Three-phase fault ride-through control method for sending end of hybrid DC transmission system of new energy

Abstract

The application discloses a sending-end three-phase fault ride-through control method of a new energy hybrid DC transmission system, and relates to the technical field of new energy, which comprises the following steps: detecting whether a fault occurs, locking the AC bus voltage outer loop control of the sending-end flexible DC converter valve if it is confirmed that the fault occurs, and adjusting the current reference instruction value of the current inner loop control of the sending-end flexible DC converter valve to a preset current instruction value; when it is confirmed that the fault is cleared, adopting open-loop voltage control to increase the AC voltage reference instruction of the sending-end flexible DC converter valve to a preset voltage instruction value in the recovery stage, and then inputting the closed-loop linkage control of the DC voltage and the AC voltage reference instruction value of the sending-end flexible DC converter valve; and when it is confirmed that the recovery stage is passed, switching the sending-end flexible DC converter valve to the AC bus voltage double-closed-loop control strategy in the normal operation condition. The application solves the problem of fault ride-through when the sending-end three-phase serious fault of the new energy hybrid DC transmission system occurs.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of new energy technology, in particular to a sending-end three-phase fault ride-through control method of a new energy hybrid DC transmission system. BACKGROUND

[0002] Taking the large-scale offshore new energy transmission as an example, the deep-sea wind power that has been put into operation at present mostly uses flexible DC transmission, but the offshore flexible DC converter platform is too large in size and weight, and has high cost. In order to realize the compactness and lightness of the offshore converter platform, and reduce the cost of the sending-end flexible DC converter, while being compatible with the grid-connected type and grid-constructing type wind turbines, the industry is exploring the DC transmission technology of the offshore wind power through diode and MMC hybrid.

[0003] However, the existing DC transmission technology of offshore wind power through diode and MMC hybrid focuses on black start and steady-state operation control strategy, and no mature technical method has been proposed for the fault ride-through problem of hybrid DC. In fact, due to the unidirectional conduction characteristic of diode, the fault ride-through of the sending end of the DC transmission system through diode and MMC hybrid is much more difficult than that of the sending end of the flexible DC transmission system. Taking the three-phase fault of the sending-end AC system in the most severe case as an example, after the fault occurs, the sending-end converter station cannot obtain energy from the sending-end new energy station. For the mature flexible DC transmission system, it can obtain energy support in the transient state from the anti-feeding power of the receiving-end converter station, while for the DC system through diode and MMC hybrid, it cannot accept the anti-feeding power and completely loses the energy source. On the other hand, during the recovery process after the fault is cleared, surplus power is easily generated to cause overvoltage of the equipment and lead to system protection trip and ride-through failure.

[0004] Therefore, for the three-phase fault ride-through problem of the sending end of the new energy hybrid DC transmission system represented by offshore wind power, effective fault ride-through technology is needed to solve the key problems in this technical route, so as to promote the application of the new energy hybrid DC transmission system. SUMMARY

[0005] The present application provides a sending-end three-phase fault ride-through control method of a new energy hybrid DC transmission system, to at least solve the problem of fault ride-through when the sending end of the new energy hybrid DC transmission system has a three-phase serious fault.

[0006] The application provides a sending end three-phase fault ride-through control method of a new energy hybrid DC transmission system, which is applied to a sending end of a new energy hybrid DC transmission system, the sending end of the system comprising: a sending end new energy station, a sending end AC line and a sending end converter station; the sending end new energy station comprising a plurality of sending end new energy units; the sending end converter station comprising a sending end AC bus, a first diode valve, a sending end HVDC valve and a second diode valve; the first diode valve, the sending end HVDC valve and the second diode valve being connected with the sending end AC bus; the new energy units being connected with the sending end AC bus through the sending end AC line; and the sending end new energy units comprising grid-side converters.

[0007] The method comprises:

[0008] detecting whether a fault occurs, if it is confirmed that a fault occurs, locking the AC bus voltage outer loop control of the sending end HVDC valve, and adjusting the current reference instruction value of the current inner loop control of the sending end HVDC valve to a preset current instruction value;

[0009] if it is confirmed that the fault is cleared, in the recovery stage, after the voltage control of the open loop is used to raise the AC voltage reference instruction of the sending end HVDC valve to a preset voltage instruction value, the closed-loop linkage control of the DC voltage and the AC voltage reference instruction value of the sending end HVDC valve is put into operation;

[0010] after it is confirmed that the recovery stage is passed, the sending end HVDC valve is switched to the AC bus voltage double-closed-loop control strategy in the normal operation condition.

