Thyristor-based integrated energy consumption module MMC and fault ride-through method thereof

Abstract

The invention discloses an integrated energy consumption module MMC (Modular Multilevel Converter) based on a thyristor and a fault ride-through method thereof, energy consumption units are additionally arranged in part of sub-modules of the MMC, so that the energy consumption units and the sub-modules share a water cooling system, an energy supply system and the like, the thyristor is used for realizing the starting of an energy consumption function, and the turn-off of the thyristor is realized through the assistance of an LC oscillation circuit. When a fault occurs, the thyristor is switched on, the energy consumption resistor consumes energy at the moment, and the LC oscillating circuit also starts to oscillate. When the oscillation current is reversed, the current flowing through the thyristor is reduced. When the current flowing through the thyristor is 0, the thyristor is closed, and follow current is performed by the first diode. And when the thyristor is turned off, the oscillation capacitor in the LC oscillation circuit is charged until the voltage of the oscillation capacitor is equal to the voltage of the sub-module capacitor, and the energy consumption process is ended. Therefore, the integrated energy consumption module MMC can control the energy consumption unit to consume surplus power, and an economical and effective offshore wind power system fault ride-through solution is provided.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible DC power transmission, and in particular to an integrated energy-consuming module MMC based on thyristors and a fault ride-through method thereof. Background Art

[0002] The offshore wind power system based on VSC-HVDC (voltage source converter-based high voltage DC power transmission) technology has broad development prospects, and the DC energy-consuming device is the core equipment for realizing the AC fault ride-through of the system. In the existing technical solutions, the adopted DC energy-consuming devices are all arranged independently of the MMC (B. Xu, C. Gao, J. Zhang, J. Yang, B. Xi and Z. He, "A Novel DC Chopper Topology for VSC-Based Offshore Wind Farm Connection," in IEEE Transactions on Power Electronics, vol. 36, no. 3, pp. 3017-3027, March 2021.): a fully controlled device is used to control the surplus power of the system to be consumed, and the cost is relatively high, which limits its further development and application.

[0003] The DC energy-consuming device is independently arranged on the onshore DC side without being restricted by the floor area, and is mainly divided into three technical routes: centralized DCC (DC energy-consuming device), distributed DCC, and hybrid DCC. However, during the fault ride-through process, the resistor will generate a large amount of heat, affecting the normal operation of power electronic devices. The centralized DCC arranges the resistor outdoors through a wall bushing, and the fully controlled device is arranged in the valve hall, thus eliminating the influence of resistor heating. The distributed DCC adopts a water cooling system to ensure that the heat generated by the resistor during the fault does not exceed the standard. Different from the distributed DCC, the energy-consuming module arranged indoors in the hybrid DCC also adopts the water cooling and heat dissipation method, but its energy is mainly consumed by the resistor arranged outdoors, so the power of the water cooling system of the energy-consuming module is smaller.

[0004] However, no matter which method is adopted, the existing technical solutions all use fully controlled devices to realize the on-off of the DC current, and the fully controlled devices are expensive. Moreover, due to the independent arrangement of the DC energy-consuming device, additional equipment such as a water cooling system, a power supply system, and a wall bushing is required. This results in a relatively high overall cost of the existing solutions and limits their further application. Summary of the Invention

[0005] An embodiment of the present invention provides an integrated energy-consuming module MMC based on thyristors and a fault ride-through method thereof. By installing energy-consuming units in some sub-modules of the MMC, the energy-consuming units share systems such as water cooling and power supply with the sub-modules, and thyristors are used to realize the opening of the energy-consuming function, which can well absorb the surplus power during fault ride-through and provides an economical and effective solution for the fault ride-through of offshore wind power systems.

[0006] An embodiment of the present invention provides an integrated energy-consuming module MMC based on thyristors, including: a plurality of bridge arms, and each of the bridge arms includes: a half-bridge sub-module without an energy-consuming unit, and a half-bridge sub-module with an energy-consuming unit;

[0007] The energy-consuming unit includes: an LC oscillation circuit, a thyristor, a first diode, and an energy-consuming resistor;

[0008] The anode of the thyristor is respectively connected to the first end of the corresponding half-bridge sub-module, the cathode of the first diode, and the first end of the LC oscillation circuit, and the cathode of the thyristor is respectively connected to the anode of the first diode, the second end of the LC oscillation circuit, and the first end of the energy-consuming resistor; the second end of the energy-consuming resistor is connected to the second end of the corresponding half-bridge sub-module.

