Embedded DC power transfer control method, apparatus and device, and storage medium

Abstract

The invention provides an embedded direct-current power transfer control method, device and equipment and a storage medium, and the method comprises the steps: a half-bridge MMC detects a direct-current line overcurrent signal, executes a locking strategy, and enters an uncontrolled rectification current-limiting mode; the time-domain current differential protection device collects and filters the current signal, identifies a sudden change moment, carries out time synchronization compensation, and calculates differential current to construct a protection criterion; when the conditions are met, a tripping signal is generated and transmitted to an alternating-current side circuit breaker to isolate a fault; and a direct-current damping switch is put in to accelerate residual current attenuation, a system power supply keeps output constant, and the transmission power of the original direct-current line is completely transferred to the alternating-current line by utilizing the short-time overload capacity of the alternating-current line, so that power transfer is realized. According to the invention, through cooperation of the DC side protection and the AC side circuit breaker, the DC fault is rapidly isolated and eliminated, and the short-time overload capability of the AC line is utilized to guarantee continuous power transfer and stable operation of the system during the fault period.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of power transfer, and particularly relates to an embedded direct-current power transfer control method, device, equipment and storage medium. BACKGROUND

[0002] The existing AC transmission line is reformed or a DC transmission line is newly built to form an embedded flexible DC transmission system in which AC and DC lines are parallelly operated. This hybrid transmission architecture makes full use of the advantages of DC transmission in long-distance and large-capacity transmission and the characteristics of AC transmission in flexibility and reliability, and effectively improves the overall performance and operation efficiency of the power grid.

[0003] However, in actual operation of the embedded flexible DC transmission system, especially in transmission lines using overhead lines and cable lines, the fault probability is relatively high due to the influence of various factors such as natural environment and equipment aging. Once a DC line fault occurs, such as DC inter-pole short circuit or grounding fault, the fault current will rise sharply, and if effective measures are not taken in time, the power grid equipment may be seriously damaged, and even the system may collapse.

[0004] At present, the DC fault clearing methods of the flexible DC system mainly include an AC circuit breaker-based clearing method, a DC circuit breaker-based clearing method and a fault self-clearing converter station-based clearing method. However, the application of these methods in the embedded flexible DC transmission system has certain limitations. Specifically, when the AC circuit breaker is used to clear the DC fault, since the sectional differential protection is usually used on the AC side, the DC side fault may not trigger the action of the AC side protection, and even if the action is triggered, the response speed is relatively slow, usually reaching the order of hundreds of milliseconds, which is difficult to meet the demand of rapid isolation of faults.

[0005] At the same time, after the AC circuit breaker trips, the DC side fault current flows through the uncontrolled rectifier bridge to continue to flow, and the current decay time constant is large, resulting in a relatively long fault clearing and power interruption time.

[0006] On the other hand, although the use of the DC circuit breaker can quickly cut off the fault current, the DC circuit breaker is high in cost, and in the embedded DC system, due to the existence of the parallel AC line, the requirement for the fault clearing speed can be appropriately relaxed, so the use of the DC circuit breaker is not advantageous in economy. The method based on the fault self-clearing converter station does not need the DC circuit breaker and the current limiting reactor, but a large number of fully controlled or semi-controlled devices are added in the hardware topology of the converter station sub-module, resulting in a significant increase in investment cost and operating loss, which is 1.2-2 times that of the conventional half-bridge MMC, and also does not meet the requirement of economy.

[0007] In view of the fact that the AC line can continue to operate and has short-time overload capacity when the DC line in the embedded flexible DC power transmission system fails, it is considered to use the short-time overload capacity of the AC line after the failure to transmit power, which is an effective way to ensure uninterrupted transmission of active power in the power grid. However, the existing DC fault clearing method is not suitable for embedded flexible DC systems, and there is an urgent need to develop a new fault clearing and power transfer control method that takes into account economy and rapidity. SUMMARY

[0008] The purpose of the present application is to overcome the defects in the prior art described above, and to provide an embedded DC power transfer control method, device, equipment and storage medium.