[0011] In some possible implementation manners, the step of raising the AC voltage reference instruction of the sending end HVDC valve to the preset voltage instruction value comprises:

[0012] the rate of controlling the AC voltage reference instruction value of the sending end HVDC valve to the preset voltage instruction value is a preset voltage raising rate.

[0013] In some possible implementation manners, the method further comprises:

[0014] if it is confirmed that the fault is cleared, the current reference instruction value of the grid-side converter of the new energy unit is adjusted to the current reference instruction value before the fault.

[0015] In some possible implementation manners, the step of adjusting the current reference instruction value of the grid-side converter of the new energy unit to the current reference instruction value before the fault comprises:

[0016] the rate of controlling the current reference instruction value of the grid-side converter of the new energy unit to the current reference instruction value before the fault is a preset current rate.

[0017] In some possible implementation manners, the step of performing closed-loop linkage control on the DC voltage reference instruction value and the AC voltage reference instruction value of the sending-end HVDC valve comprises the following steps:

[0018] The adjustment amount is obtained by PI regulation on the DC voltage reference instruction value and the actual DC voltage value;

[0019] The AC voltage reference instruction value is obtained by superimposing the adjustment amount on the preset voltage instruction value, and the AC voltage reference instruction value is used for control.

[0020] In some possible implementation manners, the step of detecting whether a fault occurs comprises the following steps:

[0021] It is detected whether the sending-end AC bus voltage is lower than a preset AC voltage value;

[0022] If it is detected that the sending-end AC bus voltage is lower than the preset AC voltage value, it is confirmed that a fault occurs.

[0023] The application further provides a sending-end three-phase fault ride-through control device of a hybrid DC transmission system of new energy, comprising:

[0024] A fault occurrence control module is configured to detect whether a fault occurs, and if it is confirmed that a fault occurs, to lock the AC bus voltage outer loop control of the sending-end HVDC valve and to adjust the current reference instruction value of the current inner loop control of the sending-end HVDC valve to a preset current instruction value;

[0025] A fault recovery control module is configured to, if it is confirmed that a fault is cleared, perform open-loop voltage control to increase the AC voltage reference instruction of the sending-end HVDC valve to a preset voltage instruction value in a recovery stage, and then to perform closed-loop linkage control on the DC voltage reference instruction value and the AC voltage reference instruction value of the sending-end HVDC valve.

[0026] A recovery completion control module is configured to, when it is confirmed that the recovery stage is passed, switch the sending-end HVDC valve to an AC bus voltage double-closed-loop control strategy in a normal operating condition.

[0027] The application further provides an electronic device, comprising a memory configured to store a computer program and a processor configured to execute the computer program to implement the steps of any one of the sending-end three-phase fault ride-through control methods of the hybrid DC transmission system of new energy.

[0028] The application further provides a computer-readable storage medium, wherein the computer-readable storage medium stores a computer program, and the computer program is executed by a processor to implement the steps of any one of the sending-end three-phase fault ride-through control methods of the hybrid DC transmission system of new energy.

[0029] The application further provides a computer program product comprising a computer program which, when executed by a processor, implements the steps of any of the new energy hybrid DC transmission system sending end three-phase fault ride-through control methods.

[0030] The new energy hybrid DC transmission system sending end three-phase fault ride-through control method provided by the application, when confirming the occurrence of a fault, locks the AC voltage outer loop control of the sending end flexible DC converter valve, only performs inner loop control, and specifically adjusts the current reference instruction value of the current inner loop control of the sending end flexible DC converter valve to a preset current instruction value, so that the DC voltage drop of the sending end flexible DC converter valve caused by the loss of the capacitor storage energy of the sending end flexible DC converter valve is avoided. Therefore, the DC voltage drop of the sending end flexible DC converter valve caused by the loss of the capacitor storage energy of the sending end flexible DC converter valve is avoided, and the system shutdown problem caused by the DC voltage drop of the sending end flexible DC converter valve is prevented. Then, after the fault is cleared, the AC voltage control of the open loop is selected for the sending end flexible DC converter valve, the AC voltage output by the sending end flexible DC converter valve is raised to a preset AC voltage reference instruction, and then the DC voltage and AC voltage linkage control of the sending end flexible DC converter valve is put into operation, so as to control the reasonable distribution of the wind farm output power between the sending end flexible DC converter valve and the DRU. When it is confirmed that the recovery stage is passed, the sending end flexible DC converter valve is switched to the double-closed-loop voltage control strategy in the normal operating condition. Therefore, the fault ride-through problem of the new energy hybrid DC transmission system sending end three-phase serious fault is solved, and the power supply reliability of the offshore wind power DC transmission system is improved. BRIEF DESCRIPTION OF DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the application, the drawings required in the embodiments will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor.