[0009] Further, the LC oscillation circuit includes: an oscillation capacitor and an oscillation inductor;

[0010] The first end of the oscillation capacitor is the first end of the LC oscillation circuit, the second end of the oscillation inductor is the second end of the LC oscillation circuit, and the second end of the oscillation capacitor is connected to the first end of the oscillation inductor.

[0011] Further, the half-bridge sub-module includes: a second diode, a third diode, a first IGBT, a second IGBT, and a sub-module capacitor;

[0012] The collector of the first IGBT is the first end of the half-bridge sub-module, and the collector of the first IGBT is also respectively connected to the cathode of the second diode and the first end of the sub-module capacitor. The emitter of the first IGBT is respectively connected to the anode of the second diode and the collector of the second IGBT;

[0013] The emitter of the second IGBT is the second end of the half-bridge sub-module, and the emitter of the second IGBT is also respectively connected to the anode of the third diode and the second end of the sub-module capacitor. The collector of the second IGBT is connected to the cathode of the third diode.

[0014] Further, a method for determining the number of energy-consuming units required to be installed on each bridge arm and the performance parameter values of the oscillation inductor and oscillation capacitor of the energy-consuming unit includes:

[0015] Construct an objective function with the goal of minimizing cost according to the energy-consuming units in the integrated energy-consuming module MMC; wherein, the objective function includes a first objective function with the lowest device cost as the goal and a second objective function with the lowest heat dissipation cost as the goal.

[0016] Construct a constraint function according to the DC voltage of the offshore wind power flexible DC system equipped with the integrated energy-consuming module MMC, the surplus power that needs to be absorbed by the energy-consuming unit under the fault ride-through condition, and the operating frequency of the energy-consuming unit.

[0017] Solve the objective function according to the constraint function, and calculate the number of energy-consuming units that need to be installed on each arm of the integrated energy-consuming module MMC, and the performance parameter values of the oscillating inductor and oscillating capacitor of the energy-consuming unit.

[0018] Furthermore, the objective function is:

[0019] W all =W ECM +W heat ;

[0020]

[0021] Among them, W all is the objective function, W ECM is the first objective function, W heat is the second objective function, m is the number of energy-consuming units that need to be installed on each arm to be solved, k 1 is the first proportionality coefficient between the performance parameter value of the oscillating capacitor and the cost, k 2 is the second proportionality coefficient between the performance parameter value of the oscillating inductor and the cost, k 3 is the cost of the thyristor, k 4 is the cost of the energy-consuming resistor, k 5 is the third proportionality coefficient between the heat dissipation cost and the average heat dissipation power, C o is the performance parameter value of the oscillating capacitor to be solved, L o is the performance parameter value of the oscillating inductor to be solved, I o is the oscillating current flowing through the oscillating inductor, T fault is the time of a single fault ride-through process, T interval is the interval time between two adjacent fault ride-through processes.

[0022] Another embodiment of the present invention provides a fault ride-through method for an integrated energy-consuming module MMC, and the integrated energy-consuming module MMC is the integrated energy-consuming module MMC described in any one of the above invention embodiments;

[0023] The method includes:

[0024] Obtain a DC voltage;

[0025] When it is detected that the DC voltage is greater than a preset first threshold, control a number of target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC to be put into or withdrawn, so that the DC voltage fluctuates within a preset fluctuation range;

[0026] When it is detected that the DC voltage is within a preset rated range, withdraw all the target half-bridge sub-modules that have been put into operation, so that the system resumes normal operation.

[0027] Further, the control of the sequential input or withdrawal of a number of target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC includes:

[0028] Adopt a DC voltage outer-loop control strategy and an energy-consuming unit input quantity inner-loop control strategy to control the input or withdrawal of a number of target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC.

