Short-circuit power flow control device and control method thereof

Abstract

The invention discloses a short-circuit power flow control device and a control method thereof, and relates to the technical field of power flow control, through mutual cooperation of a power flow adjusting unit, a reactive power coordination unit, a short-circuit blocking unit and a parallel compensation unit, specifically, the first end of the power flow adjusting unit serves as a first common connection point and is connected with a primary power supply connection end; the second end of the power flow adjusting unit serves as a second common connection point; the third end of the power flow adjusting unit is connected with the tertiary power supply connecting end; the second common connection point is connected in series with one end of the short circuit blocking unit through the reactive power coordination unit; the other end of the short circuit blocking unit serves as a third common connection point and is connected with the secondary power supply connection end; the parallel compensation unit is connected to any common connection point. By adopting the embodiment of the invention, the interconnection of the power grid can be realized with less equipment, multiple functions of power flow regulation, fault isolation and electric energy quality treatment are realized, and the operation reliability and stability of the power grid can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power flow control, and particularly relates to a short-circuit power flow control device and a control method thereof. Background Art

[0002] With the continuous development and expansion of the power system, traditional power grid structures and control methods face many challenges, and the need for power flow control emerges as the times require. In a traditional power grid, the power flow distribution of transmission lines is mainly determined by the impedance of the lines and the distribution of power sources. When the load on a certain line is too heavy, problems such as insufficient transmission capacity are likely to occur, leading to line overload and even power outages.

[0003] In recent years, the power grid has achieved the sharing and allocation of power resources through a ring network operation mode. However, the ring network structure makes the flow direction and magnitude of the power flow in the power grid more complex, difficult to predict and control, and increases the difficulty of power flow management.

[0004] In the prior art, a flexible interconnection method is adopted to achieve the interconnection operation between distribution networks. For example, two busbars at both ends are connected through an AC-DC-AC AC-DC converter. However, the current technical solutions require the configuration of two sets of converters, namely a rectifier and an inverter, resulting in a high cost. Summary of the Invention

[0005] The purpose of the embodiments of the present invention is to provide a short-circuit power flow control device and a control method thereof, which can reduce the number of devices configured in the ring network operation, and each unit is relatively independent and cooperative with each other, with clear control logic and reduced control complexity.

[0006] The embodiments of the present invention provide a short-circuit power flow control device, including a power flow regulation unit, a reactive power coordination unit, a short-circuit blocking unit, and a shunt compensation unit; The first end of the power flow regulation unit serves as a first common connection point and is connected to the primary power connection end; the second end of the power flow regulation unit serves as a second common connection point; the third end of the power flow regulation unit is connected to the tertiary power connection end; the second common connection point is connected in series with one end of the short-circuit blocking unit through the reactive power coordination unit; the other end of the short-circuit blocking unit serves as a third common connection point and is connected to the secondary power connection end; the shunt compensation unit is connected to any common connection point.

[0007] As an improvement of the above solution, the power flow regulation unit, the reactive power coordination unit, and the short-circuit blocking unit are in a split-phase structure; the shunt compensation unit is in a three-phase integrated structure.

[0008] As an improvement of the above solution, the power flow regulation unit includes a series sub-unit and a parallel sub-unit; The series sub-unit includes a number of first H-bridge sub-modules connected in cascade. The first H-bridge sub-module includes a DC capacitor and a fully-controlled semiconductor device. The DC capacitor and the fully-controlled semiconductor device form a bridge circuit. One end of the series sub-unit is the first end of the power flow regulation unit, and the other end of the series sub-module is the second end of the power flow regulation unit. The parallel sub-unit connects the DC capacitors of the first H-bridge sub-modules in parallel and then connects to the tertiary power connection terminal.

