Direct-current line fault ride-through method applied to converter valve with active energy discharge function and related device

Abstract

The invention provides a direct-current line fault ride-through method applied to a converter valve with an active energy discharge function and a related device, and the method comprises the steps: starting a direct-current fault ride-through strategy in response to a direct-current line fault signal; after the first direct-current fault ride-through strategy is started, energy release branches of the corresponding bridge arms are controlled to be switched according to the overall level of the capacitor voltage of the sub-modules in the bridge arms; after the second direct current fault ride-through strategy is started, a direct current bias is superposed on the reference value of the direct current controller; and waiting for a set time after the DC fault is cleared, and exiting the DC fault ride-through strategy. According to the invention, the switching of the energy release resistor is controlled according to the capacitor voltage level of the sub-module in the bridge arm, the overvoltage of the sub-module is accurately suppressed, the excessive difference of the action frequency of the energy release branch is avoided, and the uniform distribution of the released energy is ensured; meanwhile, a direct current bias is superposed on a reference value of a direct current controller at the initial stage of inputting a direct current fault ride-through strategy, so that direct current can quickly control zero crossing, and direct current fault clearing is accelerated.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible direct current transmission of electric power systems, and in particular relates to a direct current line fault ride-through method and related devices applied to a converter valve with an active energy discharge function. Background Art

[0002] With the continuous development of power electronics technology, Modular Multilevel Converter (MMC) has attracted wide attention due to its high integration, simple sub-module structure, and the effect of increasing the number of levels and equivalent switching frequency by cascading half / full bridge sub-modules. MMC can effectively reduce AC harmonics and DC side ripple, and has flexibility, controllability and high efficiency. It has shown great application potential in the fields of high-voltage DC transmission and renewable energy grid connection, and has gradually become one of the important means of new energy transmission.

[0003] When MMC is applied to an island power generation system, if the system DC line or the receiving end fails and the energy cannot be sent out normally, and the sending end lacks effective energy consumption devices or fails to reduce power in time, it may cause a large amount of surplus power to accumulate in the system, posing a threat to the safe and stable operation of the system. To solve this problem, a converter valve with active energy discharge function is designed. When the device detects that the capacitor voltage of the submodule reaches a dangerous level, it can automatically activate the discharge resistor to convert the excess energy into heat dissipation, thereby avoiding the occurrence of overvoltage.

[0004] Although the full-half-bridge hybrid MMC has good DC fault clearing capabilities and can quickly interrupt DC fault currents through the negative voltage output provided by the full-bridge submodule, it still faces challenges when implementing traditional DC fault ride-through strategies in systems where sea breeze is sent through flexible DC converter valves. For example, when a DC line fault occurs, although the energy discharge branch in the submodule helps maintain the capacitor voltage balance, conventional control methods will cause uneven action frequencies of the energy discharge branches between different submodules, thereby affecting the life of some components; at the same time, there are also difficulties in selecting the parameters of the DC current controller - too large a value may easily cause system oscillation instability, while too small a value may slow down the fault current clearing speed and prolong the fault handling time. Therefore, it is necessary to develop a more optimized DC line fault ride-through strategy to improve the overall system reliability and efficiency. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a DC line fault ride-through strategy applied to a converter valve with active energy discharge function, which is used to solve the problems of lack of effective control strategy for energy discharge branch, difficulty in setting parameters of DC current controller, and slow DC fault current clearing speed when the traditional DC fault ride-through strategy is applied to the sea breeze transmission system through a flexible DC converter valve with active energy discharge function.

[0006] In order to achieve the above object, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a DC line fault ride-through method applied to a converter valve with an active energy discharge function, comprising the following steps:

[0008] In response to a DC line fault, starting a DC fault ride-through strategy, the DC fault ride-through strategy including a first DC fault ride-through strategy and a second DC fault ride-through strategy;

[0009] After the first DC fault ride-through strategy is started, the energy dissipation branch of the corresponding bridge arm is controlled to be switched on and off according to the overall level of the submodule capacitor voltage in each bridge arm to ensure that the system does not experience overvoltage;

[0010] After the second DC fault ride-through strategy is started, a DC bias is superimposed on a reference value of the DC current controller to increase a DC current control target of the DC current controller, thereby accelerating a fault current clearing speed;

[0011] Continuously executing the first DC fault ride-through strategy and the second DC fault ride-through strategy until the DC fault is cleared;

[0012] After waiting for the set time, exit the DC fault ride-through strategy and complete the DC line fault ride-through.