[0029] Further, the adoption of the DC voltage outer-loop control strategy and the energy-consuming unit input quantity inner-loop control strategy to control the input or withdrawal of a number of target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC includes:

[0030] When it is detected that the DC voltage is greater than a preset first threshold, according to the DC voltage outer-loop control strategy, start and repeatedly execute a fault ride-through operation until it is detected that the DC voltage is less than a second threshold; wherein, the first threshold is greater than the second threshold;

[0031] The fault ride-through operation includes:

[0032] Generate a module input instruction according to the energy-consuming unit input quantity inner-loop control strategy;

[0033] According to the module input instruction, control a number of target half-bridge sub-modules in the integrated energy-consuming module MMC to be sequentially put into operation, so that the DC voltage gradually decreases;

[0034] When it is detected that the first voltage of the sub-module capacitor in the target half-bridge sub-module is equal to the second voltage of the oscillation capacitor, stop putting in the target half-bridge sub-module, and generate a module withdrawal instruction according to the energy-consuming unit input quantity inner-loop control strategy;

[0035] According to the module withdrawal instruction, control the already put-in target half-bridge sub-modules to be sequentially withdrawn, so that the DC voltage gradually rises;

[0036] When all the target half-bridge sub-modules are withdrawn, perform the next round of fault ride-through operation.

[0037] Further, a module input instruction is generated according to the inner loop control strategy of the energy consumption unit input quantity;

[0038] In a stepwise increasing manner, calculate the input quantity of the target half-bridge sub-module required each time, and generate a module input instruction according to the input quantity.

[0039] Further, generating a module exit instruction according to the inner loop control strategy of the energy consumption unit input quantity includes:

[0040] In a stepwise decreasing manner, calculate the exit quantity of the target half-bridge sub-module required to exit each time, and generate a module exit instruction according to the exit quantity.

[0041] Implementing the present invention has the following beneficial effects:

[0042] The present invention discloses a thyristor-based integrated energy consumption module MMC and its fault ride-through method. By installing energy consumption units in some sub-modules of the MMC, the energy consumption units share systems such as water cooling and power supply with the sub-modules, and use thyristors as the core devices to realize the opening of the energy consumption function. The turn-off of the thyristor is assisted by an LC oscillation circuit. Specifically, during normal operation, the thyristor does not act and the energy consumption resistor does not consume energy. During a fault, the energy consumption unit acts. First, the thyristor conducts, and at this time, the energy consumption resistor consumes energy, and the LC oscillation circuit also starts to oscillate. When the oscillating current reverses, the current flowing through the thyristor decreases. When the current flowing through the thyristor is 0, the thyristor turns off, and the first diode conducts for freewheeling. When the thyristor turns off, the oscillating capacitor in the LC oscillation circuit is charged until its voltage is equal to the sub-module capacitor voltage, and the energy consumption process ends. Therefore, the integrated energy consumption module MMC can replace the expensive fully controlled devices of the current DC energy consumption device, thereby controlling the energy consumption unit to absorb the surplus power, greatly reducing the cost of fault ride-through of the offshore wind power system, and providing an economical and effective fault ride-through solution. Description of the Drawings

[0043] Figure 1 is a schematic structural diagram of a half-bridge sub-module equipped with an energy consumption unit in a thyristor-based integrated energy consumption module MMC provided by an embodiment of the present invention.

[0044] Figure 2 is a schematic flow diagram of a fault ride-through method of an integrated energy consumption module MMC provided by an embodiment of the present invention.

[0045] Figure 3 is a schematic diagram of various system parameters and control signals during the fault ride-through process provided by an embodiment of the present invention. Detailed Embodiments

[0046] To make the objectives, technical solutions, and advantages of this application clearer, the following will clearly and completely describe the technical solutions in this application in conjunction with the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, but not all, of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts belong to the scope of protection of this application.

[0047] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the description of the specification, claims, and the above accompanying drawings of this application are intended to cover non-exclusive inclusion.

[0048] In the description of the embodiments of this application, technical terms such as "first" and "second" are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "a plurality of" is more than two, unless otherwise specifically defined.

[0049] Referring to "embodiments" herein means that the specific features, structures, or characteristics described in connection with the embodiments can be included in at least one embodiment of this application. The phrase appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those of ordinary skill in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0050] In the description of the embodiments of this application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. In addition, the character " / " herein generally represents an "or" relationship between the associated objects before and after.

[0051] In the description of the embodiments of this application, the term "a plurality of" refers to more than two (including two). Similarly, "a plurality of groups" refers to more than two groups (including two groups), and "a plurality of pieces" refers to more than two pieces (including two pieces).

[0052] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can also be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0053] An integrated energy-consuming module MMC based on thyristors provided by an embodiment of the present invention includes: a plurality of bridge arms, and each of the bridge arms includes: a half-bridge sub-module without an energy-consuming unit, and a half-bridge sub-module with an energy-consuming unit.

[0054] The energy-consuming unit includes: an LC oscillation circuit a, a thyristor 6, a first diode 7, and an energy-consuming resistor 10.