[0032] Figure 1 Two topological structure diagrams of the new energy hybrid DC transmission system in the prior art;

[0033] Figure 2 A flowchart of the new energy hybrid DC transmission system sending end three-phase fault ride-through control method provided by the embodiments of the application;

[0034] Figure 3 A control diagram of the sending end flexible DC converter valve in the fault occurrence and duration stage of the new energy hybrid DC transmission system sending end three-phase fault ride-through control method provided by the embodiments of the application;

[0035] Figure 4A control diagram of the wind turbine grid-side converter in the fault occurrence and duration stage of the three-phase fault ride-through control method of the sending end of the new energy hybrid DC transmission system provided by the embodiment of the present application;

[0036] Figure 5 A control diagram of the sending end flexible DC converter in the fault clearing and recovery stage of the three-phase fault ride-through control method of the sending end of the new energy hybrid DC transmission system provided by the embodiment of the present application;

[0037] Figure 6 A control diagram of the wind turbine grid-side converter in the fault clearing and recovery stage of the three-phase fault ride-through control method of the sending end of the new energy hybrid DC transmission system provided by the embodiment of the present application;

[0038] Figure 7 A control diagram of the sending end flexible DC converter and the wind turbine grid-side converter in the normal condition of the three-phase fault ride-through control method of the sending end of the new energy hybrid DC transmission system provided by the embodiment of the present application;

[0039] Figure 8 An electronic device is provided in the embodiment of the present application. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0041] It should be noted that, in the description of the present application, the terms “comprise”, “contain” or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not explicitly listed or inherent to such process, method, article or device. The terms “first”, “second” and the like in the present application are used to distinguish similar objects, and are not used to describe a specific order or sequence.

[0042] In order for those skilled in the art to better understand the present application, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0043] Taking the large-scale offshore new energy transmission as an example, the deep-sea wind power currently put into operation is mostly transmitted by flexible DC transmission, but the offshore flexible DC converter platform is too large and heavy, and the cost is high. In order to realize the compactness and lightness of the offshore converter platform, reduce the cost of the sending end flexible converter valve, and at the same time be compatible with the grid-connected type and network type wind turbine, the industry is exploring the DC transmission technology of offshore wind power through diode and MMC hybrid.

[0044] However, the existing patents of the DC transmission technology of offshore wind power through diode and MMC hybrid all focus on the black start and steady-state operation control strategy, and no mature technical method has been proposed for the fault ride-through problem of hybrid DC. In fact, due to the unidirectional conduction characteristic of diode, the fault ride-through difficulty of the sending end of the DC transmission system of diode and MMC hybrid is much greater than that of the sending end of the flexible DC transmission system. Taking the three-phase fault of the sending end AC system in the most severe case as an example, after the fault occurs, the sending end converter station cannot obtain energy from the sending end new energy station. For the mature flexible DC transmission system, it can obtain energy support in the transient state from the anti-feeding power of the receiving end converter station, while for the DC system of diode and MMC hybrid, it cannot accept the anti-feeding power and completely loses the energy source. On the other hand, during the recovery process after the fault is cleared, surplus power is easily generated to cause overvoltage of the equipment and lead to system protection trip failure of the fault ride-through.

[0045] Therefore, for the three-phase fault ride-through problem of the sending end of the new energy transmission system through hybrid DC represented by offshore wind power, effective fault ride-through technology is needed to solve the key problems in this technical route, so as to promote the application of the new energy transmission system through hybrid DC.

[0046] The existing offshore wind power DC transmission system offshore AC three-phase fault ride-through technology is for pure flexible DC transmission system. The technical target and strategy are briefly described as follows: limiting the current fed by the sending end flexible DC to the fault point during the fault and overvoltage of the AC voltage of the sending end flexible DC during the recovery stage after the fault is cleared. Different from the fault ride-through of the "pure flexible DC transmission system", the sending end MMC of the "diode-based hybrid DC transmission system" cannot obtain DC voltage support during the fault ride-through period. Therefore, in the fault ride-through stage, in addition to limiting the current fed by the sending end flexible DC to the fault point during the fault and overvoltage of the AC voltage of the sending end flexible DC during the recovery stage after the fault is cleared, it is also necessary to ensure that the DC voltage of the sending end MMC does not appear serious under-voltage which leads to system shutdown.

