Network-forming rectifier and multi-terminal flexible direct current system line fault handling method and system

Abstract

The invention provides a network-forming rectifier and a multi-terminal flexible direct current system line fault handling method and system. The network-forming rectifier comprises a first IGBT, a second IGBT, a first diode and a second diode. The first IGBT and the first diode are connected in series to form a first branch; the second IGBT and the second diode are connected in series to form a second branch; the first IGBT and the second IGBT are respectively controlled by a pulse width modulation signal; when the direct-current power grid operates normally, the second IGBT is kept in a normally-open state, and the first IGBT is controlled according to the active power reference value and the reactive power reference value; and when the DC power grid has a fault, the first IGBT is kept in a normally open state, and the second IGBT performs control according to the current reference value so as to provide current for a fault point to assist in fault positioning. Through accurate control of the IGBT, accurate control of the power of the power grid can be realized, and the load requirement and the stability requirement of the power grid are met.

Description

Technical Field

[0001] The present invention relates to the technical field of direct current transmission, and in particular to a grid-forming rectifier and a multi-terminal flexible direct current system line fault handling method and system. Background Art

[0002] With the widespread application of renewable energy and the increasing demand for high-efficiency transmission in power systems, traditional AC power grids have gradually shown some limitations, such as power loss, poor stability, and difficulty in scheduling. DC grid-forming rectification technology is one of the important development directions in the field of power systems in recent years. The DC grid-forming rectification system usually consists of multiple rectifiers and DC transmission lines. The rectifier converts AC power into DC power, thereby achieving efficient transmission of electric energy. This system not only improves the efficiency of power transmission, but also achieves more accurate power scheduling through flexible control. Especially in multi-terminal flexible DC transmission systems, DC grid-forming rectification technology can effectively solve the problems of power flow and stability in traditional power systems.

[0003] Multi-terminal flexible DC transmission system is an important development direction of DC transmission technology. Compared with the traditional point-to-point DC transmission system, the multi-terminal flexible DC system has the advantages of high flexibility, strong fault isolation capability, strong grid connection capability, and precise voltage control. Although the multi-terminal flexible DC system has many advantages, the line fault problem is still a challenge that cannot be ignored in actual operation. When a DC transmission system fails, the traditional method requires the circuit breaker to isolate the fault, reconfigure the grid, transfer the load, and so on. However, after the fault occurs, it is difficult for the traditional method to accurately determine the fault, resulting in the inability to be effectively removed in a timely manner, which affects the safety of the entire power grid. Summary of the invention

[0004] In view of this, the present invention provides a grid-type rectifier and a multi-terminal flexible DC system line fault handling method and system to solve at least one of the above-mentioned problems.

[0005] In order to achieve the above object, the present invention adopts the following scheme:

[0006] According to a first aspect of the present invention, a mesh rectifier is provided, the mesh rectifier is connected between an AC power grid and a DC power grid, and the mesh rectifier comprises: a first insulated gate bipolar transistor and a second insulated gate bipolar transistor, and a first diode and a second diode; the first insulated gate bipolar transistor is connected in series with the first diode to form a first branch; the second insulated gate bipolar transistor is connected in series with the second diode to form a second branch; the first branch and the second branch are connected in parallel to the DC power grid and are respectively connected to the positive and negative poles of the DC power grid; the first insulated gate bipolar transistor and the second insulated gate bipolar transistor are respectively controlled by a pulse width modulation signal; when the DC power grid operates normally, the second insulated gate bipolar transistor remains in a normally open state, and the first insulated gate bipolar transistor is controlled according to active power and reactive power reference values; when a fault occurs in the DC power grid, the control strategies of the first insulated gate bipolar transistor and the second insulated gate bipolar transistor are switched, the first insulated gate bipolar transistor remains in a normally open state, and the second insulated gate bipolar transistor is controlled according to a current reference value to provide current to the fault point to assist in fault location.

[0007] As an embodiment of the present invention, the first diode and the second diode are used to process reverse current, and respectively protect the first insulated gate bipolar transistor and the second insulated gate bipolar transistor connected in series from being affected by reverse current.

