A new energy transmission system through a DRU-HVDC transmission system, an AC fault ride-through control method, a device and a medium

Abstract

This invention belongs to the field of high-voltage direct current (HVDC) transmission in power systems, specifically relating to a method, equipment, and medium for AC fault ride-through control at the sending end of a new energy source transmission system via a DRU-HVDC. When an AC fault occurs at the sending end, the grid-side converter of the new energy power station exits the active, reactive, and voltage loops, retains the inner current loop, and switches to maximum current output mode, locking the frequency to the rated value. Simultaneously, the receiving-end converter station exits the DC voltage outer loop, retains the inner current loop, and controls the DC current according to preset commands. During the fault duration, the diode rectifier station remains on and transmits maximum active power. After the fault is cleared, the output current of the new energy power station is reduced to the rated value, and then the power and voltage control loops are restored; the receiving-end converter station resumes constant DC voltage operation. This invention achieves maximum power control through preset commands. By controlling and switching between the new energy power station and the receiving-end converter station, the DRU is effectively maintained on, improving the active power transmission capacity and system recovery speed during faults.

Description

Technical Field

[0001] This invention belongs to the field of high voltage direct current transmission in power systems, specifically relating to a method, equipment, and medium for AC fault ride-through control at the sending end of a new energy transmission system via DRU-HVDC. Background Technology

[0002] Large-scale renewable energy bases are typically located far from load centers, requiring high-voltage direct current (HVDC) transmission for long-distance power transmission. Currently, flexible HVDC solutions based on modular multilevel converters (MMCs) are mature, but these converter stations are large and costly. To improve the reliability and economy of renewable energy transmission systems, Siemens proposed a diode rectifier unit-based high-voltage direct current (DRU-HVDC) solution. This solution uses diode rectifier units (DRUs) to replace traditional rectifier devices, significantly simplifying the sending-end converter station structure. However, when a sending-end AC fault occurs in the DRU-HVDC transmission system, the power transmission is interrupted due to DRU shutdown, resulting in a sudden and significant active power deficit in the receiving-end grid. This can trigger frequency fluctuations and power flow abrupt changes, seriously threatening the safe operation of the power grid.

[0003] The relevant fault ride-through control mainly includes two aspects: additional energy consumption devices and current limiting control of new energy units.

[0004] Regarding additional energy-consuming devices, relevant documents stipulate that in the event of an AC fault at the sending end of the DRU-HVDC system, only the unloading load (DC chopper) of the unit's DC link is relied upon to consume the redundant power during the fault. Because the AC voltage drop causes the DRU to shut down, active power cannot be effectively delivered and thus accumulates in large quantities on the DC side of the back-to-back converter. This causes the unloading load to experience energy surges far exceeding its rated capacity, easily leading to overheating, shortened lifespan, or even failure, increasing maintenance costs.

[0005] Regarding current limiting control for new energy generating units, relevant documents stipulate that when a sending-end AC fault occurs in the DRU-HVDC system, upper and lower limit thresholds are set for the reference value of the inner loop current of the grid-side converter of the generating unit to achieve current limiting. During the fault, after the current reaches the limit, the generating unit will exhibit current source characteristics.

[0006] The relevant documents also propose a current limiting control method based on virtual impedance, which improves the voltage control loop of the grid-side converter of the unit by using virtual impedance. During AC faults at the sending end of the DRU-HVDC system, the grid-side converter actively reduces the output voltage to suppress overcurrent.

[0007] Although the aforementioned literature has achieved redundant power consumption or fault current limitation, during the fault period, the AC voltage drop at the sending end and the DC voltage at the receiving end converter station remain unchanged due to the DRU being cut off have both resulted in power transmission interruption problems.

[0008] In summary, existing research on AC fault ride-through at the sending end of the new energy transmission system via DRU-HVDC does not consider the power transmission interruption caused by DRU shutdown, which will result in an active power deficit in the receiving end grid. Furthermore, it mainly relies on the single-sided control of the new energy power station to achieve fault ride-through, without considering the control role of the receiving end converter station during the fault process, and lacks a fault ride-through mechanism for coordinated control between the sending end new energy power station and the receiving end converter station. Summary of the Invention

[0009] This invention provides a method for AC fault ride-through control at the sending end of a new energy transmission system via DRU-HVDC. By relying on local preset commands, the diode rectifier station can be kept on during a fault, achieving near-maximum active power transmission. After the fault is cleared, a graded recovery strategy is used to effectively avoid current surges and voltage overshoots, achieving a rapid and smooth transition from fault mode to normal mode.

[0010] The methods include: S1: Detect the fault status on the AC side of the new energy transmission system via DRU-HVDC; S2: When an AC fault is detected at the sending end, the grid-side converter of the new energy power station is controlled to exit the active power loop, reactive power loop and voltage loop under normal operation, while retaining the current inner loop control. The d-axis current reference value of the current inner loop is switched to the maximum output current of the new energy power station, the q-axis current reference value is switched to zero, and the frequency reference value is switched to the rated frequency. S3: Synchronous control of the receiving-end converter station exits the DC voltage outer loop under normal operation, retains the DC current inner loop control, and switches the reference value of the DC current inner loop to the preset fault ride-through DC current reference value. S4: During the duration of the AC fault at the sending end, maintain the continuous conduction of the diode rectifier station and transmit active power to the receiving end grid; S5: Real-time detection of the clearing status of AC faults at the sending end; S6: When the AC fault at the sending end is detected to be cleared, the reference value of the d-axis current of the converter on the grid side of the new energy power station is reduced from the maximum output current in step S2 to the rated current value. After the output current is reduced to the rated current value, the active power loop, reactive power loop and voltage loop are re-engaged to restore the normal operation control mode. S7: Synchronously control the receiving-end converter station to directly engage the DC voltage outer loop, restore the DC voltage to the rated value, switch back to the normal operating constant DC voltage control mode, and complete the AC fault ride-through at the sending end.