[0009] As an improvement of the above solution, the parallel sub-unit includes a multi-winding transformer and a rectification unit. The number of secondary sides of the multi-winding transformer and the number of rectification units are the same as the number of first H-bridge sub-modules. The rectification unit includes a three-phase half-bridge circuit composed of a group of power semiconductor devices, or a single-phase full-bridge circuit composed of four groups of power semiconductor devices. The primary side of the multi-winding transformer is connected to the tertiary power connection terminal, and one secondary side of the multi-winding transformer is connected to the DC capacitor of a first H-bridge sub-module through a rectification unit.

[0010] As an improvement of the above solution, the parallel sub-unit includes a high-frequency transformer, an inverter bridge, and a rectifier bridge. The DC side of the inverter bridge is connected to the low-voltage DC unit, the AC side of the inverter bridge is used as the tertiary power connection terminal and is connected to the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the AC terminal of the rectifier bridge, and the DC terminal of the rectifier bridge is connected to the DC capacitor of the first H-bridge sub-module.

[0011] As an improvement of the above solution, the reactive power coordination unit includes a number of second H-bridge sub-modules connected in cascade. The second H-bridge sub-module includes a DC capacitor and a fully-controlled semiconductor device. The DC capacitor and the fully-controlled semiconductor device form a bridge circuit.

[0012] As an improvement of the above solution, the short-circuit blocking unit includes a power semiconductor branch, a diode rectifier bridge, and a DC capacitor. The power semiconductor branch includes at least one power semiconductor device for conducting bidirectional current. The DC capacitor is connected in parallel to the DC terminal of the diode rectifier bridge, and the power semiconductor branch is connected in parallel to the AC terminal or the DC terminal of the diode rectifier bridge.

[0013] As an improvement of the above solution, the shunt compensation unit includes a number of third H-bridge sub-modules, and the third H-bridge sub-modules are connected in cascade to form a three-phase commutation chain. The three-phase commutation chain is star-connected or delta-connected. The third H-bridge sub-module includes a DC capacitor and a fully-controlled semiconductor device. The DC capacitor and the fully-controlled semiconductor device form a bridge circuit.

[0014] An embodiment of the present invention further provides a control method for a short-circuit power flow control device, which is used to control a short-circuit power flow control device as described above. The control method includes: When a power flow regulation instruction is received, turn on the short-circuit interruption unit; control the reactive power coordination unit to output a first AC voltage perpendicular to the flowing current, and at the same time control the power flow regulation unit to output a second AC voltage with an arbitrary phase relationship with the flowing current; adjust the first AC voltage and the second AC voltage according to the required line current; control the shunt compensation unit to inject reactive power into the point of common coupling to adjust the power factor of the point of common coupling; When a short-circuit interruption instruction is received, block the power flow regulation unit, the reactive power coordination unit and the short-circuit interruption unit; control the shunt compensation unit to inject reactive power into the point of common coupling to adjust the AC voltage of the point of common coupling; When a harmonic suppression instruction is received, turn on the short-circuit interruption unit; control the power flow regulation unit and the reactive power coordination unit to output harmonic voltages in the opposite direction to the harmonic voltages at the primary power connection end or the secondary power connection end; control the shunt compensation unit to inject harmonic currents in the opposite direction to the line harmonic currents.

[0015] As an improvement of the above solution, the control method of the short-circuit power flow control device further includes: When a start instruction is received, turn on the short-circuit interruption unit; start the power flow regulation unit; when the voltage difference across the reactive power coordination unit is not less than a preset voltage difference threshold, start the reactive power coordination unit; control the shunt compensation unit to start and inject reactive power from the point of common coupling.