[0047] The embodiment of the present application provides a three-phase fault ride-through control method of a new energy transmission system through hybrid DC, such as Figure 2As shown, the method is applied to a sending end of a new energy hybrid DC transmission system, the sending end of the system comprising: a sending end new energy station, a sending end AC line and a sending end converter station; the sending end new energy station comprising a plurality of sending end new energy units; the sending end converter station comprising a sending end AC bus, a first diode valve (DRU, Diode Rectifier Unit), a sending end MMC (Modular Multilevel Converter) and a second diode valve; the first diode valve, the sending end MMC and the second diode valve are connected with the sending end AC bus, and the new energy units are connected with the sending end AC bus through the sending end AC line; the sending end new energy units comprising a grid-side converter;

[0048] The method comprises:

[0049] Step S01: detecting whether a fault occurs, and if it is confirmed that a fault occurs, locking the AC bus voltage outer loop control of the sending end MMC and adjusting the current reference command value of the current inner loop control of the sending end MMC to a preset current command value;

[0050] Step S02: if it is confirmed that the fault is cleared, in the recovery stage, after the AC voltage reference command value of the sending end MMC is raised to a preset voltage command value by using open-loop voltage control, the closed-loop linkage control of the DC voltage and AC voltage reference command values of the sending end MMC is put into operation;

[0051] Step S03: when it is confirmed that the recovery stage is passed, the sending end MMC is switched to the AC bus voltage double-closed-loop control strategy in the normal operation condition.

[0052] Specifically, the first diode valve and the second diode valve are two DRUs (Diode Rectifier Unit), the sending end MMC is an MMC (Modular Multilevel Converter), and the grid-side converter is not shown in the figure. Figure 1

[0053] Specifically, the fault stage comprises two parts, the first part is a fault occurrence and duration stage, and the second part is a fault clearance and system recovery stage. Among them, the fault duration stage is the stage after the fault occurs and before it is eliminated, and the fault recovery stage is the stage after the fault is cleared and before the system recovers to normal. Referring to Figure 3 ​, before the fault occurs, the sending end flexible HVDC valve operates in the corresponding control strategy under normal working condition, controls the d, q axis components of the sending end AC bus voltage, and the sending end flexible HVDC valve is controlled as follows during the sending end AC fault: the AC bus voltage outer loop control of the sending end flexible HVDC valve is blocked, and the current inner loop control of and is performed at the same time.

[0054] In Figure 3 , , is the DC voltage reference instruction value and the measured feedback value of the sending end flexible HVDC valve, and PI is a proportional integral controller; is a voltage feedforward amount, which can be considered as a preset voltage instruction value, and here, a constant value is selected, and the purpose is to improve the dynamic response speed; , are the d, q axis component reference instruction values of the sending end AC bus voltage, in order to simplify the control, the q axis component reference instruction is generally set to 0, and the d axis component reference instruction can be adjusted, so that the regulation of the required AC bus voltage amplitude can be realized. In the figure, the difference between and is added to the voltage feedforward amount after PI controller, and the output is , which is the closed-loop linkage control between the DC voltage and the AC bus voltage reference instruction, that is, when the measured DC voltage deviates from the reference instruction value , the AC bus voltage reference instruction is adjusted through the difference output, so as to indirectly adjust the power input to the DC side of the sending end flexible HVDC valve, and then the DC voltage of the sending end flexible HVDC valve is adjusted until there is no deviation from the DC voltage reference instruction value, thus forming a linkage closed-loop feedback between the DC voltage and the AC bus voltage instruction. , are the d, q axis component measured values of the sending end AC bus voltage; , and , are respectively subtracted to input the PI controller, and the output is the d, q axis component reference instruction values of the AC side current inner loop of the sending end flexible HVDC valve 32 , , and this link constitutes the voltage outer loop of the double closed-loop control. , are respectively , , the d, q axis components of the AC voltage reference instruction values of the sending end flexible HVDC valve, which are output after the current inner loop control link is input as the control instruction.P 1 is the park transformation of the sending end HVDC valve valve side fundamental frequency electrical quantity, which belongs to the mature technology in the field (here, the park transformation and the inverse park transformation are indicated by the same icon. If it is three-phase input and two-phase output, it is the positive park transformation. If it is two-phase input and three-phase output, it is the inverse park transformation); θ 1 is the park transformation angle of the sending end HVDC valve valve side fundamental frequency electrical quantity; 、 The three-phase fundamental frequency AC voltage reference instruction value of the sending end HVDC valve output after inverse park transformation 、 、 ; 、 、 The three-phase two-frequency negative sequence AC voltage reference instruction value of the sending end HVDC valve output after circulation suppression control 、 、 、 、 、 The number of sub-modules required for the three-phase 6-bridge arms of the sending end HVDC valve 32 output by nearest level modulation (NLM) is respectively