[0011] According to another embodiment of this application, an electronic device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it implements the steps of the AC fault ride-through control method for the sending end of the new energy transmission system via DRU-HVDC.

[0012] According to another embodiment of this application, a storage medium is also provided, on which a computer program is stored, wherein when the computer program is executed by a processor, the steps of the AC fault ride-through control method of the new energy transmission system via DRU-HVDC are implemented.

[0013] As can be seen from the above technical solutions, the present invention has the following advantages: This invention constructs an equivalent circuit model of a renewable energy transmission system via DRU-HVDC under AC fault conditions at the sending end. The connection between the renewable energy power station at the sending end and the converter station at the receiving end is established through DRU. The maximum active power that can be transmitted to the receiving end grid during the fault is given, and the values ​​of the system controllable variables corresponding to this operating point are given. The power transmission characteristics of the system under AC fault conditions at the sending end are theoretically revealed.

[0014] The present invention proposes a method for AC fault ride-through control at the sending end of a new energy power plant via a DRU-HVDC transmission system. During a fault, the new energy power plant controls the output current and the receiving-end converter station controls the DC current, making full use of their coordinated capabilities. This method can maintain the DRU conduction during AC faults at the sending end, maximizing the transmission of active power, effectively alleviating the active power deficit problem in the receiving-end power grid, ensuring the safe operation of the system, and eliminating the need for fault information and communication, thus having strong applicability.

[0015] After a fault is cleared, this invention gradually lowers the d-axis current reference value of the renewable energy power station to the rated current. Once the current stabilizes, the active power, reactive power, and voltage loops are activated step by step. Simultaneously, the receiving-end converter station activates the DC voltage outer loop, calibrating the operating voltage based on the rated DC voltage, and gradually switching back to the normal voltage control mode. This achieves a smooth transition from fault mode to normal mode, shortens system recovery time, and improves system operational stability. Attached Figure Description

[0016] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the description will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 Topology diagram of the DRU-HVDC power transmission system for new energy power plants; Figure 2 The original equivalent model diagram of the sending-end AC system under sending-end AC fault; Figure 3 This is an equivalent model diagram of the AC system at the sending end under AC fault after star topology transformation. Figure 4 This is an equivalent model diagram of a DC system; Figure 5 This is a schematic diagram of maximum power coordinated control during AC faults at the sending end. Figure 6 This is a schematic diagram of an electronic device. Detailed Implementation

[0018] like Figure 1 As shown, the AC fault ride-through control method for the new energy transmission system via DRU-HVDC provided by this invention is based on the new energy power plant, the sending-end diode rectifier station (DRU), and the receiving-end converter station constituting the new energy transmission system via DRU-HVDC. The new energy power plant transmits AC power through multiple AC lines. The sending-end rectifier station adopts a 12-pulse DRU, and the receiving-end converter station adopts a hybrid MMC. The mathematical model of the 12-pulse DRU is as follows: (1) (2) In the formula: α= R μ = ;β= ; X T This is the leakage reactance of the converter transformer referred to the valve side. K T For converter transformer turns ratio; U dc and I dc These represent the DC-side voltage and current of the DRU, respectively; U ac and I ac These are the effective values ​​of the phase voltage and phase current on the AC side, respectively.

[0019] According to equation (2), the DRU on the AC side is equivalent to a controlled current source, and the new energy power station is equivalent to a constant current source. Then, all healthy branches in the sending-end transmission line, except for the faulty branch, are connected in parallel and equivalent to a single branch, resulting in the following: Figure 2 The original equivalent model of the sending-end AC system under sending-end AC fault is shown. Figure 2 A Δ-Y transformation is performed on the triangular network consisting of healthy and faulty branches to obtain the following: Figure 3 The star-shaped equivalent circuit is shown. Figure 4 This is an equivalent model for a DC system.

[0020] The maximum active power transmitted to the receiving-end power grid during an AC fault at the sending end is: (3) The value of the system controllable variable corresponding to the maximum power point is: (4) In the formula, I re θ represents the output current amplitude of the new energy power station. re For the output current phase angle of the new energy power station, I re,max The maximum output current of the new energy power station; U dc0 I is the DC side voltage of the receiving-end converter station. dc R is the direct current; c and X c R represents the branch resistance and reactance on the fault resistance side after the star connection transformation of the sending-end AC line. b R is the branch resistance on the DRU side after the star connection transformation of the sending-end AC line. dc For the DC line resistance; φ = arctan(X) c / R), R=R c +R f R f For fault resistance; β= , is the ratio coefficient between the effective value of the AC side current and the DC side current of the DRU.

[0021] Under AC fault conditions at the sending end, there is a unique maximum power point in the system. When the control output current of the new energy power station and the control DC voltage or DC current of the receiving end converter station meet the operating conditions shown in equation (4), the DRU can be continuously turned on, and the DC channel can transmit the maximum active power to the receiving end grid.