[0055] The anode of the thyristor 6 is respectively connected to the first end of the corresponding half-bridge sub-module b, the cathode of the first diode 7, and the first end of the LC oscillation circuit a. The cathode of the thyristor 6 is respectively connected to the anode of the first diode 7, the second end of the LC oscillation circuit a, and the first end of the energy-consuming resistor 10. The second end of the energy-consuming resistor 10 is connected to the second end of the corresponding half-bridge sub-module b.

[0056] Preferably, the LC oscillation circuit a includes: an oscillation capacitor 8 and an oscillation inductor 9.

[0057] The first end of the oscillation capacitor 8 is the first end of the LC oscillation circuit a, the second end of the oscillation inductor 9 is the second end of the LC oscillation circuit a, and the second end of the oscillation capacitor 8 is connected to the first end of the oscillation inductor 9.

[0058] Preferably, the half-bridge sub-module b includes: a second diode 3, a third diode 4, a first IGBT 1, a second IGBT 2, and a sub-module capacitor 5.

[0059] The collector of the first IGBT 1 is the first end of the half-bridge sub-module b. The collector of the first IGBT 1 is also respectively connected to the cathode of the second diode 3 and the first end of the sub-module capacitor 5. The emitter of the first IGBT 1 is respectively connected to the anode of the second diode 3 and the collector of the second IGBT 2.

[0060] The emitter of the second IGBT2 is the second end of the half-bridge sub-module b. The emitter of the second IGBT2 is also respectively connected to the anode of the third diode 4 and the second end of the sub-module capacitor 5. The collector of the second IGBT2 is connected to the cathode of the third diode 4.

[0061] In a preferred embodiment of the present invention, as Figure 1 shown, energy-consuming units composed of a switching circuit and a dissipative resistor are loaded on some sub-modules of each arm of the MMC. The switching circuit is composed of 1 thyristor and 1 anti-parallel diode, and the oscillating capacitor and the oscillating inductor are connected in series to form an LC oscillating circuit;

[0062] It can be understood that during normal operation, the thyristor 6 does not operate and the resistor 10 does not consume energy. When a fault occurs, the energy-consuming module operates. First, the thyristor 6 conducts, and at this time the resistor 10 consumes energy, and the LC circuit also starts to oscillate. When the oscillating current reverses, the current flowing through the thyristor 6 decreases. When the current flowing through the thyristor 6 is 0, the thyristor 6 turns off, and the diode 7 conducts for freewheeling. When the thyristor 6 turns off, the oscillating capacitor 8 is charged until its voltage is equal to the capacitor voltage of the sub-module, and the energy-consuming process ends.

[0063] Preferably, the method for determining the number of energy-consuming units to be carried on each arm, the oscillating inductor of the energy-consuming unit, and the performance parameter values of the oscillating capacitor of the energy-consuming unit includes:

[0064] S01. Construct an objective function with the goal of minimizing cost according to the energy-consuming units in the integrated energy-consuming module MMC; wherein, the objective function includes a first objective function with the goal of minimizing the device cost and a second objective function with the goal of minimizing the heat dissipation cost;

[0065] S02. Construct a constraint function according to the DC voltage of the offshore wind power flexible DC system carrying the integrated energy-consuming module MMC, the surplus power to be absorbed by the energy-consuming unit under the fault ride-through condition, and the operating frequency of the energy-consuming unit;

[0066] S03. Solve the objective function according to the constraint function, and calculate the number of energy-consuming units to be carried on each arm of the integrated energy-consuming module MMC, the oscillating inductor of the energy-consuming unit, and the performance parameter values of the oscillating capacitor.

[0067] Preferably, the objective function is:

[0068] W all =W ECM +W heat ;

[0069]

[0070] Among them, W all is the objective function, and W ECM is the first objective function, and W heat is the second objective function. m is the number of energy-consuming units required to be carried on each arm to be solved. k 1 is the first proportionality coefficient between the performance parameter value and the cost of the oscillating capacitor, and k 2 is the second proportionality coefficient between the performance parameter value and the cost of the oscillating inductor, and k 3 is the cost of the thyristor, and k 4 is the cost of the energy-consuming resistor, and k 5 is the third proportionality coefficient between the heat dissipation cost and the average heat dissipation power, and C o is the performance parameter value of the oscillating capacitor to be solved, and L o is the performance parameter value of the oscillating inductor to be solved, and I o is the oscillating current flowing through the oscillating inductor, and T fault is the time of a single fault ride-through process, and T interval is the interval time between two adjacent fault ride-through processes.