[0008] As an embodiment of the present invention, the pulse width modulation signal is generated by a proportional-integral controller, and the proportional-integral controller is adjusted according to the deviation between the active power, reactive power or current reference value and the actual value; when the DC power grid is operating normally, dual-loop control is adopted, the outer loop takes the deviation between the active power and reactive power reference value and the actual value as input, and the inner loop adopts voltage and current dual closed-loop control; when a fault occurs in the DC power grid, the control strategy is switched, the outer loop takes the deviation between the current reference value and the actual value as input, and the inner loop adopts voltage and current dual closed-loop control.

[0009] As an embodiment of the present invention, the current reference value is calculated based on the known constant terminal voltage, internal impedance and actual operating voltage.

[0010] As an embodiment of the present invention, the above-mentioned grid-type rectifier further includes a filter, which is arranged at the output end of the grid-type rectifier and is used to filter out ripple components in the DC grid voltage.

[0011] According to a second aspect of the present invention, a multi-terminal flexible DC system line fault handling method is provided, the fault handling method uses the grid-type rectifier as described above; the fault handling method comprises: when the DC power grid operates normally, controlling the grid-type rectifier according to active power and reactive power reference values; when a fault occurs in the DC power grid, switching the control strategy, controlling the grid-type rectifier according to a current reference value to provide current to the fault point; and assisting in judging the system fault according to whether the reactive power output is zero at the time of the fault.

[0012] As an embodiment of the present invention, the method of assisting in judging a system fault according to whether the reactive power output is zero at the time of the fault comprises: if the reactive power output is not zero, judging that a system fault occurs, and prompting fault occurrence information.

[0013] According to a third aspect of the present invention, there is provided a multi-terminal flexible direct current system line fault handling system, the system comprising the above-mentioned meshed rectifier, a comparator, a proportional-integral controller, a voltage-current loop control unit and a fault diagnosis unit, the comparator comparing an active power reference value, a reactive power reference value or a current reference value with their actual values; the proportional-integral controller respectively receives output deviation signals of the comparator and generates corresponding control signals; the voltage-current loop control unit receives the control signal of the proportional-integral controller and generates corresponding pulse width modulation signals to control the on and off of a first insulated gate bipolar transistor and a second insulated gate bipolar transistor in the meshed rectifier, the fault diagnosis unit monitors reactive power output, and uses the reactive power output not being zero as a basis for auxiliary judgment of system faults.

[0014] According to a fourth aspect of the present invention, there is provided an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the computer program.

[0015] According to a fifth aspect of the present invention, there is provided a computer-readable storage medium having a computer program stored thereon, wherein the computer program implements the steps of the above method when executed by a processor.

[0016] The grid-type rectifier and multi-terminal flexible direct current system line fault handling method and system proposed in the present invention utilize the grid-type rectifier (IGBT) of the present application, and adopt dual-loop control when the DC power grid is operating normally to ensure the stable operation of the system. When a fault occurs, the control strategy switches to current control, provides current to the fault point, maintains system stability, and assists in judging system faults by monitoring reactive power output, thereby enhancing system reliability. Moreover, the grid-type rectifier topology proposed in the present application utilizes dual IGBTs and dual diodes, which can effectively handle reverse currents, protect IGBTs from damage, and improve the reliability and service life of the rectifier. In addition, the present application can achieve precise control of power grid power through precise control of IGBTs, meeting the load demand and stability requirements of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0018] Figure 1 It is a structural schematic diagram of a grid-type rectifier provided in an embodiment of the present application;

[0019] Figure 2 It is a schematic diagram of the control strategy of the grid-forming rectifier when the DC grid is operating normally and when a fault occurs, provided in an embodiment of the present application;

[0020] Figure 3 It is a schematic diagram of a segmented low voltage protection structure based on a grid-type rectifier control strategy provided by an embodiment of the present invention;

[0021] Figure 4 It is a structural diagram of a multi-terminal flexible direct current system line fault handling method provided by an embodiment of the present application;

[0022] Figure 5 It is a structural schematic diagram of an electronic device provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0023] To make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments of the present invention and their descriptions are used to explain the present invention, but are not intended to limit the present invention.