[0022] The control commands, which select the output current of the renewable energy power plant and the DC current of the receiving-end converter station as control variables, and aim for maximum power transmission during AC faults at the sending end, and where neither the renewable energy power plant nor the receiving-end converter station needs fault information or communication, are as follows: (5) In the formula, and These are the reference values ​​for the d-axis and q-axis currents of the inner loop current of the converter on the new energy grid side, respectively. This is the reference value for the inner loop of DC current at the receiving-end converter station.

[0023] The specific implementation method of maximum power coordinated control is as follows: after an AC fault occurs at the sending end, the converter on the grid side of the new energy power station exits the active and reactive power loops and voltage loops under normal operation, retains the current inner loop, and directly transmits the current reference value. and Switching is performed according to equation (5), and the switching frequency reference value is the rated value ωN; the receiving-end converter station exits the DC voltage outer loop, retains the DC current inner loop, and sets the DC current reference value... Switch according to equation (5). A schematic diagram of maximum power coordinated control is shown below. Figure 5 As shown.

[0024] As an example of one implementation of the present invention, the complete implementation process of the AC fault ride-through control method at the sending end of the new energy transmission system via DRU-HVDC is as follows: 1. Upon detection of an AC fault at the sending end, maximum power coordinated control is executed without requiring fault information or communication. During the fault period, the renewable energy power station switches to maximum current output mode, and the receiving end converter station actively reduces the DC voltage to control the DC current to reach the commanded value, so that the DRU remains on during the fault period and achieves active power transmission close to the maximum value.

[0025] 2. After the fault is cleared, the output current of the new energy power station is first reduced to the rated value, and then the voltage loop, active power loop and reactive power loop are reconnected. At the same time, the receiving end converter station directly connects the DC voltage outer loop to control the DC voltage to recover to the rated value, thereby realizing a rapid recovery from the fault mode to the normal mode.

[0026] The following will describe in detail the AC fault ride-through control method at the sending end of the new energy transmission system via DRU-HVDC that relates to this application. Specific details, such as particular system structures and technologies, are presented for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of this application. However, those skilled in the art will understand that this application can also be implemented in other embodiments without these specific details.

[0027] It should be understood that, when used in this specification, the term "comprising" indicates the presence of the described feature, integral, step, operation, element, and / or component, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or collections thereof. The terms "comprising," "including," "having," and variations thereof all mean "including but not limited to," unless otherwise specifically emphasized.

[0028] The terms "one embodiment" or "some embodiments" used in this application mean that one or more embodiments of this application include the specific features, structures, or characteristics described in that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this application do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized.

[0029] The following are the specific steps of the AC fault ride-through control method at the sending end of the new energy transmission system via DRU-HVDC in a specific embodiment: S1: Detect the fault status of the AC side of the new energy transmission system via DRU-HVDC.

[0030] It should be noted that the new energy is transmitted through the DRU-HVDC system as follows: Figure 1 As shown, it mainly consists of a renewable energy power plant, a sending-end diode rectifier station (DRU), and a receiving-end converter station. The renewable energy power plant transmits AC power through multiple AC lines. The sending-end rectifier station uses a 12-pulse DRU, and the receiving-end converter station uses a hybrid MMC. In steady state, the renewable energy units adopt a grid-based control system of active power-voltage and reactive power-frequency, including a three-layer control loop of power-voltage-current. The receiving-end converter station uses constant DC voltage control to maintain the stability of the DC line.

[0031] The mathematical model for a 12-pulse DRU is: (6) (7) Furthermore, the original equivalent model of the sending-end AC system under sending-end AC fault is as follows: Figure 2 As shown. All healthy branches in the sending-end transmission line are connected in parallel and equivalent to a single branch, with Z0 = R0 + jX0 being the equivalent impedance of the healthy branch; faulty branches are segmented according to the fault point, with equivalent impedances Z1 = R1 + jX1 and Z2 = R2 + jX2; R f This is the resistance for grounding faults.

[0032] According to equation (7), the DRU on the AC side is equivalent to a controlled current source, and the new energy power station is equivalent to a constant current source. (See figure.) and These are the voltage and current phasors output by the new energy power station, P. re The active power generated by the new energy power station; and These are the voltage and current phasors on the AC side of the DRU, respectively, P dr The active power transmitted by the DRU can be considered equal to the active power on the AC side and the DC side of the DRU.

[0033] Will Figure 2 A Δ-Y transformation is performed on the triangular network consisting of Z0, Z1, and Z2 to obtain the following: Figure 3 The star-shaped equivalent circuit is shown.

[0034] In the picture: Z is the voltage phasor at the center point of the star circuit; a =R a +jX a For the impedance of the new energy side bridge arm; Z b =R b +jX b For the DRU side bridge arm impedance; Z c=R c +jX c The intermediate branch impedance and the fault resistance R are given. f Connected in series and then grounded. Denote Z. ∑ =Z0+Z1+Z2, then Z a Z b and Z c The relationship between the impedances and those in the original triangular network is as follows: (8) DC system equivalent model as follows Figure 4 As shown. According to equation (6), the DRU is equivalent to a controlled voltage source αU on the DC side. ac With series equivalent resistance R μ The receiving-end converter station is equivalent to a DC voltage source. In the diagram: U dc0 P is the DC voltage at the receiving end. s R represents the active power transferred to the receiving-end power grid. dc This is the equivalent resistance of a DC line.