[0071] In a preferred embodiment of the present invention, it is assumed that each arm has m half-bridge sub-modules equipped with energy-consuming units. When the surplus power is equal to the system rated power, m energy-consuming units need to be put into operation. When the surplus power is equal to k times the system rated power (0 < k < 1), then km sub-modules equipped with energy-consuming units need to be put into energy consumption. As the energy-consuming modules are gradually put into operation, the DC voltage of the system gradually decreases.

[0072] When the surplus power in the system is k times the system rated power (0 < k < 1), and m is the number of energy-consuming units configured for each arm. On the premise of meeting the performance requirements, the configuration of energy-consuming units should follow the principle of minimum cost. The total cost of configuring energy-consuming units is as follows, including two parts. One part is the equipment cost of the energy-consuming module (W ECM ), and the other part is the heat dissipation cost (W heat ).

[0073] W all = W ECM + W heat ;

[0074] Furthermore, the main devices of the energy-consuming unit include thyristors, oscillating capacitors, oscillating inductors, and energy-consuming resistors. Since thyristors have a high current surge capacity and can withstand the capacitor voltage of a single sub-module, the cost of thyristors can be regarded as a constant. For oscillating capacitors and oscillating inductors, their costs are related to energy. Specifically, the equipment cost of the energy-consuming unit increases with the increase in the number of energy-consuming units. After the number of energy-consuming units increases, the power that each energy-consuming unit needs to absorb becomes lower, and the heat dissipation cost also decreases accordingly. Under the fault ride-through condition, the cost of the resistor can be considered a constant. Therefore, the total equipment cost of the energy-consuming unit can be expressed as

[0075]

[0076] The heat dissipation cost of a single energy-consuming unit is related to the average power it needs to absorb. Therefore, the total heat dissipation cost can be expressed as

[0077]

[0078] where, W all is the objective function, W ECM is the first objective function, W heat is the second objective function, m is the number of energy-consuming units to be installed on each arm, k 1 is the first proportionality coefficient between the performance parameter value and the cost of the oscillating capacitor, k 2 is the second proportionality coefficient between the performance parameter value and the cost of the oscillating inductor, k 3 is the cost of the thyristor, k 4 is the cost of the energy-consuming resistor, k 5 is the third proportionality coefficient between the heat dissipation cost and the average heat dissipation power, C o is the performance parameter value (capacitance value) of the oscillating capacitor to be determined, U SM is the capacitor voltage of the oscillating capacitor in each energy-consuming unit,, L o is the performance parameter value (inductance value) of the oscillating inductor to be determined, I o is the oscillating current flowing through the oscillating inductor, T fault is the time of a single fault ride-through process, T interval is the interval time between two adjacent fault ride-through processes, P R is the surplus power consumed by the energy-consuming resistor in each energy-consuming unit.

[0079] In summary, the total cost of configuring the energy-consuming module in the MMC can be expressed by the following formula. It can be seen that W all is related to the selected C o 、L o and P RClosely related. At the same time, during the fault ride-through process, due to the system, the energy-consuming module, and the requirements for the absorbed power, DC voltage, operating frequency, etc., there are also mutual constraints among the parameters.

[0080]

[0081] Taking the lowest total cost shown in the above formula as the goal and the constraint conditions of the system and the energy-consuming module as the conditions, the values of m, R, L o and C o can be obtained.

[0082] This embodiment provides an integrated energy-consuming module MMC based on thyristors according to the present invention. By installing energy-consuming units in some sub-modules of the MMC, the energy-consuming units share systems such as water cooling and power supply with the sub-modules, and thyristors are used as the core devices to realize the opening of the energy-consuming function. The turn-off of the thyristors is assisted by an LC oscillation circuit. Specifically, during normal operation, the thyristors do not act, and the energy-consuming resistors do not consume energy. When a fault occurs, the energy-consuming units act. First, the thyristors are turned on. At this time, the energy-consuming resistors consume energy, and the LC oscillation circuit also starts to oscillate. When the oscillating current reverses, the current flowing through the thyristors decreases. When the current flowing through the thyristors is 0, the thyristors are turned off, and the first diode conducts for freewheeling. When the thyristors are turned off, the oscillating capacitors in the LC oscillation circuit are charged until their voltage is equal to the sub-module capacitor voltage, and the energy-consuming process ends. Therefore, the integrated energy-consuming module MMC can replace the expensive fully controlled devices of the current DC energy-consuming device, thereby controlling the energy-consuming units to absorb the surplus power, greatly reducing the cost of the offshore wind power system for fault ride-through, and providing an economical and effective fault ride-through solution.

