Line transfer control method and device for multi-AC-port flexible DC converter

Abstract

The invention discloses a line transfer control method and device for a multi-AC port flexible DC converter. The method comprises the following steps: monitoring a first AC line connected with the multi-AC port flexible DC converter; when the first alternating current line fails, judging the type of the second alternating current line; if the type of the second alternating current line is a balanced line, selecting a second alternating current line as a target alternating current line from the second alternating current lines corresponding to the first alternating current lines without faults, and taking the target alternating current line as the balanced line, a control mode corresponding to a port converter corresponding to a multi-AC port flexible DC converter connected with the second AC line is switched into a fixed AC voltage control mode; and if the type of the second alternating current line is an unbalanced line, switching a control mode corresponding to a port converter corresponding to a multi-alternating current port flexible direct current converter connected with the second alternating current line into a fixed alternating current voltage control mode. According to the invention, line transfer control is realized based on different control modes.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to a line transfer control method and device for a multi-AC port flexible DC converter. Background Art

[0002] With the super-large-scale offshore wind farms and the increase in offshore distances, the overvoltage and reactive power loss caused by the capacitance effect of submarine cables to the ground in the AC convergence and transmission system of wind farms are serious, which reduces the effective load capacity of the cables. Therefore, a large number of reactive power compensation devices need to be configured, which limits its application in deep-sea wind power transmission. However, flexible direct current transmission technology can improve the flexibility of system operation control due to its characteristics of independent control of active and reactive power, no need for reactive power compensation, power supply to passive networks, and unchanged voltage polarity when the tide reverses. In the past decade, it has received more and more attention in high-voltage direct current transmission, especially in deep-sea new energy power generation transmission systems.

[0003] The researchers proposed a multi-AC port flexible DC converter based on double frequency circulating current injection. The multi-AC port flexible DC converter consists of a modular multi-level DC converter and an AC power flow controller (eACPFC) embedded in the modular multi-level DC converter. The AC power flow controller can interconnect multiple AC lines and has the ability to independently decouple and control the active and reactive power of each line, thereby realizing the joint consumption of DC-transmitted sea wind power by multiple lines. By adjusting the DC component and interacting with the MMC DC circulating current, the power balance of the embedded AC power flow controller can be achieved. Compared with the traditional BTB-MMC solution, the proposed multi-AC port flexible DC converter has the advantages of compactness, low cost, and easy expansion. There is currently no research on load transfer based on multi-AC port flexible DC converters, which leads to poor power supply regulation capabilities of multi-AC port flexible DC converters during operation.

[0004] Therefore, there is an urgent need for a line transfer control strategy for a multi-AC port flexible DC converter to solve the problem of poor power supply regulation capability of the multi-AC port flexible DC converter during operation. Summary of the invention

[0005] The embodiments of the present invention provide a line transfer control method, device, terminal equipment and storage medium of a multi-AC port flexible DC converter to solve the problem of poor power supply regulation capability of the multi-AC port flexible DC converter during operation.

[0006] In order to solve the above problem, an embodiment of the present invention provides a line transfer control method of a multi-AC port flexible DC converter, comprising:

[0007] Monitoring a first AC line to which the multi-AC port flexible DC converter is connected;

[0008] When a fault occurs in the first AC line, the type of the second AC line is determined; wherein the second AC line is an upper line of the first AC line to which the multi-AC port flexible DC converter is connected;

[0009] If the type of the second AC line is a balanced line, a second AC line is selected as a target AC line from among the second AC lines corresponding to the first AC lines that have not failed, and the target AC line is used as a balanced line, and the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to constant AC voltage control;

[0010] If the type of the second AC line is an unbalanced line, the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to constant AC voltage control.

[0011] As an improvement of the above solution, the multi-AC port flexible DC converter is connected to the corresponding second AC lines through a plurality of first AC lines respectively; wherein each first AC line corresponds to a second AC line respectively.

[0012] As an improvement of the above solution, after the target AC line is used as a balanced line, the method further includes:

[0013] The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the target AC line is switched to the optimal modulation optimization control.

[0014] As an improvement of the above solution, the optimal modulation degree optimization control includes:

[0015] Obtaining a balanced line output voltage of a port converter corresponding to a multi-AC port flexible DC converter connected to a target AC line;

[0016] Based on the balanced line output voltage, reducing the maximum value of the unbalanced voltage corresponding to each type of unbalanced line to the minimum is the optimization goal, and the unbalanced voltage corresponding to each type of unbalanced line is optimized; wherein the unbalanced voltage is specifically: the output voltage of the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line corresponding to the type of unbalanced line.