[0016] Compared with the prior art, a short-circuit power flow control device and its control method disclosed by the present invention cooperate with each other through a power flow regulation unit, a reactive power coordination unit, a short-circuit interruption unit and a shunt compensation unit. Specifically, the first end of the power flow regulation unit serves as a first point of common coupling and is connected to the primary power connection end; the second end of the power flow regulation unit serves as a second point of common coupling; the third end of the power flow regulation unit is connected to the tertiary power connection end; the second point of common coupling is connected in series with one end of the short-circuit interruption unit through the reactive power coordination unit; the other end of the short-circuit interruption unit serves as a third point of common coupling and is connected to the secondary power connection end; the shunt compensation unit is connected to any point of common coupling. By adopting the embodiment of the present invention, the interconnection of the power grid can be realized with fewer devices, and it has multiple functions of power flow regulation, fault isolation and power quality governance, which can improve the reliability and stability of the power grid operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of a short-circuit power flow control device provided by an embodiment of the present invention; Figure 2 It is a schematic circuit diagram of a power flow regulation unit provided by an embodiment of the present invention; Figure 3 It is a schematic circuit diagram of a short-circuit power flow control device provided by an embodiment of the present invention; Figure 4 It is a schematic circuit diagram of another short-circuit power flow control device provided by an embodiment of the present invention; Figure 5 It is a schematic circuit diagram of another power flow regulation unit provided by an embodiment of the present invention; Figure 6 It is a schematic circuit diagram of a reactive power coordination unit provided by an embodiment of the present invention; Figure 7 It is a schematic circuit diagram of a short-circuit blocking unit provided by an embodiment of the present invention; Figure 8 It is a schematic circuit diagram of a star-connected shunt compensation unit provided by an embodiment of the present invention; Figure 9 It is a schematic circuit diagram of a delta-connected shunt compensation unit provided by an embodiment of the present invention. Detailed implementation manners

[0018] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0019] In the description of the specification and claims, it should be understood that the terms first, second, etc. in the specification and claims are only used for the purpose of distinguishing the description of the same technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features, nor necessarily describing the order or time sequence. The terms can be interchanged under appropriate circumstances. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one of the features.

[0020] The power system is a complex non-linear dynamic system, which forms a large-dimensional power network through the interconnection and interaction of transmission and distribution lines and various devices. Currently, it is developing in the direction of high voltage, large capacity, large scale, and long distance. Through interconnected operation, power can be transmitted and transformed between power grids, supporting each other, adjusting each other, and being used as backup for each other, which can improve the reliability of the power grid or power supply and ensure the power consumption of important loads.

[0021] In the prior art, a flexible interconnection device formed by back-to-back connection of voltage source converters (VSCs) based on fully controlled devices can achieve the interconnected operation of a distribution network. However, this solution is very costly and requires two sets of converters for rectification and inversion.

[0022] Based on the above considerations, please refer to Figure 1 , an embodiment of the present invention provides a short-circuit power flow control device, including a power flow regulation unit 1, a reactive power coordination unit 2, a short-circuit blocking unit 3, and a shunt compensation unit 4; The first end of the power flow regulation unit 1 serves as the first common connection point and is connected to the primary power connection end; the second end of the power flow regulation unit 1 serves as the second common connection point; the third end of the power flow regulation unit 1 is connected to the tertiary power connection end; the second common connection point is connected in series with one end of the short-circuit blocking unit 3 through the reactive power coordination unit 2; the other end of the short-circuit blocking unit 3 serves as the third common connection point and is connected to the secondary power connection end; the shunt compensation unit 4 is connected to any common connection point.

[0023] It should be noted that the primary power connection end and the secondary power connection end are the connection ends of the short-circuit power flow control device to the power grid. The tertiary power connection end is mainly used to supply power to the short-circuit power flow control device and is not the control target. In some preferred embodiments, the tertiary power connection end is the primary power connection end or the secondary power connection end. Of course, the tertiary power connection end can also be connected to other non-master control power sources.

[0024] Exemplarily, the primary power connection end is connected to the first AC power source S1, and the secondary power connection end and the tertiary power connection end are connected to the second AC power source S2. The short-circuit power flow control device described in the embodiment of the present invention realizes the interconnection of the first AC power source and the second AC power source.

[0025] It should also be noted that in the embodiment of the present invention, the shunt compensation unit 4 can be connected to the first common connection point, the second common connection point, or the third common connection point. However, it should be noted that it is only necessary to connect the shunt compensation unit to one of the common connection points. Please refer to Figure 2 , a circuit structure diagram showing the connection of the shunt compensation unit to the second common connection point is given; in addition, please refer to Figure 3 , a circuit structure diagram showing the connection of the shunt compensation unit to the first common connection point is also given.

