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

Abstract

The application discloses a current fault control method and device based on an offshore wind power sending-out system, a terminal device and a storage medium, and can realize real-time monitoring of the direct-current of the offshore wind power sending-out system; when the direct-current exceeds a preset current threshold, the reference voltage of the q-axis is set to zero, so that the reactive power output of the system can be rapidly limited during the fault, and the fluctuation of the system voltage is reduced; and in each adjustment voltage and current fault control process, the q-axis reference voltage can be gradually increased according to the preset voltage step, so that the PI controller can accurately adjust the current reference values of the q-axis and the d-axis according to the voltage difference, and direct control of the voltage and the current is realized according to the PWM modulation reference signal. The application can effectively limit the reactive power output of the system and reduce the fluctuation of the system voltage, and can quickly respond to and control the fault current, so that the safety and stability of the offshore wind power sending-out 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] The HB-MMC, a key component of flexible HVDC transmission systems for offshore wind power transmission, enables coordinated control of the system. When a short-circuit fault or current fault occurs in an offshore wind power transmission system, the fault current rises rapidly. If left uncontrolled, the AC component in the fault current can exacerbate the fluctuations in the fault current, causing a greater impact on the system. After detecting a current fault, the fault area is often isolated from the system by adjusting the switching state of the converter. During fault isolation, to prevent further expansion of the fault current, the AC phase voltage on the AC side of the offshore wind power transmission system must be controlled. By controlling the AC phase voltage on the AC side, the current on the AC side can be indirectly affected, effectively controlling 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. This cannot quickly limit the reactive output of the system, causing the system voltage fluctuation to increase and the fault current to be unable to be quickly responded to and controlled, 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 device 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. It can effectively solve the problems in the prior art of being unable to quickly limit the reactive output of the system, resulting in increased system voltage fluctuations, inability to quickly respond to and control the fault current, 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] 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;

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

[0011] 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;

[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 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.

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

[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 adjustment 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 DC current is greater than a preset current threshold, the method further includes:

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

[0020] Subtracting 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 of 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 includes:

[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 circuit 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 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 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.

[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 the offshore wind power transmission system;

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

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

[0044] 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;

[0045] 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:

[0046] 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;

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

[0048] 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;

[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 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.

[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. 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 embodiment, the present invention provides a corresponding storage medium embodiment.

[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 the current fault control method based on the offshore wind power transmission system described in the above-mentioned embodiment of the invention.

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

[0056] Embodiments of the present invention provide a current fault control method, apparatus, terminal device, 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, thereby quickly limiting the reactive output of the system during a fault and reducing system voltage fluctuations. In addition, during each fault control process for adjusting voltage and current, the actual voltage components of the q-axis and d-axis (active axis) are generated by continuously obtaining the AC phase voltage currently corresponding to the AC side and performing a synchronous rotating coordinate transformation. The q-axis reference voltage is also gradually increased according to a preset voltage step size. Therefore, each time a first voltage difference between the q-axis actual voltage component and the d-axis reference voltage, and a second voltage difference between the d-axis reference voltage and the d-axis actual voltage component, can be obtained based on the q-axis reference voltage adjusted by the preset step size. The PI controller can then accurately adjust the output q-axis and d-axis current reference values ​​based on these voltage differences, thereby reducing the impact of the fault current on the system and ensuring that the system can quickly return to normal operation. Furthermore, 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. This voltage reference signal can then be PWM modulated to generate a PWM modulation reference signal for controlling the output voltage and output current of the driving switching device. In other words, 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, thereby more effectively and quickly responding to and controlling fault current. Compared with the prior art, the present invention can effectively limit the system's reactive output and reduce system voltage fluctuations, and quickly respond to and control 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 This is a schematic diagram of a circuit structure for achieving 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 clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall 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 according to an embodiment of the present invention. The current fault control method based on an offshore wind power transmission system includes:

[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] 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;

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

[0067] 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;

[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 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.

[0070] Regarding 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 this embodiment of the present invention, the voltage change rate of the DC reactor can quickly reflect abnormal current or voltage conditions in the system. Therefore, 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 achieve rapid fault detection and help take timely measures to prevent the fault from escalating.

[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 inductor is located) by comparing the voltage fluctuation amplitude with the preset minimum voltage point, thereby achieving 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] Regarding step S2, in a preferred embodiment, by timely detecting the fault and locating the faulty line, measures can be quickly taken to cut off the fault source and prevent the fault current from causing further damage to the system. Therefore, before setting the q-axis reference voltage to zero, the following is further included:

[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 circuit 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 on 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] Further, after the DC circuit breaker is opened, the embodiment of the present application can continue to monitor the DC voltage level in the fault 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 indicates that the fault line has been effectively disconnected and the fault current in the DC system has been effectively controlled.