[0083] See Figure 2 , which is a schematic flowchart of a fault ride-through method for an integrated energy-consuming module MMC provided by an embodiment of the present invention. The integrated energy-consuming module MMC is the integrated energy-consuming module MMC described in any one of the above-mentioned invention embodiments. The method includes:

[0084] S1. Obtain the DC voltage;

[0085] In a preferred embodiment of the present invention, as Figure 3 shown, taking the t 0 moment as the fault occurrence moment, P send is the power generated by the fan, P out is the power sent out by the system, P surplus is the surplus power, U dc is the system DC voltage, U set is the voltage limit set by the system, T outer_loop is the outer loop control signal, T inner_loop is the inner loop control signal, IR I is the current flowing through the energy-consuming resistor. o I is the oscillating current. s t is the current flowing through the thyristor. 0 Before time t, the system operates normally, the energy-consuming unit does not work, and the MMC works according to the normal control logic.

[0086] S2. When it is detected that the DC voltage is greater than a preset first threshold, control some target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC to be put into or withdrawn from operation, so that the DC voltage fluctuates within a preset fluctuation range.

[0087] In a preferred embodiment of the present invention, at time t 0 A fault occurs, the AC-side voltage drops rapidly, the power transmission capacity of the system decreases, the surplus power charges the capacitors in the system, and the DC voltage of the system rises. When it reaches the set limit (first threshold) of the system, the energy-consuming unit starts to work.

[0088] Preferably, controlling some target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC to be put into or withdrawn from operation in sequence includes:

[0089] S21. Adopt a DC voltage outer-loop control strategy and an energy-consuming unit input quantity inner-loop control strategy to control some target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC to be put into or withdrawn from operation.

[0090] Preferably, the adopting of the DC voltage outer-loop control strategy and the energy-consuming unit input quantity inner-loop control strategy to control some target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC to be put into or withdrawn from operation includes:

[0091] S211. When it is detected that the DC voltage is greater than a preset first threshold, according to the DC voltage outer-loop control strategy, start and repeatedly execute the fault ride-through operation until it is detected that the DC voltage is less than a second threshold; wherein, the first threshold is greater than the second threshold.

[0092] In a preferred embodiment of the present invention, at time t 1 the DC voltage is greater than a preset first threshold, and the outer-loop control signal T outer_loop changes from 0 to 1, and the energy-consuming units act in sequence. Since the thyristor cannot directly turn off the DC current like a fully controlled device, it is necessary to turn off the current through 0 during the reverse period of the oscillating current generated by the LC circuit, and the frequency of the oscillating current is fixed, so the input frequency of the energy-consuming unit is also fixed.

[0093] The fault ride-through operation includes:

[0094] S212. Generate a module input instruction according to the inner-loop control strategy based on the number of energy-consuming units put into operation.

[0095] Preferably, generate a module input instruction according to the inner-loop control strategy based on the number of energy-consuming units put into operation.

[0096] S2121. Calculate the number of target half-bridge sub-modules to be input each time in a stepwise increasing manner, and generate a module input instruction according to the input number.

[0097] S213. According to the module input instruction, control several target half-bridge sub-modules in the integrated energy-consuming module MMC to be input in sequence, so as to gradually reduce the DC voltage.

[0098] In a preferred embodiment of the present invention, assume that each arm has m sub-modules for installing energy-consuming units. When the surplus power is equal to the system rated power, input m energy-consuming units. When the surplus power is equal to k times the system rated power (0 < k < 1), km sub-modules are put into energy consumption. As the energy-consuming units are gradually input, the system DC voltage gradually decreases. Specifically, determine the number of target half-bridge sub-modules to be input each time in a stepwise increasing manner, and generate an inner-loop control signal as shown in Figure 3 T in inner_loop shown.

[0099] S214. When it is detected that the first voltage of the sub-module capacitor in the target half-bridge sub-module is equal to the second voltage of the oscillation capacitor, stop inputting the target half-bridge sub-module, and generate a module withdrawal instruction according to the inner-loop control strategy based on the number of energy-consuming units put into operation.

