Fault ride-through control method and system for flexible direct current sending-out system

Abstract

The invention discloses a fault ride-through control method and system for a flexible direct current transmission system, and relates to the technical field of fault ride-through control of a power system, and the method comprises the steps: obtaining an alternating current voltage parameter of the flexible direct current transmission system in real time, judging whether an alternating current fault occurs or not according to the alternating current voltage parameter, and when the alternating current fault occurs, performing fault ride-through control. If yes, generating a low AC voltage signal, issuing the low AC voltage signal to the associated sending end flexible DC converter station, hydroelectric generating set or sending end new energy unit, and executing a corresponding fault ride-through control strategy in response to the low AC voltage signal through the sending end flexible DC converter station, hydroelectric generating set and new energy unit. The technical problem that the reliability of system operation is reduced due to the lack of a method for processing alternating-current faults of multiple types of units at the sending end in fault ride-through control of an existing flexible direct-current sending-out system is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of fault ride-through control of power systems, and in particular to a fault ride-through control method and system for a flexible direct current transmission system. Background Art

[0002] At present, most new energy bases are built in remote areas, where the local load level is low and the grid structure is weak, and there is an obvious demand for stable transmission of new energy islands. The flexible DC transmission system has the characteristics of flexibility, controllability, and high efficiency, and is one of the important means of power transmission for the transmission of new energy. For the sending end, the flexible DC converter can provide a stable AC voltage for the new energy electric field, can operate in an isolated island, and provide sufficient fast dynamic reactive power compensation, reduce the risk of new energy units being disconnected from the grid, and improve the utilization rate of new energy. For the receiving end, the flexible DC does not have the problem of phase change failure and can provide dynamic reactive power compensation. It can effectively solve the stability of multiple DC feeds into the AC power grid and resist serious power grid failures. It is of great significance.

[0003] However, the existing fault ride-through control method of the flexible DC transmission system is mainly aimed at the AC fault situation of a single type of unit at the sending end, and lacks a method for handling AC faults of multiple types of units at the sending end, which reduces the reliability of the operation of the flexible DC transmission system. Summary of the invention

[0004] The present invention provides a fault ride-through control method and system for a flexible DC transmission system, which solves the technical problem that the existing fault ride-through control method for a flexible DC transmission system is mainly aimed at the AC fault situation of a single type of unit at the sending end, lacks a processing method for the AC fault of multiple types of units at the sending end, and reduces the reliability of the operation of the flexible DC transmission system.

[0005] A first aspect of the present invention provides a fault ride-through control method for a flexible DC transmission system, which is applied to the flexible DC transmission system. The flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit, and a new energy unit. The method includes:

[0006] Acquiring AC voltage parameters of the flexible DC transmission system in real time, and determining whether an AC fault occurs according to the AC voltage parameters;

[0007] When an AC fault occurs, a low AC voltage signal is generated, and the low AC voltage signal is sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit;

[0008] Executing a preset first fault ride-through control strategy in response to the low AC voltage signal by the sending-end flexible DC converter station;

[0009] Executing a preset second fault ride-through control strategy by the hydroelectric generator set in response to the low AC voltage signal;

[0010] The new energy generator set executes a preset third fault ride-through control strategy in response to the low AC voltage signal.

[0011] Optionally, the AC voltage parameters include AC voltage parameters of a sending-end flexible DC converter station, AC voltage parameters of a hydropower unit, and AC voltage parameters of a sending-end new energy unit. The step of determining whether an AC fault occurs according to the AC voltage parameters includes:

[0012] Inputting the AC voltage parameters of the sending-end flexible DC converter station, the AC voltage parameters of the hydropower unit and the AC voltage parameters of the sending-end new energy unit into a preset AC voltage effective value function respectively to obtain a plurality of AC voltage effective values;

[0013] Determining whether each of the AC voltage effective values ​​is less than a preset AC fault threshold;

[0014] If any of the AC voltage effective values ​​is less than the AC fault threshold, it is determined that an AC fault occurs;

[0015] If each of the AC voltage effective values ​​is greater than or equal to the AC fault threshold, it is determined that no AC fault occurs.

[0016] Optionally, the process of the sending-end flexible DC converter station executing the first fault ride-through control strategy is specifically as follows:

[0017] Acquiring the negative sequence AC voltage parameter of the sending-end flexible DC converter station, and clearing the integral link of the sending-end converter station outer loop controller associated with the sending-end flexible DC converter station;

[0018] Inputting the negative-sequence AC voltage parameter into a preset negative-sequence AC voltage effective value function to obtain a negative-sequence AC voltage effective value;

[0019] Performing a difference operation on an AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station and the negative-sequence AC voltage effective value to obtain a first difference;

[0020] Using the first difference as an input AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station;

[0021] Limiting the d-axis current reference value and the q-axis current reference value of the sending-end flexible DC converter station, and acquiring the effective value of the AC voltage of the sending-end flexible DC converter station in real time;

[0022] When the effective value of the AC voltage of the sending-end flexible DC converter station is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the effective value of the negative-sequence AC voltage of the sending-end flexible DC converter station is reduced by a preset first slope.

[0023] Optionally, the process of the hydropower unit executing the second fault ride-through control strategy is specifically as follows:

[0024] Performing fault ride-through control on the hydropower unit based on a preset low voltage ride-through control model, and obtaining the effective value of the AC voltage of the hydropower unit in real time;

[0025] When the effective value of the AC voltage of the hydropower unit is greater than or equal to a preset recovery threshold, the PSS controller of the hydropower unit performs voltage compensation control on the voltage regulator associated with the hydropower unit.

[0026] Optionally, the process of the new energy unit executing the third fault ride-through control strategy is specifically as follows:

[0027] Clearing the integral links of the outer ring d-axis controller and the outer ring q-axis control associated with the new energy unit;

[0028] Limiting the d-axis current reference value and the q-axis current reference value of the new energy generator set, and acquiring the effective value of the AC voltage of the new energy generator set in real time;

[0029] When the effective value of the AC voltage of the new energy generator set is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the fault recovery of the new energy generator set is performed according to a preset recovery strategy.

