Current fault control method and device based on offshore wind power sending-out system, terminal equipment and storage medium

Abstract

The invention discloses a current fault control method and device based on an offshore wind power transmission system, terminal equipment and a storage medium, the direct current of the offshore wind power transmission system can be monitored in real time, when the direct current exceeds a preset current threshold value, the reference voltage of the q axis is set to be zero, and the current fault of the offshore wind power transmission system is controlled. Therefore, reactive power output of the system can be quickly limited during a fault period, fluctuation of system voltage is reduced, and q-axis reference voltage can be gradually increased according to a preset voltage step length in each fault control process of voltage and current adjustment, so that the fault control accuracy is improved. Therefore, the P I controller can accurately adjust and output current reference values of the q axis and the d axis according to the voltage difference value, and direct control over the voltage and the current is achieved according to the PWM modulation reference signal. The reactive power output of the system can be effectively limited, the voltage fluctuation of the system can be reduced, the fault current can be quickly responded and controlled, and the safety and the stability of the offshore wind power delivery system are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of current fault control, and in particular to a current fault control method, device, terminal equipment and storage medium based on an offshore wind power transmission system. Background Art

[0002] As one of the key equipment in the flexible DC transmission project of offshore wind power transmission system, the HB-MMC can realize the coordinated control of offshore wind power transmission system. When a short circuit fault or current fault occurs in the offshore wind power transmission system, the fault current will rise rapidly. If it is not controlled, the AC component may aggravate the fluctuation of the fault current and cause greater impact on the system. After the current fault is detected, the switching state of the converter is often adjusted to isolate the fault area from the system. During the fault isolation period, in order to prevent the fault current from further expanding, it is necessary to control the AC phase voltage on the AC side corresponding to the offshore wind power transmission system. By controlling the AC phase voltage on the AC side, the current on the AC side can be indirectly affected, thereby achieving effective control of the fault current.

[0003] However, when controlling the fault current during fault isolation, the existing technology often controls the voltage on the AC side based on the traditional current and voltage dual closed-loop control method, and only adjusts the voltage and current on the AC side based on the difference between the fixed reference AC phase voltage and the actual AC phase voltage on the AC side. It is impossible to quickly limit the reactive output of the system, which increases the system voltage fluctuation and makes it impossible to quickly respond to and control the fault current, resulting in low safety and stability of the offshore wind power transmission system. Summary of the invention

[0004] The embodiments of the present invention provide a current fault control method, apparatus, terminal equipment and storage medium based on an offshore wind power transmission system, which can quickly limit the reactive output of the system during a fault and reduce the fluctuation of the system voltage, so that the PI controller can accurately adjust the output q-axis and d-axis current reference values ​​according to these voltage differences, thereby reducing the impact of the fault current on the system, and can effectively solve the problems in the prior art that the reactive output of the system cannot be quickly limited, resulting in increased system voltage fluctuations, inability to quickly respond to and control fault currents, and low system safety and stability.

[0005] An embodiment of the present invention provides a current fault control method based on an offshore wind power transmission system, comprising:

[0006] Obtain the DC current corresponding to the offshore wind power transmission system at the current moment;

[0007] When it is determined that the DC current is greater than a preset current threshold, setting the q-axis reference voltage to zero;

[0008] Repeat the following fault control operations until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage:

[0009] The AC phase voltage currently corresponding to the AC side is obtained, and then the AC phase voltage is subjected to synchronous rotation coordinate transformation to generate the q-axis actual voltage component and the d-axis actual voltage component;

[0010] Increase the q-axis reference voltage according to a preset voltage step to generate an updated q-axis reference voltage;

[0011] Inputting the updated first voltage difference between the q-axis reference voltage and the q-axis actual voltage component and the updated second voltage difference between the d-axis reference voltage and the d-axis actual voltage component into the first PI controller respectively, so that the first PI controller performs proportional and integral adjustment according to each voltage difference, and outputs the q-axis current reference value and the d-axis current reference value;

[0012] Inputting the q-axis current reference value and the d-axis current reference value into the current inner loop respectively, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side;

[0013] The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotation coordinate transformation to generate a voltage reference signal; the voltage reference signal is then subjected to PWM modulation to generate a PWM modulation reference signal; wherein the PWM modulation reference signal is used to control the output voltage and output current of the driving switch device.

[0014] Preferably, before setting the q-axis reference voltage to zero, the method further comprises:

[0015] Subtracting the DC current from the rated DC current to generate a current deviation;

[0016] Inputting the current deviation into a second PI controller, so that the second PI controller performs proportional and integral regulation according to the current deviation and outputs a voltage control signal;

[0017] The voltage of the DC power supply or the inverter is adjusted according to the voltage control signal.

