AC end, the first DC end and the second DC end being electrically connected with the DC bus.

9. The converter of claim 1, wherein, The switching module comprises semiconductor devices and voltage equalization circuits electrically connected, different semiconductor devices corresponding to different voltage equalization circuits, and the semiconductor devices being one of thyristor, IGCT device and IGBT device.

10. A power transmission system characterized by, The converter comprises: The converter of any one of claims 1 to 9.

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