[0017] As an improvement of the above solution, the constant AC voltage control includes:

[0018] Obtaining a d-axis component of a port voltage of a first AC line having a fault, a q-axis component of a port voltage of a first AC line having a fault, a d-axis component of an MMC port output voltage, a q-axis component of an MMC port output voltage, an angular frequency of a power frequency, a d-axis component of an MMC AC output current, and a q-axis component of an MMC AC output current;

[0019] Substitute the port voltage d-axis component of the first AC line with a fault, the port voltage q-axis component of the first AC line with a fault, the MMC port output voltage d-axis component, the MMC port output voltage q-axis component, the power frequency angular frequency, the MMC AC output current d-axis component, and the MMC AC output current q-axis component into the fixed AC voltage control equation to obtain the MMC port modulated output voltage and the port modulated voltage of the first AC line with a fault; wherein the MMC port modulated output voltage includes: the MMC port modulated output voltage d-axis component and the MMC port modulated output voltage q-axis component; the port modulated voltage of the second AC line with a fault includes: the port modulated voltage q-axis component of the first AC line with a fault and the port modulated voltage d-axis component of the first AC line with a fault; the fixed AC voltage control equation satisfies the following conditions:

[0020]

[0021] Where V ck_diffd * is the d-axis component of the modulated output voltage of the MMC port, V ck_diffq * is the q-axis component of the modulated output voltage of the MMC port, k p is the proportionality coefficient, k i is the integral coefficient, s is the Laplace operator, V Lkd * is the d-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkd is the d-axis component of the port voltage of the first AC line where the fault occurs, V Lkq * is the q-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkq is the q-axis component of the port voltage of the first AC line where the fault occurs, V diffd is the d-axis component of the MMC port output voltage, V diffq is the q-axis component of the output voltage of the MMC port, ω is the angular frequency of the power frequency, I od is the d-axis component of the MMC AC output current, I oq is the q-axis component of the MMC AC output current;

[0022] Based on the MMC port modulated output voltage and the port modulated voltage of the second AC line having a fault, the second AC line having a fault is controlled through the P1 controller.

[0023] Correspondingly, an embodiment of the present invention further provides a line transfer control device for a multi-AC port flexible DC converter, comprising: a data monitoring module, a data judgment module, a balanced line module and an unbalanced line module;

[0024] The data monitoring module is used to monitor the first AC line to which the multi-AC port flexible DC converter is connected;

[0025] The data judgment module is used to judge the type of the second AC line when a fault occurs in the first AC line; wherein the second AC line is the previous line of the first AC line connected to the multi-AC port flexible DC converter;

[0026] The balanced line module is used for selecting a second AC line as a target AC line from the second AC lines corresponding to the first AC lines that have not failed, if the type of the second AC line is a balanced line, and using the target AC line as a balanced line, and switching the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line to a constant AC voltage control;

[0027] The unbalanced line module is used to switch the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line to constant AC voltage control if the type of the second AC line is an unbalanced line.

[0028] As an improvement of the above solution, the multi-AC port flexible DC converter is connected to the corresponding second AC lines through a plurality of first AC lines respectively; wherein each first AC line corresponds to a second AC line respectively.

[0029] As an improvement of the above solution, after the target AC line is used as a balanced line, the method further includes:

[0030] The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the target AC line is switched to the optimal modulation optimization control.

[0031] As an improvement of the above solution, the optimal modulation degree optimization control includes:

[0032] Obtaining a balanced line output voltage of a port converter corresponding to a multi-AC port flexible DC converter connected to a target AC line;

[0033] Based on the balanced line output voltage, reducing the maximum value of the unbalanced voltage corresponding to each type of unbalanced line to the minimum is the optimization goal, and the unbalanced voltage corresponding to each type of unbalanced line is optimized; wherein the unbalanced voltage is specifically: the output voltage of the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line corresponding to the type of unbalanced line.

[0034] As an improvement of the above solution, the constant AC voltage control includes:

[0035] Obtaining a d-axis component of a port voltage of a first AC line having a fault, a q-axis component of a port voltage of a first AC line having a fault, a d-axis component of an MMC port output voltage, a q-axis component of an MMC port output voltage, an angular frequency of a power frequency, a d-axis component of an MMC AC output current, and a q-axis component of an MMC AC output current;

[0036] Substitute the port voltage d-axis component of the first AC line with a fault, the port voltage q-axis component of the first AC line with a fault, the MMC port output voltage d-axis component, the MMC port output voltage q-axis component, the power frequency angular frequency, the MMC AC output current d-axis component, and the MMC AC output current q-axis component into the fixed AC voltage control equation to obtain the MMC port modulated output voltage and the port modulated voltage of the first AC line with a fault; wherein the MMC port modulated output voltage includes: the MMC port modulated output voltage d-axis component and the MMC port modulated output voltage q-axis component; the port modulated voltage of the second AC line with a fault includes: the port modulated voltage q-axis component of the first AC line with a fault and the port modulated voltage d-axis component of the first AC line with a fault; the fixed AC voltage control equation satisfies the following conditions:

[0037]

[0038] Where V ck_diffd * is the d-axis component of the modulated output voltage of the MMC port, V ck_diffq * is the q-axis component of the modulated output voltage of the MMC port, k p is the proportionality coefficient, k i is the integral coefficient, s is the Laplace operator, V Lkd * is the d-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkd is the d-axis component of the port voltage of the first AC line where the fault occurs, V Lkq * is the q-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkqis the q-axis component of the port voltage of the first AC line where the fault occurs, V diffd is the d-axis component of the MMC port output voltage, V diffq is the q-axis component of the output voltage of the MMC port, ω is the angular frequency of the power frequency, I od is the d-axis component of the MMC AC output current, I oq is the q-axis component of the MMC AC output current;

[0039] Based on the MMC port modulated output voltage and the port modulated voltage of the second AC line having a fault, the second AC line having a fault is controlled through a PI controller.

[0040] As can be seen from the above, the present invention has the following beneficial effects:

[0041] The present invention provides a line transfer control method for a multi-AC port flexible DC converter, which monitors a first AC line connected to the multi-AC port flexible DC converter; when a fault occurs in the first AC line, the type of the second AC line is judged; if the type of the second AC line is a balanced line, a second AC line is selected as a target AC line from the second AC lines corresponding to the first AC lines that have not failed, the target AC line is used as a balanced line, and the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to a fixed AC voltage control; if the type of the second AC line is an unbalanced line, the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to a fixed AC voltage control. The present invention performs fault identification on the first AC line connected to the multi-AC port flexible DC converter. After the fault is identified, different controls are performed based on the different types of second AC lines corresponding to the faulty first AC line: when the first AC line corresponding to the balanced line fails, the balanced line is re-searched, and the faulty circuit is controlled with a constant AC voltage; when the second AC line corresponding to the unbalanced line fails, the constant AC voltage control is directly performed. The present invention realizes line transfer control based on different control methods. The present invention solves the problem of poor power supply regulation capability of the multi-AC port flexible DC converter during operation based on different control methods of balanced lines and unbalanced lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a flow chart of a line transfer control method of a multi-AC port flexible DC converter provided by an embodiment of the present invention;

[0043] Figure 2 It is a structural schematic diagram of a line transfer control device for a multi-AC port flexible DC converter provided by an embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of the structure of a terminal device provided by an embodiment of the present invention;

[0045] Figure 4 It is a topological diagram of a multi-AC port flexible DC converter interconnecting multiple transmission lines provided by an embodiment of the present invention;

[0046] Figure 5 This is a connection diagram of a multi-AC port flexible DC converter for load transfer provided by an embodiment of the present invention;

[0047] Figure 6 It is a block diagram of a constant AC voltage control of a multi-AC port flexible DC converter provided by an embodiment of the present invention;

[0048] Figure 7 It is an active power waveform of line 1 connected to a multi-AC port flexible DC converter provided by an embodiment of the present invention;

[0049] Figure 8 It is a reactive power waveform of line 1 connected to a multi-AC port flexible DC converter provided by an embodiment of the present invention;

[0050] Fig. 9 It is an active power waveform of line 2 connected to a multi-AC port flexible DC converter provided by an embodiment of the present invention;

[0051] Fig.10 It is the reactive power waveform of line 2 connected to the multi-AC port flexible DC converter provided by one embodiment of the present invention;

[0052] Fig.11 It is an active power waveform of line 3 connected to a multi-AC port flexible DC converter provided in one embodiment of the present invention;

[0053] Fig.12 It is the reactive power waveform of line 3 connected to the multi-AC port flexible DC converter provided by one embodiment of the present invention;

[0054] Fig.13 This is an active power waveform of a DC line connected to a multi-AC port flexible DC converter provided in one embodiment of the present invention. DETAILED DESCRIPTION

[0055] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0056] Embodiment 1

[0057] See also Figure 1, Figure 1 FIG. 1 is a flow chart of a line transfer control method of a multi-AC port flexible DC converter provided by an embodiment of the present invention. Figure 1 As shown, this embodiment includes steps 101 to 104, and each step is specifically as follows:

[0058] Step 101: monitor a first AC line to which the multi-AC port flexible DC converter is connected.