[0018] Preferably, when it is determined that the direct current is greater than a preset current threshold, the method further includes:

[0019] Obtaining an actual DC component in the DC current;

[0020] Subtract the rated DC current from the actual DC component to obtain a deviation of the DC component;

[0021] Inputting the deviation of the DC component into a third PI controller so that the third PI controller outputs a voltage deviation value;

[0022] Subtract the voltage deviation value from the DC voltage in the current DC signal on the DC side to generate a DC reference signal;

[0023] A PWM DC reference signal for adjusting the DC side voltage is generated according to the DC reference signal.

[0024] Preferably, the obtaining of the direct current corresponding to the offshore wind power transmission system at the current moment includes:

[0025] Obtain the voltage change rate of the DC reactor of the offshore wind power transmission system;

[0026] When it is determined that the voltage change rate is greater than a preset change rate range, obtaining a voltage fluctuation amplitude of the system;

[0027] When it is determined that the voltage fluctuation amplitude is less than a preset minimum voltage point, marking the line where the DC reactor is located as a fault line;

[0028] Obtain the direct current corresponding to the fault line at the current moment.

[0029] Preferably, before setting the q-axis reference voltage to zero, the method further comprises:

[0030] Disconnecting the DC circuit breaker on the DC side of the onshore converter in the faulty line;

[0031] Determining whether the DC voltage in the faulty line is less than a preset DC voltage value;

[0032] If so, disconnect the AC circuit breaker on the AC side of the offshore converter in the faulty line.

[0033] Preferably, it also includes:

[0034] When it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is closed, and the voltage on the AC side is lower than the preset voltage threshold, the DC current value corresponding to the offshore converter is used as the upper limit value of the current dynamic limiter;

[0035] When it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is disconnected, the real-time voltage on the AC side is obtained;

[0036] The real-time voltage is compared with a preset voltage reference value, and the input amount of the reactive power compensation device of the offshore converter is adjusted according to the comparison result to achieve closed-loop control of the AC side voltage.

[0037] Preferably, it also includes:

[0038] Compare the DC voltage on the DC side of the offshore converter in the faulty line with the DC voltage of other lines in the offshore wind power transmission system;

[0039] When the comparison result is determined to be equal voltages, the DC circuit breaker on the DC side of the onshore converter in the faulty line is closed, and then the AC circuit breaker on the AC side of the offshore converter is closed.

[0040] Based on the above method embodiments, the present invention provides corresponding device embodiments.

[0041] An embodiment of the present invention provides a current fault control device based on an offshore wind power transmission system, which is applicable to an offshore wind power transmission system;

[0042] The current fault control device comprises: a direct current acquisition module, a reference voltage setting module and a fault control operation module;

[0043] The DC current acquisition module is used to acquire the DC current corresponding to the offshore wind power transmission system at the current moment;

[0044] The reference voltage setting module is used to set the q-axis reference voltage to zero when it is determined that the DC current is greater than a preset current threshold;

[0045] The fault control operation module is used to repeatedly perform the following fault control operations until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage:

[0046] The AC phase voltage currently corresponding to the AC side is obtained, and then the AC phase voltage is subjected to synchronous rotation coordinate transformation to generate the q-axis actual voltage component and the d-axis actual voltage component;

[0047] Increase the q-axis reference voltage according to a preset voltage step to generate an updated q-axis reference voltage;

[0048] Inputting the updated first voltage difference between the q-axis reference voltage and the q-axis actual voltage component and the updated second voltage difference between the d-axis reference voltage and the d-axis actual voltage component into the first PI controller respectively, so that the first PI controller performs proportional and integral adjustment according to each voltage difference, and outputs the q-axis current reference value and the d-axis current reference value;

[0049] Inputting the q-axis current reference value and the d-axis current reference value into the current inner loop respectively, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side;

[0050] The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotation coordinate transformation to generate a voltage reference signal; the voltage reference signal is then subjected to PWM modulation to generate a PWM modulation reference signal; wherein the PWM modulation reference signal is used to control the output voltage and output current of the driving switch device.

[0051] Based on the above method embodiments, the present invention provides corresponding terminal device embodiments.

[0052] Another embodiment of the present invention provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, and when the processor executes the computer program, it implements the current fault control method based on the offshore wind power transmission system described in the above-mentioned embodiment of the invention.

[0053] Based on the above method embodiments, the present invention provides corresponding storage medium item embodiments.