[0013] Furthermore, the energy dissipation branch of the corresponding bridge arm is controlled to be switched on and off according to the overall level of the capacitor voltage of the submodules in each bridge arm, including:

[0014] Calculate the average value of the submodule capacitor voltage of each bridge arm;

[0015] The average value of the submodule capacitor voltage of each bridge arm is compared with the switching voltage setting value of the energy dissipation branch of each bridge arm, and the switching of the energy dissipation branch is controlled according to the comparison result.

[0016] Furthermore, the switching voltage setting of the energy-discharging branch is calculated according to the following formula:

[0017] Input setting: U in =1.1k1U0, where U0 is the rated operating voltage of the submodule and k1 is the margin coefficient;

[0018] Exit setting: U out =U in -k2U0, where k2 is a constant.

[0019] Further, the second DC fault ride-through strategy is continuously executed until the DC fault is cleared, including:

[0020] At the beginning of the second DC fault ride-through strategy, the parameters of the DC current controller are adjusted to be small and a DC bias is superimposed on the reference value of the DC current controller;

[0021] Controlled by a DC current controller until the DC current is controlled to near 0;

[0022] Clear the DC fault at the DC current zero crossing point;

[0023] When the DC fault is cleared, the DC bias is restored to 0.

[0024] Furthermore, after a DC bias is added to the reference value of the DC current controller, the reference value of the DC current controller is determined according to the following formula:

[0025] I dc_ref =0+ΔI dc_ref

[0026] Among them, I dc_ref is the reference value of the DC current controller, ΔI dc_ref is a DC bias that satisfies the following conditions:

[0027] ΔI dcF +ΔI dc_ref ≤0

[0028] Among them, ΔI dcF It is the per-unit value of the fault point current after the DC line fault state is stabilized.

[0029] Furthermore, when the DC fault is cleared, the DC bias ramp returns to zero.

[0030] Furthermore, the ramp time range of the DC bias is 1 to 2 power frequency cycles.

[0031] In a second aspect, the present invention provides a DC line fault ride-through device applied to a converter valve with an active energy discharge function, comprising:

[0032] A strategy starting module, in response to a DC line fault, for starting a DC fault ride-through strategy, the DC fault ride-through strategy including a first DC fault ride-through strategy and a second DC fault ride-through strategy;

[0033] A first strategy execution module is used to control the switching on and off of the energy dissipation branch of the corresponding bridge arm according to the overall level of the capacitor voltage of the submodules in each bridge arm after the first DC fault ride-through strategy is started, so as to ensure that the system does not have overvoltage;

[0034] a second strategy execution module, configured to superimpose a DC bias on a reference value of a DC current controller after the second DC fault ride-through strategy is started, so as to increase a DC current control target of the DC current controller, thereby accelerating a fault current clearing speed;

[0035] A DC fault judgment module, used for continuously executing the first DC fault ride-through strategy and the second DC fault ride-through strategy until it is determined that the DC fault is cleared;

[0036] The strategy exit module is used to exit the DC fault ride-through strategy after waiting for a set time and complete the DC line fault ride-through.

[0037] In a third aspect, the present invention provides a computer device, the device comprising a processor and a memory:

[0038] The memory is used to store the computer program and send the instructions of the computer program to the processor;

[0039] The processor executes a DC line fault ride-through method applied to a converter valve with an active energy discharge function as described in the first aspect according to instructions of the computer program.

[0040] In a fourth aspect, the present invention provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, a DC line fault riding method for a converter valve with an active energy discharge function as in the first aspect is implemented.

[0041] In summary, the present invention provides a DC line fault ride-through method and related device applied to a converter valve with active energy discharge function, including starting a DC fault ride-through strategy in response to a DC line fault, the DC fault ride-through strategy including a first DC fault ride-through strategy and a second DC fault ride-through strategy; after the first DC fault ride-through strategy is started, the energy discharge branch of the corresponding bridge arm is controlled to be thrown in and out according to the overall level of the sub-module capacitor voltage in each bridge arm to ensure that the system does not have overvoltage; after the second DC fault ride-through strategy is started, a DC bias is superimposed on a reference value of a DC current controller to increase the DC current control target of the DC current controller, thereby accelerating the fault current clearing speed; the first DC fault ride-through strategy and / or the second DC fault ride-through strategy are continuously executed until the DC fault is cleared; and the DC fault ride-through strategy is exited after waiting for a set time to complete the DC line fault ride-through. The present invention controls the switching of energy-discharging resistors according to the voltage level of the submodule capacitors in the bridge arm, accurately suppresses overvoltage of the submodules, and avoids excessive differences in the action frequency of the energy-discharging branches, thereby ensuring uniform energy distribution of each submodule; at the same time, at the initial stage of the DC fault ride-through strategy, a DC bias is superimposed on the reference value of the DC current controller, so that the DC current is quickly controlled to cross zero, thereby accelerating the clearing of the DC fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0043] Figure 1 It is a flow chart of a DC line fault ride-through method applied to a converter valve with active energy discharge function provided by an embodiment of the present invention;