[0030] Optionally, the step of performing fault recovery on the new energy generator set according to a preset recovery strategy includes:

[0031] Obtaining a fault clearing waiting time of the new energy generator set, and determining whether the fault clearing waiting time is greater than a preset recovery waiting threshold;

[0032] If the fault clearing waiting time is greater than the recovery waiting threshold, the d-axis current value of the new energy generator set is regulated by a preset second slope to be restored to the d-axis current value before the fault;

[0033] If the fault clearing waiting time is less than or equal to the recovery threshold, the step of obtaining the fault clearing waiting time of the new energy generator set is skipped and executed until the fault clearing waiting time is greater than the recovery threshold.

[0034] Optionally, the first slope is 1 pu / s~3 pu / 100 ms.

[0035] Optionally, the recovery waiting threshold is 300ms.

[0036] Optionally, the second slope is 0.45~1 pu / s.

[0037] A second aspect of the present invention provides a fault ride-through control system for a flexible DC transmission system, which is applied to the flexible DC transmission system. The flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit, and a new energy unit, including:

[0038] A collection module, used for acquiring AC voltage parameters of the flexible DC transmission system in real time, and judging whether an AC fault occurs according to the AC voltage parameters;

[0039] An analysis module, used for generating a low AC voltage signal when an AC fault occurs, and sending the low AC voltage signal to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit;

[0040] A first control module, configured to execute a preset first fault ride-through control strategy in response to the low AC voltage signal through the sending-end flexible DC converter station;

[0041] A second control module, configured to execute a preset second fault ride-through control strategy in response to the low AC voltage signal through the hydropower unit;

[0042] The third control module is used to execute a preset third fault ride-through control strategy in response to the low AC voltage signal through the new energy generator set.

[0043] It can be seen from the above technical solutions that the present invention has the following advantages:

[0044] The present invention generates a low AC voltage signal when an AC fault occurs, and sends the low AC voltage signal to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit. It overcomes the technical problem that the existing fault ride-through control method of the flexible DC transmission system is mainly aimed at the AC fault situation of a single type of unit at the sending end, lacks a processing method for AC faults of multiple types of units at the sending end, and reduces the reliability of the operation of the flexible DC transmission system. Compared with the traditional fault ride-through control method, the present invention samples the preset fault ride-through control strategy to regulate the sending-end flexible DC converter station, hydropower unit and new energy unit when an AC fault occurs, thereby realizing the coordinated control of AC faults of multiple types of units and improving the reliability of the operation of the flexible DC transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] 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 labor.

[0046] Figure 1 A flowchart of the steps of a fault ride-through control method for a flexible DC transmission system provided in Embodiment 1 of the present invention;

[0047] Figure 2 A flowchart of a fault ride-through control method for a flexible DC transmission system provided in Embodiment 2 of the present invention;

[0048] Figure 3 A schematic diagram of the structure of a flexible DC transmission system provided in Embodiment 2 of the present invention;

[0049] Figure 4 A schematic diagram of the structure of a fault control model provided in the second embodiment of the present invention;

[0050] Figure 5 This is a structural block diagram of a fault ride-through control system of a flexible DC transmission system provided in Embodiment 3 of the present invention. DETAILED DESCRIPTION

[0051] The embodiments of the present invention provide a fault ride-through control method and system for a flexible DC transmission system, which are used to solve the technical problem that the existing fault ride-through control method for a flexible DC transmission system is mainly aimed at the AC fault situation of a single type of unit at the sending end, lacks a processing method for the AC fault of multiple types of units at the sending end, and reduces the reliability of the operation of the flexible DC transmission system.

[0052] 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.

[0053] See also Figure 1 , Figure 1 A flowchart of the steps of a fault ride-through control method for a flexible DC transmission system provided in Embodiment 1 of the present invention.

[0054] The present invention provides a fault ride-through control method for a flexible DC transmission system, which is applied to the flexible DC transmission system. The flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit and a new energy unit. The method includes:

[0055] Step 101: acquiring AC voltage parameters of the flexible DC transmission system in real time, and determining whether an AC fault occurs according to the AC voltage parameters;

[0056] In an embodiment of the present invention, AC voltage parameters of the mid-range flexible DC converter station, hydropower unit and new energy unit in the flexible DC transmission system are obtained in real time, and whether an AC fault occurs is determined based on the AC voltage parameters.

[0057] Step 102: When an AC fault occurs, a low AC voltage signal is generated, and the low AC voltage signal is sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit;

[0058] In an embodiment of the present invention, when an AC fault occurs, a low AC voltage signal is generated and sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit.

[0059] Step 103: executing a preset first fault ride-through control strategy in response to the low AC voltage signal by the sending-end flexible DC converter station;

[0060] In an embodiment of the present invention, when an AC fault occurs in the sending-end flexible DC converter station, a preset first fault ride-through control strategy is executed by the sending-end flexible DC converter station in response to a low AC voltage signal.

[0061] Step 104, executing a preset second fault ride-through control strategy by the hydropower unit in response to the low AC voltage signal;

[0062] In the embodiment of the present invention, when an AC fault occurs in the hydroelectric generator set, the preset second fault ride-through control strategy is executed by the hydroelectric generator set in response to the low AC voltage signal.

[0063] Step 105: executing a preset third fault ride-through control strategy in response to the low AC voltage signal by the new energy generator set.

[0064] In an embodiment of the present invention, when an AC fault occurs in the new energy generator set, the new energy generator set executes a preset third fault ride-through control strategy in response to a low AC voltage signal.