[0054] Another embodiment of the present invention provides a storage medium, wherein the computer-readable storage medium includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute a current fault control method based on an offshore wind power transmission system as described in the above-mentioned embodiment of the invention.

[0055] The following beneficial effects are achieved by implementing the present invention:

[0056] The embodiment of the present invention provides a current fault control method, device, terminal equipment and storage medium based on an offshore wind power transmission system. The present invention can monitor the DC current of the offshore wind power transmission system in real time. When the DC current exceeds a preset current threshold, the reference voltage of the q-axis (reactive axis) is set to zero, so that the reactive output of the system can be quickly limited during the fault period, and the fluctuation of the system voltage can be reduced. In addition, in each fault control process of adjusting the voltage and current, the AC phase voltage currently corresponding to the AC side is continuously obtained, and a synchronous rotating coordinate transformation is performed to generate the actual voltage components of the q-axis and the d-axis (active axis), and the q-axis reference voltage is gradually increased according to a preset voltage step size, so that each time the first voltage difference between the q-axis actual voltage component and the d-axis reference voltage adjusted by the preset step size can be obtained, and the second voltage difference between the d-axis reference voltage and the d-axis actual voltage component can be obtained, so that the PI controller can accurately adjust the output q-axis and d-axis current reference values ​​according to these voltage differences, which can reduce the impact of the fault current on the system and ensure that the system can quickly return to normal operation. And based on the output of the PI controller, the current inner loop can also obtain the q-axis voltage signal value and the d-axis voltage signal value according to the current current state and reference value, and perform synchronous rotating coordinate transformation to generate a voltage reference signal, so that the voltage reference signal can be PWM modulated to generate a PWM modulation reference signal for controlling the output voltage and output current of the driving switch device, that is, the voltage reference signal can be converted into a control signal for driving the switching device, thereby achieving direct control of the output voltage and current, so as to more effectively and quickly respond to and control the fault current. Compared with the prior art, the present invention can effectively limit the reactive output of the system and reduce the voltage fluctuation of the system, and quickly respond to and control the fault current, thereby improving the safety and stability of the offshore wind power transmission system. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] Figure 1 It is a flow chart of a current fault control method based on an offshore wind power transmission system provided by one embodiment of the present invention.

[0058] Figure 2 It is a schematic diagram of a circuit structure for realizing active fault current suppression provided by an embodiment of the present invention.

[0059] Figure 3 It is a structural schematic diagram of a current fault control device based on an offshore wind power transmission system provided by one embodiment of the present invention. DETAILED DESCRIPTION

[0060] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] like Figure 1 FIG. 1 is a flow chart of a current fault control method based on an offshore wind power transmission system provided by an embodiment of the present invention. The current fault control method based on an offshore wind power transmission system comprises:

[0062] Step S1: obtaining the DC current corresponding to the offshore wind power transmission system at the current moment;

[0063] Step S2: when it is determined that the DC current is greater than a preset current threshold, setting the q-axis reference voltage to zero;

[0064] Step S3: Repeat the following fault control operations until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage:

[0065] The AC phase voltage currently corresponding to the AC side is obtained, and then the AC phase voltage is subjected to synchronous rotation coordinate transformation to generate the q-axis actual voltage component and the d-axis actual voltage component;

[0066] Increase the q-axis reference voltage according to a preset voltage step to generate an updated q-axis reference voltage;

[0067] Inputting the updated first voltage difference between the q-axis reference voltage and the q-axis actual voltage component and the updated second voltage difference between the d-axis reference voltage and the d-axis actual voltage component into the first PI controller respectively, so that the first PI controller performs proportional and integral adjustment according to each voltage difference, and outputs the q-axis current reference value and the d-axis current reference value;

[0068] Inputting the q-axis current reference value and the d-axis current reference value into the current inner loop respectively, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side;

[0069] The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotation coordinate transformation to generate a voltage reference signal; the voltage reference signal is then subjected to PWM modulation to generate a PWM modulation reference signal; wherein the PWM modulation reference signal is used to control the output voltage and output current of the driving switch device.

[0070] For step S1, in a preferred embodiment, obtaining the DC current corresponding to the offshore wind power transmission system at the current moment includes:

[0071] Obtain the voltage change rate of the DC reactor of the offshore wind power transmission system;

[0072] When it is determined that the voltage change rate is greater than a preset change rate range, obtaining a voltage fluctuation amplitude of the system;

[0073] When it is determined that the voltage fluctuation amplitude is less than a preset minimum voltage point, marking the line where the DC reactor is located as a fault line;

[0074] Obtain the direct current corresponding to the fault line at the current moment.