[0024] As mentioned above, when a fault occurs in a DC transmission system, the traditional method requires isolating the fault with a circuit breaker, reconfiguring the grid, transferring the load, etc. However, after a fault occurs, it is difficult to accurately determine the fault using the traditional method, resulting in the failure to be removed in a timely and effective manner, thus affecting the safety of the entire grid.

[0025] At present, the rapid development of power electronics technology has made it occupy an important position in the power system. The rectifier is one of the key devices in the multi-terminal DC power grid. In addition to converting AC power into DC power, it can also control the output DC voltage and current to meet the load demand and stability requirements of the power grid. By adjusting the operation of the rectifier, precise control of the power grid power can be achieved. Therefore, on this basis, the inventor adjusted its structure, proposed a meshed rectifier topology, and studied its control strategy during normal operation and failure of the DC power grid, and introduced the segmented low-voltage protection of relay protection on the basis of the control strategy so that the fault location can be quickly and timely located.

[0026] like Figure 1 The figure shows a schematic diagram of the structure of a grid-type rectifier provided in an embodiment of the present application. The "grid-type rectifier" here refers to a rectifier with a special control strategy and topological structure in a multi-terminal flexible direct current transmission system, which can participate in fault diagnosis and location, and assist in fault isolation. Its function and role in the multi-terminal direct current grid is that it participates in the construction and fault handling of the grid, rather than being just a simple power conversion device.

[0027] The grid-type rectifier is connected between the AC grid and the DC grid. Figure 1 As shown, the grid-type rectifier includes: a first insulated gate bipolar transistor 10, a second insulated gate bipolar transistor 20, a first diode 30 and a second diode 40. The first insulated gate bipolar transistor 10 and the first diode 30 are connected in series to form a first branch, and the second insulated gate bipolar transistor 20 and the second diode 40 are connected in series to form a second branch. The first branch and the second branch are connected in parallel to the DC grid and are respectively connected to the positive and negative electrodes of the DC grid.

[0028] The first insulated gate bipolar transistor 10 and the second insulated gate bipolar transistor 20 are respectively controlled by a pulse width modulation signal. When the DC power grid operates normally, the second insulated gate bipolar transistor 20 remains in a normally open state, and the first insulated gate bipolar transistor 10 is controlled according to active power and reactive power reference values. When a fault occurs in the DC power grid, the control strategies of the first insulated gate bipolar transistor 10 and the second insulated gate bipolar transistor 20 are switched, the first insulated gate bipolar transistor 10 remains in a normally open state, and the second insulated gate bipolar transistor 20 is controlled according to a current reference value to provide current to the fault point to assist in fault location.

[0029] Insulated gate bipolar transistor (IGBT) is a semiconductor material that can switch quickly in power conversion and is suitable for high voltage and high current applications. In addition, because it can accurately control the flow of current and achieve power regulation, when a fault occurs, the IGBT can control the output current and voltage by adjusting its gate voltage. This control capability enables the IGBT to simulate the behavior of a controlled voltage source in the event of a fault, that is, it can adjust the output voltage as needed to maintain system stability and safety.

[0030] In this application, the mesh rectifier topology structure using dual IGBTs and dual diodes combines the advantages of IGBTs and diodes, thereby achieving efficient power conversion and control. Through fine control, IGBTs can achieve pulse width modulation: when forward conducting, in the positive half cycle of AC, one IGBT is turned on, allowing current to flow to the load, while the other IGBT remains in the off state; when reverse blocking, in the negative half cycle of AC, the previously turned-on IGBT is turned off in time, and the previously turned-off IGBT remains in the blocking state to prevent current from flowing in the reverse direction.