[0035] Furthermore, in Figure 3 In this context, the output current phasor of the new energy unit is taken as the reference phasor, and θ is set as follows: re =0°. Define the impedance between the star's center point and ground as Z. f =Z c +R f =R+jX c In the formula, R=R c +R f The voltage at the center point of the star configuration is: (9) During the fault, the AC side voltage of the DRU was: (10) because and Let and be the effective values ​​of the phase voltage and phase current, respectively. Then, the active power absorbed by the DRU can be expressed as: (11) exist Figure 3 In the DC system model shown, the power P transmitted to the receiving-end grid is... s for: (12) From the above formula, it can be seen that P s with I dc The relationship is that of a parabola opening downwards, when I re Take the maximum value I re,max At that time, the maximum active power transmitted to the receiving-end power grid under fault conditions can be obtained as follows: (13) The value of the system controllable variable corresponding to the maximum power point is: (14) As can be seen from the above analysis, there is a unique maximum power point in the system under AC fault at the sending end. When the control output current of the new energy power station and the control DC voltage or DC current of the receiving end converter station meet the operating conditions shown in equation (14), the DRU can be continuously turned on, and the DC channel can transmit the maximum active power to the receiving end grid.

[0036] In equation (14), the expressions for the DC voltage and DC current of the receiving-end converter station both include R (R=R). c +R f ) and cos(θ) ac -φ) Two items, in actual engineering, it is necessary to measure the fault resistance R. f and the phase angle θ of the AC side current of the DRU ac The command value is then sent to the receiving converter station via communication to calculate the command value.

[0037] Fault information is difficult to obtain in a timely and accurate manner, and the introduction of communication introduces transmission delays, thereby reducing control effectiveness. Therefore, it is necessary to approximate the relevant controllable variables to eliminate the impact of fault information and communication.

[0038] The expression for DC current in equation (14) is simplified by approximation. Where R = R c +R f Because of R f Since the line parameters are relatively large, the terms related to line parameters and fault resistance in the numerator and denominator of the expression can be simplified: (15) Further analysis of the cosine term cos(θ) ac Simplify by -φ). The fundamental power factor angle on the DRU AC side is φ. dr The AC side voltage phasor of the DRU can be expressed as: Substituting this into equation (10) yields (16) Due to Z f =R+jX c Its impedance angle is φ = arctan(X). c / R), then the above formula can be further expressed as (17) Multiply both sides of the equation by e -jθac ,have to (18) Comparing the real and imaginary parts on both sides of the equation above, we have: (19) Dividing the two equations, we get (20) Because (X) c +X b ) is very small relative to R, and cosφ dr Greater than sinφ dr Therefore, it can be assumed that the numerator of the above equation is much smaller than the denominator, tan(φ-θ) ac It is close to 0.

[0039] From cos(θ) ac -φ) and cos(φ-θ) ac Equal to (twenty one) Because tan(φ-θ ac Since θ is close to 0, we can consider cos(θ) to be close to 0. ac -φ) is approximately equal to 1.

[0040] Based on the above analysis, the simplified result of the DC current expression in equation (9) is as follows: (twenty two) Compared to equation (14), the simplified expression above does not include fault information and sending-end current parameters. It can be directly used as the control command for the DC current inner loop of the receiving-end converter station. In engineering applications, it can achieve maximum power transmission without real-time measurement of relevant parameters and long-distance communication.

[0041] S2: When step S1 detects an AC fault at the sending end, the grid-side converter of the new energy power station exits the active power loop, reactive power loop, and voltage loop under normal operation, retains the current inner loop control, switches the d-axis current reference value of the current inner loop to the maximum output current of the new energy power station, switches the q-axis current reference value to zero, and switches the frequency reference value to the rated frequency.

[0042] S3: Synchronous control of the receiving-end converter station exits the DC voltage outer loop under normal operation, retains the DC current inner loop control, and switches the reference value of the DC current inner loop to the preset fault ride-through DC current reference value.

[0043] S4: During the duration of the AC fault at the sending end, maintain the continuous conduction of the diode rectifier station and transmit active power to the receiving end grid.

[0044] S5: Real-time monitoring of the clearing status of the AC fault at the sending end during the duration of the AC fault.

[0045] S6: When the AC fault at the sending end is detected to be cleared, the reference value of the d-axis current of the converter on the grid side of the new energy power station is reduced from the maximum output current in step S2 to the rated current value. After the output current is reduced to the rated current value, the active power loop, reactive power loop and voltage loop are re-engaged to restore the normal operation control mode.

[0046] S7: Synchronized with step S6, control the receiving-end converter station to directly engage the DC voltage outer loop, restore the DC voltage to the rated value, switch back to the normal operating constant DC voltage control mode, and complete the AC fault ride-through at the sending end.

[0047] In some specific embodiments, based on step S1, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0048] S11: The instantaneous value of the three-phase voltage of the new energy power station's outlet bus is collected, and the effective value of the AC voltage and its rate of change are calculated. When the rate of change is negative and the effective value is lower than the normal operating voltage threshold, it is determined that an AC fault has occurred at the sending end. S12: The receiving-end converter station collects the instantaneous value of the DC side current and calculates the rate of change of the DC current. When the rate of change is negative and the DC current is higher than the normal operating current threshold, it is determined that an AC fault has occurred at the sending end. S13: The new energy power station and the receiving-end converter station output fault signals according to their respective local judgment results, and switch to fault control mode at the same time.