[0026] Using the short-circuit power flow control device described in the embodiment of the present invention can achieve the interconnection of the power grid with fewer devices, and has multiple functions such as power flow regulation, fault isolation, and power quality improvement, which can improve the reliability and stability of the power grid operation.

[0027] As a preferred embodiment, the power flow regulation unit 1, the reactive power coordination unit 2, and the short-circuit blocking unit 3 are of a split-phase structure; the shunt compensation unit 4 is of a three-phase integrated structure.

[0028] In the embodiment of the present invention, the power flow regulation unit 1, the reactive power coordination unit 2, and the short-circuit blocking unit 3 are independently designed and configured for each phase (phase A, phase B, and phase C) in the power system to achieve precise control and processing of each phase, so as to more accurately achieve functions such as power flow regulation, reactive power coordination, and short-circuit blocking, and meet the different control requirements of different phases in the power system. The function of the shunt compensation unit 4 is to inject or absorb reactive power into the short-circuit power flow control device to balance the reactive power demand of the three-phase system. Therefore, a three-phase integrated structure is adopted.

[0029] As a preferred embodiment, the power flow regulation unit 1 includes a series sub-unit and a parallel sub-unit; The series sub-unit includes a number of first H-bridge sub-modules connected in cascade. The first H-bridge sub-module includes a DC capacitor and a fully controlled semiconductor device; the DC capacitor and the fully controlled semiconductor device form a bridge circuit; one end of the series sub-unit is the first end of the power flow regulation unit, and the other end of the series sub-module is the second end of the power flow regulation unit; The parallel sub-unit connects the DC capacitors of each of the first H-bridge sub-modules in parallel and then connects them to the tertiary power connection end.

[0030] In the above solution, the first H-bridge sub-module can flexibly change the output voltage by controlling the on and off of the fully controlled semiconductor device. The commutation chain formed by cascading a large number of sub-modules can achieve fine adjustment of the output voltage, and then accurately control the line power flow. The DC capacitor can store and release energy, and achieve reactive power compensation to a certain extent. By reasonably controlling the working state of the sub-module, the reactive power flow of the line can be adjusted, the system voltage can be maintained stable, the power factor of the power grid can be improved, the reactive power loss can be reduced, and the system stability can be enhanced.

[0031] Further, in a preferred embodiment, the parallel sub-unit includes a multi-winding transformer and a rectifying unit; The number of secondary sides of the multi-winding transformer and the number of rectifying units are the same as the number of first H-bridge sub-modules; the rectifying unit includes a three-phase half-bridge circuit composed of a group of power semiconductor devices, or a single-phase full-bridge circuit composed of four groups of power semiconductor devices; The primary side of the multi-winding transformer is connected to the tertiary power connection end, and one secondary side of the multi-winding transformer is connected to the DC capacitor of one of the first H-bridge sub-modules through the rectifying unit.

[0032] Please refer to Figure 4, in the embodiment of the present invention, the parallel sub-unit forms an AC isolation unit through a multi-winding transformer and a rectification unit, which can achieve electrical isolation between the tertiary power connection terminal and the first H-bridge sub-module, effectively blocking electrical interference and fault propagation on the AC side.

[0033] Moreover, the winding structure and leakage inductance and other characteristics of the multi-winding transformer have a certain inhibitory effect on harmonics. In the power system, various harmonic components may exist at the tertiary power connection terminal. The multi-winding transformer can attenuate some harmonics through its own impedance characteristics, reducing the harmonic content injected into the first H-bridge sub-module. In addition, the power semiconductor devices in the rectification unit also generate harmonics during operation. The isolation function of the multi-winding transformer can prevent these harmonics from being fed back to the tertiary power connection terminal, thereby improving the power quality of the entire system.