[0065] In an embodiment of the present invention, when an AC fault occurs, a low AC voltage signal is generated, and the low AC voltage signal is sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit. The existing fault ride-through control method of the flexible DC transmission system is overcome, which is mainly aimed at the AC fault situation of a single type of unit at the sending end, lacks a processing method for AC faults of multiple types of units at the sending end, and reduces the technical problem of reliability of the operation of the flexible DC transmission system. Compared with the traditional fault ride-through control method, the present invention samples the preset fault ride-through control strategy to regulate the sending-end flexible DC converter station, hydropower unit and new energy unit when an AC fault occurs, thereby realizing coordinated control of AC faults of multiple types of units and improving the reliability of the operation of the flexible DC transmission system.

[0066] See also Figure 2 , Figure 2 A flowchart of the steps of a fault ride-through control method for a flexible DC transmission system provided in Embodiment 2 of the present invention.

[0067] The present invention provides a fault ride-through control method for a flexible DC transmission system, which is applied to the flexible DC transmission system. The flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit and a new energy unit. The method includes:

[0068] Step 201: Acquire AC voltage parameters of the flexible DC transmission system in real time, wherein the AC voltage parameters include AC voltage parameters of the sending-end flexible DC converter station, AC voltage parameters of the hydropower unit, and AC voltage parameters of the sending-end new energy unit.

[0069] In an embodiment of the present invention, AC voltage parameters of the sending-end flexible DC converter station, AC voltage parameters of the hydropower unit, and AC voltage parameters of the sending-end new energy unit of the flexible DC transmission system are obtained in real time.

[0070] Step 202: inputting the AC voltage parameters of the sending-end flexible DC converter station, the AC voltage parameters of the hydropower unit, and the AC voltage parameters of the sending-end new energy unit into a preset AC voltage effective value function to obtain a plurality of AC voltage effective values;

[0071] The AC voltage parameters of the sending-end flexible DC converter station refer to the voltage of the d-axis component and the voltage of the q-axis component of the sending-end flexible DC converter station.

[0072] The AC voltage parameters of a hydropower unit refer to the voltage of the d-axis component and the voltage of the q-axis component of the hydropower unit.

[0073] The AC voltage parameters of the sending-end new energy unit refer to the voltage of the d-axis component and the voltage of the q-axis component of the sending-end new energy unit.

[0074] In an embodiment of the present invention, the AC voltage parameters of the sending-end flexible DC converter station, the AC voltage parameters of the hydropower unit and the AC voltage parameters of the sending-end new energy unit are respectively input into a preset AC voltage effective value function to obtain the AC voltage effective values ​​of the sending-end flexible DC converter station, the hydropower unit and the sending-end new energy unit.

[0075] Step 203: determine whether each AC voltage effective value is less than a preset AC fault threshold;

[0076] In the embodiment of the present invention, it is determined whether the AC voltage efficiency values ​​of the sending-end flexible DC converter station, the hydropower unit and the sending-end new energy unit are less than a preset AC fault threshold.

[0077] Step 204: If any AC voltage effective value is less than the AC fault threshold, it is determined that an AC fault occurs;

[0078] In the embodiment of the present invention, when any AC voltage effective value is less than the AC fault threshold, it is determined that an AC fault occurs.

[0079] Step 205: If the effective values ​​of each AC voltage are greater than or equal to the AC fault threshold, it is determined that no AC fault occurs.

[0080] In the embodiment of the present invention, when the effective values ​​of each AC voltage are greater than or equal to the AC fault threshold, it is determined that no AC fault occurs.

[0081] Step 206: When an AC fault occurs, a low AC voltage signal is generated, and the low AC voltage signal is sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit;

[0082] In an embodiment of the present invention, when an AC fault occurs, a low AC voltage signal (Uac_low is 1) is generated and sent to the sending-end flexible DC converter station, hydropower unit or sending-end new energy unit where the fault occurs.

[0083] Step 207: executing a preset first fault ride-through control strategy in response to the low AC voltage signal by the sending-end flexible DC converter station;

[0084] It should be noted that the specific process of the sending-end flexible DC converter station executing the first fault ride-through control strategy is as follows:

[0085] S1. Obtain the negative sequence AC voltage parameter of the sending-end flexible DC converter station, and clear the integral link of the sending-end converter station outer loop controller associated with the sending-end flexible DC converter station;

[0086] It should be noted that the negative-sequence AC voltage parameter refers to the negative-sequence voltage of the d-axis component in the dq-axis component of the sending-end flexible DC converter station and the negative-sequence voltage of the q-axis component in the dq-axis component.

[0087] In an embodiment of the present invention, the negative-sequence AC voltage parameter of the sending-end flexible DC converter station is obtained, and the integral links of the outer-loop d-axis and q-axis controllers associated with the sending-end flexible DC converter station are cleared.

[0088] S11, inputting the negative-sequence AC voltage parameter into a preset negative-sequence AC voltage effective value function to obtain the negative-sequence AC voltage effective value;

[0089] In the embodiment of the present invention, the negative-sequence AC voltage parameter is used as an input of a preset negative-sequence AC voltage effective value function to obtain the negative-sequence AC voltage effective value.

[0090] S12, performing a difference operation on an AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station and an effective value of a negative-sequence AC voltage to obtain a first difference;

[0091] S13, using the first difference as an input AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station;

[0092] In the embodiment of the present invention, the voltage reference value input to the d-axis outer loop controller of the sending-end converter station is equal to the original AC voltage reference value minus the negative-sequence AC voltage at this time, so as to avoid AC overvoltage during the fault period.

[0093] S14, limiting the d-axis current reference value and the q-axis current reference value of the sending-end flexible DC converter station, and obtaining the effective value of the AC voltage of the sending-end flexible DC converter station in real time;

[0094] In the embodiment of the present invention, the d-axis and q-axis current reference values ​​of the sending-end flexible DC converter station are limited, and the effective value of the AC voltage of the sending-end flexible DC converter station is obtained in real time.