[0031] In the mesh rectifier of the present application, dual diodes are connected in series on both sides of the dual IGBTs to handle reverse current, especially when the IGBT is turned off. During forward conduction, in the positive half cycle of the alternating current, the diode is suppressed, and the current is mainly conducted by the left IGBT; during reverse breakdown, in the negative half cycle of the alternating current, the left IGBT is turned off, the diode breaks down and conducts, and the current flows to the load through the diode. Since the IGBT cannot withstand reverse voltage, the presence of the diode can protect the IGBT from the influence of reverse current and prevent it from reverse breakdown damage. It can be seen that the dual diodes can respectively protect the first insulated gate bipolar transistor 10 and the second insulated gate bipolar transistor 20 connected in series from the influence of reverse current.

[0032] Preferably, the pulse width modulation signal (PWM) is generated by a proportional integral controller, and the proportional integral controller (PI controller) is adjusted according to the deviation between the active power, reactive power or current reference value and the actual value; when the DC power grid operates normally, dual-loop control is adopted, the outer loop takes the deviation between the active power and reactive power reference value and the actual value as input, and the inner loop adopts voltage and current dual closed-loop control; when a fault occurs in the DC power grid, the control strategy is switched, the outer loop takes the deviation between the current reference value and the actual value as input, and the inner loop adopts voltage and current dual closed-loop control, and finally flows into the AC power grid after passing through the filter.

[0033] Specifically, the control strategy of the grid-forming rectifier during normal operation and fault condition of the DC grid can be found in Figure 2 As shown. Figure 2It can be seen that when the DC power grid is operating normally, a dual-loop control method is adopted, the outer loop uses active power and reactive power as input, and the inner loop uses voltage and current loop control. ref , Q ref , and then compare it with the actual input active and reactive power, respectively enter the voltage and current inner loop control through the PI controller, and then output the PWM signal to the mesh rectifier bridge circuit. In this case, it should be noted that the output PWM is for the IGBT on the left side of the mesh rectifier bridge circuit (i.e., the first insulated gate bipolar transistor 10), and the IGBT on the right side of the bridge (the second insulated gate bipolar transistor 20) remains in a normally open state, and at this time the mesh rectifier plays the role of inverter. The DC voltage output by the mesh rectifier will contain a certain degree of ripple, i.e., AC component. Since the average voltage output by the rectifier is usually less than the ideal DC voltage, there will be instantaneous voltage fluctuations. Furthermore, preferably, the present embodiment may also include a filter, which is arranged at the output end of the mesh rectifier, and is used to filter out the ripple component in the DC grid voltage to reduce its volatility.

[0034] Continue to see Figure 2 When the DC grid fails, the input reference value changes. Since the grid-type rectifier is on the DC grid side, it only consumes active power. Although the reactive power is still the reference value, Q ref =0; after a fault occurs, according to the control method of the grid-type rectifier, a voltage source with a known constant terminal voltage and internal impedance is set, and another reference input quantity at the input end is the current I ref ,have:

[0035]

[0036] Where: is a known constant terminal voltage; R x is the internal impedance; U DC is the actual operating voltage.

[0037] Q ref ,I ref As a reference value, it is compared with the reactive power Q and current I in the actual power grid, and after PI control, the voltage and current inner loop control outputs the PWM signal. At this time, the PWM signal is aimed at the IGBT on the right side of the bridge circuit, and the IGBT on the left side remains in a normally open state, and the entire grid-type rectifier plays a rectifying role.

[0038] By comparing the changes in operating parameters under different conditions, through different control methods of the grid-forming rectifier, it is possible to determine whether a fault has occurred in the power grid, thereby providing a basis for further fault removal. During normal operation, the reference value is active and reactive power; after a fault occurs, since the IGBT is equivalent to a controlled voltage source, only active power is output at this time, and the reference value is current. If reactive power occurs in the system, it is diagnosed as a fault.