[0044] Figure 2 is a topological structure diagram of a converter valve with active energy discharge function provided by an embodiment of the present invention;

[0045] Figure 3 is a control block diagram of a DC fault current clearing strategy provided by an embodiment of the present invention;

[0046] Figure 4 is a flow chart of a DC fault current clearing strategy provided by an embodiment of the present invention;

[0047] Figure 5 is an overall flow chart of a DC fault ride-through strategy provided by an embodiment of the present invention;

[0048] Figure 6 It is a waveform diagram of the overall EMTDC simulation of a DC fault ride-through provided by an embodiment of the present invention;

[0049] Figure 7a This is a fault point current EMTDC simulation waveform diagram when a conventional DC current control strategy is adopted according to an embodiment of the present invention;

[0050] Figure 7b It is a fault point current EMTDC simulation waveform diagram when the control strategy of the present invention is adopted according to an embodiment of the present invention;

[0051] Figure 8 It is a block diagram of a DC line fault ride-through device applied to a converter valve with an active energy discharge function provided by an embodiment of the present invention;

[0052] Fig. 9 The present invention provides a block diagram of a computer device. DETAILED DESCRIPTION

[0053] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] The full-half-bridge hybrid MMC has the ability to clear DC faults, and it uses the negative pressure output capability of the full-bridge submodule to quickly clear the DC fault current. When the traditional DC fault ride-through strategy is applied to the sea breeze through the flexible DC converter valve with active energy discharge function, when a DC line fault occurs in the system, the submodule energy discharge branch can maintain the submodule capacitor voltage balanced and within a safe range, so there is no need for a separate submodule voltage control loop. However, the energy discharge branch is dispersed among the submodules, and the conventional method for controlling it is to output the number of input energy discharge branches of each bridge arm through the DC side voltage control, and input the energy discharge branch of the submodule with higher voltage in real time according to the submodule capacitor voltage. The overvoltage suppression of the submodule is not direct, and it will cause the difference in the action frequency of the energy discharge branch to be too large, and the number of switching times of some submodule energy discharge branches is too high, which reduces the service life. Therefore, the engineering applicability is poor.

[0055] In addition, the full half-bridge hybrid MMC usually performs closed-loop control of the DC current with zero as the reference value for the DC fault current generated under the DC line fault, and uses the closed-loop output result as the DC bias component of the three-phase modulation wave to form zero or negative pressure at the DC port of the valve group to clear the fault current. Due to the existence of the equivalent ground capacitance of the long-distance DC submarine cable in the sea breeze transmission system, the rising speed and development trend of the DC fault current are relatively fast. At this time, if a larger DC current controller parameter is selected, the controller output will oscillate between the upper and lower limits, causing the system to become unstable; if a smaller controller parameter is selected, although the stability of the system is guaranteed, the DC current clearing speed is too slow, the DC current does not exceed zero for a long time, and the arc at the fault point cannot be extinguished for a long time, which greatly prolongs the system DC fault ride-through time. In severe cases, it even leads to a long waiting time for de-ionization and failure of fault ride-through.

[0056] Therefore, the present invention provides a DC line fault ride-through method and related devices applied to a converter valve with active energy discharge function to solve the above-mentioned problems.

[0057] See also Figure 1 This embodiment provides a DC line fault ride-through method applied to a converter valve with an active energy discharge function, comprising the following steps:

[0058] S11: In response to a DC line fault, starting a DC fault ride-through strategy, where the DC fault ride-through strategy includes a first DC fault ride-through strategy and a second DC fault ride-through strategy.

[0059] It should be noted that DC fault ride-through refers to the ability of a DC transmission system to take a series of measures to enable the power system to safely survive the fault period and resume normal operation as soon as possible when a line short circuit or other types of faults occur.

