A thyristor-based controllable modular energy dissipator and a control method thereof

Abstract

This invention belongs to the field of new energy power transmission technology, and discloses a controllable modular energy dissipation device based on thyristors and its control method. The energy dissipation device includes a fixed part and a controllable part connected in series with the fixed part; the fixed part is composed of a metal oxide surge arrester and an energy-dissipating resistor connected in parallel; the controllable part includes several structurally identical and cascaded MOA sub-modules, each of which includes a pair of anti-parallel thyristors, a metal oxide surge arrester, and a voltage equalizing resistor; wherein, one side of the controllable part is connected to the fixed part, and the other side is connected to the ground. In offshore wind power systems, when the AC voltage exceeds a set threshold, the energy dissipation device enters the working state, and the number of MOA sub-modules put into operation is determined according to the degree of AC voltage overvoltage; when the AC voltage drops below the set threshold, the energy dissipation device exits the working state and returns to a high-impedance state.

Description

Technical Field

[0001] This invention belongs to the field of new energy power transmission technology, specifically relating to a controllable modular energy dissipation device based on thyristors and its control method. Background Technology

[0002] As offshore wind power development accelerates into mid- and far-sea areas, flexible low-frequency AC transmission technology is showing broad application prospects due to its significant advantages in improving the current-carrying capacity of submarine cables, suppressing reactive power during charging, and saving on converter station investment. However, this technology faces a severe overvoltage challenge when dealing with grid faults at the receiving end. When the voltage drop in the receiving end grid leads to a decrease in power reception capacity, the surplus power generated by the offshore wind farm will be injected into components such as line capacitors, causing severe overvoltages and directly threatening the insulation safety of core equipment such as transformers, cables, and converter valves.

[0003] Currently, the following two types of solutions are mainly used in engineering to suppress overvoltage: 1. Additional energy-absorbing devices are installed on the low-frequency AC bus of the offshore converter station to absorb surplus power. For example... Figure 1 As shown in (a), the AC power dissipation device uses thyristors and power dissipation resistors, and is switched in groups according to the fault type and DC power. The thyristor valve is controlled to conduct at the phase zero crossing point by the trigger control system, and the fan is cut off in an orderly manner in conjunction with the safety control strategy to maintain the power balance of the AC system.

[0004] While this approach can maintain power balance, its switching action is often delayed when dealing with microsecond (μs) level transient overvoltages. Furthermore, the rapid switching process causes drastic changes in loop current, impacting the DC bus voltage and generating significant voltage ripple and high-frequency oscillations. Simultaneously, the protective function of the energy dissipation device is limited to longer-duration power frequency overvoltages or power overshoots, and cannot suppress extremely short-duration operational overvoltages.

[0005] 2. Install a controllable surge arrester made of power electronic devices to temporarily suppress overvoltage. For example... Figure 1 As shown in (b), a conventional power electronic controllable surge arrester is configured with a series arrangement consisting of a fixed part and a controllable part (including a metal oxide surge arrester (MOA) and a bypass switch connected in parallel). Under normal conditions, the bypass switch is open, and the MOA in both the fixed and controllable parts share the voltage and exhibit a high-resistance state. When the DC voltage is too high, the bypass switch is activated, reducing the number of MOA connected during a fault, thereby dynamically changing the surge arrester's volt-ampere characteristics to reduce overvoltage.

[0006] Traditional power electronic controllable surge arresters have a relatively simple structure and a good suppression effect on transient overvoltages. However, they rely on the operation of bypass switches to change the number of MOA series connections, which may not be able to effectively suppress fast-rising-edge overvoltages and rapidly rising slow-rising-edge overvoltages. At the same time, the series-connected semiconductor bypass switches also have problems such as not being able to turn off in time and voltage equalization. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a thyristor-based controllable modular energy dissipation device and its control method. The energy dissipation device combines basic voltage support with dynamic adjustment capabilities by connecting a fixed part in series with a modular controllable part. By utilizing the automatic turn-off characteristic of thyristors at zero crossing points in AC systems, it achieves effective decoupling of energy consumption and overvoltage suppression. The independent MOA sub-module design solves the voltage balancing problem caused by multiple devices being connected in series, significantly improving the reliability and flexibility of flexible low-frequency AC transmission systems during fault ride-through.