[0049] In some embodiments, the renewable energy power station continuously monitors the three-phase voltage of the outlet bus and calculates the effective value of the AC voltage and the rate of change of the effective value over time. When the rate of change of the effective voltage is negative, it indicates that the voltage is dropping rapidly. When the effective value is lower than a preset normal operating voltage threshold, the renewable energy power station determines that a fault has occurred on the AC side of the sending end.

[0050] The receiving-end converter station continuously monitors the DC-side current and calculates the rate of change of the DC current. When the rate of change of the DC current is negative and the instantaneous value of the DC current is higher than the normal operating current threshold, the receiving-end converter station also determines that a fault has occurred on the sending-end AC side. After the new energy power plant and the receiving-end converter station obtain their local fault determination results, both output fault signals and switch their respective control systems from normal operating mode to fault control mode. In some specific embodiments, based on step S2, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0051] S21: After step S1 outputs the AC fault judgment signal, the enable terminals of the active power loop, reactive power loop, and voltage loop of the converter on the grid side of the new energy power station are set to low level, and the output control signals of the three control loops are cut off; the enable terminal of the current inner loop is set to high level to keep the current inner loop signal path unobstructed.

[0052] S22: Call the maximum output current parameter I pre-stored in the grid-side converter of the new energy power station. re,max The value is assigned to the d-axis current reference value register of the inner current loop, and the q-axis current reference value register of the inner current loop is set to zero, thus completing the switching of the reference value of the inner current loop.

[0053] S23: Retrieve the system's pre-stored rated frequency, configure it to the frequency reference value register of the new energy power station's grid-side converter, overwrite the frequency reference value during normal operation, and lock the frequency reference value until a fault clearing signal is received and then unlocked.

[0054] In some embodiments, the active power loop, reactive power loop, and voltage loop of the grid-side converter in a new energy power station are all equipped with enable control terminals. The fault determination signal is a high-level trigger signal. When the high-level trigger signal is input, the enable terminals of the three control loops are synchronously set low, cutting off the output signals of their respective PI regulators and stopping the output of control commands to the converter switching devices. The enable terminal of the current inner loop is linked with the fault determination signal and is synchronously set high when a fault occurs, maintaining the normal operation of its PI regulator and signal feedback path, ensuring that the current inner loop independently undertakes the control task of the converter and does not cause signal interference with the other three control loops.

[0055] In step S22, the maximum output current I of the grid-side converter of the new energy power station re,max These are inherent parameters of the converter, determined based on the converter's power rating and device rated current. They are pre-stored in the converter controller's registers. When a fault occurs, the controller retrieves these parameters and writes them into the d-axis current reference register of the inner current loop. The q-axis current reference register is directly set to zero to ensure no current output on the q-axis.

[0056] The reference value switching process can be based on current control at renewable energy power plants. The current control command for the grid-side converter is as follows: (twenty three) In the formula, I re,max This represents the maximum output current of the grid-side converter for new energy sources. I * re,d and I* re and q are the reference values ​​for the d-axis and q-axis currents of the inner current loop of the new energy grid-side converter, respectively. Here, the requirements for setting the reference values ​​of the d-axis and q-axis of the inner current loop under fault conditions are clarified. The d-axis current reference value can enable the new energy power station to output the maximum active power, and the q-axis current reference value is set to zero. During the fault, the pre-stored parameters are retrieved and processed according to formula (23), which can quickly realize the switching of the current control mode.

[0057] In some specific embodiments, based on step S3, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0058] S31: Synchronously receive the AC fault trigger command output in step S1, perform a blocking operation on the regulation link of the DC voltage outer loop of the receiving end hybrid MMC converter station, and cut off the signal transmission channel from the DC voltage outer loop regulator to the lower-level control unit.

[0059] S32: Maintain the connection between the DC current inner loop sampling circuit and the regulation circuit of the receiving-end converter station, and do not apply blocking or disconnection operations to the signal acquisition and calculation output link of the DC current inner loop.

[0060] S33: Recall the setpoint parameters stored in the receiver-end converter station controller, based on... It overwrites the original reference value of the DC current inner loop and locks the real-time modification permission of the reference value.

[0061] In some embodiments, during step S32, the DC-side current sampling sensor, signal filtering circuit, proportional-integral (PI) arithmetic module, and pulse modulation execution circuit of the DC current inner loop of the receiving-end converter station remain in a continuously connected state, without any circuit disconnection, parameter freezing, or mode restriction being executed upon fault triggering command. The DC-side current sampling sensor continuously collects real-time current data of the DC line, which, after processing by the signal filtering circuit, is directly sent to the feedback input terminal of the PI arithmetic module of the DC current inner loop. This enables the PI arithmetic module to continuously obtain the actual current value, ensuring the integrity of the signal path for closed-loop regulation and preventing interruption of the entire data flow from sampling to pulse modulation.

[0062] In step S33, the fault ride-through DC current reference value is determined in advance based on... After completing offline tuning and storage, the parameters are directly retrieved upon fault triggering, written to the reference value register of the DC current inner loop, and the hardware write protection enable bit of the register is set to 1 to prevent any subsequent operation from modifying the value of the register.