[0039] The grid-forming rectifier of the present application is applied in a multi-terminal flexible DC transmission system, and after a fault is determined to occur in the above manner, in order to further determine the fault and quickly remove the fault, a segmented low voltage protection may also be added, such as Figure 3 The figure shows a schematic diagram of the segmented low voltage protection structure based on the grid-type rectifier control strategy. Figure 3 It can be seen that multiple mesh-type rectifiers are respectively connected between the AC power grid and the DC power grid. When a fault occurs in the DC power grid, the first section of low voltage protection is for the instantaneous period, which is mainly used to deal with the problem of instantaneous voltage drop. When the voltage drops rapidly below the set threshold, it will immediately take action to prevent the equipment from being affected by the voltage sag; the second section of low voltage protection is for the delay period, and usually a longer delay time is set to deal with the situation where the voltage is continuously lower than the set threshold, to ensure that the equipment will not act frequently when the voltage fluctuates, and at the same time, the protection can be triggered when the voltage is continuously lower than the set value; the third section of low voltage protection is for the disconnection section, which is used to deal with serious and continuous low voltage problems. This section of protection usually has a longer delay and a lower set value, which is used to ensure that the load can be disconnected under long-term low voltage conditions to protect the equipment and system.

[0040] Segmented low voltage protection can locate the fault position quickly and timely because it divides the DC transmission line into several protection sections, each of which is equipped with an independent low voltage protection device. When a line fault occurs, the voltage of the protection section near the fault point will drop rapidly, while the voltage of other protection sections will remain relatively stable. By monitoring the voltage changes of each protection section, the location of the fault can be quickly determined. In addition, there are mechanical switches at the nodes in the DC power grid, which can be turned off according to the determination of the fault location, thereby quickly removing the fault.

[0041] From the above, it can be seen that the grid-type rectifier topology proposed in this application, using dual IGBTs and dual diodes, can effectively handle reverse current, protect IGBTs from damage, and improve the reliability and service life of the rectifier. In addition, this application can achieve precise control of the power of the power grid through precise control of the IGBT, meeting the load demand and stability requirements of the power grid. Finally, the introduction of segmented low-voltage protection on the basis of the grid-type rectifier control strategy can effectively solve the problems of difficult line fault location and low handling efficiency in multi-terminal flexible direct current systems.

[0042] like Figure 4 The figure shows a schematic diagram of a multi-terminal flexible direct current system line fault handling method provided by an embodiment of the present application. The fault handling method uses the above-mentioned grid-type rectifier. The fault handling method includes the following steps:

[0043] Step S401: When the DC power grid operates normally, the grid-connected rectifier is controlled according to active power and reactive power reference values.

[0044] Step S402: When a fault occurs in the DC grid, the control strategy is switched to control the grid-forming rectifier according to the current reference value to provide current to the fault point, and the system fault is auxiliary judged according to whether the reactive power output is zero at the time of the fault.

[0045] Preferably, the above-mentioned auxiliary judgment of system fault according to whether the reactive power output is zero at the time of fault includes: if the reactive power output is not zero, it is determined that the system has a fault, and the fault occurrence information is prompted.

[0046] The above method has been described in detail in the above description of the grid-type rectifier, and will not be further described here.

[0047] As can be seen from the foregoing, the multi-terminal flexible direct current system line fault handling method proposed in the present invention utilizes the grid-forming rectifier (IGBT) of the present application, and adopts dual-loop control when the DC power grid is operating normally to ensure stable operation of the system. When a fault occurs, the control strategy switches to current control, provides current to the fault point, maintains system stability, and assists in judging system faults by monitoring reactive power output, thereby enhancing system reliability. Moreover, the grid-forming rectifier topology proposed in the present application utilizes dual IGBTs and dual diodes, which can effectively handle reverse currents, protect IGBTs from damage, and improve the reliability and service life of the rectifier. In addition, the present application can achieve precise control of the power grid through precise control of the IGBT, thereby meeting the load demand and stability requirements of the power grid.