[0060] When the system detects a DC line fault, it will immediately respond and activate the pre-set DC fault ride-through strategy. The first DC fault ride-through strategy and the second DC fault ride-through strategy are two different response measures, which are used for system overvoltage control and DC current rapid clearing respectively.

[0061] In the specific implementation, the real-time value of the DC current is detected. If the DC current is greater than I set It is considered that a DC line fault occurs in the system, and the system enters the DC fault ride-through strategy; where I set It can be 1.2~1.3 times the rated DC current value.

[0062] S12: After the first DC fault ride-through strategy is started, the energy dissipation branch of the corresponding bridge arm is controlled to be switched on and off according to the overall level of the submodule capacitor voltage in each bridge arm to ensure that the system does not experience overvoltage.

[0063] It should be noted that the first DC fault ride-through strategy is a key measure for overvoltage protection. In a DC transmission system, especially when a modular multilevel converter (MMC) is used, each bridge arm consists of multiple submodules connected in series, each of which contains a storage capacitor. If a fault occurs, the voltage on these capacitors may increase. By monitoring the capacitor voltage of each submodule and calculating the relevant indicators of the capacitor voltage of all submodules in the system (such as average value, root mean square value, etc.), the overall voltage level of the system can be reflected, and the energy discharge branch connected to it can be adjusted in time accordingly, which can effectively prevent capacitor overcharging and avoid equipment damage.

[0064] S13: After the second DC fault ride-through strategy is started, a DC bias is superimposed on a reference value of the DC current controller to increase a DC current control target of the DC current controller, thereby accelerating a fault current clearing speed.

[0065] It should be noted that the second DC fault ride-through strategy is designed to accelerate the clearing of fault current. Normally, the DC current controller is responsible for maintaining the set DC current level. However, under fault conditions, in order to reduce the current level near the fault point more quickly, the reference input of the controller can be temporarily modified, that is, an offset is added to prompt the system to generate a larger reverse current to offset and eliminate the fault current. The advantage of this is that the fault handling time can be shortened.

[0066] S14: Continue to execute the first DC fault ride-through strategy and the second DC fault ride-through strategy until the DC fault is cleared.

[0067] It should be noted that during the DC fault ride-through period, the first DC fault ride-through strategy and the second DC fault ride-through strategy will remain activated until the DC fault is cleared.

[0068] S15: After waiting for a set time, the DC fault ride-through strategy is exited and the DC line fault ride-through is completed.

[0069] It should be noted that before all countermeasures are completed, a period of time is required to ensure that the system is in a stable state before exiting all DC fault ride-through strategies.

[0070] The present embodiment provides a DC line fault ride-through method applied to a converter valve with an active energy discharge function. The method controls the switching of energy discharge resistors according to the voltage level of the sub-module capacitors in the bridge arm, accurately suppresses the overvoltage of the sub-modules, and avoids excessive differences in the action frequency of the energy discharge branches, thereby ensuring that the energy discharged by each sub-module is evenly distributed. At the same time, a DC bias is superimposed on the reference value of the DC current controller at the initial stage of the DC fault ride-through strategy, so that the DC current is quickly controlled to cross zero, thereby accelerating the clearing of the DC fault.

[0071] See also Figure 2 , Figure 2 The topological structure of a converter valve with active energy discharge function is shown. The converter valve includes 6 bridge arms, each of which is composed of several sub-modules connected in series. In order to achieve DC line fault ride-through, the sub-modules in the bridge arm can adopt a half-bridge or full-bridge mixed series structure or other sub-module topologies with DC fault ride-through capability; an active energy discharge branch composed of a fully controlled power electronic switch and a resistor is connected in parallel at both ends of each sub-module capacitor, which can actively discharge energy when the capacitor voltage is too high, thereby lowering the capacitor voltage and ensuring the safety of the sub-module. The above-mentioned first DC fault ride-through strategy can be applied to Figure 2 The changeover valve shown.

[0072] See also Figure 3 , Figure 3The control principle of the DC fault current clearing strategy is shown in Figure 1. It adopts dual-loop control, where the first block is the outer loop voltage control and the second block is the inner loop current control. In the outer loop control, V dref 、V qref are the d-axis and q-axis reference voltages, V d 、V q are the d-axis and q-axis voltages respectively. d * and i q * are the d-axis and q-axis reference currents output by the outer loop control, i d and i q are the d and q components of the valve side AC current, U d and U q are the d-axis and q-axis components of the valve side AC voltage, respectively, d and v q are the d-axis and q-axis reference voltages output by the inner loop control, which are converted by dp / abc to obtain the AC voltage reference value v abc . V arm is the bridge arm voltage command value, U dc_m is the DC voltage command value of the DC current controller, I dc is the current difference between the two ends of the DC transmission line, ΔI dc_ref The second DC fault ride-through strategy can be applied to Figure 3 The structure shown.