[0075] In the embodiment of the present invention, since the voltage change rate of the DC reactor can quickly reflect the abnormal current or voltage in the system, when a short circuit, overload or other current fault occurs in the system, the voltage change rate will increase significantly. Therefore, monitoring the voltage change rate can realize the rapid detection of faults, which helps to take timely measures to prevent the fault from expanding.

[0076] After determining that the voltage change rate is abnormal, the embodiment of the present invention can further confirm the existence of the fault and locate the specific fault line (such as the line where the DC reactor is located) by comparing the voltage fluctuation amplitude with the preset minimum voltage point, thereby realizing rapid detection, accurate identification and positioning of system faults, and obtaining the DC current corresponding to the fault line at the current moment for the next step of judgment and current control.

[0077] For step S2, in a preferred embodiment, by timely detecting the fault and locating the fault line, measures can be taken quickly to cut off the fault source to prevent the fault current from causing further damage to the system. Therefore, before setting the q-axis reference voltage to zero, the method further includes:

[0078] Disconnecting the DC circuit breaker on the DC side of the onshore converter in the faulty line;

[0079] Determining whether the DC voltage in the faulty line is less than a preset DC voltage value;

[0080] If so, disconnect the AC circuit breaker on the AC side of the offshore converter in the faulty line.

[0081] It is understandable that when a fault is detected in a line, by disconnecting the DC circuit breaker on the DC side of the onshore converter, the direct connection between the faulty line and the DC system can be cut off, which can immediately prevent the fault current from propagating in the DC system and reduce the further impact of the fault on the DC grid.

[0082] Furthermore, after disconnecting the DC circuit breaker, the embodiment of the present invention can continue to monitor the DC voltage level in the faulty line to determine whether the fault has been effectively isolated and whether the system has stabilized. If the DC voltage drops below the preset DC voltage value, it means that the faulty line has been effectively disconnected and the fault current in the DC system has been effectively controlled.

[0083] After confirming that the DC side fault has been isolated and the DC voltage has dropped to a safe level, the AC circuit breaker on the AC side of the offshore converter in the faulty line can be further disconnected, thereby completely cutting off the connection between the faulty line and the AC power grid, ensuring the safe and stable operation of the AC power grid. Therefore, the embodiment of the present invention can achieve comprehensive fault isolation by disconnecting the circuit breakers on the DC side and the AC side at the same time.

[0084] In a preferred embodiment, before setting the q-axis reference voltage to zero, the method further includes:

[0085] Subtracting the DC current from the rated DC current to generate a current deviation;

[0086] Inputting the current deviation into a second PI controller, so that the second PI controller performs proportional and integral regulation according to the current deviation and outputs a voltage control signal;

[0087] The voltage of the DC power supply or the inverter is adjusted according to the voltage control signal.

[0088] It can be understood that the embodiment of the present invention can start the DC current correction control after the circuit breakers on the DC side and the AC side are disconnected at the same time, that is, the current deviation between the DC current and the rated DC current can be calculated, so that based on the second PI controller, a voltage control signal can be output according to the size and duration of the current deviation; finally, according to the voltage control signal output by the second PI controller, the voltage of the DC power supply or inverter is adjusted, so that the deviation between the DC current and the rated DC current can be eliminated or reduced, so that the DC current is as close to its rated value as possible.

[0089] In the process of DC current correction control, the embodiment of the present invention can more effectively control the DC current by accurately adjusting the voltage of the DC power supply or inverter, so that the DC current can be more stably maintained near the rated value, thereby reducing current fluctuations and deviations.

[0090] In a preferred embodiment, when it is determined that the DC current is greater than a preset current threshold, the present invention can also actively control the DC component of the fault current, specifically including:

[0091] Obtaining an actual DC component in the DC current;

[0092] Subtract the rated DC current from the actual DC component to obtain a deviation of the DC component;

[0093] Inputting the deviation of the DC component into a third PI controller so that the third PI controller outputs a voltage deviation value;

[0094] Subtract the voltage deviation value from the DC voltage in the current DC signal on the DC side to generate a DC reference signal;

[0095] A PWM DC reference signal for adjusting the DC side voltage is generated according to the DC reference signal.

[0096] It can be understood that the present invention can be obtained from the actual DC current i dc Rated DC current I dc The DC component of the fault current is obtained from the deviation of dcfref The PI control feedback is used to generate a fault DC voltage deviation value, and a DC reference signal is obtained by subtracting the generated fault DC voltage deviation value from the measured DC signal, so as to generate a PWM DC reference signal for adjusting the DC side voltage according to the DC reference signal, so as to modify the DC reference signal for generating the PWM wave.