[0048] This embodiment also provides a multi-terminal flexible direct current system line fault handling system. The system can refer to Figure 2 and Figure 3As shown, the system includes the above-mentioned meshed rectifier, comparator, proportional-integral controller, voltage-current loop control unit and fault diagnosis unit, the comparator compares the active power reference value, reactive power reference value or current reference value with their actual values; the proportional-integral controller receives the output deviation signal of the comparator respectively, and generates a corresponding control signal; the voltage-current loop control unit receives the control signal of the proportional-integral controller, generates a corresponding pulse width modulation signal to control the conduction and shutoff of the first insulated gate bipolar transistor and the second insulated gate bipolar transistor in the meshed rectifier, and the fault diagnosis unit monitors the reactive power output, and uses the reactive power output not being zero as a basis for auxiliary judgment of system faults.

[0049] The above system has been described in detail in the above description of the grid-type rectifier, and will not be further described here.

[0050] As can be seen from the foregoing, the multi-terminal flexible direct current system line fault handling system proposed in the present invention utilizes the grid-type rectifier (IGBT) of the present application, and adopts dual-loop control when the DC power grid is operating normally to ensure stable operation of the system. When a fault occurs, the control strategy switches to current control, provides current to the fault point, maintains system stability, and assists in judging system faults by monitoring reactive power output, thereby enhancing system reliability. Moreover, the grid-type rectifier topology proposed in the present application utilizes dual IGBTs and dual diodes, which can effectively handle reverse currents, protect IGBTs from damage, and improve the reliability and service life of the rectifier. In addition, the present application can achieve precise control of power grid power through precise control of IGBTs, meeting the load demand and stability requirements of the power grid.

[0051] Figure 5 is a schematic diagram of an electronic device provided by an embodiment of the present invention. Figure 5 The electronic device shown is a general data processing device, which includes a general computer hardware structure, which at least includes a processor 801 and a memory 802. The processor 801 and the memory 802 are connected via a bus 803. The memory 802 is suitable for storing one or more instructions or programs executable by the processor 801. The one or more instructions or programs are executed by the processor 801 to implement the steps in the above-mentioned end flexible direct current system line fault handling method.

[0052] The processor 801 may be an independent microprocessor or a collection of one or more microprocessors. Thus, the processor 801 executes the commands stored in the memory 802 to execute the method flow of the embodiment of the present invention as described above to realize the processing of data and the control of other devices. The bus 803 connects the above-mentioned multiple components together, and at the same time connects the above-mentioned components to the display controller 804 and the display device and the input / output (I / O) device 805. The input / output (I / O) device 805 may be a mouse, a keyboard, a modem, a network interface, a touch input device, a somatosensory input device, a printer, and other devices known in the art. Typically, the input / output (I / O) device 805 is connected to the system via an input / output (I / O) controller 806.

[0053] The memory 802 may store software components such as an operating system, a communication module, an interaction module, and an application program. Each of the modules and applications described above corresponds to a set of executable program instructions that implement one or more functions and methods described in the embodiments of the invention.

[0054] An embodiment of the present invention further provides a computer-readable storage medium on which a computer program is stored. When the computer program is executed by a processor, the steps of the above-mentioned method for handling line faults in a flexible direct current system are implemented.

[0055] The grid-type rectifier and multi-terminal flexible direct current system line fault handling method and system proposed in the present invention utilize the grid-type rectifier (IGBT) of the present application, and adopt dual-loop control when the DC power grid is operating normally to ensure the stable operation of the system. When a fault occurs, the control strategy switches to current control, provides current to the fault point, maintains system stability, and assists in judging system faults by monitoring reactive power output, thereby enhancing system reliability. Moreover, the grid-type rectifier topology proposed in the present application utilizes dual IGBTs and dual diodes, which can effectively handle reverse currents, protect IGBTs from damage, and improve the reliability and service life of the rectifier. In addition, the present application can achieve precise control of power grid power through precise control of IGBTs, meeting the load demand and stability requirements of the power grid.

[0056] The preferred embodiments of the present invention are described above with reference to the accompanying drawings. Many features and advantages of these embodiments are clear from this detailed description, and therefore the claims are intended to cover all such features and advantages of these embodiments that fall within their true spirit and scope. In addition, since many modifications and changes are easily conceivable to those skilled in the art, it is not intended to limit the embodiments of the present invention to the precise structure and operation illustrated and described, but all suitable modifications and equivalents falling within its scope may be covered.