[0073] In one embodiment, controlling the switching on and off of the energy dissipation branch of the corresponding bridge arm according to the overall level of the submodule capacitor voltage in each bridge arm includes:

[0074] S21: Calculate the average voltage U of the submodule capacitors of each bridge arm ave .

[0075] S22: comparing the average value of the submodule capacitor voltage of each bridge arm with the switching voltage setting value of the energy dissipation branch of each bridge arm, and controlling the switching of the energy dissipation branch according to the comparison result.

[0076] Record the voltage setting U of the energy-discharging branch circuit in , U out , for each bridge arm U ave Make a separate judgment, when U ave >U in When U ave out When this happens, the energy dissipation branch of the bridge arm is controlled to exit.

[0077] ​The converter valve with active energy discharge function means that the power submodule contains an energy discharge unit. When the system DC line or the receiving end fails and surplus power occurs, causing the submodule capacitor voltage to rise, the surplus power is converted into resistor heat energy dissipation by putting into use the discharge resistor in the discharge unit, ensuring that the capacitor voltage between each power unit is balanced and the system does not have overvoltage. The average voltage of the submodule in the bridge arm is used to control the unified input and exit of the bridge arm energy discharge branch, which can directly and effectively suppress the overvoltage of the submodule in the bridge arm, and the number of actions of the energy discharge branch in the bridge arm is greatly reduced, and the energy discharge of each submodule is evenly distributed.

[0078] In a further embodiment, the switching voltage setting value of the energy dissipation branch is calculated according to the following formula:

[0079] Input setting: U in =1.1k1U0, where U0 is the rated operating voltage of the submodule, k1 is the margin factor, and 1.15~1.2 is recommended;

[0080] Exit setting: U out =U in -k2U0, where k2 is a constant and the recommended value is 0.1~0.15.

[0081] In the sea breeze transmission system via long-distance DC submarine cables, due to the material characteristics of the cable, its equivalent capacitance to the ground is much larger than that of the overhead line. According to relevant literature analysis and calculation, the equivalent capacitance to the ground of a 100km cable is about 20μF, which is at the same order of magnitude as the equivalent capacitance of the bridge arm. Therefore, the impact of the equivalent capacitance of the submarine cable to the ground under the system fault state cannot be ignored.

[0082] When a DC single-pole to ground fault occurs in the system, due to the existence of the equivalent to-ground capacitance of the DC submarine cable, the rising speed and development trend of the DC current after the fault are relatively fast. At this time, if a larger DC current PI controller parameter is selected, the controller output will oscillate between the upper and lower limits, causing system instability; if appropriate DC current controller parameters are selected while ensuring system stability, the DC current clearing speed will be too slow, the DC current will not exceed zero for a long time, and the arc at the fault point will not be extinguished for a long time, thereby greatly prolonging the system DC fault ride-through time, and even the de-ionization waiting time will be too long, resulting in fault ride-through failure.

[0083] In order to solve the above problem, in one embodiment, the second DC fault ride-through strategy is continuously executed until the DC fault is cleared, including:

[0084] S31: At the beginning of the second DC fault ride-through strategy, the parameters of the DC current controller are reduced and a DC bias is superimposed on the reference value of the DC current controller.

[0085] It should be noted that the proportional gain (Kp) and integral gain (Ki) of the DC current controller are reduced in order to slow down the controller's response to current changes and prevent system instability due to over-control. At the same time, a preset DC bias is added to the reference value of the DC current controller to guide the system to adjust in a specific direction, such as by increasing the positive or negative bias to make the actual current close to zero.

[0086] S32: Control is performed through a DC current controller until the DC current is controlled to near 0.

[0087] It should be noted that the output is gradually adjusted using the adjusted DC current controller until the actual DC current monitored is very close to zero.

[0088] S33: Clear the DC fault when the DC current crosses zero.

[0089] It should be noted that the fault clearing operation is performed at the moment when the DC current crosses zero because the energy stored in the circuit is minimal at this time, thereby reducing the risk of arcing when disconnecting.