[0034] In another preferred embodiment, the parallel sub-unit includes a high-frequency transformer, an inverter bridge, and a rectifier bridge; The DC side of the inverter bridge is connected to the low-voltage DC unit. The AC side of the inverter bridge serves as the tertiary power connection terminal and is connected to the primary side of the high-frequency transformer. The secondary side of the high-frequency transformer is connected to the AC terminal of the rectifier bridge, and the DC terminal of the rectifier bridge is connected to the DC capacitor of the first H-bridge sub-module.

[0035] Please refer to Figure 5 , in the embodiment of the present invention, the parallel sub-unit forms a DC isolation unit through a high-frequency transformer, an inverter bridge, and a rectifier bridge, which can achieve effective DC isolation between the inverter bridge and the rectifier bridge, preventing the mutual propagation of interference and faults on the DC side.

[0036] The embodiment of the present invention provides two circuit structures of the parallel sub-unit, namely an AC isolation unit and a DC isolation unit. In practical applications, the more adaptable parallel sub-unit can be selected according to their characteristics and grid requirements.

[0037] From the perspective of power conversion mode, in the AC isolation unit, the primary side of the multi-winding transformer is connected to the tertiary power connection terminal, and the input is an AC power supply. The AC is converted into DC through the transformer and the rectification unit to charge the DC capacitor of the first H-bridge sub-module. In the DC isolation unit, the DC side of the inverter bridge is connected to the low-voltage DC unit. First, the low-voltage DC is converted into high-frequency AC, and then it is converted into DC through the high-frequency transformer and the rectifier bridge. The power input is DC, and the conversion process is DC-AC-DC.

[0038] From the perspective of transformer characteristics, the AC isolation unit uses a multi-winding transformer, which is suitable for lower frequencies and has a relatively large volume, and can be effectively used in scenarios where AC power supplies are directly processed. The DC isolation unit uses a high-frequency transformer, which has a high working frequency, small volume, light weight, and high energy conversion efficiency, and is more suitable for use in scenarios of DC isolation and high-frequency energy conversion.

[0039] In terms of circuit structure and complexity, the rectifier unit of the AC isolation unit is a three-phase half-bridge circuit or a single-phase full-bridge circuit, with a relatively simple circuit structure, mainly for processing AC power supplies. The DC isolation unit includes an inverter bridge and a rectifier bridge, adding an inversion link, with a relatively complex circuit structure, but can achieve more flexible voltage regulation and DC isolation functions.

[0040] As a preferred embodiment, the reactive power coordination unit 2 includes a number of cascaded second H-bridge sub-modules; The second H-bridge sub-module includes a DC capacitor and a fully controlled semiconductor device; the DC capacitor and the fully controlled semiconductor device form a bridge circuit.

[0041] A number of cascaded second H-bridge sub-modules can achieve continuous voltage regulation, so the reactive power coordination unit can achieve continuous regulation of reactive power, avoiding the stepped changes that occur in traditional reactive power compensation devices during the regulation process, and improving the smoothness and accuracy of reactive power compensation.

[0042] In some preferred embodiments, please refer to Figure 6 , the reactive power coordination unit 2 further includes a reactor L; the reactor L is connected in series with the number of cascaded second H-bridge sub-modules.

[0043] The series reactor can limit the inrush current generated when the reactive power coordination unit is put into or cut out, and limit the magnitude of the fault current when a power grid fault occurs, protecting the reactive power coordination unit and other equipment in the power grid from overcurrent damage.

[0044] As a preferred embodiment, please refer to Figure 7 , the short-circuit blocking unit 3 includes a power semiconductor branch, a diode rectifier bridge and a DC capacitor; the power semiconductor branch includes at least one power semiconductor device for conducting bidirectional current; The DC capacitor is connected in parallel at the DC end of the diode rectifier bridge, and the power semiconductor branch is connected in parallel at the AC end or the DC end of the diode rectifier bridge.

[0045] In some preferred embodiments, the short-circuit blocking unit includes a number of cascaded short-circuit blocking sub-units, and the short-circuit blocking sub-unit is composed of a group of power semiconductor branches, a diode rectifier bridge and a DC capacitor.