[0063] In some specific embodiments, based on step S4, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0064] S41: During the continuous period of AC fault at the sending end, the grid-side converter of the new energy power station continuously collects real-time d-axis current and q-axis current sampling signals. Based on the reference value of d-axis and q-axis 0 set in step S22, and the real-time phase defined in step S23 as the synchronization reference, the current closed-loop following adjustment is executed cycle by cycle. The remote scheduling signal and the fault parameter data at the sending end are not received.

[0065] S42: During the synchronization period, the receiving end hybrid MMC converter station continuously acquires the real-time current sampling signal of the DC loop, and completes the DC current closed-loop correction and adjustment based on the locked fault ride-through DC current reference setpoint.

[0066] S43: Based on the proportional constraint formula of AC side current and DC side current of 12-pulse DRU Based on the set output current of the new energy side and the set DC current Under the influence of this, the AC side current of the DRU satisfies:

[0067] Impedance parameters after star-equivalent configuration of the sending-end AC network This ensures that the active power transmitted by the system to the receiving-end grid during a fault falls near the maximum power point determined by the following formula:

[0068] Maintain continuous conduction of the diode rectifier valve group at the sending end, and prevent blockage.

[0069] In some embodiments, the new energy side adopts a fixed d-axis full-amplitude and q-axis zero-current output, eliminating the complex calculations of the power loop and voltage loop during transient processes, resulting in a fast response speed. The receiving end uses a constant DC current command, eliminating the need for real-time measurement of difficult-to-obtain fault variables such as fault resistance and AC side phase angle, thus reducing the computational load.

[0070] In some specific embodiments, based on step S5, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0071] S51: During the continuous AC fault at the sending end, the multi-channel sampling circuits of the AC outgoing line, DRU AC side bus, and DC outgoing line of the new energy power station are kept in operation for a long time to continuously and synchronously collect the real-time sampling of three-phase electrical data at each point.

[0072] S52: Retrieve DRU's inherent parameters based on real-time acquired AC and DC side operating data. Complete the theoretical numerical recalculation of the DC side and retain the original difference data for each set of calculations.

[0073] S53: Continuously accumulate AC voltage amplitude data and AC / DC difference data for multiple power frequency cycles, respectively, and compare them with the locally pre-stored steady-state threshold range. Based on the data convergence status, generate a fault clearing determination trigger signal.

[0074] In some embodiments, step S51, based on the sampling point layout of step S1, ensures that the sampling channels are not reduced and the signal acquisition process is not paused throughout the entire operation of the fault collaborative control in step S4. The current and voltage sensing circuits of the AC bus, the 12-pulse DRU AC side bus, and the DRU DC outgoing line of the new energy power station remain connected throughout the entire process. The original electrical analog quantities are synchronously captured according to a fixed power frequency cycle. The entire process does not rely on external auxiliary detection devices, but only on the system's existing measurement hardware to complete continuous data acquisition. In step S52, the fixed values ​​of α and Rμ determined by the inherent parameters of the converter transformer are used, and no real-time parameter correction is performed. The effective value of the DRU AC side voltage Uac and the effective value of the DC side current I collected in each cycle are... dc Substitution The theoretical calculation value of the DC-side voltage is solved successively. The difference between the theoretical calculation value and the measured value of the DC-side voltage on site is calculated, and the original deviation value is directly stored without applying smoothing filtering or compensation correction. In step S53, the amplitude distribution range of the AC-side voltage of the new energy power station and DRU is sorted out and statistically analyzed using multiple consecutive power frequency durations as statistical units. The calculated AC / DC voltage difference fluctuation range is used to bind the AC voltage amplitude and numerical deviation to preset steady-state allowable ranges. Only when both sets of data fall within the threshold range simultaneously, the internal level signal is flipped, and a valid AC fault clearing command is output to the sending end. In this way, misjudgments and malfunctions caused by transient impacts at the moment the fault disappears are effectively avoided, and there is no long-distance communication interaction throughout the process.

[0075] In some specific embodiments, based on step S6, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0076] S61: Receive the AC fault clearing feedback signal output in step S5, release the locking restriction of the d-axis current reference value of the grid-side converter of the new energy power station, gradually reduce the d-axis current reference value with a fixed step size, and keep the q-axis current reference value constant throughout the process.

[0077] S62: During the entire process of adjusting the d-axis current reference value, the actual d-axis operating current of the grid-side converter of the new energy power station is continuously collected, and the measured current data is continuously compared and calculated with the locally fixed rated current value in real time to keep the inner loop current regulation link working continuously.

[0078] S63: After the actual d-axis operating current stabilizes within the rated current range, the active power loop, reactive power loop, and voltage loop are unlocked one by one in the preset order, and the control output links of each outer loop are turned on step by step.

[0079] In some specific embodiments, based on step S7, the following will provide a possible embodiment and describe its specific implementation in a non-limiting manner.

[0080] S71: Cancel the DC current inner loop reference value lock set in step S33, remove the DC voltage outer loop blocking level signal, and connect all signal paths from the DC voltage outer loop regulator to the internal control execution loop of the receiving-end converter station.

[0081] S72: Retrieve the locally preset rated DC voltage of the receiving-end converter station, use the rated DC voltage as the reference value of the outer loop of DC voltage, and continuously collect the actual operating voltage signal of the DC line.

[0082] S73: The DC line operating voltage is calibrated based on the rated DC voltage to lock the control operation mode under normal operating conditions of the converter station.