[0100] Preferably, generating a module withdrawal instruction according to the inner-loop control strategy based on the number of energy-consuming units put into operation includes:

[0101] S2141. Calculate the number of target half-bridge sub-modules to be withdrawn each time in a stepwise decreasing manner, and generate a module withdrawal instruction according to the withdrawal number.

[0102] In a preferred embodiment of the present invention, at time t 2 determine the number of target half-bridge sub-modules to be withdrawn each time in a stepwise decreasing manner, and generate an inner-loop control signal as shown in Figure 3 T in inner_loop shown.

[0103] S215. According to the module withdrawal instruction, control the already input target half-bridge sub-modules to withdraw in sequence, so as to gradually increase the DC voltage.

[0104] S216. When all target half-bridge sub-modules have withdrawn, perform the next round of fault ride-through operation.

[0105] In a preferred embodiment of the present invention, as Figure 3 shown, at time t 3 , the energy-consuming unit completely exits, and the DC voltage rises again. Then, the above-mentioned fault ride-through operation is repeated, and the DC voltage of the system will also fluctuate within a certain range. Until time t 4 , the AC side voltage starts to recover, and the surplus power gradually decreases. There will be a power overshoot at the moment when the grid-connected power of the onshore converter station recovers, resulting in the DC voltage of the system dropping below the rated value (the second threshold). At this time, the outer-loop control signal becomes 0, and the energy-consuming unit no longer operates.

[0106] S3. When it is detected that the DC voltage is within a preset rated range, all the target half-bridge sub-modules that have been put into operation are exited to enable the system to resume normal operation.

[0107] In a preferred embodiment of the present invention, as Figure 3 shown, at time t 5 , the DC voltage of the system gradually recovers to near the rated value, the energy-consuming unit is controlled to completely exit, the fault is recovered, and the system operates normally.

[0108] The above are the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art of the present technology, 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. An integrated energy consumption module MMC based on thyristor, characterized in that: include: A plurality of bridge arms, each of the bridge arms comprising: a half-bridge submodule without an energy consumption unit, and a half-bridge submodule with an energy consumption unit; The energy consumption unit comprises: an LC oscillating circuit, a thyristor, a first diode, and an energy consumption resistor; The anode of the thyristor is respectively connected to the first end of the corresponding half-bridge sub-module, the cathode of the first diode, and the first end of the LC oscillation circuit; the cathode of the thyristor is respectively connected to the anode of the first diode, the second end of the LC oscillation circuit, and the first end of the energy dissipation resistor; the second end of the energy dissipation resistor is connected to the second end of the corresponding half-bridge sub-module.

2. The thyristor-based integrated energy consumption module MMC according to claim 1, characterized in that: The LC oscillation circuit comprises: an oscillation capacitor and an oscillation inductor; The first end of the oscillating capacitor is the first end of the LC oscillating circuit, the second end of the oscillating inductor is the second end of the LC oscillating circuit, and the second end of the oscillating capacitor is connected to the first end of the oscillating inductor.

3. The thyristor-based integrated energy consumption module MMC according to claim 2, characterized in that: The half-bridge submodule comprises: a second diode, a third diode, a first IGBT, a second IGBT, and a submodule capacitor; The collector of the first IGBT is the first end of the half-bridge submodule, the collector of the first IGBT is also connected to the cathode of the second diode and the first end of the submodule capacitor respectively, and the emitter of the first IGBT is connected to the anode of the second diode and the collector of the second IGBT respectively; The emitter of the second IGBT is the second end of the half-bridge sub-module, and the emitter of the second IGBT is also respectively connected to the anode of the third diode and the second end of the sub-module capacitor, and the collector of the second IGBT is connected to the cathode of the third diode.

4. The thyristor-based integrated energy consumption module MMC according to claim 3, characterized in that: The method for determining the number of energy consumption units required to be carried on each bridge arm, and the performance parameter values ​​of the oscillating inductance and oscillating capacitance of the energy consumption units includes: According to the energy consumption unit in the integrated energy consumption module MMC, an objective function with the goal of minimizing cost is constructed; wherein the objective function includes: a first objective function with the goal of minimizing device cost, and a second objective function with the goal of minimizing heat dissipation cost; Constructing a constraint function according to the DC voltage of the offshore wind power flexible DC system equipped with the integrated energy consumption module MMC, the surplus power required to be absorbed by the energy consumption unit under the fault ride-through condition, and the operation frequency of the energy consumption unit; The objective function is solved according to the constraint function to calculate the number of energy consumption units required to be carried on each bridge arm of the integrated energy consumption module MMC, and the performance parameter values ​​of the oscillating inductance and oscillating capacitance of the energy consumption units.