[0046] Power semiconductor devices can act quickly at the moment of detecting a short - circuit fault. When a short - circuit occurs in the power grid, the short - circuit current will increase sharply. The power semiconductor devices in the power semiconductor branch can quickly switch their working states to achieve rapid blocking of the short - circuit current, limit the impact of the fault to the minimum range, and effectively protect other devices in the power system from overload damage. The diode rectifier bridge converts the AC short - circuit current into DC, enabling the DC capacitor to better absorb and store energy. It can also prevent the energy in the DC capacitor from flowing back into the AC side, ensuring the unidirectionality of energy flow and improving the efficiency of energy storage and management. The DC capacitor is connected in parallel at the DC end of the diode rectifier bridge. When a short - circuit fault occurs, it can absorb and store a part of the short - circuit energy.

[0047] As a preferred embodiment, the shunt compensation unit 4 includes a number of third H - bridge sub - modules, and the third H - bridge sub - modules are cascaded to form a three - phase commutation chain; The three - phase commutation chain is in star connection or delta connection; the third H - bridge sub - module includes a DC capacitor and a fully - controlled semiconductor device; the DC capacitor and the fully - controlled semiconductor device form a bridge circuit.

[0048] In the embodiment of the present invention, the shunt compensation unit is a three - phase integrated structure. The three - phase commutation chain formed by cascading the third H - bridge sub - modules is respectively connected to the A - phase, B - phase, and C - phase in the power system.

[0049] Please refer to Figure 8 , one end of the head and tail of the three - phase commutation chain in the shunt compensation unit is connected into a common point, and the other end leads out three - phase output terminals to form a star connection. Please refer to Figure 9 , the head and tail of the three - phase commutation chain in the shunt compensation unit are connected to each other, and three head ends or tail ends lead out three - phase output terminals to form a delta connection.

[0050] The short - circuit power flow control device described in the above solution has multiple functions of power flow regulation, fault isolation, and power quality governance. In order to better control the above - mentioned short - circuit power flow control device, the embodiment of the present invention also provides a control method for the short - circuit power flow control device, including: When receiving a power flow regulation command, turn on the short - circuit blocking unit; control the reactive power coordination unit to output a first AC voltage perpendicular to the flowing current, and at the same time control the power flow regulation unit to output a second AC voltage with an arbitrary phase relationship with the flowing current; adjust the first AC voltage and the second AC voltage according to the required line current; control the shunt compensation unit to inject reactive power into the common connection point to adjust the power factor of the common connection point; When receiving a short - circuit blocking command, block the power flow regulation unit, the reactive power coordination unit, and the short - circuit blocking unit; control the shunt compensation unit to inject reactive power into the common connection point to adjust the AC voltage of the common connection point; When receiving a harmonic suppression instruction, turn on the short - circuit blocking unit; control the power flow regulating unit and the reactive power coordination unit to output harmonic voltages in the opposite direction of the harmonic voltages at the primary power connection end or the secondary power connection end; control the shunt compensation unit to inject harmonic currents in the opposite direction of the line harmonic currents.

[0051] When the short - circuit power flow control device of the embodiment of the present invention is in stable operation, there are at least three modes, namely, the power flow regulation mode, the short - circuit blocking mode, and the harmonic suppression mode, and the modes are switched through different instructions.

[0052] In some preferred embodiments, turning on the short - circuit blocking unit when receiving a short - circuit blocking instruction or when receiving a harmonic suppression instruction includes: Turn on the power semiconductor branch in the short - circuit blocking unit.

[0053] In some preferred embodiments, blocking the power flow regulating unit, the reactive power coordination unit, and the short - circuit blocking unit when receiving a short - circuit blocking instruction includes: Block the power semiconductor devices in the power flow regulating unit, the reactive power coordination unit, and the short - circuit blocking unit.

[0054] It should be noted that when receiving a power flow regulation instruction, the AC voltages output by the reactive power coordination unit and the power flow regulating unit will be superimposed, and by adjusting the AC voltage, the line current can be changed to match the required line current.