[0008] This invention provides the following technical solution: The primary objective of this invention is to provide a controllable modular energy dissipation device based on a thyristor, comprising a fixed part and a controllable part connected in series with the fixed part; The fixed part consists of a metal oxide surge arrester and a power dissipation resistor connected in parallel. The controllable part includes several MOA sub-modules with identical structures and cascaded connections. Each MOA sub-module includes a pair of anti-parallel thyristors, a metal oxide surge arrester and a voltage equalizing resistor. One side of the controllable part is connected to the fixed part, and the other side is connected to the ground.

[0009] By connecting the fixed part in series with the modular controllable part, a combination of basic voltage support and dynamic adjustment capability is achieved. Based on traditional power electronic surge arresters, the controllable part adopts an independent MOA sub-module design. Each sub-module integrates an independent resistor and MOA, similar to a voltage balancing resistor, improving the inconsistency in action and voltage balancing problems caused by the series connection of numerous power electronic components. This enhances the consistency of action and control accuracy of the device during overvoltage suppression and energy dissipation. A semi-controlled thyristor is used as a bypass switch, simplifying control requirements and enabling automatic zero-crossing turn-off in AC systems. The excellent performance of the thyristor ensures rapid response while effectively improving the system's operational reliability.

[0010] As a further improvement of the present invention, the negative terminal of each MOA submodule is connected to the positive terminal of its adjacent subsequent MOA submodule. This cascaded connection effectively distributes the high voltage of the system, reducing the voltage withstand requirements of individual submodules on power electronic devices. This structure also provides a physical basis for achieving precise hierarchical switching, ensuring the overall reliability of the device.

[0011] As a further improvement of the present invention, the metal oxide surge arrester and voltage equalizing resistor of each MOA submodule are connected in parallel across a pair of anti-parallel thyristors. Using thyristors as bypass switches provides stronger current surge withstand capability and lower cost compared to fully controlled devices (such as IGBTs). The integrated voltage equalizing resistor effectively solves the problems of inconsistent operation and uneven static voltage distribution caused by the series connection of numerous power electronic components, significantly enhancing the operational stability of the device.

[0012] As a further improvement of the present invention, the thyristor includes a forward thyristor and a reverse thyristor; wherein, the anode of the reverse thyristor is connected to the cathode of the forward thyristor, and the cathode of the reverse thyristor is connected to the anode of the forward thyristor; one end of the metal oxide surge arrester is connected to the anode of the forward thyristor, and the other end is connected to the cathode of the forward thyristor. Through the parallel structure of the forward and reverse thyristors, the device is ensured to have the ability to bidirectionally absorb surplus power, and can simultaneously cope with transient overvoltages in different directions.

[0013] As a further improvement of the present invention, the input terminal of the MOA submodule is connected to the anode of the forward thyristor, and the output terminal is connected to the cathode of the forward thyristor.

[0014] As a further improvement of the present invention, the device also includes a control unit, which detects the AC bus voltage in real time and changes the number of MOA sub-modules put into operation in a stepwise manner according to the degree of AC voltage overvoltage.

[0015] By changing the input quantity in a stepped manner, the drastic current surges caused by the large-capacity one-time switching of traditional energy-consuming devices are avoided, effectively suppressing voltage ripple and high-frequency oscillations on the AC bus, and achieving flexible and adaptable adjustment of surplus power.

[0016] As a further improvement of the present invention, when a certain MOA submodule is put into operation, the control unit simultaneously triggers the thyristors within the MOA submodule using a signal with a fixed pulse width, causing current to bypass the metal oxide surge arrester and flow through the thyristors. Simultaneous triggering with a fixed pulse width signal ensures that during AC overvoltage, regardless of phase, at least one of the forward or reverse thyristors can reliably conduct. The current bypassing the MOA and flowing through the thyristors achieves decoupling between voltage limiting and energy management.

[0017] The second objective of this invention is to provide a fault ride-through control method, implemented based on the aforementioned energy dissipation device, comprising: The AC voltage is monitored in real time. When the detected AC voltage exceeds the set threshold, the energy dissipation device enters the working state and determines the number of MOA sub-modules to be put into operation based on the degree of AC voltage overvoltage. When the AC voltage drops below the set threshold, the energy dissipation device exits the working state and returns to the high impedance state.

[0018] It can quickly detect voltage rises caused by grid faults at the receiving end and automatically enter and exit the energy dissipation device through set values, ensuring the continuous operation capability of the offshore wind power system during faults.