[0009] The present application provides an embedded DC power transfer control method, characterized in that it comprises:

[0010] Detecting an overcurrent signal of the DC line by a half-bridge modular multilevel converter (MMC);

[0011] According to the overcurrent signal, the MMC executes a blocking strategy, turns off the insulated gate bipolar transistor (IGBT) of the associated converter station, and makes the MMC enter a non-controlled rectification current limiting mode;

[0012] In the non-controlled rectification current limiting mode, a time-domain current differential protection device acquires current signals at both ends of the DC line in real time, filters the current signals, identifies the starting time of current mutation through differential processing based on the filtered current signals, compensates the current signals at both ends based on the starting time of the mutation, calculates the differential current, and constructs a protection criterion based on the differential current;

[0013] When the protection criterion meets the action condition, the differential protection device generates a trip signal;

[0014] The trip signal is transmitted to the AC side circuit breaker through a communication channel;

[0015] The AC side circuit breaker receives the trip signal and performs a tripping operation to isolate the fault DC line;

[0016] A DC damping switch is put into operation to accelerate the decay of residual current, and the total output is kept constant by the system power supply;

[0017] Under the conditions of isolating the fault DC line, putting the DC damping switch into operation, and keeping the total output constant by the system power supply, the AC line uses its short-time overload capacity to transfer all the power originally transmitted by the DC line to the AC line, realizing power transfer.

[0018] Optionally, identifying the starting time of current mutation through differential processing based on the filtered current signal comprises:

[0019] performing differential processing on the filtered current signal to generate a current differential value;

[0020] determining a current sudden change starting moment when the current differential value exceeds a product of a reliability coefficient and a maximum error value;

[0021] The reliability coefficient is a preset reliability parameter, and the maximum error value is a maximum error value caused by a normal power fluctuation disturbance of a system.

[0022] Optionally, time compensation is performed on the two-terminal current signals based on the sudden change starting moment to calculate a differential current, including:

[0023] According to the difference of the sudden change starting moment, a time delay is calculated;

[0024] Based on the time delay, time delay processing is performed on the later-arriving current signal to synchronize the two-terminal current signals;

[0025] The differential current is calculated according to the synchronized current signals.

[0026] Optionally, the protection criterion is constructed according to the differential current, including:

[0027] The protection criterion is constructed using the reliability coefficient and an error threshold value;

[0028] When the differential current is greater than a product of the reliability coefficient and the error threshold value, it is determined that the protection criterion meets an action condition;

[0029] The reliability coefficient is used to adjust protection sensitivity, and the error threshold value is set based on a maximum value of a differential current fluctuation caused by an external fault.

[0030] Optionally, the trip signal is transmitted to an alternating current side circuit breaker through a communication channel, including:

[0031] The trip signal is transmitted through a protection communication channel;

[0032] The protection communication channel is a dedicated communication link, which is used to ensure fast and reliable transmission of the trip signal.

[0033] Optionally, a direct current damping switch is put into operation, including:

[0034] The direct current damping switch is put into operation at the same time as the alternating current side circuit breaker performs a tripping operation;

[0035] The timing of putting the direct current damping switch into operation is synchronized with the tripping operation to accelerate the decay of residual current.

[0036] Optionally, the current mutation starting moment is identified through differential processing according to the filtered current signal, and the method further comprises the following steps of intercepting the current mutation starting moment to construct a time window, comprising:

[0037] The time window is constructed based on the current mutation starting moment;

[0038] The steady-state operation data before the reference is removed, and the current data segment after the mutation is retained;

[0039] The retained current data segment is compensated for time and the differential current is calculated.

[0040] The application also provides an embedded direct current power transfer control device, comprising:

[0041] A detection module detects an overcurrent signal of a direct current line through a half-bridge type modular multilevel converter (MMC);

[0042] A shutdown module, according to the overcurrent signal, the MMC executes a blocking strategy, and turns off an insulated gate bipolar transistor of an associated converter station, so that the MMC enters a non-controlled rectification current limiting mode;

[0043] A criterion module, in the non-controlled rectification current limiting mode, a time-domain current differential protection device collects current signals at both ends of the direct current line in real time, filters the current signals, identifies a current mutation starting moment through differential processing according to the filtered current signals, compensates for time for the current signals at both ends based on the mutation starting moment, calculates a differential current, and constructs a protection criterion according to the differential current;

[0044] A signal module, when the protection criterion meets an action condition, the differential protection device generates a trip signal;

[0045] A transmission module, the trip signal is transmitted to an alternating current side circuit breaker through a communication channel;

[0046] An isolation module, after the trip signal is received by the alternating current side circuit breaker, a tripping operation is performed to isolate a fault direct current line;

[0047] An input module, a direct current damping switch is inputted to accelerate residual current attenuation; and a system power source keeps total output constant;

[0048] A transfer module, under the conditions of the isolated fault direct current line, the inputted direct current damping switch, and the constant total output of the system power source, the original power transmitted by the direct current line is completely transferred to an alternating current line by using a short-time overload capacity of the alternating current line, so that power transfer is realized.