[0095] S15. When the effective value of the AC voltage of the sending-end flexible DC converter station is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the effective value of the negative-sequence AC voltage of the sending-end flexible DC converter station is reduced by a preset first slope.

[0096] In an embodiment of the present invention, when the effective value of the AC voltage of the sending-end flexible DC converter station is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the effective value of the actual negative-sequence AC voltage is reduced by a preset first slope, wherein the first slope is 1pu / s~3pu / 100ms.

[0097] It should be noted that the first slope is 1 pu / s~3 pu / 100ms.

[0098] Step 208, executing a preset second fault ride-through control strategy by the hydropower unit in response to the low AC voltage signal;

[0099] It should be noted that the specific process of the hydropower unit executing the second fault ride-through control strategy is as follows:

[0100] S21, performing fault ride-through control on the hydropower unit based on a preset low voltage ride-through control model, and obtaining the effective value of the AC voltage of the hydropower unit in real time;

[0101] In the embodiment of the present invention, the control system of each turbine unit at the sending end normally enters the low voltage ride-through logic and obtains the effective value of the AC voltage of the hydropower unit in real time.

[0102] S22. When the effective value of the AC voltage of the hydropower unit is greater than or equal to a preset recovery threshold, the PSS controller of the hydropower unit performs voltage compensation control on the voltage regulator associated with the hydropower unit.

[0103] In an embodiment of the present invention, when the effective value of the AC voltage of the hydropower unit is greater than or equal to a preset recovery threshold, an additional control signal is provided to its voltage regulator through the self-configured power system stability controller (PSS) controller to generate a positive additional damping torque to compensate for the negative damping torque that may be generated by the voltage regulator with the terminal voltage as input, thereby improving the damping capacity of the generator and the entire power system, accelerating the attenuation of power oscillations, thereby suppressing the power fluctuation of the sending-end power grid and solving the problem of long power fluctuation time of the sending-end power grid during recovery.

[0104] Step 209: executing a preset third fault ride-through control strategy in response to the low AC voltage signal by the new energy generator set.

[0105] It should be noted that the specific process of the new energy unit executing the third fault ride-through control strategy is as follows:

[0106] S31, clearing the integral link of the outer ring d-axis controller and the outer ring q-axis control associated with the new energy unit;

[0107] In the embodiment of the present invention, the integral links of the controllers of the outer ring d-axis and q-axis of the new energy generator set are cleared.

[0108] S32, limiting the d-axis current reference value and the q-axis current reference value of the new energy generator set, and obtaining the effective value of the AC voltage of the new energy generator set in real time;

[0109] In an embodiment of the present invention, the d-axis and q-axis current reference values ​​of the double closed-loop control of the sending-end new energy generator set are limited, and the effective value of the AC voltage of the new energy generator set is obtained in real time.

[0110] S33. When the effective value of the AC voltage of the new energy generator set is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the fault recovery of the new energy generator set is performed according to a preset recovery strategy.

[0111] Further, S33 includes the following sub-steps:

[0112] S331, obtaining the fault clearing waiting time of the new energy unit, and determining whether the fault clearing waiting time is greater than a preset recovery waiting threshold;

[0113] It should be noted that the recovery waiting threshold is 300ms.

[0114] In the embodiment of the present invention, the fault clearing waiting time of the new energy generator set is obtained, and it is determined whether the fault clearing waiting time is greater than 300 ms.

[0115] S332, if the fault clearing waiting time is greater than the recovery waiting threshold, the d-axis current value of the new energy unit is regulated by a preset second slope to be restored to the d-axis current value before the fault;

[0116] It should be noted that the second slope is 0.45~1pu / s.

[0117] In an embodiment of the present invention, if the fault clearing waiting time is greater than 300 ms, the d-axis current value of the new energy generator set is regulated by a preset second slope to restore to the d-axis current value before the fault.

[0118] S333: If the fault clearing waiting time is less than or equal to the recovery threshold, jump to the step of obtaining the fault clearing waiting time of the new energy generator set until the fault clearing waiting time is greater than the recovery threshold.

[0119] In the embodiment of the present invention, if the fault clearing waiting time is less than or equal to 300 ms, the process jumps to the step of obtaining the fault clearing waiting time of the new energy generator set until the fault clearing waiting time is greater than 300 ms.

[0120] In another embodiment, a fault ride-through control method of a flexible DC transmission system includes:

[0121] A1. Obtain the electrical parameters of each device in the flexible DC transmission system in real time, and screen each device according to the electrical parameters to obtain the corresponding faulty device;

[0122] It should be noted that, see Figure 3As shown, the flexible DC transmission system includes: a new energy power field, a sending-end converter station, a receiving-end converter station and a DC line. The sending-end converter station is connected to the isolated power grid of the hydropower new energy hybrid power generation base. The isolated power grid of the hydropower new energy hybrid power generation base includes several new energy generator sets and several turbine generator sets, which are all connected to the sending-end converter station through three-phase AC lines. The new energy power field includes renewable energy such as wind farms and photovoltaics. The sending-end converter station and the receiving-end converter station can adopt a single valve group form or a double valve group series form. The converter valve adopts a full-bridge submodule, a half-bridge submodule or a module mixed with a full-bridge submodule and a half-bridge submodule. The number of the sending-end converter stations is one or more, which is used to realize single power supply or multi-power supply. The sending-end flow station can be connected to the receiving-end converter station through a bipolar DC line or a unipolar DC line. The DC line can be an overhead line or a DC cable. If there are multiple sending-end or multiple receiving-end converter stations, the DC line mainly connects the DC sides of the converter stations at each end to each other, and the connection methods include star connection and delta connection.

[0123] It is worth mentioning that the voltage and frequency at the sending end are jointly constructed by flexible DC and hydropower generator sets. Flexible DC adopts a dual closed-loop constant AC voltage and frequency (VF) control strategy to provide the AC voltage and frequency required for the work of each sending-end island power grid. There is only one receiving-end converter station that adopts a fixed DC voltage control strategy to provide a stable DC voltage for the DC system, and the remaining receiving-end converter stations adopt a fixed active power control strategy. New energy units mainly adopt grid-following control to achieve maximum power tracking control. The turbine unit adopts a constant power and constant voltage (PV) control mode, which participates in the construction of the grid voltage while outputting power.