[0083] In some embodiments, the fixed parameters of the rated DC voltage stored in the receiving-end converter station are called and written into the voltage outer loop setpoint register. Measured data of the DC-side outgoing line voltage of the DRU are continuously collected, and the difference between the setpoint value and the sampled value is calculated in real time. In step S73, combined with... Under the constraint that the DC voltage at the receiving end stabilizes, the DRU rectifier output state can be stabilized in reverse, and in conjunction with the multi-loop coordinated control restored by S6 at the sending-end renewable energy power station, a steady-state transmission link can be re-established. This method involves minimal control modifications, orderly transitions the fault control strategy to a normal, stable state, avoids sudden rises and falls in DC voltage caused by hard switching of control modes, and achieves closed-loop operation through AC faults at the sending end.

[0084] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0085] like Figure 6 As shown, this application also provides an electronic device, including a display module 103, a memory 102, a processor 101, a communication module 104, and a computer program stored in the memory and executable on the processor 101. When the processor 101 executes the program, it implements the steps of the AC fault ride-through control method for the sending end of the new energy transmission system via DRU-HVDC.

[0086] In embodiments of the present invention, electronic devices include, but are not limited to, laptop computers, desktop computers, workstations, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. Electronic devices may also represent various forms of mobile devices, such as personal digital processors, cellular phones, smartphones, wearable devices, and other similar computing devices. The components shown herein, their connections and relationships, and their functions are merely examples and are not intended to limit the implementation of the embodiments described and / or claimed herein.

[0087] In this embodiment, processor 101 may be implemented using at least one of an application-specific integrated circuit, a programmable logic device, a field-programmable gate array, a processor, a controller, a microcontroller, a microprocessor, or an electronic unit designed to perform the functions described herein. In some cases, such an implementation may be implemented within a controller. For software implementation, implementations such as processes or functions may be implemented with separate software modules that allow the performance of at least one function or operation. Software code may be implemented by a software application (or program) written in any suitable programming language, and the software code may be stored in memory and executed by the controller.

[0088] The display module 103 is used to display information input by the user or information provided to the user. The display module 103 may include a display panel, which may be configured in the form of a liquid crystal display, an organic light-emitting diode, or the like.

[0089] The memory 102 can be used to store software programs and various data. The memory 102 may include high-speed random access memory, and may also include non-volatile memory, such as at least one disk storage device, flash memory device, or other volatile solid-state storage device.

[0090] The communication module 104 transmits radio signals to and / or receives radio signals from at least one of a base station, an external terminal, and a server. Such radio signals may include voice call signals, video call signals, or various types of data sent and / or received according to text and / or multimedia messages.

[0091] The present invention also provides a storage medium storing a computer program thereon, wherein when the computer program is executed by a processor, the steps of the AC fault ride-through control method of the new energy transmission system via DRU-HVDC are implemented.

[0092] The storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example,, but not limited to, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any combination thereof. More specific examples (a non-exhaustive list) of readable storage media include: electrical connections having one or more wires, portable disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage devices, magnetic storage devices, or any suitable combination thereof.

[0093] The storage medium stores a program product capable of implementing the methods described above in this specification. In some possible implementations, various aspects of this disclosure may also be implemented as a program product comprising program code that, when run on a terminal device, causes the terminal device to perform the steps described in the "Exemplary Methods" section of this specification according to various exemplary embodiments of this disclosure.

[0094] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for AC fault ride-through control of a new energy sending terminal of a DRU-HVDC sending system, characterized in that the method comprises the steps of include: S1: Detect the fault status on the AC side of the new energy transmission system via DRU-HVDC; S2: When an AC fault is detected at the sending end, the grid-side converter of the new energy power station is controlled to exit the active power loop, reactive power loop and voltage loop under normal operation, while retaining the current inner loop control. The d-axis current reference value of the current inner loop is switched to the maximum output current of the new energy power station, the q-axis current reference value is switched to zero, and the frequency reference value is switched to the rated frequency. S3: Synchronous control of the receiving-end converter station exits the DC voltage outer loop under normal operation, retains the DC current inner loop control, and switches the reference value of the DC current inner loop to the preset fault ride-through DC current reference value. S4: During the duration of the AC fault at the sending end, maintain the continuous conduction of the diode rectifier station and transmit active power to the receiving end grid; S5: Real-time detection of the clearing status of AC faults at the sending end; S6: When the AC fault at the sending end is detected to be cleared, the reference value of the d-axis current of the converter on the grid side of the new energy power station is reduced from the maximum output current in step S2 to the rated current value. After the output current is reduced to the rated current value, the active power loop, reactive power loop and voltage loop are re-engaged to restore the normal operation control mode. S7: Synchronously control the receiving-end converter station to directly engage the DC voltage outer loop, restore the DC voltage to the rated value, switch back to the normal operating constant DC voltage control mode, and complete the AC fault ride-through at the sending end.