[0090] S34: When the DC fault is cleared, the DC bias is restored to 0.

[0091] It should be noted that the previously applied DC bias is removed, and the various parameters of the DC current controller are reset to their standard values ​​as needed, so that the system can continue to operate in a normal mode.

[0092] In a further embodiment, after a DC bias is superimposed on the reference value of the DC current controller, the reference value of the DC current controller is determined according to the following formula:

[0093] I dc_ref =0+ΔI dc_ref

[0094] Among them, I dc_ref is the reference value of the DC current controller, ΔI dc_ref is a DC bias that satisfies the following conditions:

[0095] ΔI dcF +ΔI dc_ref ≤0

[0096] Among them, ΔI dcF It is the per-unit value of the fault point current after the DC line fault state is stabilized.

[0097] In a further embodiment, the DC bias ramp is restored to zero when the DC fault is cleared.

[0098] In a further embodiment, the ramp time range of the DC bias is 1 to 2 power frequency cycles.

[0099] See also Figure 4 , Figure 4 This is the DC fault current clearing strategy process. This process method selects smaller DC current PI controller parameters to ensure system stability. At the same time, at the beginning of the DC fault ride-through strategy, a DC bias ΔI is added to the reference value of the DC current controller. dc_ref (ΔI dc_ref <0), speeding up the DC current clearing speed and accelerating the DC fault riding process.

[0100] After the DC fault is cleared, ΔI dc_ref The ramp is restored to 0 to ensure that there is no obvious reverse current in the flexible DC valve, thereby ensuring that no excessive overshoot occurs when exiting the DC fault ride-through strategy.

[0101] Specifically, at the initial stage of entering the DC fault ride-through strategy, the reference value Idc_ref of the DC current controller is set to be 0+ΔIdc_ref.

[0102] ΔI in DC current controller dc_ref Selection basis: In order to make the controller output stable and the DC current can be quickly controlled near 0, ΔI dc_ref It is generally selected based on the sum of the static errors of the DC current at the sending and receiving ends when the DC current reference value in the controller is 0, that is, based on the fault point current per unit value ΔI after the DC line fault state stabilizes. dcF (like Figure 7a As shown) to select (ΔI dcF The recommended value range is 0.03 pu ~0.1pu), so that ΔI dcF +ΔI dc_ref ≤0, and then combined with simulation verification to verify ΔI dc_ref The final selected value is adjusted.

[0103] In selecting the appropriate DC current controller parameters and ΔI dc_ref After the value is taken, the DC fault ride-through strategy can quickly reduce the DC current to 0 while ensuring system stability, thereby achieving rapid clearance of the DC fault.

[0104] After the DC fault is cleared, ΔI dc_ref The value ramp is restored to 0 to ensure that there is no excessive overshoot when exiting the DC fault ride-through strategy, and the DC fault ride-through strategy is exited after waiting for the de-ionization time (usually about 250ms~350ms). Among them, the ramp time is recommended to be 1~2 power frequency cycles.

[0105] See also Figure 5 , Figure 5 The overall process of the DC fault ride-through strategy is shown. In this process, both the first DC fault ride-through strategy and the second DC fault ride-through strategy are started to simultaneously control the energy discharge branch and handle the DC fault.

[0106] See also Figure 6 -7, Figure 6 It is the overall EMTDC simulation waveform of DC fault crossing. Figure 7a a and b are respectively the fault point current EMTDC simulation waveforms when the conventional DC current control strategy and the control strategy of the present invention are adopted.

[0107] like Figure 7a As shown in the simulation, a DC single-pole to ground fault occurs at 1.5s and lasts for 100ms. When the conventional DC current control strategy is adopted, the reference value of the DC current controller is 0. The simulation results show that the DC current is not controlled to 0 for a long time (ΔI dcF >0), resulting in the fault current not crossing the zero point and unable to be cleared.

[0108] like Figure 7b As shown, after adopting the control strategy of the present invention, the DC current controller reference value is 0+ΔI dc_ref ,contrast Figure 7a It can be seen that after the fault occurred, the current at the fault point was controlled to decrease rapidly and was quickly controlled to near 0. At about 1.61s, the fault was quickly cleared.

[0109] Based on the same inventive concept, the embodiment of the present application also provides a DC line fault ride-through device for a converter valve with an active energy discharge function, which is used to implement the DC line fault ride-through method for a converter valve with an active energy discharge function. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations in the embodiment of the DC line fault ride-through device for a converter valve with an active energy discharge function provided below can refer to the limitations of the DC line fault ride-through method for a converter valve with an active energy discharge function in the above text, and will not be repeated here.