[0049] The application also provides an electronic device comprising a memory and a processor, the memory stores a computer program, and the processor executes the computer program to realize the method described above.

[0050] This application also provides a computer-readable storage medium having a computer program stored thereon, which, when executed in a computer, causes the computer to perform the above-described method.

[0051] The beneficial effects of this application are:

[0052] This application provides an embedded DC power transfer control method, characterized by comprising: detecting overcurrent signals of the DC line through a half-bridge modular multilevel converter (MMC); based on the overcurrent signal, the MMC executes a blocking strategy, turning off the insulated gate bipolar transistor (IGBT) of the associated converter station, causing the MMC to enter an uncontrolled rectification current-limiting mode; in the uncontrolled rectification current-limiting mode, a time-domain current differential protection device collects current signals at both ends of the DC line in real time, filters the current signals, identifies the start time of current mutation through differential processing based on the filtered current signals, and performs time-synchronization compensation on the current signals at both ends based on the start time of the mutation. The differential current is calculated, and a protection criterion is constructed based on the differential current. When the protection criterion meets the operating conditions, the differential protection device generates a trip signal. The trip signal is transmitted to the AC side circuit breaker through a communication channel. After receiving the trip signal, the AC side circuit breaker performs a tripping operation to isolate the faulty DC line. A DC damping switch is engaged to accelerate the decay of residual current. The total output of the system power supply is kept constant. Under the conditions of isolating the faulty DC line, engaging the DC damping switch, and maintaining a constant total output of the system power supply, the AC line utilizes its short-time overload capacity to transfer all the power originally transmitted by the DC line to the AC line, thus achieving power transfer. This application achieves rapid isolation and clearing of DC faults through the coordinated operation of DC side time-domain current differential protection and AC side circuit breaker, and fully utilizes the short-time overload capacity of the AC line to complete continuous power transfer during the fault period, thereby ensuring the stable operation of the system. Attached Figure Description

[0053] Figure 1 This is a schematic diagram of the power supply control process;

[0054] Figure 2 This is a schematic diagram of the topology of an embedded flexible DC system;

[0055] Figure 3 This is a schematic diagram of time-domain current differential protection;

[0056] Figure 4 This is a schematic diagram of a simulation example process;

[0057] Figure 5 This is a schematic diagram of the differential current of a time-domain differential protection device based on the instantaneous change in current.

[0058] Figure 6 is a schematic diagram of a differential current simulation of a time-difference protection device at the starting moment of a current mutation;

[0059] Figure 7 is a schematic diagram of a system power transmission simulation before and after a fault. DETAILED DESCRIPTION

[0060] Exemplary embodiments of the present disclosure will be described in greater detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it is understood that various forms of the present disclosure are implemented without being limited by the embodiments set forth herein. Rather, the embodiments are provided so that the present disclosure can be more thoroughly understood, and the scope of the present disclosure can be accurately conveyed to those skilled in the art.

[0061] Referring to Figures 1-4 , the present application provides a power transfer control method using overload capacity of an AC line under fault of an embedded DC system, which is applied to the technical field of power equipment and used to solve the problem of quickly removing faults and realizing continuous power transfer of an embedded flexible DC system when a DC fault occurs. The method comprises the following steps:

[0062] S101, detecting an overcurrent signal of a DC line through a half-bridge type modular multilevel converter (MMC);

[0063] In a normal operation state of the embedded DC system, the DC line and the AC line are operated in parallel and jointly bear the total transmission power of the system. When a fault occurs on the DC side, the system quickly detects the overcurrent signal, and the half-bridge type MMC immediately detects the overcurrent signal.

[0064] The structure of the half-bridge type modular multilevel converter (MMC) adopts a symmetric monopolar wiring form, and the DC line can adopt multiple laying forms such as cables, overhead lines or a mixture of the two. The current sensor built in the MMC monitors the DC line current in real time, and when the fault causes the current to abnormally rise, the MMC can quickly identify the overcurrent signal.