[0124] Further, the electrical parameter includes a first component voltage and a second component voltage, and A1 includes the following sub-steps:

[0125] A11, respectively summing the square value of the first component voltage and the square value of the second component voltage corresponding to each device to obtain a plurality of first sum values;

[0126] A12, performing square root operations on each first sum value respectively to obtain an effective value of an AC voltage corresponding to each device;

[0127] The first component voltage refers to the voltage of the d-axis component among the dq-axis components of the device.

[0128] The second component voltage refers to the voltage of the q-axis component among the dq-axis components of the device.

[0129] It should be noted that the electrical parameters of each device in the flexible DC transmission system are obtained in real time, and the first component voltage and the second component voltage of each electrical parameter are respectively input into a preset AC voltage effective value function to obtain the AC voltage effective value corresponding to each device.

[0130] It should be noted that the AC voltage effective value function is specifically:

[0131] The effective value of AC voltage =

[0132] in, is the first component voltage, is the second component voltage.

[0133] A13, determining whether the effective value of each AC voltage is less than a preset AC fault threshold;

[0134] A14. When the effective value of the AC voltage is less than the AC fault threshold, the device associated with the effective value of the AC voltage is determined as a faulty device.

[0135] It should be noted that it is determined whether each AC voltage effective value is less than the preset AC fault threshold. If the AC voltage effective value is less than the AC fault threshold, it means that an AC fault has occurred in the device, and the device associated with the AC voltage effective value is determined as a faulty device. If the AC voltage effective value is greater than or equal to the AC fault threshold, it means that no AC fault has occurred in the device.

[0136] A2. When the device type of the faulty device is a sending-end flexible DC converter station, an integral reset process is performed on the fault control model associated with the faulty device to obtain a first fault control model;

[0137] In the embodiment of the present invention, refer to Figure 4 As shown, when the device type of the faulty device is a sending-end flexible DC converter station, the integral links of the outer-loop d-axis voltage controller and the q-axis voltage controller of the fault control model associated with the faulty device are cleared to obtain a first fault control model.

[0138] A3. Using electrical parameters of the faulty device and a pre-acquired initial voltage reference value to perform voltage limiting processing on the first fault control model to obtain a first ride-through control model;

[0139] Further, see Figure 4 As shown, the electrical parameters also include a first negative sequence component voltage and a second negative sequence component voltage, and step 203 includes the following sub-steps:

[0140] A31, adding the square value of the first negative-sequence component voltage and the square value of the second negative-sequence component voltage to obtain a second sum value;

[0141] A32. Perform square root operation on the second sum to obtain the effective value of the negative sequence AC voltage;

[0142] The first negative-sequence component voltage refers to the negative-sequence voltage of the d-axis component in the dq-axis components.

[0143] The second negative-sequence component voltage refers to the negative-sequence voltage of the q-axis component in the dq-axis components.

[0144] It should be noted that the first negative-sequence component voltage and the second negative-sequence component voltage are input into a preset negative-sequence AC voltage function to obtain a negative-sequence AC voltage effective value.

[0145] It should be noted that the negative sequence AC voltage function is specifically:

[0146] Negative sequence AC voltage effective value =

[0147] in, is the first negative sequence component voltage, is the second negative sequence component voltage.

[0148] A33, performing difference processing on the pre-acquired initial voltage reference value and the negative sequence AC voltage effective value to obtain a target voltage reference value;

[0149] It should be noted that the target voltage reference value is obtained by calculating the difference between the pre-acquired initial voltage reference value and the effective value of the negative-sequence AC voltage.

[0150] A34. Input the target voltage reference value into the first fault control model to obtain a first ride-through control model.

[0151] The initial voltage reference value refers to the original AC voltage reference value of the first fault control model.

[0152] It should be noted that the target voltage reference value is used as the AC voltage reference value of the first fault control model to obtain the first ride-through control model.

[0153] It should be noted that by subtracting the negative-sequence AC voltage at the current moment from the initial voltage reference value as the AC voltage reference value of the first fault control model, AC overvoltage phenomenon during the fault period can be avoided.

[0154] A4. Use the electrical parameters of the faulty device to perform voltage regulation on the first ride-through control model to obtain a fault regulation instruction corresponding to the faulty device;

[0155] Further, see Figure 4 As shown, the electrical parameters also include a first component current limit and a second component current limit, and step A4 includes the following sub-steps:

[0156] A41. Performing difference processing on the square value of the AC current limit value obtained in advance and the square value of the first component current limit value to obtain a first difference value;

[0157] A42, performing difference processing on the square value of the AC current limit value and the square value of the second component current limit value to obtain a second difference value;

[0158] A43. Use the first difference and the negative value of the first difference to construct a first current reference interval;

[0159] A44, constructing a second current parameter interval by using the second difference and the negative value of the second difference;

[0160] The first component current limit refers to the maximum value of the d-axis current.

[0161] The second component current limit refers to the maximum value of the q-axis current.

[0162] It should be noted that the pre-acquired AC current limit, the first component current limit, and the second component current limit are input into the preset limit function to obtain the maximum d-axis current limit and the maximum q-axis current limit. The d-axis current limit and the negative value of the d-axis current limit are used to construct the first current reference interval. The q-axis current limit and the negative value of the q-axis current limit are used to construct the second current reference interval.

[0163] It should be noted that the specific limit function is:

[0164]

[0165]

[0166] in, is the maximum limit of q-axis current, is the maximum limit of d-axis current, Imax_set is the AC current limit, Idmax is the first component current limit, and Iqmax is the second component current limit.