[0055] Reference Figure 4 , Figure 4 is the control of the new energy unit grid side converter during the fault. It is worth noting that the fault means that the sending end AC bus voltage drops sharply. The grid side converter cancels the outer loop control during the fault and only uses the current inner loop control. The d, q axis current reference instructions of the current inner loop control and can refer to the wind turbine fault ride-through standard, which is specifically:

[0056]

[0057] is the amplitude of the maximum AC current allowed to flow through the grid side converter, is the positive sequence voltage reference value of the grid side converter grid connection point, is the AC current rating of the grid side converter. The current feedback quantity and are the d, q axis components of the measured AC current of the grid side converter. The d, q axis components of the AC voltage reference instruction value output by the current inner loop control of the grid side converter are 、 , θ 2 is the park transformation angle of the grid side converter AC side fundamental frequency electrical quantity; , The three-phase AC voltage reference command value of the output grid-side converter after inverse Park transformation , , ; , , , , , These are the trigger pulse signals of the three-phase 6-bridge arm of the grid-side converter, output through pulse width modulation (PWM).

[0058] Specifically, upon confirmation of a fault, the voltage loop of the sending-end flexible DC converter valve reaches its limit, losing control over the AC bus voltage at the sending end. At this time, the outer loop control of the AC voltage of the sending-end flexible DC converter valve is locked; that is, under fault conditions, the outer loop control of the voltage is canceled, and only the inner loop control remains. The inner loop current control specifically lowers the current reference command value of the sending-end flexible DC converter valve's inner loop control to a preset command value, thereby preventing the loss of energy stored in the capacitor of the sending-end flexible DC converter valve, which could cause a drop in the DC voltage of the sending-end flexible DC converter valve. This, in turn, prevents system shutdown caused by a drop in the DC voltage of the sending-end flexible DC converter valve.

[0059] It is worth noting that fault clearing refers to the disconnection of the AC line where the fault occurred at the sending end.

[0060] Specifically, when confirming that the fault has been cleared, refer to Figure 5 By employing open-loop AC voltage control of the sending-end flexible DC converter valve, the AC voltage of the sending-end converter valve is boosted to a preset AC voltage reference command value. Then, closed-loop linkage control between the DC voltage and the AC voltage reference command value of the sending-end flexible DC converter valve is implemented to control the reasonable distribution of wind farm output power between the sending-end flexible DC converter valve and the DRU. The reference command value of the d-axis component of the AC fundamental frequency reference wave of the sending-end flexible DC converter valve is changed from... Upgraded to .in, The measured value of the d-axis component of the AC fundamental frequency reference wave of the DC-DC converter valve at the sending end at the moment of fault clearance. This is the preset AC voltage d-axis reference command value. When the d-axis reference command... Rise to After that, then Figure 5 Switching Ctrl from 0 to 1 activates the control of the DC voltage-linked AC voltage reference command, thereby controlling the optimal distribution of wind farm output power between the sending-end flexible DC converter valve and the DRU. Additionally, for simplified control, as... Figure 5 As shown, during this period Always set to 0.

[0061] For example, In the interval of [0.9pu, 0.95pu], because 0.9pu is the lower limit of the wind turbine disengaging from low voltage ride through, and less than 0.95pu can ensure that the DRU DC side is not turned on temporarily, avoiding the original little energy from the sending end flexible HVDC converter valve to the DRU.

[0062] Exemplarily, when confirming the fault clearance, the AC bus voltage value of the sending end flexible HVDC converter valve is raised to 0.92pu, and then the DC voltage and AC voltage linkage control of the sending end flexible HVDC converter valve is put into operation until the DRU DC side is smoothly turned on.

[0063] Specifically, after the power and voltage are restored to the normal state before the fault occurs, the sending end flexible HVDC converter valve is switched from open-loop AC voltage control to closed-loop AC voltage control, and the grid-side converter control of the wind turbine is also switched to normal constant DC voltage control, referring to Figure 7 , Figure 7 The sending end flexible HVDC converter valve control strategy and the wind turbine grid-side converter control strategy under normal conditions.

[0064] Optionally, passing through the recovery stage means that the AC voltage of the sending end flexible HVDC converter valve reaches the AC voltage reference instruction value.