[0097] Indicatively, in the event of a fault, excessive DC current may cause damage to power equipment and systems. The embodiments of the present invention can limit the current to a safe range by actively controlling the DC component of the fault current, thereby protecting the safe and stable operation of the equipment and systems. In addition, the real-time detection, feedback control and PWM modulation technologies are combined to automatically adjust the operating parameters according to the actual situation, improve the overall performance and efficiency of fault control, and enhance the system's ability to cope with faults.

[0098] For step S3, when the embodiment of the present invention determines that the DC current is greater than the preset current threshold, the q-axis reference voltage can be set to zero, and the fault control operation can be repeatedly performed until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage, so that the excessive fault current can be quickly suppressed at the early stage of the fault to prevent equipment damage, and the system state can be stabilized by gradually adjusting the q-axis reference voltage until it returns to an acceptable voltage level.

[0099] Specifically, Figure 2 The circuit structure diagram shown in the figure is as follows:

[0100] The AC phase voltage currently corresponding to the AC side is obtained, and then the AC phase voltage is subjected to synchronous rotation coordinate transformation to generate the q-axis actual voltage component and the d-axis actual voltage component;

[0101] Each time a fault control operation is performed, the q-axis reference voltage of the last fault control operation is increased according to a preset voltage step size, thereby generating an updated q-axis reference voltage, and the updated q-axis reference voltage is used as the q-axis reference voltage corresponding to this fault control operation; therefore, the embodiment of the present invention can dynamically adjust the q-axis reference voltage according to the current fault condition, thereby improving the flexibility of voltage control and the ability to cope with complex fault conditions.

[0102] Moreover, in the motor control system, the motor's operating state and load conditions may change. By gradually adjusting the q-axis reference voltage, these changes can be better adapted in the process of controlling the fault current, ensuring that the offshore wind power transmission system maintains stable performance during the fault control process.

[0103] Further, the first voltage difference between the updated q-axis reference voltage and the q-axis actual voltage component and the second voltage difference between the d-axis reference voltage and the d-axis actual voltage component can be respectively input into the first PI controller, so that the first PI controller performs proportional and integral adjustments according to the respective voltage differences, and outputs the q-axis current reference value and the d-axis current reference value;

[0104] Thereby, the q-axis current reference value and the d-axis current reference value are respectively input into the current inner loop, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side; it can be understood that the current inner loop can output the q-axis voltage signal value and the d-axis voltage signal value according to these reference values ​​and the current actual current value of the AC side through the corresponding control algorithm (such as vector control), so as to control the voltage signal of the voltage outer loop, thereby indirectly controlling the current on the AC side.

[0105] Finally, the d-axis voltage signal and the q-axis voltage signal can be subjected to synchronous rotation coordinate transformation (such as Park transformation) to generate a voltage reference signal; the voltage reference signal is then PWM modulated to generate a PWM modulation reference signal; schematically, the PWM modulation reference signal is used to control the output voltage and output current of the driving switching device.

[0106] The embodiment of the present invention can obtain the AC phase voltage currently corresponding to the AC side, and after converting it into q-axis and d-axis components, it can achieve fine control of the AC side current. By acquiring the AC phase voltage currently corresponding to the AC side and performing synchronous rotation coordinate transformation, as well as applying the PI controller and the current inner loop control strategy, the embodiment of the present invention can achieve fine control of the AC side current, so that the offshore wind power transmission system can maintain high stability and controllability during faults, and reduce the impact and damage of faults on the system.

[0107] In a preferred embodiment, after the fault control operation is performed until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage, the embodiment of the present invention further includes the following control process:

[0108] When it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is closed, and the voltage on the AC side is lower than the preset voltage threshold, the DC current value corresponding to the offshore converter is used as the upper limit value of the current dynamic limiter;

[0109] When it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is disconnected, the real-time voltage on the AC side is obtained;

[0110] The real-time voltage is compared with a preset voltage reference value, and the input amount of the reactive power compensation device of the offshore converter is adjusted according to the comparison result to achieve closed-loop control of the AC side voltage.

[0111] It can be understood that after the offshore wind power transmission system undergoes a specific fault control operation, the embodiment of the present invention adopts a more detailed control strategy according to the state of the fault line (especially the blocking state of the offshore converter and the opening and closing state of the AC circuit breaker) and the voltage condition on the AC side:

[0112] When it is detected that the offshore converter in the faulty line has been locked (ie stopped working to prevent further damage or fault expansion) and the AC circuit breaker is still closed, it is further determined whether the voltage on the AC side is lower than a preset voltage threshold.

