Voltage polarity inversion method and system for direct-current power supply system of submarine observation network

Abstract

The invention discloses a voltage polarity reversal method and system for a direct current power supply system of a submarine observation network, and relates to the technical field of submarine power grid control, and the method comprises the steps: controlling a matrix converter to execute voltage polarity reversal operation when a submarine cable fault is detected or a seawater electrode needs to be replaced; during a voltage polarity reversal operation period, collecting related data of the matrix converter in real time; performing dq decoupling on the alternating current, the valve side voltage and the additional voltage to obtain respective corresponding direct-axis components and quadrature-axis components; according to the decoupled component and the collected data, determining the stage of the matrix converter in the period of executing the voltage polarity reversal operation, and generating a corresponding AC voltage instruction or a DC voltage instruction; performing SPWM control on the matrix converter according to the instruction; according to the invention, non-overcurrent DC voltage polarity inversion can be completed within nearly 1 s, rapid transfer of a standby loop is realized, and the dual requirements of overcurrent suppression and rapid inversion are considered.

Description

Technical Field

[0001] The present invention relates to the technical field of submarine power grid control, and particularly to a method and system for voltage polarity reversal of a DC power supply system for a submarine observation network. Background Art

[0002] In the related art, most of the submarine observation networks adopt a monopolar power transmission topology composed of a seawater circuit and a single submarine cable. This topology can configure a standby seawater electrode and a standby submarine cable in the vulnerable section, and reverse the voltage polarity during a fault or electrode maintenance, and then put into the standby submarine cable and the standby electrode to realize the redundant loop transfer. Its topological structure is as Figure 1 shown. However, when the above topological structure performs voltage polarity reversal, the following defects and deficiencies exist: First, the arm overcurrent problem of the two-level converter is not fully considered during the polarity reversal stage, and there are a large number of hard polarity switches with non-zero crossing voltages during the reversal process, which is easy to cause irreversible damage to the converter; Second, the impact on the power supply system caused by the switching process between the normal operation control mode and the reversal control mode is ignored; Third, it is limited to the design of current limiting control during the power supply switching process, lacking qualitative analysis of the influencing factors of the polarity reversal speed. The long reversal time increases the risk of system outage, and it is difficult to balance the dual requirements of overcurrent suppression and rapid reversal.

[0003] Therefore, there is an urgent need for a method for voltage polarity reversal of a DC power supply system for a submarine observation network that can balance the dual requirements of overcurrent suppression and rapid reversal and does not affect the converter or the power supply system. Summary of the Invention

[0004] In view of this, the present invention provides a method and system for voltage polarity reversal of a DC power supply system for a submarine observation network to solve the technical problems existing in the related art.

[0005] In a first aspect, the present invention provides a method for voltage polarity reversal of a DC power supply system for a submarine observation network, including:

[0006] S1. When a submarine cable fault or seawater electrode replacement is detected, control the matrix converter to perform a voltage polarity reversal operation;

[0007] S2. During the voltage polarity reversal operation of the matrix converter, collect the grid-side voltage, valve-side voltage, AC current, DC voltage, and additional voltage of the matrix converter in real time; the additional voltage is the total voltage on the AC filter inductor, variable inductor, and AC line resistance;

[0008] S3. Perform dq decoupling on the AC current, valve-side voltage, and additional voltage to obtain the direct-axis component and quadrature-axis component of the valve-side voltage, the direct-axis component and quadrature-axis component of the additional voltage, and the direct-axis component and quadrature-axis component of the AC current;

[0009] S4. Determine the stage that the matrix converter is in during the execution of the voltage polarity reversal operation according to S2 and S3; and generate corresponding AC voltage commands or DC voltage commands according to the current stage; the stages include: the first AC voltage independent regulation stage, the polarity reversal stage, and the second AC voltage independent regulation stage; the polarity reversal stage further includes: the first DC voltage independent regulation sub-stage, the first AC-DC voltage parallel regulation sub-stage, the second AC-DC voltage parallel regulation sub-stage, and the second DC voltage independent regulation sub-stage;

[0010] S5. Perform SPWM control on the matrix converter according to the AC voltage command or DC voltage command corresponding to the current stage to regulate the valve-side voltage or DC voltage.