[0065] The sending end three-phase fault ride-through control method of the hybrid DC transmission system of new energy provided in the application, when confirming the fault occurrence, the AC voltage outer loop control of the sending end flexible HVDC converter valve is locked out, and only the inner loop control is performed, and when the inner loop control is performed, the current reference instruction value of the current inner loop control of the sending end flexible HVDC converter valve is adjusted to a preset current instruction value, so as to avoid the energy loss of the capacitor of the sending end flexible HVDC converter valve and make the DC voltage of the sending end flexible HVDC converter valve drop. Further, the system shutdown problem caused by the DC voltage drop of the sending end flexible HVDC converter valve is prevented. Then, after the fault is cleared, the open-loop AC voltage control is selected for the sending end flexible HVDC converter valve, the AC voltage output by the sending end flexible HVDC converter valve is raised to a preset AC voltage reference instruction, and then the DC voltage and AC voltage linkage control of the sending end flexible HVDC converter valve is put into operation, so as to control the reasonable distribution of the wind farm output power between the sending end flexible HVDC converter valve and the DRU. When confirming that the recovery stage is passed, the sending end flexible HVDC converter valve is switched to the double-closed-loop voltage control strategy under the normal operating condition. Thus, the fault ride-through problem of the sending end three-phase serious fault of the hybrid DC transmission system of new energy is solved, and the power supply reliability of the offshore wind power DC transmission system is improved.

[0066] In some possible embodiments, the step of "raising the AC voltage reference instruction of the sending end flexible HVDC converter valve to a preset voltage instruction value" in step S02 comprises:

[0067] Step a1: control the rate of the AC voltage reference command value of the sending end HVDC valve to the preset voltage command value to be a preset voltage raising rate.

[0068] Specifically, reducing the rate of raising to the preset voltage command value means taking a certain slope to raise the MMC AC fundamental frequency reference wave d-axis component from to .

[0069] Exemplarily, the voltage amplitude is raised from to 0.92pu within 200ms.

[0070] In some possible implementations, the method further includes:

[0071] Step b1: if it is confirmed that the fault is cleared, adjust the current reference command value of the grid-side converter of the new energy unit to be the current reference command value before the fault.

[0072] Specifically, the new energy unit can be a wind turbine, and for the control of the wind farm, the grid-side converter of the wind turbine still adopts current control during the fault recovery.

[0073] Specifically, with reference to Figure 6 , when the positive sequence voltage per unit of the grid-side converter grid connection point is less than 0.9pu, that is, A < 0.9pu, the output LVRT_over is 0. When A > 0.9pu, that is, A > B, the output LVRT_over is 1, and at this time, the current reference command value of the grid-side converter of the wind turbine is adjusted to be the current reference command value before the fault.

[0074] Figure 6 In some possible implementations, as shown in , step b1 includes:

[0075] Step (1): control the rate of adjusting the current reference command value of the grid-side converter of the new energy unit to be the current reference command value before the fault to be a preset current rate.

[0076] Figure 6 Specifically, with reference to , in order to avoid the impact of rapid recovery of the wind turbine power on the sending end AC bus, the d-axis current command corresponding to the active power is taken to recover from the command before the fault at a preset slope , and the q-axis current command corresponding to the reactive power is taken to recover rapidly from the command before the fault , which is actually 0 in normal non-fault state.

[0077] In some possible implementation manners, the step of "closed-loop linkage control of the DC voltage and AC voltage reference instruction values of the sending-end HVDC valve" in step S02 comprises the following steps.

[0078] Step c1: obtaining an adjustment amount by PI adjustment of the DC voltage reference instruction value and the actual DC voltage value;

[0079] Step c2: superimposing the adjustment amount on the preset voltage instruction value to obtain an AC voltage reference instruction value, and controlling through the AC voltage reference instruction value.

[0080] Specifically, referring to Figure 5 , the DC voltage reference instruction value is , and the actual DC voltage value is , After filtering through a first-order inertia link (i.e. ), the difference between is obtained after PI control to obtain an adjustment amount. The adjustment amount is superimposed on to obtain , and control is performed through , and is 0. It should be noted that the circulating current suppression control is a conventional technology, and will not be described in detail here.

[0081] In some possible implementation manners, the step of "detecting whether a fault occurs" in step S01 comprises the following steps.

[0082] Step d1: detecting whether the sending-end AC bus voltage is lower than a preset AC voltage value;

[0083] Step d2: if it is detected that the sending-end AC bus voltage is lower than the preset AC voltage value, it is determined that a fault occurs.