[0019] As a further improvement of the present invention, the method also includes: according to the change of AC voltage, increasing or decreasing the number of MOA sub-modules in operation in a stepped manner to suppress overvoltages of different degrees. This provides the ability to track overvoltage fluctuations in real time, improving the system's flexibility and overall stability in dealing with complex fault conditions (such as repetitive voltage drops or multi-stage overvoltage).

[0020] As a further improvement of this invention, the number of MOA sub-modules in operation is positively correlated with the degree of AC voltage overvoltage. This achieves precise absorption of surplus power within the range of 0% to 100%, minimizes the disturbance of the overvoltage suppression process to normal power grid operation, and significantly improves the system's flexibility and overall stability in response to different overvoltage levels.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention employs a semi-controlled thyristor as the core bypass switch, cleverly utilizing the characteristic of the current naturally crossing zero point in an AC system to achieve automatic turn-off. The device can autonomously deactivate after suppressing transient overvoltages, preventing the surge arrester from being in a low-impedance state for extended periods and absorbing excessive energy. This solves the technical problem of traditional trigger gaps or fully controlled devices being difficult to turn off under DC interference.

[0022] Through a modular, independent MOA submodule design, each module integrates an independent voltage-equalizing resistor and surge arrester unit, which functions similarly to a voltage balancing resistor. This structure significantly improves the inconsistency caused by the series connection of numerous power electronic components, enhancing the control accuracy and operational stability of the device during overvoltage suppression.

[0023] The submodule employs a parallel structure of forward and reverse thyristors, enabling the device to bidirectionally absorb excess power and simultaneously handle transient overvoltages in different directions. This not only solves the problem that traditional energy-consuming devices cannot suppress operational overvoltages due to action delays, but also improves the system's reliability in handling complex fault conditions.

[0024] This invention employs a strategy of tiered activation of sub-modules based on the degree of overvoltage, enabling precise absorption of surplus power within the range of 0% to 100%. This stepped adjustment method avoids drastic current surges caused by switching traditional devices, significantly reduces voltage ripple and high-frequency oscillations, and improves the overall stability of the system in the face of different levels of overvoltage. Attached Figure Description

[0025] Figure 1 This is an electrical topology diagram of an overvoltage suppression device in the prior art; Figure 2 The circuit diagram of the controllable modular energy dissipation device based on thyristors provided by the present invention; Figure 3 This is a structural diagram of the controllable modular energy dissipation device based on thyristors provided by the present invention installed on an offshore wind power system; Figure 4 A schematic diagram of the working state of the controllable modular energy dissipation device based on thyristors provided by the present invention; Figure 5 Control diagram for fault ride-through of offshore wind power systems using the thyristor-based controllable modular energy dissipation device provided by this invention.

[0026] Explanation of reference numerals in the attached diagram: 1. Fixed part, 2. Controllable part, 3. MOA submodule, 4. First metal oxide surge arrester, 5. Energy dissipation resistor, 6. Reverse thyristor, 7. Forward thyristor, 8. Second metal oxide surge arrester, 9. Equalizing resistor. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] The present invention will now be described in further detail with reference to the accompanying drawings: Example 1: like Figure 2As shown, this embodiment provides a controllable modular energy dissipation device based on thyristors, including a fixed part 1 and a controllable part 2 connected in series with the fixed part 1. One side of the controllable part 2 is connected to the fixed part 1, and the other side of the controllable part 2 is connected to the ground. The fixed part 1 is composed of a first metal oxide surge arrester 4 and an energy dissipation resistor 5 connected in parallel. The controllable part 2 includes several MOA sub-modules 3 with identical structures and cascaded connection. The negative terminal of each MOA sub-module 3 is connected to the positive terminal of its adjacent next-level MOA sub-module 3.

[0029] Specifically: Each MOA submodule 3 includes a forward thyristor 7, a reverse thyristor 6, a second metal oxide surge arrester 8, and a voltage equalizing resistor 9; the anode of the reverse thyristor 6 is connected to the cathode of the forward thyristor 7, and the cathode of the reverse thyristor 6 is connected to the anode of the forward thyristor 7; one end of the second metal oxide surge arrester 8 is connected to the anode of the forward thyristor 7, and the other end is connected to the cathode of the forward thyristor 7; the voltage equalizing resistor 9 is connected in parallel across the two ends of the forward thyristor 7 and the reverse thyristor 6; the input terminal of the MOA submodule 3 is connected to the anode of the forward thyristor 7, and the output terminal is connected to the cathode of the forward thyristor 7.