[0055] When receiving a short - circuit blocking instruction, by blocking the power flow regulating unit, the reactive power coordination unit, and the short - circuit blocking unit, the DC voltages of the DC capacitors in the power flow regulating unit, the reactive power coordination unit, and the short - circuit blocking unit will rise. When the sum of the DC voltages in each unit rises to the peak value of the voltage difference between the primary power connection end and the secondary power connection end, the short - circuit current drops to 0, realizing short - circuit blocking. At the same time, the shunt compensation unit can accelerate the speed of the short - circuit current drop by adjusting the injected reactive power to change the AC voltage at the common connection point.

[0056] When receiving a harmonic suppression instruction, controlling the power flow regulating unit and the reactive power coordination unit to output harmonic voltages in the opposite direction of the harmonic voltages at the primary power connection end or the secondary power connection end can prevent the harmonic voltages from being transmitted to the opposite side; controlling the shunt compensation unit to inject harmonic currents in the opposite direction of the line harmonic currents can suppress the harmonic currents at the common connection point.

[0057] Furthermore, as a preferred implementation manner, the control method of the short - circuit power flow control device further includes: When a start instruction is received, turn on the short-circuit blocking unit; start the power flow regulating unit; when the voltage difference across the reactive power coordination unit is not less than a preset voltage difference threshold, start the reactive power coordination unit; control the shunt compensation unit to start and inject reactive power from the point of common coupling.

[0058] It should be noted that in the embodiments of the present invention, a control method for a short-circuit power flow control device to start from the off state / fault state and enter the steady-state operation is provided. At the beginning of the start of the power flow regulating unit, the output AC voltage is 0, and then it gradually increases, which will cause the voltage difference across the reactive power coordination unit to increase and charge the DC capacitors of the modules in the reactive power coordination unit; when the voltage difference across the reactive power coordination unit is not less than the preset voltage difference threshold, the charging threshold is reached and the reactive power coordination unit starts.

[0059] By adopting the control method of a short-circuit power flow control device provided in the embodiments of the present invention, the short-circuit power flow control device can be accurately controlled to operate in multiple modes, realizing multiple functions of power flow regulation, fault isolation, and power quality improvement.

[0060] Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be completed by instructing relevant hardware through a computer program. The program can be stored in a computer-readable storage medium. When the program is executed, it can include the processes of the embodiments of the above methods. Among them, the storage medium can be a magnetic disk, an optical disk, a read-only memory (ROM), or a random access memory (RAM), etc.

[0061] The above is the preferred embodiment of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can still be made, and these improvements and refinements are also regarded as the protection scope of the present invention.

Claims

1. A short-circuit power flow control device, characterized in that, It includes a power flow regulation unit, a reactive power coordination unit, a short-circuit blocking unit, and a shunt compensation unit; The first end of the power flow regulation unit serves as the first common connection point and is connected to the primary power connection end; the second end of the power flow regulation unit serves as the second common connection point; the third end of the power flow regulation unit is connected to the tertiary power connection end; the second common connection point is connected in series with one end of the short-circuit blocking unit through the reactive power coordination unit; the other end of the short-circuit blocking unit serves as the third common connection point and is connected to the secondary power connection end; the shunt compensation unit is connected to any common connection point.

2. The short-circuit power flow control device according to claim 1, wherein, The power flow regulation unit, the reactive power coordination unit, and the short-circuit blocking unit are in a split-phase structure; the shunt compensation unit is in a three-phase integrated structure.

3. The short-circuit power flow control device according to claim 1, characterized in that, The power flow regulation unit includes a series sub-unit and a parallel sub-unit; The series sub-unit includes a number of first H-bridge sub-modules connected in cascade. The first H-bridge sub-module includes a DC capacitor and a fully controlled semiconductor device; the DC capacitor and the fully controlled semiconductor device form a bridge circuit; one end of the series sub-unit is the first end of the power flow regulation unit, and the other end of the series sub-module is the second end of the power flow regulation unit; The parallel sub-unit connects the DC capacitors of each of the first H-bridge sub-modules in parallel and then connects them to the tertiary power connection end.