[0084] Specifically, when an AC short-circuit fault occurs at the sending end, the sending-end AC bus voltage will sharply decrease, at which time the voltage loop PI of the sending-end HVDC valve is limited to an amplitude, and the control of the sending-end AC bus voltage is lost. When the system detects that the amplitude of the sending-end AC bus voltage is less than a threshold value , the sending-end HVDC valve automatically switches to a control strategy under a fault, that is, the AC voltage outer loop control of the sending-end HVDC valve is locked, and the current reference instruction value of the current inner loop control of the sending-end HVDC valve is adjusted to a preset current instruction value. Thus, the energy stored in the capacitor of the sending-end HVDC valve is prevented from being lost, so that the DC voltage of the sending-end HVDC valve is prevented from dropping. In turn, the system shutdown problem caused by the DC voltage drop of the sending-end HVDC valve is prevented.

[0085] Through the description of the above embodiments, those skilled in the art can clearly understand that the method according to the above embodiments can be realized by means of software on a necessary general hardware platform, and of course can also be realized by hardware, but in many cases the former is a better embodiment.

[0086] The embodiment of the present application also provides a sending end three-phase fault ride-through control device of a new energy hybrid DC transmission system, the sending end three-phase fault ride-through control device of the new energy hybrid DC transmission system comprising:

[0087] A fault occurrence control module is configured to detect whether a fault occurs, and if it is confirmed that a fault occurs, to lock the AC bus voltage outer loop control of the sending end HVDC valve and to adjust the current reference instruction value of the current inner loop control of the sending end HVDC valve to a preset current instruction value;

[0088] A fault recovery control module is configured to, if it is confirmed that the fault is cleared, adopt open-loop voltage control to increase the AC voltage reference instruction of the sending end HVDC valve to a preset voltage instruction value in a recovery stage, and then to input the closed-loop linkage control of the DC voltage and AC voltage reference instruction values of the sending end HVDC valve;

[0089] A recovery completion control module is configured to, when it is confirmed that the recovery stage is passed, switch the sending end HVDC valve to the AC bus voltage double closed loop control strategy in a normal operation condition.

[0090] The features of the embodiment of the sending end three-phase fault ride-through control device of the new energy hybrid DC transmission system can be referred to the related description of the embodiment of the sending end three-phase fault ride-through control method of the new energy hybrid DC transmission system, which will not be repeated here.

[0091] The embodiment of the present application also provides an electronic device, as shown in the figure, comprising a memory 10 and a processor 20, the memory 10 stores a computer program, and the processor 20 is configured to run the computer program to execute the steps in any one of the above new energy hybrid DC transmission system sending end three-phase fault ride-through control method embodiments. Figure 8

[0092] The embodiment of the present application also provides a computer readable storage medium, which stores a computer program, wherein the computer program is configured to execute the steps in any one of the above new energy hybrid DC transmission system sending end three-phase fault ride-through control method embodiments when running.

[0093] ​In an example embodiment, the computer readable storage medium described above can include, but is not limited to, a U disk, a read-only memory (ROM), a random access memory (RAM), a mobile hard disk, a magnetic disk or an optical disk, and various media that can store computer programs.

[0094] Embodiments of the present application also provide a computer program product, which comprises a computer program, and the computer program, when executed by a processor, implements the steps in any of the above-mentioned new energy through hybrid DC transmission system sending end three-phase fault ride-through control method embodiments.

[0095] Embodiments of the present application also provide another computer program product, which comprises a non-volatile computer readable storage medium, and the non-volatile computer readable storage medium stores a computer program, and the computer program, when executed by a processor, implements the steps in any of the above-mentioned new energy through hybrid DC transmission system sending end three-phase fault ride-through control method embodiments.