[0057] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0058] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0059] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0060] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0061] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A grid-type rectifier, characterized in that: The mesh rectifier is connected between an AC power grid and a DC power grid, and comprises: a first insulated gate bipolar transistor and a second insulated gate bipolar transistor, and a first diode and a second diode; the first insulated gate bipolar transistor is connected in series with the first diode to form a first branch; the second insulated gate bipolar transistor is connected in series with the second diode to form a second branch; the first branch and the second branch are connected in parallel to the DC power grid and are respectively connected to the positive and negative poles of the DC power grid; the first insulated gate bipolar transistor and the second insulated gate bipolar transistor are respectively controlled by a pulse width modulation signal; when the DC power grid operates normally, the second insulated gate bipolar transistor remains in a normally open state, and the first insulated gate bipolar transistor is controlled according to active power and reactive power reference values; when a fault occurs in the DC power grid, the control strategies of the first insulated gate bipolar transistor and the second insulated gate bipolar transistor are switched, the first insulated gate bipolar transistor remains in a normally open state, and the second insulated gate bipolar transistor is controlled according to a current reference value to provide current to a fault point to assist in fault location.

2. The grid-type rectifier according to claim 1, characterized in that: The first diode and the second diode are used to handle reverse current, and respectively protect the first insulated gate bipolar transistor and the second insulated gate bipolar transistor connected in series from being affected by reverse current.

3. The grid-type rectifier according to claim 1, characterized in that: The pulse width modulation signal is generated by a proportional-integral controller, and the proportional-integral controller is adjusted according to the deviation between the active power, reactive power or current reference value and the actual value; when the DC power grid is operating normally, a dual-loop control is adopted, the outer loop takes the deviation between the active power and reactive power reference value and the actual value as input, and the inner loop adopts voltage and current dual closed-loop control; when a fault occurs in the DC power grid, the control strategy is switched, the outer loop takes the deviation between the current reference value and the actual value as input, and the inner loop adopts voltage and current dual closed-loop control.

4. The grid-type rectifier according to claim 3, characterized in that: The current reference value is calculated based on the known constant terminal voltage, internal impedance and actual operating voltage.

5. The grid-type rectifier according to claim 1, characterized in that: The grid-type rectifier further comprises a filter, which is arranged at the output end of the grid-type rectifier and is used to filter out ripple components in the DC grid voltage.

6. A method for handling line faults in a multi-terminal flexible direct current system, characterized in that: The fault handling method uses a grid-type rectifier as described in any one of claims 1 to 5; The fault handling method comprises: when the DC power grid is operating normally, controlling the grid-forming rectifier according to active power and reactive power reference values; When a fault occurs in the DC power grid, the control strategy is switched to control the grid-forming rectifier according to the current reference value to provide current to the fault point; and the system fault is auxiliary judged according to whether the reactive power output is zero at the time of the fault.

7. The multi-terminal flexible direct current system line fault handling method according to claim 6, characterized in that: The auxiliary determination of system fault according to whether the reactive power output is zero at the time of fault includes: if the reactive power output is not zero, determining that a system fault occurs, and prompting fault occurrence information.

8. A multi-terminal flexible direct current system line fault handling system, characterized in that: The system includes a meshed rectifier, a comparator, a proportional-integral controller, a voltage-current loop control unit and a fault diagnosis unit as described in any one of claims 1 to 5, wherein the comparator compares an active power reference value, a reactive power reference value or a current reference value with its actual value; the proportional-integral controller receives the output deviation signal of the comparator respectively and generates a corresponding control signal; the voltage-current loop control unit receives the control signal of the proportional-integral controller and generates a corresponding pulse width modulation signal to control the conduction and shutoff of the first insulated gate bipolar transistor and the second insulated gate bipolar transistor in the meshed rectifier; the fault diagnosis unit monitors the reactive power output and uses the reactive power output not being zero as a basis for auxiliary judgment of system faults.

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the steps of the method according to any one of claims 6 to 7 are implemented.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 6 to 7 are implemented.

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