5. The thyristor-based integrated energy consumption module MMC according to claim 4, characterized in that: The objective function is: IN all =In ECM +W heat ; Among them, W all is the objective function, W ECM is the first objective function, W heat is the second objective function, m is the number of energy-consuming units required to be carried on each bridge arm to be determined, k1 is the first proportional coefficient between the performance parameter value of the oscillating capacitor and the cost, k2 is the second proportional coefficient between the performance parameter value of the oscillating inductor and the cost, k3 is the cost of the thyristor, k4 is the cost of the energy-consuming resistor, k5 is the third proportional coefficient between the heat dissipation cost and the average heat dissipation power, U SM is the capacitance voltage of the oscillating capacitor in each energy consumption unit, C o is the performance parameter value of the oscillating capacitor to be determined, L o is the performance parameter value of the oscillating inductor to be determined, I o is the oscillating current flowing through the oscillating inductor, T fault is the time of a single fault ride-through process, T interval is the interval time between two adjacent fault-crossing processes, P R It is the surplus power consumed by the absorption resistor in each energy consumption unit.

6. A fault ride-through method for an integrated energy consumption module MMC, characterized in that: The integrated energy consumption module MMC is the integrated energy consumption module MMC according to any one of claims 1 to 5; The method comprises: Get DC voltage; When it is detected that the DC voltage is greater than a preset first threshold, a plurality of target half-bridge sub-modules equipped with energy-consuming units in the integrated energy-consuming module MMC are controlled to be put into operation or withdrawn, so that the DC voltage fluctuates within a preset fluctuation range; When it is detected that the DC voltage is within a preset rated range, all the put-in-service target half-bridge sub-modules are exited to restore the system to normal operation.

7. The fault ride-through method of the integrated energy consumption module MMC according to claim 6, characterized in that: The control of the integrated energy consumption module MMC to sequentially activate or deactivate a plurality of target half-bridge sub-modules equipped with energy consumption units includes: The DC voltage outer loop control strategy and the energy consumption unit input quantity inner loop control strategy are adopted to control the input or output of several target half-bridge sub-modules equipped with energy consumption units in the integrated energy consumption module MMC.

8. The fault ride-through method of the integrated energy consumption module MMC according to claim 7, characterized in that: The DC voltage outer loop control strategy and the energy consumption unit input quantity inner loop control strategy are used to control the input or output of several target half-bridge sub-modules equipped with energy consumption units in the integrated energy consumption module MMC, including: When it is detected that the DC voltage is greater than a preset first threshold, the fault ride-through operation is started and repeatedly performed according to the DC voltage outer loop control strategy until it is detected that the DC voltage is less than a second threshold; wherein the first threshold is greater than the second threshold; The fault ride-through operation includes: Generate module input instructions based on the inner loop control strategy of the number of energy-consuming units put into use; According to the module input instruction, a plurality of target half-bridge sub-modules in the integrated energy consumption module MMC are controlled to be input in sequence, so that the DC voltage is gradually reduced; When it is detected that the first voltage of the submodule capacitor in the target half-bridge submodule is equal to the second voltage of the oscillating capacitor, the target half-bridge submodule is stopped from being put into operation, and a module exit instruction is generated according to the inner loop control strategy of the number of energy consumption units put into operation; According to the module exit instruction, the target half-bridge sub-modules that have been put into use are controlled to exit in sequence, so that the DC voltage gradually increases; When all target half-bridge sub-modules exit, the next round of fault ride-through operation is performed.

9. The fault ride-through method of the integrated energy consumption module MMC according to claim 8, characterized in that: The inner loop control strategy according to the number of energy consumption units put into use generates module input instructions; The number of target half-bridge sub-modules required to be put into operation each time is calculated in a step-by-step increasing manner, and a module putting-in-operation instruction is generated according to the number of said target half-bridge sub-modules put into operation.

10. The fault ride-through method of the integrated energy consumption module MMC according to claim 9, characterized in that: The generating module exit instruction according to the inner loop control strategy of the number of energy consumption units input includes: The exit quantity of the target half-bridge sub-modules that need to be exited each time is calculated in a step-by-step decreasing manner, and a module exit instruction is generated according to the exit quantity.

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