[0110] See also Figure 8 The embodiment of the present invention further provides a DC line fault ride-through device applied to a converter valve with an active energy discharge function, comprising:

[0111] A strategy starting module, in response to a DC line fault signal, for starting a DC fault ride-through strategy, wherein the DC fault ride-through strategy includes a first DC fault ride-through strategy and a second DC fault ride-through strategy;

[0112] A first strategy execution module is used to control the switching on and off of the energy dissipation branch of the corresponding bridge arm according to the overall level of the capacitor voltage of the submodules in each bridge arm after the first DC fault ride-through strategy is started, so as to ensure that the system does not have overvoltage;

[0113] a second strategy execution module, configured to superimpose a DC bias on a reference value of a DC current controller after the second DC fault ride-through strategy is started, so as to increase a DC current control target of the DC current controller, thereby accelerating a fault current clearing speed;

[0114] A DC fault judgment module, used for continuously executing the first DC fault ride-through strategy and the second DC fault ride-through strategy until it is determined that the DC fault is cleared;

[0115] The strategy exit module is used to exit the DC fault ride-through strategy after waiting for a set time and complete the DC line fault ride-through.

[0116] Those skilled in the art can clearly understand that, for the convenience and simplicity of description, only the division of the above-mentioned functional units and modules is used as an example for illustration. In practical applications, the above-mentioned function allocation can be completed by different functional units and modules as needed, that is, the internal structure of the system can be divided into different functional units or modules to complete all or part of the functions described above. The functional units and modules in the embodiment can be integrated in a processing unit, or each unit can exist physically separately, or two or more units can be integrated in one unit. The above-mentioned integrated unit can be implemented in the form of hardware or in the form of software functional units. In addition, the specific names of the functional units and modules are only for the convenience of distinguishing each other, and are not used to limit the scope of protection of this application. The specific working process of the units and modules in the above-mentioned system can refer to the corresponding process in the aforementioned method embodiment, which will not be repeated here.

[0117] Reference Fig. 9 An embodiment of the present invention further provides a computer device, comprising: a memory and a processor and a computer program stored in the memory. When the computer program is executed on the processor, a DC line fault ride-through method for a converter valve with an active energy discharge function as described in any one of the above methods is implemented.

[0118] The computer device may be a desktop computer, a notebook, a PDA, a cloud server or other computing device. The computer device may include, but is not limited to, a processor and a memory. Those skilled in the art will understand that Fig. 9 It is only an example of a computer device and does not constitute a limitation of the computer device. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components. For example, it may also include input and output devices, network access devices, etc.

[0119] The processor may be a central processing unit (CPU), other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc.

[0120] In some embodiments, the memory may be an internal storage unit of the computer device, such as a hard disk or memory of the computer device. In other embodiments, the memory may also be an external storage device of the computer device, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the computer device. Further, the memory may include both an internal storage unit and an external storage device of the computer device. The memory is used to store an operating system, an application program, a boot loader (BootLoader), data, and other programs, such as the program code of the computer program. The memory may also be used to temporarily store data that has been output or is to be output.

[0121] An embodiment of the present invention further provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the method for riding through a DC line fault applied to a converter valve with an active energy discharge function as described in any one of the above methods is implemented.

[0122] In this embodiment, if the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present application implements all or part of the processes in the above-mentioned embodiment method, which can be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium. When the computer program is executed by the processor, the steps of the above-mentioned various method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium can at least include: any entity or device that can carry the computer program code to the camera / terminal device, recording medium, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. For example, USB flash drive, mobile hard disk, disk or optical disk. In some jurisdictions, according to legislation and patent practice, computer-readable media cannot be electric carrier signals and telecommunication signals.

[0123] In the above embodiments, the description of each embodiment has its own emphasis. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0124] Those of ordinary skill in the art will appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0125] In the embodiments disclosed in the present application, it should be understood that the disclosed devices / terminal equipment and methods can be implemented in other ways. For example, the device / terminal equipment embodiments described above are only schematic. For example, the division of the modules or units is only a logical function division. There may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms.