[0167] A45. Perform amplitude limiting processing on the first crossing control model according to the first current reference interval and the second current reference interval to obtain a fault control instruction corresponding to the faulty device.

[0168] It should be noted that the d-axis current reference value and the q-axis current reference value in the first ride-through control model are limited according to the first current reference interval and the second current reference interval to obtain a fault control instruction corresponding to the faulty device.

[0169] A5. When the device type of the faulty device is a new energy unit, the fault control model associated with the faulty device is reset to obtain a second fault control model;

[0170] It should be noted that when the device type of the faulty device is a new energy unit, the integral links of the outer loop d-axis voltage controller and q-axis voltage controller of the fault control model associated with the faulty device are cleared to obtain a second fault control model.

[0171] A6. Use the electrical parameters of the faulty device to perform voltage regulation on the second fault control model to obtain a fault regulation instruction corresponding to the faulty device;

[0172] It should be noted that the second fault control model is subjected to voltage stabilization control according to the methods of A41-A45 to obtain a fault control instruction corresponding to the faulty device.

[0173] A7. When the equipment type of the faulty equipment is a hydropower unit, the electrical parameters of the faulty equipment are input into the associated low voltage ride through control model to obtain the fault control instructions corresponding to the faulty equipment.

[0174] It should be noted that, when the device type of the faulty device is a hydropower unit, the faulty device is regulated by adopting the existing hydropower unit regulation strategy to obtain a fault regulation instruction corresponding to the faulty device.

[0175] A8. Use each fault control instruction to control the corresponding faulty equipment, and obtain the effective value of the AC voltage of each faulty equipment in real time;

[0176] It should be noted that each fault control instruction is used to control the corresponding faulty device, and the effective value of the AC voltage of each faulty device is obtained in real time according to the methods A11-A14.

[0177] It should be noted that the recovery speed of the AC voltage controlled by the flexible DC and the recovery speed of the power controlled by the new energy units at the sending end need to be coordinated, because if the recovery speed of the AC voltage and the recovery speed of the new energy power are too fast, if the flexible DC system at the sending end does not have time to send out the recovered power at this time, the flexible DC control at the sending end will be saturated and lose the AC voltage control, which will cause the AC voltage at the sending end to recover too high in an instant, and even cause the system to continue to oscillate, which is not conducive to the recovery of the system. During the fault period, the power of the hydropower unit cannot be sent out, and the surplus power is all accumulated on the generator rotor, resulting in an increase in the generator speed. During the AC fault recovery period, the hydropower unit will have a large DC power overshoot and a long fluctuation time, which requires the control of new energy power to cooperate. Therefore, it is necessary to obtain the effective value of the AC voltage of each faulty device in real time, and control each faulty device to cooperate and gradually restore the power transmission at the sending end.

[0178] A9. When the effective value of the AC voltage is greater than the preset clearing threshold, the fault recovery process is performed on the faulty device according to the device type of the faulty device.

[0179] Further, A9 includes the following sub-steps:

[0180] A91. When the device type of the faulty device is a sending-end flexible DC converter station, the fault control model associated with the faulty device is controlled to perform an active power recovery operation on the faulty device according to a preset first slope;

[0181] The first slope refers to the rate at which active power is restored when the sending-end flexible DC converter station resumes power transmission, which can be set to 1pu / s~3pu / s or 100ms.

[0182] In an embodiment of the present invention, when the effective value of the AC voltage is greater than a preset clearing threshold, the fault recovery process is performed on the faulty device according to the device type of the faulty device. When the device type of the faulty device is a sending-end flexible DC converter station, the fault control model associated with the faulty device is controlled to perform an active power recovery operation on the faulty device according to a preset first slope to solve the problem of too fast AC voltage recovery.

[0183] A92. When the device type of the faulty device is a new energy unit, obtain the fault clearing waiting time of the faulty device, and determine whether the fault clearing waiting time is greater than a preset recovery threshold;

[0184] A93. If the fault clearing waiting time is greater than the restoration threshold, the fault control model associated with the faulty device is controlled to perform an active power restoration operation on the faulty device according to a preset second slope;

[0185] The second slope refers to the rate of active power recovery when the new energy unit resumes power transmission, which can be set to 0.45~1pu / s.

[0186] In an embodiment of the present invention, when the device type of the faulty equipment is a new energy unit, the fault clearing waiting time of the faulty equipment is obtained, and it is determined whether the fault clearing waiting time is greater than a preset recovery threshold. If the fault clearing waiting time is greater than the recovery threshold, the fault control model associated with the faulty equipment is controlled to perform active power recovery operation on the faulty equipment according to a preset second slope to solve the problem of DC power overshoot.

[0187] A94. If the fault clearing waiting time is less than or equal to the recovery threshold, jump to the step of performing low voltage ride-through analysis on the electrical parameters of each faulty device based on the device type of each faulty device to obtain the fault control instructions corresponding to each faulty device until the fault clearing waiting time is greater than the recovery threshold;

[0188] In the embodiment of the present invention, when the fault clearing waiting time is less than or equal to the recovery threshold, the fault control instruction is continuously used to control the corresponding faulty device until the fault clearing waiting time is greater than the recovery threshold.

[0189] A95. When the equipment type of the faulty device is a hydropower unit, voltage compensation control is performed on the voltage regulator associated with the faulty device through the PSS controller of the faulty device.

[0190] It should be noted that when the faulty device is a hydropower unit, the faulty device itself is configured with a power system stability controller (PSS) to provide an additional control signal to its voltage regulator, generating a positive additional damping torque to compensate for the negative damping torque that may be generated by the voltage regulator with the terminal voltage as input, thereby improving the damping capacity of the generator and the entire power system, accelerating the attenuation of power oscillations, and thereby suppressing the power fluctuations of the sending-end power grid and solving the problem of long power fluctuations during the recovery period of the sending-end power grid.