[0065] The embedded DC system is a hybrid power transmission architecture in which an AC line and a DC line are operated in parallel. The sending end and the receiving end are connected to the same AC power grid, and the DC system adopts the architecture of a half-bridge type modular multilevel converter (MMC) + DC damping switch. When operating stably, the DC line transmits power, for example, set to 200 MW, the AC line transmits 100 MW, and the total power is 300 MW. When a fault occurs in the DC line, such as a two-pole short circuit, the fault current rises sharply, and the MMC detects that the current exceeds the threshold through a high-precision sampling unit, thereby triggering subsequent actions. This detection mechanism is based on the change of electrical quantity, ensuring the timeliness and accuracy of fault identification.

[0066] The embedded flexible HVDC system model adopts a double-ended power supply mode, the DC line is a flexible HVDC line using MMC, and the MMC connection mode is symmetric monopole connection. The DC line and the AC line are in parallel mode, and the full length of the two lines is set to 200 km; the AC power supply 1 is an active power sending end, and the active power sent by the AC power supply 1 is controlled to be a certain value, and the certain value is set to 300 MW; the control mode of the MMC 1 at the sending end of the DC line is fixed DC voltage / fixed reactive power control, the control mode of the MMC 2 at the receiving end is fixed active power / fixed reactive power control, the active power reference value is 200 MW, the reactive power reference value is 0 MVar, and the DC voltage reference value is ±200 kV; under the control mode, the DC line and the AC line jointly share the power transmission responsibility in stable operation, and the transmission power of the DC line is stable at 200 MW, and the transmission power of the AC line is stable at 100 MW.

[0067] S102, according to the overcurrent signal, the MMC executes a blocking strategy, turns off the insulated gate bipolar transistor associated with the converter station, and makes the MMC enter a non-controlled rectification current limiting mode;

[0068] After the MMC detects the overcurrent signal, an emergency blocking strategy is immediately executed to turn off all the insulated gate bipolar transistors (IGBTs) associated with the converter station. At this time, the anti-parallel diodes of the half-bridge sub-modules in the MMC form a non-controlled rectification circuit to limit the continuous rise of the fault current.

[0069] The blocking mechanism of the MMC and the non-controlled rectification bridge structure formed by the anti-parallel diodes; the IGBTs are quickly turned off to cut off the capacitor discharge circuit.

[0070] When a fault occurs on the DC side of the system, the associated converter station can quickly detect the overcurrent signal and immediately execute a blocking strategy to block all the converter stations. In this process, the capacitor discharge circuit of the half-bridge sub-modules is cut off, thereby avoiding the continuous injection of energy to the fault point.

[0071] The AC system feeds current to the fault point through the impedance path formed by the leakage reactance of the converter transformer and the bridge arm reactor of the MMC. At this time, the anti-parallel diodes in the MMC are turned on to form a non-controlled rectification bridge structure, and the amplitude and rising rate of the fault current are constrained by multiple parameters, mainly including the leakage reactance of the transformer, the inductance value of the bridge arm reactor, and the short-circuit impedance of the AC system. This mechanism can effectively suppress the further development of the fault current in the initial stage of the fault, for example, the blocking is completed within a few milliseconds after the fault occurs to avoid damage to the equipment. Through the rapid blocking of the converter station, the system can quickly limit the current rise after the fault occurs to ensure the transient stability of the system.

[0072] S103、In the uncontrolled rectification current limiting mode, the time-domain current differential protection device collects current signals at both ends of the DC line in real time, filters the current signals, identifies the starting time of current mutation through differential processing based on the filtered current signals, compensates the current signals at both ends in time based on the starting time of the mutation, calculates the differential current, and constructs a protection criterion based on the differential current;

[0073] The DC line is configured with a time-domain current differential protection device based on time synchronization of the current mutation time. The protection device collects current signals at both ends of the line in real time and filters and preprocesses the sampling data to eliminate the interference of high-frequency signals.

[0074] Then, the starting time of the current waveform mutation is extracted by differentiating the current signals at both ends of the line, and is set as the time synchronization reference. The current data at both ends are compensated in time based on this reference. The differential current is calculated based on the processed current data, and a protection criterion is constructed.

[0075] The filtering, differential processing, time compensation, and differential current calculation mechanism of the time-domain current differential protection device; the protection accuracy is improved through current mutation point identification and synchronization processing.