[0059] In this embodiment, when monitoring the first AC line to which the multi-AC port flexible DC converter is connected, when electrical data of the first AC line is abnormal, it is determined that a fault occurs in the first AC line.

[0060] Step 102: When a fault occurs in the first AC line, determine the type of the second AC line; wherein the second AC line is an upper line of the first AC line to which the multi-AC port flexible DC converter is connected.

[0061] In this embodiment, the multi-AC port flexible DC converter is connected to the corresponding second AC lines through a plurality of first AC lines respectively; wherein each first AC line corresponds to a second AC line respectively.

[0062] In a specific embodiment, when a fault occurs in the upper level line of the line connected to the multi-AC port flexible DC converter, in order to prevent the fault from being transmitted to the current level line and excessive short-circuit current from damaging the power devices, the upper level power grid should be quickly disconnected after the fault occurs. At this time, since the multi-AC port flexible DC converter has the ability to regulate power flow, the remaining capacity of the remaining normal lines can be used to supply power to all or part of the load of the faulty line, that is, load transfer is realized. At this time, the port converter connected to the faulty line adopts constant AC voltage control.

[0063] Step 103: If the type of the second AC line is a balanced line, a second AC line is selected as a target AC line from the second AC lines corresponding to the first AC lines that have not failed, and the target AC line is used as a balanced line. The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to constant AC voltage control.

[0064] In this embodiment, after the target AC line is used as a balanced line, the method further includes:

[0065] The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the target AC line is switched to the optimal modulation optimization control.

[0066] In this embodiment, the optimal modulation degree optimization control includes:

[0067] Obtaining a balanced line output voltage of a port converter corresponding to a multi-AC port flexible DC converter connected to a target AC line;

[0068] Based on the balanced line output voltage, reducing the maximum value of the unbalanced voltage corresponding to each type of unbalanced line to the minimum is the optimization goal, and the unbalanced voltage corresponding to each type of unbalanced line is optimized; wherein the unbalanced voltage is specifically: the output voltage of the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line corresponding to the type of unbalanced line.

[0069] In a specific implementation, for a multi-AC port flexible DC converter, one of the connected AC lines is a balanced line, which is used to maintain the overall power balance of the system. When the upper line of the balanced line is disconnected, a normal line needs to be selected as a new balanced line. The control mode of the port converter connected to the line is switched from the original active and reactive power control to the optimal modulation optimization control. The port converter of the faulty line adopts constant AC voltage control, and the control strategy of the remaining lines remains unchanged. The specific power flow regulation instructions can be changed according to the upper-level scheduling.

[0070] Step 104: If the type of the second AC line is an unbalanced line, the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to constant AC voltage control.

[0071] In a specific implementation, for a multi-AC port flexible DC converter, one of the connected AC lines is a balanced line, which is used to maintain the overall power balance of the system. When the upper line of the unbalanced line is disconnected, the control mode of the port converters connected to the remaining lines can remain unchanged, and the control mode of the port converter connected to the faulty line adopts constant AC voltage control.

[0072] In this embodiment, the constant AC voltage control includes:

[0073] Obtaining a d-axis component of a port voltage of a first AC line having a fault, a q-axis component of a port voltage of a first AC line having a fault, a d-axis component of an MMC port output voltage, a q-axis component of an MMC port output voltage, an angular frequency of a power frequency, a d-axis component of an MMC AC output current, and a q-axis component of an MMC AC output current;

[0074] Substitute the port voltage d-axis component of the first AC line with a fault, the port voltage q-axis component of the first AC line with a fault, the MMC port output voltage d-axis component, the MMC port output voltage q-axis component, the power frequency angular frequency, the MMC AC output current d-axis component, and the MMC AC output current q-axis component into the fixed AC voltage control equation to obtain the MMC port modulated output voltage and the port modulated voltage of the first AC line with a fault; wherein the MMC port modulated output voltage includes: the MMC port modulated output voltage d-axis component and the MMC port modulated output voltage q-axis component; the port modulated voltage of the second AC line with a fault includes: the port modulated voltage q-axis component of the first AC line with a fault and the port modulated voltage d-axis component of the first AC line with a fault; the fixed AC voltage control equation satisfies the following conditions:

[0075]

[0076] Where V ck_diffd * is the d-axis component of the modulated output voltage of the MMC port, V ck_diffq * is the q-axis component of the modulated output voltage of the MMC port, k p is the proportionality coefficient, k i is the integral coefficient, s is the Laplace operator, V Lkd * is the d-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkd is the d-axis component of the port voltage of the first AC line where the fault occurs, V Lkq * is the q-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkq is the q-axis component of the port voltage of the first AC line where the fault occurs, V diffd is the d-axis component of the MMC port output voltage, V diffq is the q-axis component of the output voltage of the MMC port, ω is the angular frequency of the power frequency, I od is the d-axis component of the MMC AC output current, I oq is the q-axis component of the MMC AC output current;

[0077] Based on the MMC port modulated output voltage and the port modulated voltage of the second AC line having a fault, the second AC line having a fault is controlled through a PI controller.