[0191] In an embodiment of the present invention, when an AC fault occurs, a low AC voltage signal is generated, and the low AC voltage signal is sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit. The existing fault ride-through control method of the flexible DC transmission system is overcome, which is mainly aimed at the AC fault situation of a single type of unit at the sending end, lacks a processing method for AC faults of multiple types of units at the sending end, and reduces the technical problem of reliability of the operation of the flexible DC transmission system. Compared with the traditional fault ride-through control method, the present invention samples the preset fault ride-through control strategy to regulate the sending-end flexible DC converter station, hydropower unit and new energy unit when an AC fault occurs, thereby realizing coordinated control of AC faults of multiple types of units and improving the reliability of the operation of the flexible DC transmission system.

[0192] See also Figure 5 , Figure 5 This is a structural block diagram of a fault ride-through control system of a flexible DC transmission system provided in Embodiment 3 of the present invention.

[0193] The present invention provides a fault ride-through control system for a flexible DC transmission system, wherein the flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit and a new energy unit, including:

[0194] The acquisition module 301 is used to obtain the AC voltage parameters of the flexible DC transmission system in real time, and determine whether an AC fault occurs according to the AC voltage parameters;

[0195] The analysis module 302 is used to generate a low AC voltage signal when an AC fault occurs, and send the low AC voltage signal to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit;

[0196] A first control module 303, configured to execute a preset first fault ride-through control strategy in response to a low AC voltage signal through a sending-end flexible DC converter station;

[0197] A second control module 304, configured to execute a preset second fault ride-through control strategy in response to the low AC voltage signal through the hydropower unit;

[0198] The third control module 305 is used to execute a preset third fault ride-through control strategy in response to the low AC voltage signal through the new energy generator set.

[0199] Furthermore, the AC voltage parameters include the AC voltage parameters of the sending-end flexible DC converter station, the AC voltage parameters of the hydropower unit, and the AC voltage parameters of the sending-end new energy unit. The acquisition module 301 includes:

[0200] The first analysis submodule is used to input the AC voltage parameters of the sending-end flexible DC converter station, the AC voltage parameters of the hydropower unit and the AC voltage parameters of the sending-end new energy unit into a preset AC voltage effective value function to obtain multiple AC voltage effective values;

[0201] The second analysis submodule is used to determine whether each AC voltage effective value is less than a preset AC fault threshold;

[0202] If any AC voltage effective value is less than the AC fault threshold, it is determined that an AC fault has occurred;

[0203] If the effective values ​​of each AC voltage are greater than or equal to the AC fault threshold, it is determined that no AC fault has occurred.

[0204] Furthermore, the process of the sending-end flexible DC converter station executing the first fault ride-through control strategy is specifically as follows:

[0205] Obtaining the negative sequence AC voltage parameter of the sending-end flexible DC converter station, and clearing the integral link of the sending-end converter station outer loop controller associated with the sending-end flexible DC converter station;

[0206] Inputting the negative-sequence AC voltage parameter into a preset negative-sequence AC voltage effective value function to obtain the negative-sequence AC voltage effective value;

[0207] Performing a difference operation on an AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station and an effective value of a negative-sequence AC voltage to obtain a first difference value;

[0208] Using the first difference as an input AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station;

[0209] Limiting the d-axis current reference value and the q-axis current reference value of the sending-end flexible DC converter station, and obtaining the effective value of the AC voltage of the sending-end flexible DC converter station in real time;

[0210] When the effective value of the AC voltage of the sending-end flexible DC converter station is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the effective value of the negative-sequence AC voltage of the sending-end flexible DC converter station is reduced by a preset first slope.

[0211] Furthermore, the process of the hydropower unit executing the second fault ride-through control strategy is specifically as follows:

[0212] Perform fault ride-through control on the hydropower unit based on the preset low voltage ride-through control model, and obtain the effective value of the AC voltage of the hydropower unit in real time;

[0213] When the effective value of the AC voltage of the hydropower unit is greater than or equal to a preset recovery threshold, the PSS controller of the hydropower unit performs voltage compensation control on the voltage regulator associated with the hydropower unit.

[0214] Furthermore, the process of the new energy unit executing the third fault ride-through control strategy is specifically as follows:

[0215] Clear the integral link of the outer ring d-axis controller and the outer ring q-axis control associated with the new energy unit;

[0216] Limit the d-axis current reference value and the q-axis current reference value of the new energy unit, and obtain the AC voltage effective value of the new energy unit in real time;

[0217] When the effective value of the AC voltage of the new energy unit is greater than or equal to the preset recovery threshold, the low AC voltage signal is set to zero, and the fault recovery of the new energy unit is performed according to the preset recovery strategy.

[0218] Furthermore, the steps of performing fault recovery on the new energy unit according to the preset recovery strategy include:

[0219] Obtaining the fault clearing waiting time of the new energy unit, and determining whether the fault clearing waiting time is greater than a preset recovery waiting threshold;

[0220] If the fault clearing waiting time is greater than the recovery waiting threshold, the d-axis current value of the new energy unit is regulated by a preset second slope to be restored to the d-axis current value before the fault;

[0221] If the fault clearing waiting time is less than or equal to the recovery threshold, the process jumps to the step of obtaining the fault clearing waiting time of the new energy generator set until the fault clearing waiting time is greater than the recovery threshold.

[0222] Furthermore, the first slope is 1 pu / s~3 pu / 100 ms.

[0223] Furthermore, the recovery wait threshold is 300ms.

[0224] Furthermore, the second slope is 0.45~1pu / s.

[0225] Those skilled in the art can clearly understand that, for the convenience and brevity of description, the specific working processes of the systems, devices and units described above can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0226] In the several embodiments provided in the present application, it should be understood that the disclosed systems, devices and methods can be implemented in other ways. For example, the device embodiments described above are only schematic. For example, the division of units is only a logical function division. There may be other division methods in actual implementation. For example, 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 an indirect coupling or communication connection through some interfaces, devices or units, which can be electrical, mechanical or other forms.