[0096] The skilled in the art can further realize that the units and algorithm steps of the examples described in combination with the embodiments disclosed herein can be realized in electronic hardware, computer software or a combination of both. In order to clearly illustrate the interchangeability of hardware and software, the components and steps of the examples have been described in the above description in general terms. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. The skilled in the art can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0097] The above describes in detail a new energy through hybrid DC transmission system sending end three-phase fault ride-through control method provided by the present application. The principles and implementation manners of the present application are described by applying specific examples in this paper, and the above description of the examples is only applicable to help understand the method of the present application and its core idea. It should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, some improvements and modifications can be made to the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for three-phase fault ride-through control at the sending end of a new energy transmission system via hybrid DC transmission, characterized in that, The method is applied to the sending end of a new energy transmission system via a hybrid DC transmission line. The sending end of the system includes: a sending-end new energy power station, a sending-end AC line, and a sending-end converter station. The sending-end new energy power station comprises several sending-end new energy generating units. The sending-end converter station includes a sending-end AC bus, a first diode valve, a sending-end flexible DC converter valve, and a second diode valve. The first diode valve, the sending-end flexible DC converter valve, and the second diode valve are all connected to the sending-end AC bus. The new energy generating units are connected to the sending-end AC bus via the sending-end AC line. The sending-end new energy generating units include grid-side converters. The method includes: Detect whether a fault has occurred. If a fault is confirmed, lock the outer loop control of the AC bus voltage of the sending end flexible DC converter valve and adjust the current reference command value of the inner loop control of the current of the sending end flexible DC converter valve to the preset current command value. If the fault is confirmed to be cleared, during the recovery phase, open-loop voltage control is used to raise the AC voltage reference command of the sending-end flexible DC converter valve to the preset voltage command value, and then closed-loop linkage control of the DC voltage and AC voltage reference command value of the sending-end flexible DC converter valve is put into operation. Once the recovery phase is confirmed to have passed, the sending-end flexible DC converter valve will be switched to the AC bus voltage dual closed-loop control strategy under normal operating conditions.

2. The three-phase fault ride-through control method at the sending end of the new energy hybrid DC transmission system according to claim 1, characterized in that, The step of raising the AC voltage reference command of the feed-end flexible DC converter valve to a preset voltage command value includes: The rate at which the AC voltage reference command value of the control end flexible DC converter valve rises to the preset voltage command value is the preset voltage boost rate.

3. The three-phase fault ride-through control method at the sending end of the new energy hybrid DC transmission system according to claim 1, characterized in that, The method further includes: If the fault is confirmed to be cleared, adjust the current reference command value of the grid-side converter of the new energy unit to the current reference command value before the fault.

4. The three-phase fault ride-through control method at the sending end of the new energy hybrid DC transmission system according to claim 3, characterized in that, The step of adjusting the current reference command value of the grid-side converter of the new energy unit to the current reference command value before the fault includes: The current reference command value of the grid-side converter of the new energy unit is controlled and adjusted at the rate of the current reference command value before the fault, which is the preset current rate.

5. The three-phase fault ride-through control method at the sending end of a new energy hybrid DC transmission system according to claim 1, characterized in that, The steps of the closed-loop linkage control of the DC voltage and AC voltage reference command values ​​of the input-side flexible DC converter valve include: The adjustment amount is obtained by PI regulation using the DC voltage reference command value and the actual DC voltage value. The adjustment amount is superimposed on the preset voltage command value to obtain the AC voltage reference command value, and control is performed using the AC voltage reference command value.

6. The three-phase fault ride-through control method at the sending end of the new energy hybrid DC transmission system according to claim 1, characterized in that, The step of detecting whether a fault has occurred includes: Check whether the AC bus voltage at the sending end is lower than the preset AC voltage value; If the AC bus voltage at the sending end is detected to be lower than the preset AC voltage value, a fault is confirmed to have occurred.

7. A three-phase fault ride-through control device for a new energy transmission system via hybrid DC transmission, characterized in that, include: The fault occurrence control module is used to detect whether a fault has occurred. If a fault is confirmed, the outer loop control of the AC bus voltage of the sending end flexible DC converter valve is locked, and the current reference command value of the inner loop control of the current of the sending end flexible DC converter valve is adjusted to the preset current command value. The fault recovery control module is used to, when the fault is confirmed to be cleared, use open-loop voltage control to raise the AC voltage reference command of the sending-end flexible DC converter valve to the preset voltage command value during the recovery phase, and then put into closed-loop linkage control of the DC voltage and AC voltage reference command value of the sending-end flexible DC converter valve. The recovery completion control module is used to switch the sending-end flexible DC converter valve to the AC bus voltage dual closed-loop control strategy under normal operating conditions after confirming that the recovery phase has passed.

8. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor, configured to execute the computer program to implement the steps of the three-phase fault ride-through control method for the new energy transmission system via a hybrid DC transmission system as described in any one of claims 1 to 6.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program, wherein when the computer program is executed by a processor, it implements the steps of the three-phase fault ride-through control method for the new energy transmission system via a hybrid DC transmission system as described in any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by the processor, it implements the steps of the three-phase fault ride-through control method at the sending end of the new energy transmission system via hybrid DC as described in any one of claims 1 to 6.

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