[0113] If the voltage on the AC side is lower than the preset threshold, the DC current value corresponding to the offshore converter will be used as the upper limit of the current dynamic limiter, thereby limiting the DC side current and preventing excessive DC current from adversely affecting the system when the converter is locked. At the same time, it can also ensure that the system can operate stably within a safe current range when the converter cannot work normally.

[0114] Furthermore, when it is detected that the offshore converter in the faulty line has been locked and the AC circuit breaker has been disconnected, the real-time voltage on the AC side is acquired and compared with a preset voltage reference value to evaluate the current state of the AC side voltage.

[0115] According to the comparison result, the present invention can adjust the input amount of the reactive power compensation device of the offshore converter accordingly. Specifically, if the real-time voltage is lower than the preset reference value, the input amount of the reactive power compensation device is increased to increase the AC side voltage; conversely, if the real-time voltage is higher than the preset reference value, the input amount of the reactive power compensation device is reduced to avoid excessive voltage.

[0116] The embodiment of the present invention can continuously adjust the input amount of the reactive compensation device according to the difference between the real-time voltage and the preset reference value, realize closed-loop control of the AC side voltage, and ensure that when the AC circuit breaker is disconnected and the converter is locked, the AC side voltage can be restored to a normal level or maintained within an appropriate range.

[0117] Indicatively, when increasing the amount of reactive power compensation equipment to increase the voltage on the AC side, this can be achieved by increasing the number of parallel capacitors or increasing the total reactive power compensation capacity. Since reactive power compensation equipment (such as parallel capacitors) can provide the system with reactive power required by the inductive load, it can reduce the flow of reactive power in the power supply and the power grid, reduce the loss of lines and transformers, and thus increase the system voltage.

[0118] When reducing the input amount of reactive power compensation devices to avoid overcompensation, since the real-time voltage is higher than the reference value, in order to avoid overcompensation and possible overvoltage problems, it is necessary to reduce the input amount of reactive power compensation devices. Overcompensation means that the capacitive reactive power emitted by the capacitor exceeds the reactive power required by the inductive load, resulting in excess capacitive reactive power in the power grid, which will make the system voltage too high. Therefore, by reducing the number of parallel capacitors or reducing the total reactive power compensation capacity, the capacitive reactive power emitted by the capacitor can be reduced to keep the system voltage within an appropriate range.

[0119] In a preferred embodiment, after completing the current fault control of the system, that is, after the fault of the faulty line is removed, the present invention can also restore the operation of the equipment of the faulty line, specifically:

[0120] Compare the DC voltage on the DC side of the offshore converter in the faulty line with the DC voltage of other lines in the offshore wind power transmission system;

[0121] When the comparison result is determined to be equal voltages, the DC circuit breaker on the DC side of the onshore converter in the faulty line is closed, and then the AC circuit breaker on the AC side of the offshore converter is closed.

[0122] Specifically, after confirming that the voltages are equal and stable, the next step is performed - closing the DC circuit breaker on the DC side of the onshore converter in the faulty line to restore the circuit connection on the DC side so that current can flow in the faulty line again.

[0123] After ensuring the stability of the DC side connection, the AC circuit breaker on the AC side of the offshore converter is closed, thereby restoring the AC side connection of the faulty line, allowing the faulty line to be reconnected to the entire offshore wind power transmission system and achieving full recovery of the equipment.

[0124] like Figure 3As shown, based on the above-mentioned various embodiments of the current fault control method based on the offshore wind power transmission system, the present invention provides a corresponding device embodiment;

[0125] An embodiment of the present invention provides a current fault control device based on an offshore wind power transmission system, which is applicable to an offshore wind power transmission system;

[0126] The current fault control device comprises: a direct current acquisition module, a reference voltage setting module and a fault control operation module;

[0127] The DC current acquisition module is used to acquire the DC current corresponding to the offshore wind power transmission system at the current moment;

[0128] The reference voltage setting module is used to set the q-axis reference voltage to zero when it is determined that the DC current is greater than a preset current threshold;

[0129] The fault control operation module is used to repeatedly perform the following fault control operations until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage:

[0130] The AC phase voltage currently corresponding to the AC side is obtained, and then the AC phase voltage is subjected to synchronous rotation coordinate transformation to generate the q-axis actual voltage component and the d-axis actual voltage component;

[0131] Increase the q-axis reference voltage according to a preset voltage step to generate an updated q-axis reference voltage;

[0132] Inputting the updated first voltage difference between the q-axis reference voltage and the q-axis actual voltage component and the updated second voltage difference between the d-axis reference voltage and the d-axis actual voltage component into the first PI controller respectively, so that the first PI controller performs proportional and integral adjustment according to each voltage difference, and outputs the q-axis current reference value and the d-axis current reference value;

[0133] Inputting the q-axis current reference value and the d-axis current reference value into the current inner loop respectively, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side;

[0134] The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotation coordinate transformation to generate a voltage reference signal; the voltage reference signal is then subjected to PWM modulation to generate a PWM modulation reference signal; wherein the PWM modulation reference signal is used to control the output voltage and output current of the driving switch device.