[0078] For a better explanation of constant AC voltage control, see Figure 6 , Figure 6 It is a block diagram of constant AC voltage control of a multi-AC port flexible DC converter provided by an embodiment of the present invention.

[0079] In a specific embodiment, see Figure 4 ,according to Figure 4 From the equivalent circuit of the multi-AC port flexible DC converter shown in Figure 1, it can be seen that the fault line port voltage satisfies:

[0080]

[0081] in, is the terminal voltage of the first AC line where a fault occurs; Output voltage of MMC port; Modulate the output voltage of the MMC port to adjust the voltage of the fault line port; is the voltage drop on the MMC equivalent line inductor. From equation (1), it can be seen that by adjusting the output voltage of the fault port converter, the port voltage of the fault line can be indirectly controlled.

[0082] Perform park transformation on equation (1) and convert it into frequency domain, and we can get

[0083]

[0084] From formula (2), the control equation of the port constant voltage control can be obtained as follows:

[0085]

[0086] In formula (3), the PI controller can realize zero-net-difference control of the port voltage; by adding the feedforward term, the dynamic performance of the system can be improved.

[0087] See also Figure 5 This embodiment provides a method for designing main circuit parameters of a multi-AC port flexible DC converter based on double frequency circulating current injection. In this embodiment, the multi-AC port flexible DC converter is connected to three 220kV transmission lines. The specific steps are as follows:

[0088] In order to verify the effectiveness of the proposed control strategy, MATLAB / Simulink software is used to simulate the system. The power flow of each line in the simulation is shown in Table 1, and the simulation parameters are shown in Table 2. Line 1 is the original balanced line. When the upper line of line 1 fails, the section switch on line 1 and the circuit breaker at the port outlet of MMC-eACPFC trip. At this time, feeder 2 is selected as the new balanced feeder, and the control mode of the port converter connected to feeder 2 is switched from active and reactive control to optimal modulation optimization control. Then, the port converter connected to line 1 adopts constant voltage control to restore the power supply to the load connected to line 1, and at the same time adjusts the active power instruction of line 3 so that line 2 and line 3 jointly supply the active power required by the load of line 1, thereby realizing load transfer.

[0089] Table 1

[0090]

[0091] Table 2

[0092]

[0093] The simulation sequence is as follows: when t = 9s, the upper line of line 1 fails, line 1 is cut off, line 2 is selected as the new balanced feeder, and the control mode of the corresponding port converter is changed; when t = 9.1s, the port converter connected to line 1 is switched to the constant voltage control mode; when t = 9.2s, line 1 is connected to a 0.6pu active load. The given power flow conditions of the simulation are shown in Table 1. Table 2 shows the simulation parameters.

[0094] like Figures 4 to 9 As shown, they are respectively the active power waveform and reactive power waveform of each line. Fig.10 It is the active power waveform on the DC side. It can be seen from the waveform that after the power failure of line 1, the power supply of line 1 was restored through the constant voltage control of MMC-eACPFC.

[0095] The simulation results show that the power supply restoration strategy for power-off areas based on MMC-eACPFC proposed in this paper can provide power to the passive network through Vf control, and at the same time, cooperate with line flow control to realize load distribution during flow transfer.

[0096] See also Figure 2 , Figure 2 It is a structural diagram of a line transfer control device for a multi-AC port flexible DC converter provided by an embodiment of the present invention, comprising: a data monitoring module 201, a data judgment module 202, a balanced line module 203 and an unbalanced line module 204;

[0097] The data monitoring module is used to monitor the first AC line to which the multi-AC port flexible DC converter is connected;

[0098] The data judgment module is used to judge the type of the second AC line when a fault occurs in the first AC line; wherein the second AC line is the previous line of the first AC line connected to the multi-AC port flexible DC converter;

[0099] The balanced line module is used for selecting a second AC line as a target AC line from the second AC lines corresponding to the first AC lines that have not failed, if the type of the second AC line is a balanced line, and using the target AC line as a balanced line, and switching the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line to a constant AC voltage control;

[0100] The unbalanced line module is used to switch the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line to constant AC voltage control if the type of the second AC line is an unbalanced line.

[0101] As an improvement of the above solution, the multi-AC port flexible DC converter is connected to the corresponding second AC lines through a plurality of first AC lines respectively; wherein each first AC line corresponds to a second AC line respectively.