[0083] Then, 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 fault line can be further opened, thereby completely disconnecting the fault line from the AC power grid and ensuring the safe and stable operation of the AC power grid. Therefore, the embodiment of the present application can achieve comprehensive fault isolation by simultaneously opening the DC side and AC side circuit breakers.

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

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

[0086] inputting the current deviation into a second PI controller to cause the second PI controller to perform proportional and integral adjustment according to the current deviation and output a voltage control signal;

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

[0088] It can be understood that, after the DC side and AC side circuit breakers are opened, the embodiment of the present application can start the DC current correction control, 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, the voltage of the DC power supply or the inverter can be adjusted according to the voltage control signal output by the second PI controller, so that the deviation between the DC current and the rated DC current can be eliminated or reduced, and the DC current can be as close as possible to its rated value.

[0089] Therefore, during the DC current correction control, the embodiment of the present application can more effectively control the DC current by precisely adjusting the voltage of the DC power supply or the inverter, so that the DC current can be more stably maintained around the rated value, reducing current fluctuation and deviation.

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

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

[0092] Subtracting the actual direct current component from the rated direct current to obtain a deviation of the direct current component;

[0093] Inputting the deviation of the direct current component into a third PI controller to make the third PI controller output a voltage deviation value;

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

[0095] Generating a PWM direct reference signal for adjusting the direct side voltage according to the direct reference signal.

[0096] It can be understood that the present application can obtain the fault current direct component from the deviation between the actual direct current i dc and the rated direct current I dc , and use it as the PI control feedback of I dcfref to generate a fault direct voltage deviation value, and then subtract the generated fault direct voltage deviation value from the measured direct signal to obtain a direct reference signal, so as to generate a PWM direct reference signal for adjusting the direct side voltage according to the direct reference signal, so as to modify the direct reference signal of the generated PWM wave.

[0097] Illustratively, in the case of a fault, an excessively high direct current may cause damage to the power equipment and system, and the embodiment of the present application can limit the current within a safe range by actively controlling the fault current direct component, thereby protecting the safe and stable operation of the equipment and system. And combining real-time detection, feedback control and PWM modulation technology, so as to automatically adjust the operating parameters according to the actual situation, improve the overall performance and fault control efficiency, and enhance the ability of the system to respond to faults.

[0098] For step S3, when the direct current is greater than the preset current threshold, the embodiment of the present application can set the q-axis reference voltage to zero, and repeatedly execute the fault control operation until the AC phase voltage corresponding to the offshore wind power transmission system is half of the direct voltage, so that the excessively large fault current can be quickly suppressed in 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, as shown in the circuit structure diagram of Figure 2 , when executing the fault control operation each time, specifically:

[0100] Obtaining the AC phase voltage corresponding to the current AC side, and then performing synchronous rotating coordinate transformation on the AC phase voltage to generate a q-axis actual voltage component and a d-axis actual voltage component;

[0101] Each time a fault control operation is performed, the q-axis reference voltage at the time 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 situation, thereby improving the flexibility of voltage control and the ability to cope with complex fault situations.

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

[0103] Furthermore, 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 can be respectively input into the first PI controller, 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;

[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) 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; then the voltage reference signal is 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, reducing the impact and damage of the fault on the system.

[0107] In a preferred embodiment, after executing the fault control operation 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 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 is understandable that after the offshore wind power transmission system experiences a specific fault control operation, the embodiment of the present invention adopts a more detailed control strategy based on the state of the fault line (particularly the blocking state of the offshore converter and the open / close 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 AC voltage falls below a preset threshold, the DC current corresponding to the offshore converter is used as the upper limit of the dynamic current limiter. This limits the DC current and prevents excessive DC current from adversely affecting the system when the converter is locked. This also ensures that the system can operate stably within a safe current range even if the converter fails to operate 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 obtained and compared with a preset voltage reference value to evaluate the current state of the AC side voltage.

[0115] Based on the comparison results, the present invention can adjust the reactive power compensation device input of the offshore converter accordingly. Specifically, if the real-time voltage is lower than a preset reference value, the reactive power compensation device input is increased to increase the AC side voltage. Conversely, if the real-time voltage is higher than the preset reference value, the reactive power compensation device input is reduced to prevent 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, thereby realizing closed-loop control of the AC side voltage and ensuring that when the AC circuit breaker is disconnected and the converter is locked, the AC side voltage can return to a normal level or remain within an appropriate range.