[0135] It should be noted that the device embodiments described above are merely schematic, wherein the modules described as separate components may or may not be physically separated, and the components displayed as modules may or may not be physical modules, and may be located in one place or distributed on multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the accompanying drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. Those of ordinary skill in the art can understand and implement it without paying creative labor.

[0136] Those skilled in the art can clearly understand that, for the sake of convenience and simplicity, the specific working process of the device described above can refer to the corresponding process in the aforementioned method embodiment, and will not be repeated here.

[0137] Based on the above-mentioned various embodiments of the current fault control method based on the offshore wind power transmission system, the present invention provides corresponding terminal equipment embodiments.

[0138] An embodiment of the present invention provides a terminal device, including a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, it implements a current fault control method based on an offshore wind power transmission system as described in any method embodiment of the present invention.

[0139] The terminal device may be a computing terminal device such as a desktop computer, a notebook, a palm computer, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0140] The processor may be a central processing unit (CPU), or other general-purpose processors, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor, etc. The processor is the control center of the terminal device, and uses various interfaces and lines to connect various parts of the entire terminal device.

[0141] The memory can be used to store the computer program, and the processor realizes various functions of the terminal device by running or executing the computer program stored in the memory and calling the data stored in the memory. The memory can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, at least one application required for a function, etc.; the data storage area can store data created according to the use of the mobile phone, etc. In addition, the memory can include a high-speed random access memory, and can also include a non-volatile memory, such as a hard disk, a memory, a plug-in hard disk, a smart memory card (Smart Med i aCard, SMC), a secure digital (Secure Digital, SD) card, a flash card (Flash Card), at least one disk storage device, a flash memory device or other volatile solid-state storage device.

[0142] Based on the above-mentioned various embodiments of the current fault control method based on the offshore wind power transmission system, the present invention provides a corresponding storage medium item embodiment.

[0143] An embodiment of the present invention provides a storage medium, which includes a stored computer program, wherein when the computer program is running, the device where the computer-readable storage medium is located is controlled to execute a current fault control method based on an offshore wind power transmission system as described in any method embodiment of the present invention.

[0144] The storage medium is a computer-readable storage medium, and the computer program is stored in the computer-readable storage medium. When the computer program is executed by the processor, the steps of each of the above-mentioned method embodiments can be implemented. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, USB flash drive, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0145] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A current fault control method based on an offshore wind power transmission system, characterized in that: include: Obtain the DC current corresponding to the offshore wind power transmission system at the current moment; When it is determined that the DC current is greater than a preset current threshold, setting the q-axis reference voltage to zero; Repeat the following fault control operations until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage: Obtain the current AC phase voltage corresponding to the AC side, and then perform synchronous rotation coordinate transformation on the AC phase voltage to generate the q-axis actual voltage component and the d-axis actual voltage component; increasing the q-axis reference voltage according to a preset voltage step size to generate an updated q-axis reference voltage; inputting a first voltage difference between the updated q-axis reference voltage and the q-axis actual voltage component and a second voltage difference between the updated d-axis reference voltage and the d-axis actual voltage component into a first PI controller, respectively, so that the first PI controller performs proportional and integral adjustment according to the respective voltage differences and outputs a q-axis current reference value and a d-axis current reference value; Inputting the q-axis current reference value and the d-axis current reference value into the current inner loop respectively, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side; The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotation coordinate transformation to generate a voltage reference signal; the voltage reference signal is then PWM modulated to generate a PWM modulation reference signal; wherein the PWM modulation reference signal is used to control the output voltage and output current of the driving switching device.

2. A current fault control method based on an offshore wind power transmission system according to claim 1, characterized in that: Before setting the q-axis reference voltage to zero, also include: Subtracting the DC current from the rated DC current to generate a current deviation; Inputting the current deviation into a second PI controller, so that the second PI controller performs proportional and integral adjustment according to the current deviation and outputs a voltage control signal; The voltage of the DC power supply or the inverter is adjusted according to the voltage control signal.