[0076] The time-domain current differential protection device based on time synchronization of the current mutation time is configured on the DC side. Considering the wave process characteristics of the transmission line, the current signals received by the devices at both ends of the line (denoted as j and k) will be affected by the line propagation delay and the traveling wave reflection. Direct differential calculation has a large deviation from the actual fault current. After the fault current wave from the fault point is detected by the devices at both ends after different time delays, the current at both ends rises rapidly. Therefore, the differential current is calculated after the time compensation of the current at both ends, which is more consistent with the actual fault current. The protection device first differentiates the current to obtain the starting time of the current mutation

[0077] When the current differential value meets the condition, it can be considered that the current starts to mutate:

[0078]

[0079] where K is a reliability coefficient, is the maximum error caused by normal power fluctuation disturbance of the system, is the threshold value.

[0080] When the current differential value exceeds the product of the reliability coefficient and the maximum error, the starting time of the current mutation is determined. The reliability coefficient is a pre-set reliability parameter used to adjust the protection sensitivity, and the maximum error is the maximum error value caused by the normal power fluctuation disturbance of the system, which is set based on historical data. ​

[0081] The differential current is calculated based on the time compensation of the two-terminal current signals at the mutation starting moment, including calculating the time delay according to the difference of the mutation starting moment; if , the time delay is defined , and the differential current is constructed: ; if , the time delay is defined , and the differential current is constructed: .

[0082] Through the time compensation, the calculation result of the differential current is closer to the time domain distribution characteristics of the actual fault current.

[0083] In addition, the method of intercepting the current mutation starting moment to construct a time window can also be used, that is, the current mutation starting moment is taken as the reference to construct a time window; the steady-state operation data before the reference is removed, and the current data segment after the mutation is retained; the differential current is calculated after the retained current data segment is time-compensated.

[0084] Specifically, when the mutation moment of the line two-terminal current is detected , the new time coordinate system is established with the moment as the zero time point respectively, and the new time window of the two-terminal current is constructed based on the coordinate system; the steady-state operation data before the reference is removed, and only the current data segment after the mutation starting point is retained:

[0085] ,

[0086] Among them , is the current under the new coordinate system, and the zero time is the original current mutation point moment.

[0087] The differential current is calculated after the zero points of the processed two-terminal current signals are time-compensated, and the differential protection criterion is constructed accordingly:

[0088]

[0089]

[0090] Among them, is the differential current calculation value; represents the reliability coefficient; represents the maximum value of the differential current fluctuation caused by the external fault, and the mew subscript indicates that the current signal has been preprocessed.

[0091] ​​When the calculated differential current value meets the criterion, it can be judged that the DC line section has a fault. The protection method improves the action accuracy through different time synchronization methods. For example, in the simulation, the differential current waveform is basically consistent with the actual fault current, which proves its reliability.

[0092] Further, the specific implementation process of the time-domain current differential protection device includes:

[0093] S1, the protection devices at both ends of the DC line (located at j and k ends respectively) collect local voltage and current signals in real time, and filter and preprocess the sampling data; the processed data is transmitted to the protection device at the opposite end of the line through the communication channel, realizing synchronization and sharing of information at both ends.

[0094] S2, by differentiating the current signals at both ends of the line, the mutation start time of the current waveform is extracted, and it is set as the time synchronization reference; based on this reference, the current data at both ends is compensated for time synchronization; the differential current is calculated for the processed current data.

[0095] S3, when the differential protection criterion meets the action condition, the protection device sends a trip command, and transmits the command signal to the AC side circuit breaker; after receiving the signal, the circuit breaker quickly executes the trip operation, thereby reliably opening the fault line and completing the fault isolation process. In the construction of the protection criterion, the reliability coefficient K or is a pre-set reliability parameter for adjusting the protection sensitivity, which is set based on the system redundancy design, for example, the value is 1.2-1.5 to avoid misoperation; the maximum error or the error threshold is the maximum differential current fluctuation caused by normal power fluctuation or external fault, which is determined by historical data or simulation to ensure the accuracy of the criterion.

[0096] S104, when the protection criterion meets the action condition, the differential protection device generates a trip signal;

[0097] When the differential protection criterion meets the action condition, that is, the differential current is greater than the product of the reliability coefficient and the error threshold, it is determined that the protection criterion meets the action condition; wherein the reliability coefficient is used to adjust the protection sensitivity, and the error threshold is set based on the maximum differential current fluctuation caused by external fault. The protection device generates a trip signal based on a logic circuit, which is a high-level pulse or a digital signal, ensuring fast response, for example, within about 2 milliseconds after the fault occurs, the criterion is met, the trip signal is generated, providing a basis for subsequent isolation operation.