2. The method of claim 1, wherein the method further comprises: S1 specifically includes the following steps: S11: The instantaneous value of the three-phase voltage of the new energy power station's outlet bus is collected, and the effective value of the AC voltage and its rate of change are calculated. When the rate of change is negative and the effective value is lower than the normal operating voltage threshold, it is determined that an AC fault has occurred at the sending end. S12: The receiving-end converter station collects the instantaneous value of the DC side current and calculates the rate of change of the DC current. When the rate of change is negative and the DC current is higher than the normal operating current threshold, it is determined that an AC fault has occurred at the sending end. S13: The new energy power station and the receiving-end converter station output fault signals according to their respective local judgment results, and switch to fault control mode at the same time. 3.The new energy system through DRU-HVDC sending end AC fault ride through control method of claim 1, characterized in that, S2 specifically includes the following steps: S21: After step S1 outputs the AC fault judgment signal at the sending end, the enable terminals of the active power loop, reactive power loop, and voltage loop of the converter on the grid side of the new energy power station are set to low level, and the output control signals of the three control loops are cut off; the enable terminal of the current inner loop is set to high level to keep the control signal path of the current inner loop unobstructed. S22: call the maximum output current parameter I pre-stored by the new energy station grid-side converter re,max , assign it to the d-axis current reference value register of the current inner loop, set the q-axis current reference value register of the current inner loop to zero, complete the switching of the current inner loop reference value; S23: Retrieve the system's pre-stored rated frequency, configure it to the frequency reference value register of the new energy power station's grid-side converter, overwrite the frequency reference value during normal operation, and lock the frequency reference value until a fault clearing signal is received and then unlocked.

4. The method of claim 1, wherein the method further comprises: S3 specifically includes the following steps: S31: Synchronously receive the AC fault trigger command output in step S1, perform a blocking operation on the regulation link of the DC voltage outer loop of the receiving end hybrid MMC converter station, and cut off the signal transmission channel from the DC voltage outer loop regulator to the lower-level control unit. S32: Maintain the connection between the DC current inner loop sampling circuit and the regulation circuit of the receiving-end converter station, and do not apply blocking or disconnection operations to the signal acquisition and calculation output link of the DC current inner loop. S33: call the constant value parameters stored in the receiving end converter station controller, and modify the real-time reference value according to , the original reference value of the DC current inner loop is covered, and the real-time modification authority of the reference value is locked. wherein I re,max is the maximum output current of the new energy station, is the reference value of the DC current inner loop of the receiving end converter station, and β is the proportional coefficient of the effective value of the AC side current of the DRU and the DC side current.

5. The method of claim 3, wherein the method further comprises: S4 specifically includes the following steps: S41: During the continuous period of AC fault at the sending end, the grid-side converter of the new energy power station continuously collects real-time d-axis current and q-axis current sampling signals. Based on the reference value of d-axis and q-axis 0 set in step S22, and the real-time phase output of the phase-locked loop defined in step S23 as the synchronization reference, the current closed-loop following adjustment is executed cycle by cycle. S42: During the synchronization period, the receiving end hybrid MMC converter station continuously collects the real-time current sampling signal of the DC loop, and completes the DC current closed-loop correction and adjustment based on the locked fault ride-through DC current reference setpoint. S43: the pulsation DRU AC side current and the DC side current according to the proportion constraint formula 12 , based on the set new energy side output current and the set DC current , the DRU AC side current satisfies: Impedance parameters of the star equivalent of the sending end ac network R = R c + R f to make the DRU actual operating point fall near the maximum power point determined by the following formula: Maintain all rectifier valve groups continuously conducting; R f For fault resistance, R c And X c For fault resistance, 6. The method of claim 1, wherein the method further comprises: S5 specifically includes the following steps: S51: During the continuous AC fault at the sending end, keep the multi-channel sampling circuits of the AC outgoing line, DRU AC side bus, and DC outgoing line of the new energy power station in operation for a long time, and continuously and synchronously collect the real-time sampling of three-phase electrical data at each point. S52: retrieve DRU inherent parameters, based on real-time collected AC side and DC side operation data, retrieve complete DC side theoretical numerical recalculation; S53: Continuously accumulate AC voltage amplitude data and AC / DC difference data for multiple power frequency cycles, respectively, and compare them with the locally pre-stored steady-state threshold range. Based on the data convergence status, generate a fault clearing determination trigger signal.

7. The method of claim 1, wherein the method further comprises: S6 specifically includes the following steps: S61: Receive the AC fault clearing feedback signal output in step S5, release the locking restriction of the d-axis current reference value of the grid-side converter of the new energy power station, gradually reduce the d-axis current reference value with a fixed step size, and keep the q-axis current reference value constant throughout the process. S62: During the entire process of adjusting the d-axis current reference value, the actual d-axis operating current of the converter on the grid side of the new energy power station is continuously collected, and the measured current data is continuously compared and calculated with the locally fixed rated current value in real time to keep the current inner loop regulation link working continuously. S63: After the actual d-axis operating current stabilizes within the rated current range, the active power loop, reactive power loop, and voltage loop are unlocked one by one in the preset order, and the control output links of each outer loop are turned on step by step.

8. The method of claim 1, wherein the method further comprises: S7 specifically includes the following steps: S71: Cancel the setting of the DC current inner loop reference value lock, remove the DC voltage outer loop blocking level signal, and connect all signal paths from the DC voltage outer loop regulator to the internal control execution loop of the receiving-end converter station. S72: Retrieve the locally preset rated DC voltage of the receiving-end converter station, use the rated DC voltage as the reference value of the DC voltage outer loop, and continuously collect the actual operating voltage signal of the DC line. S73: The DC line operating voltage is calibrated based on the rated DC voltage to lock the control operation mode under normal operating conditions of the converter station.

9. An electronic device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the program, it implements the steps of the AC fault ride-through control method for the sending end of the new energy transmission system via DRU-HVDC as described in any one of claims 1 to 8.

10. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the steps of the AC fault ride-through control method for the new energy transmission system via DRU-HVDC as described in any one of claims 1 to 8.

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