[0030] Furthermore, the device also includes a control unit for real-time detection of the AC bus voltage and, based on the degree of AC voltage overvoltage, stepwise changes in the number of MOA sub-modules 3 in operation, thereby achieving precise absorption of surplus power within the range of 0% to 100%. When a certain MOA sub-module 3 is put into operation, the control unit simultaneously triggers the thyristor within that MOA sub-module 3 with a signal of fixed pulse width, causing the current to bypass the second metal oxide surge arrester 8 and flow through the thyristor.

[0031] like Figure 3 As shown, the controllable modular energy dissipation device based on thyristors provided in this embodiment is connected to an offshore wind power system. The working process of the energy dissipation device is as follows: When an offshore wind power system is operating normally, the energy dissipation device is not working and is in the off state.

[0032] In offshore wind power systems, fault conditions such as commutation failure or DC fault blocking at the receiving end often prevent reactive power compensation equipment from switching on and off in a timely manner, resulting in a large amount of reactive power being injected into the AC system. This excess reactive power causes transient impulse overvoltages on the AC bus. If the AC voltage exceeds a set value, the energy dissipation device activates a corresponding number of MOA submodules to absorb the excess power based on the degree of overvoltage. At this time, for each conducting MOA submodule, a pulse signal with a fixed pulse width simultaneously triggers the internal forward and reverse thyristors, ensuring that one of them can reliably conduct, and the current bypasses the internal metal oxide surge arrester and flows through the thyristor. Finally, when the overvoltage disappears and the voltage returns to normal operation, the AC current flowing through the thyristor is 0, and the thyristor automatically turns off at the zero-crossing point. Therefore, during the fault, most of the current is ultimately transferred to the bypass switch, i.e., the thyristor, and the metal oxide surge arresters inside the MOA submodule are short-circuited. Only a fixed portion of the metal oxide surge arresters are put into operation, utilizing the nonlinear impedance characteristics of the metal oxide surge arresters to dynamically adjust the protection level, ultimately reducing the AC bus overvoltage level.

[0033] When the AC bus voltage drops to the set value, the energy dissipation device automatically shuts down.

[0034] Example 2: This embodiment provides a fault ride-through control method, implemented based on the energy dissipation device provided in Embodiment 1, including: The system monitors the AC voltage in real time. When the detected AC voltage exceeds a set threshold, the energy dissipation device activates and determines the number of MOA submodules to be engaged based on the degree of AC voltage overvoltage. The number of engaged MOA submodules is positively correlated with the degree of AC voltage overvoltage. Based on changes in AC voltage, the number of MOA sub-modules put into operation is increased or decreased in a stepwise manner to suppress overvoltage of varying degrees. When the AC voltage drops below the set threshold, the energy dissipation device exits the working state and returns to the high impedance state.

[0035] Using the energy dissipation device provided in Embodiment 1, the system can quickly detect voltage surges caused by grid faults at the receiving end. By setting parameters, the energy dissipation device can automatically enter and exit the grid, ensuring the continuous operation of the offshore wind power system during faults. Simultaneously, the system has the ability to track overvoltage fluctuations in real time, deploying the corresponding number of MOA sub-modules based on the degree of overvoltage to accurately absorb surplus power within the range of 0% to 100%, improving the system's flexibility and overall stability in dealing with different overvoltage levels and complex fault conditions.

[0036] The control process is described in detail below according to the timing sequence: tBefore time 0, the offshore wind power system is operating normally. The energy dissipation device monitors the effective value of the three-phase AC voltage at the wind turbine outlet in real time. When the detected value is lower than the set value, the MOA submodule is not activated. The voltage is shared by both the fixed and controllable parts of the energy dissipation device, resulting in a high-resistance state. The operating state is as follows: Figure 4 As shown in (a).