[0227] The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed on multiple network units. Some or all of the units may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0228] 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 fault ride-through control method for a flexible DC transmission system, characterized in that: Applied to a flexible DC transmission system, the flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit and a new energy unit, and the method includes: Acquiring AC voltage parameters of the flexible DC transmission system in real time, and determining whether an AC fault occurs according to the AC voltage parameters; When an AC fault occurs, a low AC voltage signal is generated, and the low AC voltage signal is sent to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit; Executing a preset first fault ride-through control strategy in response to the low AC voltage signal by the sending-end flexible DC converter station; Executing a preset second fault ride-through control strategy by the hydroelectric generator set in response to the low AC voltage signal; The new energy generator set executes a preset third fault ride-through control strategy in response to the low AC voltage signal.

2. The fault ride-through control method of the flexible DC transmission system according to claim 1 is characterized in that: The AC voltage parameters include AC voltage parameters of the sending-end flexible DC converter station, AC voltage parameters of the hydropower unit, and AC voltage parameters of the sending-end new energy unit. The step of judging whether an AC fault occurs according to the AC voltage parameters includes: Inputting the AC voltage parameters of the sending-end flexible DC converter station, the AC voltage parameters of the hydropower unit and the AC voltage parameters of the sending-end new energy unit into a preset AC voltage effective value function respectively to obtain a plurality of AC voltage effective values; Determining whether each of the AC voltage effective values ​​is less than a preset AC fault threshold; If any of the AC voltage effective values ​​is less than the AC fault threshold, it is determined that an AC fault occurs; If each of the AC voltage effective values ​​is greater than or equal to the AC fault threshold, it is determined that no AC fault occurs.

3. The fault ride-through control method of the flexible DC transmission system according to claim 1 is characterized in that: The specific process of the sending-end flexible DC converter station executing the first fault ride-through control strategy is as follows: Acquiring the negative sequence AC voltage parameter of the sending-end flexible DC converter station, and clearing the integral link of the sending-end converter station outer loop controller associated with the sending-end flexible DC converter station; Inputting the negative-sequence AC voltage parameter into a preset negative-sequence AC voltage effective value function to obtain a negative-sequence AC voltage effective value; Performing a difference operation on an AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station and the negative-sequence AC voltage effective value to obtain a first difference; Using the first difference as an input AC voltage reference value of a d-axis outer loop controller associated with the sending-end flexible DC converter station; Limiting the d-axis current reference value and the q-axis current reference value of the sending-end flexible DC converter station, and acquiring the effective value of the AC voltage of the sending-end flexible DC converter station in real time; When the effective value of the AC voltage of the sending-end flexible DC converter station is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the effective value of the negative-sequence AC voltage of the sending-end flexible DC converter station is reduced by a preset first slope.

4. The fault ride-through control method of the flexible DC transmission system according to claim 1, characterized in that: The process of the hydropower unit executing the second fault ride-through control strategy is specifically as follows: Performing fault ride-through control on the hydropower unit based on a preset low voltage ride-through control model, and obtaining the effective value of the AC voltage of the hydropower unit in real time; When the effective value of the AC voltage of the hydropower unit is greater than or equal to a preset recovery threshold, the PSS controller of the hydropower unit performs voltage compensation control on the voltage regulator associated with the hydropower unit.

5. The fault ride-through control method of the flexible DC transmission system according to claim 1, characterized in that: The process of the new energy unit executing the third fault ride-through control strategy is specifically as follows: Reset the integral links of the outer ring d-axis controller and the outer ring q-axis control associated with the new energy unit; Limiting the d-axis current reference value and the q-axis current reference value of the new energy generator set, and acquiring the effective value of the AC voltage of the new energy generator set in real time; When the effective value of the AC voltage of the new energy generator set is greater than or equal to a preset recovery threshold, the low AC voltage signal is set to zero, and the fault recovery of the new energy generator set is performed according to a preset recovery strategy.

6. The fault ride-through control method of the flexible DC transmission system according to claim 5, characterized in that: The step of performing fault recovery on the new energy generator set according to a preset recovery strategy includes: Obtaining a fault clearing waiting time of the new energy generator set, and determining whether the fault clearing waiting time is greater than a preset recovery waiting threshold; If the fault clearing waiting time is greater than the recovery waiting threshold, the d-axis current value of the new energy generator set is regulated by a preset second slope to be restored to the d-axis current value before the fault; If the fault clearing waiting time is less than or equal to the recovery threshold, the step of obtaining the fault clearing waiting time of the new energy generator set is skipped and executed until the fault clearing waiting time is greater than the recovery threshold.

7. The fault ride-through control method of the flexible DC transmission system according to claim 3 is characterized in that: The first slope is 1 pu / s~3 pu / 100 ms.

8. The fault ride-through control method of the flexible DC transmission system according to claim 6, characterized in that: The recovery waiting threshold is 300ms.

9. The fault ride-through control method of the flexible DC transmission system according to claim 6, characterized in that: The second slope is 0.45~1pu / s.

10. A fault ride-through control system for a flexible DC transmission system, characterized in that: Applied to a flexible DC transmission system, the flexible DC transmission system includes a sending-end flexible DC converter station, a hydropower unit and a new energy unit, including: A collection module, used for acquiring AC voltage parameters of the flexible DC transmission system in real time, and judging whether an AC fault occurs according to the AC voltage parameters; An analysis module, used for generating a low AC voltage signal when an AC fault occurs, and sending the low AC voltage signal to the associated sending-end flexible DC converter station, hydropower unit or sending-end new energy unit; A first control module, configured to execute a preset first fault ride-through control strategy in response to the low AC voltage signal through the sending-end flexible DC converter station; A second control module, configured to execute a preset second fault ride-through control strategy in response to the low AC voltage signal through the hydropower unit; The third control module is used to execute a preset third fault ride-through control strategy in response to the low AC voltage signal through the new energy generator set.

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