4. The short-circuit power flow control device according to claim 3, characterized in that, The parallel sub-unit includes a multi-winding transformer and a rectification unit; The number of secondary sides of the multi-winding transformer and the number of rectification units are the same as the number of first H-bridge sub-modules; the rectification unit includes a three-phase half-bridge circuit composed of a group of power semiconductor devices, or a single-phase full-bridge circuit composed of four groups of power semiconductor devices; The primary side of the multi-winding transformer is connected to the tertiary power connection end, and one secondary side of the multi-winding transformer is connected to the DC capacitor of one of the first H-bridge sub-modules through the rectification unit.

5. The short-circuit power flow control device according to claim 3, characterized in that, The parallel sub-unit includes a high-frequency transformer, an inverter bridge, and a rectifier bridge; The DC side of the inverter bridge is connected to the low-voltage DC unit, the AC side of the inverter bridge serves as the tertiary power connection end and is connected to the primary side of the high-frequency transformer; the secondary side of the high-frequency transformer is connected to the AC end of the rectifier bridge, and the DC end of the rectifier bridge is connected to the DC capacitor of the first H-bridge sub-module.

6. The short-circuit power flow control device according to claim 1, wherein The reactive power coordination unit includes a number of second H-bridge sub-modules connected in cascade; The second H-bridge sub-module includes a DC capacitor and a fully controlled semiconductor device; the DC capacitor and the fully controlled semiconductor device form a bridge circuit.

7. The short-circuit power flow control device according to claim 1, characterized in that, The short-circuit blocking unit includes a power semiconductor branch, a diode rectifier bridge, and a DC capacitor; the power semiconductor branch includes at least one power semiconductor device for conducting bidirectional current; The DC capacitor is connected in parallel at the DC end of the diode rectifier bridge, and the power semiconductor branch is connected in parallel at the AC end or the DC end of the diode rectifier bridge.

8. The short-circuit power flow control device according to claim 1, characterized in that, The shunt compensation unit includes a number of third H-bridge sub-modules, and the third H-bridge sub-modules are connected in cascade to form a three-phase commutation chain; The three-phase commutation chain is in a star connection or a delta connection; the third H-bridge sub-module includes a DC capacitor and a fully controlled semiconductor device; the DC capacitor and the fully controlled semiconductor device form a bridge circuit.

9. A control method for a short-circuit power flow control device, characterized in that, For controlling a short-circuit power flow control device as described in any one of claims 1-8, the control method includes: When a power flow regulation instruction is received, turn on the short-circuit blocking unit; control the reactive power coordination unit to output a first AC voltage perpendicular to the flowing current, and at the same time control the power flow regulation unit to output a second AC voltage with an arbitrary phase relationship with the flowing current; adjust the first AC voltage and the second AC voltage according to the required line current; control the shunt compensation unit to inject reactive power into the point of common coupling to regulate the power factor of the point of common coupling. When a short-circuit blocking instruction is received, block the power flow regulation unit, the reactive power coordination unit and the short-circuit blocking unit; control the shunt compensation unit to inject reactive power into the point of common coupling to regulate the AC voltage of the point of common coupling. When a harmonic suppression instruction is received, turn on the short-circuit blocking unit; control the power flow regulation unit and the reactive power coordination unit to output harmonic voltages in the opposite direction of the harmonic voltages at the primary power connection end or the secondary power connection end; control the shunt compensation unit to inject harmonic currents in the opposite direction of the line harmonic currents.

10. The control method of a short-circuit power flow control device according to claim 9, characterized in that, The control method of the short-circuit power flow control device further includes: When a start instruction is received, turn on the short-circuit blocking unit; start the power flow regulation unit; when the voltage difference across the reactive power coordination unit is not less than a preset voltage difference threshold, start the reactive power coordination unit; control the shunt compensation unit to start and inject reactive power from the point of common coupling.

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