[0098] S105, the trip signal is transmitted to the AC side circuit breaker through the communication channel; the trip signal is transmitted to the AC side circuit breaker through the protection communication channel.

[0099] The protection communication channel is a dedicated communication link, which is used to ensure the fast and reliable transmission of the trip signal and avoid delay or loss. The channel uses optical fiber or wireless mode, which has high bandwidth and low delay characteristics, such as transmission time less than 1 millisecond. The differential protection device transmits the action signal to the AC side circuit breaker through the channel to ensure signal synchronization and accuracy.

[0100] S106, after receiving the trip signal by the AC side circuit breaker, performing the opening operation to isolate the fault DC line;

[0101] After the circuit breaker receives the signal, it performs the opening operation to open the fault line, and the DC line exits operation, realizing effective isolation of the fault.

[0102] The AC side circuit breaker uses a high-speed circuit breaker, which receives the trip signal and performs the opening operation under mechanical drive to isolate the fault DC line. For example, within about 43 milliseconds after the fault occurs, the trip is completed, and the DC line is cut off to avoid the expansion of the fault. At the same time, this operation cooperates with the DC damping switch to ensure complete isolation of the fault point.

[0103] S107, put in the DC damping switch to accelerate the decay of residual current; keep the total output of the system power constant;

[0104] The DC damping switch is put in to accelerate the decay of the residual current oscillation after the fault is removed; under the condition that the output power of the power supply side remains unchanged, the total output of the system power remains constant.

[0105] At the same time of the opening operation of the AC side circuit breaker, the DC damping switch is put in; the timing of putting in the damping switch is synchronized with the opening operation to accelerate the decay of the residual current. The damping switch promotes the rapid decay of the fault residual current through the resistance or inductance path, and realizes reliable arc extinction when the current crosses zero. The system power maintains the total output constant through closed-loop control, for example, the power supply output power is stable at 300 MW during the fault, avoiding power imbalance leading to frequency fluctuation.

[0106] S108, under the condition of isolating the fault DC line, putting in the DC damping switch, and keeping the total output of the system power constant, using the short-time overload capability of the AC line to transfer all the power originally transmitted by the DC line to the AC line to realize power transfer.

[0107] After the fault line is cut off, its transmission power drops to zero. In this process, the system uses the short-time overload capability of the AC line to transfer all the power originally transmitted by the DC line to the AC line, and finally reaches a new steady state, the AC line transmission power is balanced with the power supply output, ensuring continuous power supply and system stability.

[0108] The AC line bears the whole power transmission of the system due to its inherent short-time overload capability (e.g. 150% rated power for several seconds). During the power transfer process, the total power output of the power supply remains constant, and the power of the original DC line (e.g. 200 MW) is completely transferred to the AC line, so that the power of the AC line is increased to 300 MW.

[0109] The system enters a new steady state through transient regulation, and the whole power transfer process lasts about 150 milliseconds, ensuring the continuity and stability of power supply.

[0110] Please refer to Figures 5-7 Further, an example is described as follows: at t0=2.000 s, a DC two-pole short-circuit fault occurs at a distance of 50 km from the left converter station, and the fault current rises sharply. The MMC detects the overcurrent signal in time and immediately blocks the associated converter station, thereby effectively suppressing the further increase of the fault current. Before t1=2.002 s, the DC line time-domain differential protection identifies the fault state, generates an action signal and transmits it to the AC side circuit breaker. Considering the influence of the mechanical action time of the circuit breaker and other time delay factors, the circuit breaker is tripped at about t2=2.043 s, and the DC line is quickly isolated and taken out of operation.

[0111] At the same time, the DC damping switch is put into operation to accelerate the attenuation of the residual current on the line after the fault is removed. Since the active power output of the power supply remains constant, when the DC line is taken out of operation, the whole transmission power will be transferred to the AC line. The fault will cause the initial power supply-demand imbalance of the system, which will gradually recover to the original state under the action of the power supply power regulation system, and the system output power will be stabilized at the set value 300 MW after a short time fluctuation. At the same time, the transmission power of the AC line will increase accordingly, and finally it will be balanced with the power output. At about t3=2.15 s, the system completes the whole power transfer process, at this time the AC line continuously and stably transmits 300 MW power, and the system enters a new stable state, ensuring the continuity and reliability of power transmission of the power grid.