[0102] As an improvement of the above solution, after the target AC line is used as a balanced line, the method further includes:

[0103] The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the target AC line is switched to the optimal modulation optimization control.

[0104] As an improvement of the above solution, the optimal modulation degree optimization control includes:

[0105] Obtaining a balanced line output voltage of a port converter corresponding to a multi-AC port flexible DC converter connected to a target AC line;

[0106] Based on the balanced line output voltage, reducing the maximum value of the unbalanced voltage corresponding to each type of unbalanced line to the minimum is the optimization goal, and the unbalanced voltage corresponding to each type of unbalanced line is optimized; wherein the unbalanced voltage is specifically: the output voltage of the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line corresponding to the type of unbalanced line.

[0107] As an improvement of the above solution, the constant AC voltage control includes:

[0108] Obtaining a d-axis component of a port voltage of a first AC line having a fault, a q-axis component of a port voltage of a first AC line having a fault, a d-axis component of an MMC port output voltage, a q-axis component of an MMC port output voltage, an angular frequency of a power frequency, a d-axis component of an MMC AC output current, and a q-axis component of an MMC AC output current;

[0109] Substitute the port voltage d-axis component of the first AC line with a fault, the port voltage q-axis component of the first AC line with a fault, the MMC port output voltage d-axis component, the MMC port output voltage q-axis component, the power frequency angular frequency, the MMC AC output current d-axis component, and the MMC AC output current q-axis component into the fixed AC voltage control equation to obtain the MMC port modulated output voltage and the port modulated voltage of the first AC line with a fault; wherein the MMC port modulated output voltage includes: the MMC port modulated output voltage d-axis component and the MMC port modulated output voltage q-axis component; the port modulated voltage of the second AC line with a fault includes: the port modulated voltage q-axis component of the first AC line with a fault and the port modulated voltage d-axis component of the first AC line with a fault; the fixed AC voltage control equation satisfies the following conditions:

[0110]

[0111] Where V ck_diffd * is the d-axis component of the modulated output voltage of the MMC port, V ck_diffq * is the q-axis component of the modulated output voltage of the MMC port, k p is the proportionality coefficient, k i is the integral coefficient, s is the Laplace operator, V Lkd * is the d-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkd is the d-axis component of the port voltage of the first AC line where the fault occurs, V Lkq * is the q-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkq is the q-axis component of the port voltage of the first AC line where the fault occurs, V diffd is the d-axis component of the MMC port output voltage, V diffq is the q-axis component of the output voltage of the MMC port, ω is the angular frequency of the power frequency, I od is the d-axis component of the MMC AC output current, I oq is the q-axis component of the MMC AC output current;

[0112] Based on the MMC port modulated output voltage and the port modulated voltage of the second AC line having a fault, the second AC line having a fault is controlled through a PI controller.

[0113] This embodiment monitors the first AC line connected to the multi-AC port flexible DC converter; when the first AC line fails, the type of the second AC line is determined; if the type of the second AC line is a balanced line, a second AC line is selected as the target AC line from the second AC lines corresponding to the first AC line that has not failed, and the target AC line is used as a balanced line, and the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to a fixed AC voltage control; if the type of the second AC line is an unbalanced line, the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to a fixed AC voltage control. The present invention identifies the fault of the first AC line connected to the multi-AC port flexible DC converter, and after identifying the fault, different controls are performed based on the different types of the second AC line corresponding to the faulty first AC line: when the first AC line corresponding to the balanced line fails, the balanced line is re-searched, and the faulty circuit is controlled with a fixed AC voltage; when the second AC line corresponding to the unbalanced line fails, the fixed AC voltage control is directly performed. The present invention realizes line transfer control based on different control modes. The present invention solves the problem of poor power supply regulation capability of a multi-AC port flexible DC converter during operation based on different control modes of a balanced line and an unbalanced line.

[0114] Embodiment 2

[0115] See also Figure 3 , Figure 3 It is a schematic diagram of the structure of a terminal device provided in one embodiment of the present invention.

[0116] A terminal device of this embodiment includes: a processor 301, a memory 302, and a computer program stored in the memory 302 and executable on the processor 301. When the processor 301 executes the computer program, the steps of the line transfer control method of each multi-AC port flexible DC converter in the embodiment are implemented, such as Figure 1 Alternatively, when the processor executes the computer program, the functions of each module in the above-mentioned device embodiments are realized, for example: Figure 2 All modules of the line transfer control device of the multi-AC port flexible DC converter are shown.

[0117] In addition, an embodiment of the present invention further provides a computer-readable 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 the line transfer control method of the multi-AC port flexible DC converter as described in any of the above embodiments.