[0126] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A DC line fault ride-through method applied to a converter valve with active energy discharge function, characterized in that: The steps include: In response to a DC line fault, starting a DC fault ride-through strategy, the DC fault ride-through strategy comprising a first DC fault ride-through strategy and a second DC fault ride-through strategy; After the first DC fault ride-through strategy is started, the energy dissipation branch of the corresponding bridge arm is controlled to be switched on and off according to the overall level of the submodule capacitor voltage in each bridge arm to ensure that the system does not have overvoltage; After the second DC fault ride-through strategy is started, a DC bias is superimposed on a reference value of a DC current controller to increase a DC current control target of the DC current controller, thereby accelerating a fault current clearing speed; Continuously executing the first DC fault ride-through strategy and the second DC fault ride-through strategy until the DC fault is cleared; After waiting for a set time, the DC fault ride-through strategy is exited to complete the DC line fault ride-through.

2. The DC line fault ride-through method applied to a converter valve with active energy discharge function according to claim 1, characterized in that: According to the overall level of the submodule capacitor voltage in each bridge arm, the energy dissipation branch of the corresponding bridge arm is controlled to be switched on and off, including: Calculate the average value of the submodule capacitor voltage of each bridge arm; The average value of the submodule capacitor voltage of each bridge arm is compared with the switching voltage setting value of the energy dissipation branch of each bridge arm, and the switching of the energy dissipation branch is controlled according to the comparison result.

3. The DC line fault ride-through method applied to a converter valve with active energy discharge function according to claim 2, characterized in that: The switching voltage setting value of the energy dissipation branch is calculated according to the following formula: Input setting: U in =1.1k1U0, where U0 is the rated operating voltage of the submodule and k1 is the margin coefficient; Exit setting: U out =U in -k2U0, where k2 is a constant.

4. The DC line fault ride-through method applied to a converter valve with active energy discharge function according to claim 1, characterized in that: Continuously executing the second DC fault ride-through strategy until the DC fault is cleared, including: At the beginning of the second DC fault ride-through strategy, the parameters of the DC current controller are adjusted to be small and a DC bias is superimposed on a reference value of the DC current controller; Controlling by the DC current controller until the DC current is controlled to near 0; Clear the DC fault at the DC current zero crossing point; When the DC fault is cleared, the DC bias is restored to 0.

5. The DC line fault ride-through method applied to a converter valve with active energy discharge function according to claim 1 or 4, characterized in that: After a DC bias is added to the reference value of the DC current controller, the reference value of the DC current controller is determined according to the following formula: I dc_ref =0+ΔI dc_ref Among them, I dc_ref is the reference value of the DC current controller, ΔI dc_ref is the DC bias, and the DC bias satisfies the following conditions: ΔI dcF +ΔI dc_ref ≤0 Among them, ΔI dcF It is the per-unit value of the fault point current after the DC line fault state is stabilized.

6. The DC line fault ride-through method applied to a converter valve with active energy discharge function according to claim 4, characterized in that: When the DC fault is cleared, the DC bias ramp returns to 0.

7. The DC line fault ride-through method applied to a converter valve with active energy discharge function according to claim 4, characterized in that: The ramp time range of the DC bias is 1 to 2 power frequency cycles.

8. A DC line fault ride-through device applied to a converter valve with active energy discharge function, characterized in that: include: a strategy starting module, in response to a DC line fault, for starting a DC fault ride-through strategy, wherein the DC fault ride-through strategy includes a first DC fault ride-through strategy and a second DC fault ride-through strategy; A first strategy execution module is used to control the switching on and off of the energy dissipation branch of the corresponding bridge arm according to the overall level of the capacitor voltage of the submodules in each bridge arm after the first DC fault ride-through strategy is started, so as to ensure that the system does not have overvoltage; a second strategy execution module, configured to superimpose a DC bias on a reference value of a DC current controller after the second DC fault ride-through strategy is started, so as to increase a DC current control target of the DC current controller, thereby accelerating a fault current clearing speed; a DC fault judgment module, configured to continuously execute the first DC fault ride-through strategy and the second DC fault ride-through strategy until it is determined that the DC fault is cleared; The strategy exit module is used to exit the DC fault ride-through strategy after waiting for a set time and complete the DC line fault ride-through.

9. A computer device, characterized in that: The device comprises a processor and a memory: The memory is used to store a computer program and send instructions of the computer program to the processor; The processor executes a DC line fault ride-through method applied to a converter valve with an active energy discharge function according to any one of claims 1 to 7 according to the instructions of the computer program.

10. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by the processor, a DC line fault ride-through method for a converter valve with an active energy discharge function according to any one of claims 1 to 7 is implemented.

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