[0112] As shown in Figure 5 , the differential current simulation diagram of the time-domain differential protection device configured based on the time of the current sudden change moment, , the differential current after time delay and time processing, , the post-fault traveling wave current will pass through a short time delay before reaching the j end and the k end, so the differential current detected after time processing rises rapidly. It can be seen that the differential current is basically consistent with the actual fault current value, proving that the differential current calculated by this method can well reflect the fault current on the actual line, and the reliability of the protection is improved.

[0113] As shown in Figure 6 , the differential current simulation diagram of the time-domain differential protection device configured based on the time of the current sudden change moment, For the processed differential current, since the data segment before the abrupt change point has been removed, the time axis starts from 0 in this case, and... Figure 5 A comparison shows that the differential current waveforms of the two methods are basically the same, and this method can also identify faults in the area more accurately and act quickly.

[0114] In addition, such as Figure 7 The figure shows a simulation diagram of system power transmission before and after a fault. Before the fault, the system was in steady-state operation, with the DC and AC lines sharing the total active power generated by the power source, and the power transmission on both sides was in a balanced state. When a fault occurred in the DC line, the protection system responded quickly, the circuit breaker tripped, and the DC line was taken out of operation, with its transmitted power gradually decreasing to zero. During this period, the power regulation system on the power source side played its role, stabilizing the total power output at a given value through closed-loop control, preventing system frequency instability caused by sudden power changes. All the power originally transmitted through the DC channel was transferred to the AC line. The AC line, with its short-term overload capacity, took on the additional power, and its transmitted power gradually increased during the transient process, eventually reaching a new stable value and balancing with the power output. Simulation results show that the entire power transfer process lasted approximately 150 milliseconds. With the inherent short-term overload capacity of the AC line, a full automatic transfer of power to the AC channel was achieved, proving the effectiveness of the control strategy in maintaining power balance and transmission continuity.

[0115] This application also provides an embedded DC power conversion control device, comprising:

[0116] The detection module detects the overcurrent signal of the DC line through a half-bridge modular multilevel converter (MMC).

[0117] The shutdown module, based on the overcurrent signal, the MMC executes a latch-up strategy to shut down the insulated gate bipolar transistor of the associated converter station, causing the MMC to enter the uncontrolled rectification current limiting mode.

[0118] In the uncontrolled rectification current limiting mode, the criterion module uses a time-domain current differential protection device to collect current signals at both ends of the DC line in real time, filters the current signals, identifies the start time of current change through differential processing based on the filtered current signals, performs time-synchronization compensation on the current signals at both ends based on the start time of the change, calculates the differential current, and constructs protection criteria based on the differential current.

[0119] The signal module generates a trip signal when the protection criteria meet the operating conditions.

[0120] The transmission module transmits the trip signal to the AC side circuit breaker through the communication channel;

[0121] An isolation module, which performs an isolation operation after receiving the trip signal by the AC side breaker, isolates the fault DC line;

[0122] A feeding module, which feeds the DC damping switch, accelerates the residual current attenuation, and keeps the total power constant by the system power supply;

[0123] A transfer module, which, under the conditions of the isolation of the fault DC line, the feeding of the DC damping switch, and the keeping of the total power constant by the system power supply, transfers all the power originally transmitted by the DC line to the AC line by using the short-time overload capacity of the AC line, and realizes the power transfer.

[0124] The application further provides an electronic device, which comprises a memory and a processor, the memory stores a computer program, and the processor executes the computer program to realize the method.

[0125] The application provides a computer readable storage medium, which stores a computer program, and the computer program, when executed in a computer, makes the computer execute the method.

[0126] The above description of the embodiments is for facilitating the general technical personnel in the art to understand and apply the application. The skilled in the art can easily make various modifications to the above embodiments, and apply the general principles described herein to other embodiments without creative labor. Therefore, the application is not limited to the above embodiments, and the improvements and modifications made to the application by the skilled in the art according to the disclosure of the application should be within the protection scope of the application.