[0117] Schematically, increasing the amount of reactive power compensation equipment to boost the AC voltage can be achieved by increasing the number of shunt capacitors or increasing the total reactive power compensation capacity. Because reactive power compensation devices (such as shunt capacitors) can provide the system with the reactive power required by inductive loads, they can reduce the flow of reactive power in the power supply and grid, lowering losses in lines and transformers, and ultimately boosting system voltage.

[0118] When reducing the amount of reactive power compensation equipment to avoid overcompensation, the real-time voltage is higher than the reference value. To avoid overcompensation and possible voltage overshoot, the reactive power compensation equipment needs to be reduced. Overcompensation means that the capacitive reactive power generated by the capacitor exceeds the reactive power required by the inductive load, resulting in excess capacitive reactive power in the grid and excessive system voltage. Therefore, by reducing the number of parallel capacitors or lowering the total reactive power compensation capacity, the capacitive reactive power generated by the capacitors can be reduced, keeping 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 cleared, the present invention can also restore the operation of the equipment on 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 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.

[0122] Specifically, after confirming that the voltage is equal and stable, the next step is to close 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, allowing current to 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 was 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 3Based on the above various embodiments of the offshore wind power transmission system based current fault control method, the application correspondingly provides device embodiments;

[0125] An embodiment of the application provides a current fault control device based on an offshore wind power transmission system, which is suitable for the 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 direct current acquisition module is used to acquire the direct current corresponding to the current time of the offshore wind power transmission system.

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

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

[0130] An alternating current phase voltage corresponding to the current alternating current side is acquired, and then the q-axis actual voltage component and the d-axis actual voltage component are generated after synchronous rotating coordinate transformation of the alternating current phase voltage.

[0131] The q-axis reference voltage is increased by a preset voltage step to generate an updated q-axis reference voltage.

[0132] 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 are input into the first PI controller, 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] The q-axis current reference value and the d-axis current reference value are 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 corresponding to the current alternating current side.

[0134] The d-axis voltage signal and the q-axis voltage signal are subjected to synchronous rotating coordinate transformation to generate a voltage reference signal, and then the voltage reference signal is 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 the output current of the driving switching device.

[0135] It should be noted that the device embodiments described above are merely illustrative, 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 across multiple network modules. Some or all of the modules may be selected according to actual needs to achieve the purpose of the present embodiment. In addition, in the 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. A person of ordinary skill in the art can understand and implement the present invention without paying any creative effort.

[0136] Those skilled in the art can clearly understand that, for the sake of convenience and brevity, 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 embodiments of terminal equipment.

[0138] An embodiment of the present invention provides a terminal device, comprising a processor, a memory, and a computer program stored in the memory and configured to be executed by the processor. 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 computer, a palmtop 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 connects various parts of the entire terminal device using various interfaces and lines.

[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 corresponding storage medium item embodiments.

[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, it can implement the steps of the above-mentioned various method embodiments. 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 that can carry the computer program code, recording medium, USB flash drive, mobile hard disk, magnetic 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 for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles 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; Performing synchronous rotation coordinate transformation on the d-axis voltage signal and the q-axis voltage signal to generate a voltage reference signal; then performing PWM modulation on the voltage reference signal 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; When it is determined that the offshore converter in the faulty line is locked, the AC circuit breaker is closed, and the voltage on the AC side is lower than a 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.

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: 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.

7. 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, a fault control operation module, a current regulation module and a voltage control 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; Performing synchronous rotation coordinate transformation on the d-axis voltage signal and the q-axis voltage signal to generate a voltage reference signal; then performing PWM modulation on the voltage reference signal 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; The current regulating module is configured to use the DC current value corresponding to the offshore converter as the upper limit of the current dynamic limiter when it is determined that the offshore converter in the faulty line is locked, the AC circuit breaker is closed, and the voltage on the AC side is lower than a preset voltage threshold; The voltage control module is configured to obtain the real-time voltage on the AC side when it is determined that the offshore converter in the faulty line is locked and the AC circuit breaker is disconnected; compare the real-time voltage with a preset voltage reference value; and adjust the input amount of the reactive power compensation device of the offshore converter based on the comparison result to achieve closed-loop control of the AC side voltage.

8. 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 6.

9. 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 6.

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