[0118] Those skilled in the art will understand that the schematic diagram is merely an example of a terminal device and does not constitute a limitation on the terminal device. The terminal device may include more or fewer components than shown in the diagram, or a combination of certain components, or different components. For example, the terminal device may also include input and output devices, network access devices, buses, etc.

[0119] The processor 301 may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor may be a microprocessor or any conventional processor, etc. The processor 301 is the control center of the terminal device, and uses various interfaces and lines to connect various parts of the entire terminal device.

[0120] The memory 302 can be used to store the computer program and / or module. The processor 301 implements various functions of the terminal device by running or executing the computer program and / or module stored in the memory and calling the data stored in the memory 302. The memory 302 can mainly include a program storage area and a data storage area, wherein the program storage area can store an operating system, an application required for at least one function (such as a sound playback function, an image playback function, etc.), etc.; the data storage area can store data created according to the use of the mobile phone (such as audio data, a phone book, etc.), 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 Media Card, 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 devices.

[0121] Wherein, if the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Wherein, 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, etc. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, 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, etc.

[0122] It should be noted that the device embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. In addition, in the accompanying drawings of the device embodiments provided by the present invention, the connection relationship between the modules indicates that there is a communication connection between them, which may be specifically implemented as one or more communication buses or signal lines. A person of ordinary skill in the art may understand and implement it without paying any creative effort.

[0123] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A line transfer control method for a multi-AC port flexible DC converter, characterized in that: include: Monitoring a first AC line to which the multi-AC port flexible DC converter is connected; When a fault occurs in the first AC line, the type of the second AC line is determined; wherein the second AC line is an upper line of the first AC line to which the multi-AC port flexible DC converter is connected; If the type of the second AC line is a balanced line, a second AC line is selected as a target AC line from among the second AC lines corresponding to the first AC lines that have not failed, and the target AC line is used as a balanced line, and the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to constant AC voltage control; If the type of the second AC line is an unbalanced line, the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line is switched to constant AC voltage control.

2. The line transfer control method of a multi-AC port flexible DC converter according to claim 1, characterized in that: The multi-AC port flexible DC converter is connected to corresponding second AC lines through a plurality of first AC lines respectively; wherein each first AC line corresponds to a second AC line respectively.

3. The line transfer control method of a multi-AC port flexible DC converter according to claim 2, characterized in that: After the target AC line is used as a balanced line, the method further includes: The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the target AC line is switched to the optimal modulation optimization control.

4. The line transfer control method of a multi-AC port flexible DC converter according to claim 3 is characterized in that: The optimal modulation degree optimization control includes: Obtaining a balanced line output voltage of a port converter corresponding to a multi-AC port flexible DC converter connected to a target AC line; Based on the balanced line output voltage, reducing the maximum value of the unbalanced voltage corresponding to each type of unbalanced line to the minimum is the optimization goal, and the unbalanced voltage corresponding to each type of unbalanced line is optimized; wherein the unbalanced voltage is specifically: the output voltage of the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line corresponding to the type of unbalanced line.

5. The line transfer control method of a multi-AC port flexible DC converter according to claim 4, characterized in that: The constant AC voltage control comprises: Obtaining a d-axis component of a port voltage of a first AC line having a fault, a q-axis component of a port voltage of a first AC line having a fault, a d-axis component of an MMC port output voltage, a q-axis component of an MMC port output voltage, an angular frequency of a power frequency, a d-axis component of an MMC AC output current, and a q-axis component of an MMC AC output current; Substitute the port voltage d-axis component of the first AC line with a fault, the port voltage q-axis component of the first AC line with a fault, the MMC port output voltage d-axis component, the MMC port output voltage q-axis component, the power frequency angular frequency, the MMC AC output current d-axis component, and the MMC AC output current q-axis component into the fixed AC voltage control equation to obtain the MMC port modulated output voltage and the port modulated voltage of the first AC line with a fault; wherein the MMC port modulated output voltage includes: the MMC port modulated output voltage d-axis component and the MMC port modulated output voltage q-axis component; the port modulated voltage of the second AC line with a fault includes: the port modulated voltage q-axis component of the first AC line with a fault and the port modulated voltage d-axis component of the first AC line with a fault; the fixed AC voltage control equation satisfies the following conditions: Where V ck_diffd * is the d-axis component of the modulated output voltage of the MMC port, V ck_diffq * is the q-axis component of the modulated output voltage of the MMC port, k p is the proportionality coefficient, k i is the integral coefficient, s is the Laplace operator, V Lkd * is the d-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkd is the d-axis component of the port voltage of the first AC line where the fault occurs, V Lkq * is the q-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkq is the q-axis component of the port voltage of the first AC line where the fault occurs, V diffd is the d-axis component of the MMC port output voltage, V diffq is the q-axis component of the output voltage of the MMC port, ω is the angular frequency of the power frequency, I od is the d-axis component of the MMC AC output current, I oq is the q-axis component of the MMC AC output current; Based on the MMC port modulated output voltage and the port modulated voltage of the second AC line having a fault, the second AC line having a fault is controlled through a PI controller.