Claims

1. An embedded DC power conversion control method, characterized in that, include: Overcurrent signals in DC lines are detected using a half-bridge modular multilevel converter (MMC). Based on the overcurrent signal, the MMC executes a latch-up strategy, turns off the insulated gate bipolar transistor of the associated converter station, and puts the MMC into an uncontrolled rectification current limiting mode. In the uncontrolled rectification current limiting mode, the time-domain current differential protection device collects the current signals at both ends of the DC line in real time, filters the current signals, identifies the start time of the current change through differential processing based on the filtered current signals, performs time compensation on the current signals at both ends based on the start time of the change, calculates the differential current, and constructs protection criteria based on the differential current. When the protection criteria meet the operating conditions, the differential protection device generates a trip signal; The trip signal is transmitted to the AC side circuit breaker through the communication channel; After receiving the trip signal, the AC-side circuit breaker performs a tripping operation to isolate the faulty DC line. Engage the DC damping switch to accelerate the decay of residual current; The total output is kept constant by the system power supply; With the DC line isolated from the fault, the DC damping switch engaged, and the total output maintained constant by the system power supply, the AC line utilizes its short-term overload capacity to transfer all the power originally transmitted by the DC line to the AC line, thus achieving power transfer.

2. The method according to claim 1, characterized in that, The starting time of the current surge is identified by differentiating the filtered current signal, including: The filtered current signal is differentiated to generate a current differential value; When the differential value of the current exceeds the product of the reliability coefficient and the maximum error, the start time of the current sudden change is determined; The reliability coefficient is a preset reliability parameter, and the maximum error value is the maximum error value caused by normal power fluctuation disturbances in the system.

3. The method according to claim 1, characterized in that, Based on the time-synchronized compensation of the current signals at both ends at the abrupt change initiation moment, the differential current is calculated, including: Calculate the delay time based on the difference in the mutation initiation time; The delayed current signal is processed based on the delay time to synchronize the current signals at both ends; Calculate the differential current based on the synchronized current signal.

4. The method according to claim 1, characterized in that, The protection criteria are constructed based on the differential current, including: The protection criterion is constructed using a reliability coefficient and an error threshold. When the differential current is greater than the product of the reliability coefficient and the error threshold, the protection criterion is determined to meet the operating conditions. The reliability coefficient is used to adjust the protection sensitivity, and the error threshold is set based on the maximum value of differential current fluctuation caused by faults outside the protection zone.

5. The method according to claim 1, characterized in that, Transmitting the trip signal to the AC side circuit breaker via a communication channel includes: The trip signal is transmitted through a protected communication channel; The protection communication channel is a dedicated communication link used to ensure fast and reliable transmission of trip signals.

6. The method according to claim 1, characterized in that, Engaging a DC damping switch includes: While the AC side circuit breaker performs the tripping operation, the DC damping switch is engaged; The DC damping switch is engaged in sync with the tripping operation to accelerate the decay of residual current.

7. The method according to claim 1, characterized in that, The method involves identifying the start time of a current surge based on the filtered current signal through differentiation, and also includes a method for constructing a time window by extracting the start time of the current surge. A time window is constructed based on the start time of the current surge; Remove the steady-state operating data prior to the reference, and retain the current data segment after the abrupt change; The differential current is calculated after time-compensation is performed on the retained current data segment.

8. An embedded DC power conversion and control device, characterized in that, include: The detection module detects the overcurrent signal of the DC line through a half-bridge modular multilevel converter (MMC). The shutdown module, based on the overcurrent signal, the MMC executes a latch-up strategy to shut down the insulated gate bipolar transistor of the associated converter station, causing the MMC to enter the uncontrolled rectification current limiting mode. In the uncontrolled rectification current limiting mode, the criterion module uses a time-domain current differential protection device to collect current signals at both ends of the DC line in real time, filters the current signals, identifies the start time of current change through differential processing based on the filtered current signals, performs time-synchronization compensation on the current signals at both ends based on the start time of the change, calculates the differential current, and constructs protection criteria based on the differential current. The signal module generates a trip signal when the protection criteria meet the operating conditions. The transmission module transmits the trip signal to the AC side circuit breaker through the communication channel; The isolation module receives the trip signal from the AC-side circuit breaker and performs a tripping operation to isolate the faulty DC line. Activate the module and the DC damping switch to accelerate the decay of residual current. The total output is kept constant by the system power supply; The power transfer module, under the conditions of isolating the faulty DC line, engaging the DC damping switch, and maintaining a constant total output by the system power supply, transfers all the power originally transmitted by the DC line to the AC line using the short-term overload capacity of the AC line, thereby realizing power transfer.

9. An electronic device, characterized in that, It includes a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the method as described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, It stores a computer program that, when executed in a computer, causes the computer to perform the method described in any one of claims 1-7.

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