[0037] t After time 0, a low-voltage fault occurred on the receiving end of the wind power system, resulting in surplus power and a continuous rise in AC voltage. t At moment 1, if the real-time detected effective value of the AC voltage exceeds the threshold, the energy dissipation device is activated. The energy dissipation device adjusts the number of MOA sub-modules deployed in a stepped manner according to the degree of overvoltage, with the number of MOA sub-modules deployed being directly proportional to the degree of overvoltage. This effectively suppresses overvoltages of varying degrees at each moment. The internal flow path of the energy dissipation device at this time is as follows: Figure 4 As shown in (b). For each MOA submodule that is put into operation, a pulse signal with a fixed pulse width is sent to the positive and negative thyristors inside it (i.e., a trigger pulse is sent); if the overvoltage occurs during the positive half-cycle, the positive thyristor is turned on, the current bypasses the controllable part of the MOA, and the voltage of the controllable part drops to 0, transferring the overvoltage pressure to the fixed part for suppression. As a result, the voltage of the fixed part rises rapidly while the voltage at the port of the entire energy dissipation device drops rapidly.

[0038] The current change of the thyristor in the MOA submodule when it is put into operation is as follows: Figure 5 As shown, the current increases when the thyristor is turned on in the initial stage of overvoltage. As the energy dissipation device suppresses the overvoltage and the energy-consuming resistor continuously consumes energy, the current decreases accordingly.

[0039] As the AC voltage decreases, the MOA submodules gradually shut down. t At time 2, the AC voltage drops below the energy dissipation device's operating threshold, stopping the sending of trigger pulses to the thyristors in the MOA submodule. The AC current flowing through the thyristors gradually decreases to 0, and the thyristors enter the turn-off recovery phase.

[0040] t At time 3, the energy dissipation device monitors the AC voltage at the fan outlet in real time. When the AC voltage drops below the set value, the device controls all sub-modules to be locked and the energy dissipation device is deactivated.

[0041] Throughout the entire control process, changes in AC voltage, the number of MOA submodules in operation, and the thyristor current values ​​within the MOA submodules, such as... Figure 5 As shown.

[0042] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A controllable modular energy dissipation device based on thyristors, characterized in that, Includes a fixed part and a controllable part connected in series with the fixed part; The fixed part consists of a metal oxide surge arrester and a power dissipation resistor connected in parallel. The controllable part includes several MOA sub-modules with identical structures and cascaded connections. Each MOA sub-module includes a pair of anti-parallel thyristors, a metal oxide surge arrester and a voltage equalizing resistor. One side of the controllable part is connected to the fixed part, and the other side is connected to the ground.

2. The energy dissipation device according to claim 1, characterized in that, The negative terminal of each MOA submodule is connected to the positive terminal of its adjacent subsequent MOA submodule.

3. The energy dissipation device according to claim 1, characterized in that, The metal oxide surge arrester and voltage equalization resistor of each MOA submodule are connected in parallel across a pair of anti-parallel thyristors.

4. The energy dissipation device according to claim 3, characterized in that, The thyristor includes a forward thyristor and a reverse thyristor; wherein, the anode of the reverse thyristor is connected to the cathode of the forward thyristor, and the cathode of the reverse thyristor is connected to the anode of the forward thyristor; one end of the metal oxide surge arrester is connected to the anode of the forward thyristor, and the other end is connected to the cathode of the forward thyristor.

5. The energy dissipation device according to claim 4, characterized in that, The input terminal of the MOA submodule is connected to the anode of the forward thyristor, and the output terminal is connected to the cathode of the forward thyristor.

6. The energy dissipation device according to claim 1, characterized in that, The device also includes a control unit, which monitors the AC bus voltage in real time and adjusts the number of MOA sub-modules in operation in a stepwise manner according to the degree of AC voltage overvoltage.

7. The energy dissipation device according to claim 6, characterized in that, When a certain MOA submodule is put into operation, the control unit simultaneously triggers the thyristor in the MOA submodule through a signal with a fixed pulse width, so that the current bypasses the metal oxide surge arrester and flows through the thyristor.

8. A fault ride-through control method, implemented based on the energy dissipation device according to any one of claims 1 to 7, characterized in that, include: The AC voltage is monitored in real time. When the detected AC voltage exceeds the set value, the energy dissipation device enters the working state and determines the number of MOA sub-modules to be put into operation based on the degree of AC voltage overvoltage. When the AC voltage drops below the set value, the energy dissipation device exits the working state and returns to the high impedance state.

9. The method according to claim 8, characterized in that, The method also includes: adjusting the number of MOA sub-modules in operation in a stepped manner according to changes in AC voltage to suppress overvoltage of different degrees.

10. The method according to claim 8, characterized in that, The number of MOA submodules put into operation is positively correlated with the degree of AC voltage overvoltage.

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