3. The current fault control method based on the offshore wind power transmission system according to claim 1, characterized in that: When it is determined that the direct current is greater than a preset current threshold, the method further includes: obtaining an actual DC component in the DC current; Subtracting the rated DC current from the actual DC component to obtain a deviation of the DC component; inputting the deviation of the DC component into a third PI controller so that the third PI controller outputs a voltage deviation value; Subtract the voltage deviation value from the DC voltage of the current DC signal on the DC side to generate a DC reference signal; A PWM DC reference signal for adjusting the DC side voltage is generated according to the DC reference signal.

4. A current fault control method based on an offshore wind power transmission system according to claim 3, characterized in that: The obtaining of the direct current corresponding to the offshore wind power transmission system at the current moment includes: Obtain the voltage change rate of the DC reactor of the offshore wind power transmission system; When it is determined that the voltage change rate is greater than a preset change rate range, obtaining a voltage fluctuation amplitude of the system; When it is determined that the voltage fluctuation amplitude is less than a preset minimum voltage point, marking the line where the DC reactor is located as a fault line; Obtain the direct current corresponding to the fault line at the current moment.

5. A current fault control method based on an offshore wind power transmission system according to claim 4, characterized in that: Before setting the q-axis reference voltage to zero, also include: disconnecting the DC circuit breaker on the DC side of the onshore converter in the faulty line; Determining whether the DC voltage in the faulty circuit is less than a preset DC voltage value; If so, disconnect the AC circuit breaker on the AC side of the offshore converter in the faulty line.

6. A current fault control method based on an offshore wind power transmission system according to claim 5, characterized in that: Also includes: When it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is closed, and the voltage on the AC side is lower than the preset voltage threshold, the DC current value corresponding to the offshore converter is used as the upper limit value of the current dynamic limiter; When it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is disconnected, the real-time voltage on the AC side is obtained; The real-time voltage is compared with a preset voltage reference value, and the input amount of the reactive compensation device of the offshore converter is adjusted according to the comparison result to achieve closed-loop control of the AC side voltage.

7. A current fault control method based on an offshore wind power transmission system according to claim 6, characterized in that: Also includes: Compare the DC voltage on the DC side of the offshore converter in the faulty line with the DC voltage of other lines in the offshore wind power transmission system; When the comparison result determines that the voltages are equal, the DC circuit breaker on the DC side of the onshore converter in the faulty line is closed, and then the AC circuit breaker on the AC side of the offshore converter is closed.

8. A current fault control device based on an offshore wind power transmission system, characterized in that: Applicable to offshore wind power transmission system; The current fault control device includes: a DC current acquisition module, a reference voltage setting module and a fault control operation module; The DC current acquisition module is used to obtain the DC current corresponding to the offshore wind power transmission system at the current moment; The reference voltage setting module is configured to set the q-axis reference voltage to zero when it is determined that the DC current is greater than a preset current threshold; The fault control operation module is configured to repeatedly perform the following fault control operations until the AC phase voltage corresponding to the offshore wind power transmission system is half of the DC voltage: Obtain the current AC phase voltage corresponding to the AC side, and then perform synchronous rotation coordinate transformation on the AC phase voltage to generate the q-axis actual voltage component and the d-axis actual voltage component; increasing the q-axis reference voltage according to a preset voltage step size to generate an updated q-axis reference voltage; inputting a first voltage difference between the updated q-axis reference voltage and the q-axis actual voltage component and a second voltage difference between the updated d-axis reference voltage and the d-axis actual voltage component into a first PI controller, respectively, so that the first PI controller performs proportional and integral adjustment according to the respective voltage differences and outputs a q-axis current reference value and a d-axis current reference value; Inputting the q-axis current reference value and the d-axis current reference value into the current inner loop respectively, so that the current inner loop outputs the q-axis voltage signal value and the d-axis voltage signal value according to the q-axis current reference value, the d-axis current reference value and the actual current value currently corresponding to the AC side; The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotation coordinate transformation to generate a voltage reference signal; the voltage reference signal is then PWM modulated to generate a PWM modulation reference signal; wherein the PWM modulation reference signal is used to control the output voltage and output current of the driving switching device.

9. A terminal device, characterized in that: The method comprises a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor, wherein when the processor executes the computer program, the method implements a current fault control method based on an offshore wind power transmission system as claimed in any one of claims 1 to 7.

10. A storage medium, characterized in that: The storage medium includes a stored computer program, wherein when the computer program is running, the device where the storage medium is located is controlled to execute the current fault control method based on the offshore wind power transmission system according to any one of claims 1 to 7.

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