6. A line transfer control device for a multi-AC port flexible DC converter, characterized in that: include: Data monitoring module, data judgment module, balanced line module and unbalanced line module; The data monitoring module is used to monitor the first AC line to which the multi-AC port flexible DC converter is connected; The data judgment module is used to judge the type of the second AC line when a fault occurs in the first AC line; wherein the second AC line is the previous line of the first AC line connected to the multi-AC port flexible DC converter; The balanced line module is used for selecting a second AC line as a target AC line from the second AC lines corresponding to the first AC lines that have not failed, if the type of the second AC line is a balanced line, and using the target AC line as a balanced line, and switching the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line to a constant AC voltage control; The unbalanced line module is used to switch the control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line to constant AC voltage control if the type of the second AC line is an unbalanced line.

7. The line transfer control device for a multi-AC port flexible DC converter according to claim 6, characterized in that: The multi-AC port flexible DC converter is connected to corresponding second AC lines through a plurality of first AC lines respectively; wherein each first AC line corresponds to a second AC line respectively.

8. The line transfer control device for a multi-AC port flexible DC converter according to claim 7, characterized in that: After the target AC line is used as a balanced line, the method further includes: The control mode corresponding to the port converter corresponding to the multi-AC port flexible DC converter connected to the target AC line is switched to the optimal modulation optimization control.

9. The line transfer control device for a multi-AC port flexible DC converter according to claim 8, characterized in that: The optimal modulation degree optimization control includes: Obtaining a balanced line output voltage of a port converter corresponding to a multi-AC port flexible DC converter connected to a target AC line; Based on the balanced line output voltage, reducing the maximum value of the unbalanced voltage corresponding to each type of unbalanced line to the minimum is the optimization goal, and the unbalanced voltage corresponding to each type of unbalanced line is optimized; wherein the unbalanced voltage is specifically: the output voltage of the port converter corresponding to the multi-AC port flexible DC converter connected to the second AC line corresponding to the type of unbalanced line.

10. The line transfer control device of a multi-AC port flexible DC converter according to claim 9, characterized in that: The constant AC voltage control comprises: Obtaining a d-axis component of a port voltage of a first AC line having a fault, a q-axis component of a port voltage of a first AC line having a fault, a d-axis component of an MMC port output voltage, a q-axis component of an MMC port output voltage, an angular frequency of a power frequency, a d-axis component of an MMC AC output current, and a q-axis component of an MMC AC output current; Substitute the port voltage d-axis component of the first AC line with a fault, the port voltage q-axis component of the first AC line with a fault, the MMC port output voltage d-axis component, the MMC port output voltage q-axis component, the power frequency angular frequency, the MMC AC output current d-axis component, and the MMC AC output current q-axis component into the fixed AC voltage control equation to obtain the MMC port modulated output voltage and the port modulated voltage of the first AC line with a fault; wherein the MMC port modulated output voltage includes: the MMC port modulated output voltage d-axis component and the MMC port modulated output voltage q-axis component; the port modulated voltage of the second AC line with a fault includes: the port modulated voltage q-axis component of the first AC line with a fault and the port modulated voltage d-axis component of the first AC line with a fault; the fixed AC voltage control equation satisfies the following conditions: Where V ck_diffd * is the d-axis component of the modulated output voltage of the MMC port, V ck_diffq * is the q-axis component of the modulated output voltage of the MMC port, k p is the proportionality coefficient, k i is the integral coefficient, s is the Laplace operator, V Lkd * is the d-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkd is the d-axis component of the port voltage of the first AC line where the fault occurs, V Lkq * is the q-axis component of the modulation voltage at the port of the first AC line where the fault occurs, V Lkq is the q-axis component of the port voltage of the first AC line where the fault occurs, V diffd is the d-axis component of the MMC port output voltage, V diffq is the q-axis component of the output voltage of the MMC port, ω is the angular frequency of the power frequency, I od is the d-axis component of the MMC AC output current, I oq is the q-axis component of the MMC AC output current; Based on the MMC port modulated output voltage and the port modulated voltage of the second AC line having a fault, the second AC line having a fault is controlled through a PI controller.

Images