[0011] In an optional implementation manner, S4 includes:

[0012] Calculate the variable inductor according to the grid-side voltage, valve-side voltage, and AC current;

[0013] When the variable inductor does not meet the first condition, determine that the current stage is the first AC voltage independent regulation stage;

[0014] The first condition includes:

[0015] L v = L max

[0016] where L max is the maximum inductor allowed for the variable inductor, and L v is the variable inductor;

[0017] The maximum inductor allowed for the variable inductor is:

[0018]

[0019] where L max is the maximum inductor allowed for the variable inductor, U g is the grid-side voltage; I ac max is the maximum current allowed for the AC line; R is the AC line resistance; L s is the AC filter inductor; ω is the angular frequency;

[0020] When the variable inductor meets the first condition and the DC voltage and valve-side voltage do not meet the second condition, determine that the current stage is the first DC voltage independent regulation sub-stage;

[0021] The second condition is:

[0022] |U dc |-|U c |≤δ

[0023] Among them, U dc is the DC voltage; U c is the valve side voltage; δ is the maximum measurement error of the voltage sensor;

[0024] When the DC voltage and the valve side voltage satisfy the second condition and the DC voltage does not satisfy the third condition, it is determined that the current stage is the first AC-DC voltage parallel regulation sub-stage;

[0025] The third condition is:

[0026] |U dc | ≤ δ

[0027] Among them, U dc is the DC voltage; δ is the maximum measurement error of the voltage sensor;

[0028] When the DC voltage satisfies the third condition and the valve side voltage does not satisfy the fourth condition, it is determined that the current stage is the second AC-DC voltage parallel regulation sub-stage;

[0029] The fourth condition is:

[0030] |U c | - |U c.t3 | ≤ δ

[0031] Among them, U c is the valve side voltage; δ is the maximum measurement error of the voltage sensor; U c.t3 is the first preset voltage;

[0032] The first preset voltage is

[0033]

[0034] Among them, U g is the grid side voltage; L max is the maximum inductance allowed by the variable inductor; L s is the AC filter inductor; ω is the angular frequency; U LRq is the quadrature axis component of the additional voltage;

[0035] When the valve side voltage satisfies the fourth condition and the DC voltage does not satisfy the fifth condition, it is determined that the current stage is the second DC voltage independent regulation sub-stage;

[0036] The fifth condition is:

[0037] |U dc | - |U dc.rating | ≤ δ

[0038] Among them, U dc is the DC voltage; δ is the maximum measurement error of the voltage sensor; U dc.rating is the rated value of the DC voltage;

[0039] When the DC voltage satisfies the fifth condition and the valve-side voltage does not satisfy the sixth condition, it is determined that the current stage is the second AC voltage independent regulation stage;

[0040] The sixth condition is:

[0041] |U c |-|U c.rating |≤δ

[0042] where U c is the valve-side voltage; δ is the maximum measurement error of the voltage sensor; U c.rating is the rated value of the valve-side voltage;

[0043] When the valve-side voltage satisfies the sixth condition, it is determined that the voltage polarity inversion operation of the matrix converter ends.

[0044] In an optional implementation, the S4 further includes:

[0045] When the current stage is the first AC voltage independent regulation stage, determine whether the AC current satisfies the seventh condition;

[0046] The seventh condition is:

[0047] I ac =I ac max

[0048] where I ac is the AC current, and I ac max is the maximum allowable current of the AC line;

[0049] When the AC current satisfies the seventh condition, calculate the total inductance on the AC line according to the grid-side voltage, the valve-side voltage, and the AC current:

[0050]

[0051] where U g is the grid-side voltage; U c is the valve-side voltage; δ is the angle between the grid-side voltage and the valve-side voltage; I ac is the AC current; ω is the angular frequency; R is the resistance of the AC line;

[0052] Calculate the variable inductance L v :

[0053] L sum =L v +L s

[0054] where L s is the AC filter inductance, and L vis a variable inductor;

[0055] Moreover, the S5 further includes:

[0056] According to the value corresponding to the variable inductor, adjust the variable inductor on the AC side of the matrix converter to the corresponding value.

[0057] In an optional implementation manner, the S5 further includes:

[0058] At the initial moment when the DC voltage satisfies the third condition, control the reverse IGBT of the matrix converter to adopt SPWM modulation, and the forward IGBT conducts continuously.

[0059] In an optional implementation manner, the AC voltage command or the DC voltage command is generated based on an additional voltage control loop: the additional voltage control loop includes: an overcurrent suppression control loop, a voltage conversion, a reverse rate control loop, and a voltage-current double closed loop;

[0060] The generation process of the AC voltage command or the DC voltage command is as follows:

[0061] Input the AC current into the overcurrent suppression control loop, and calculate the error between the AC current and the reference current;

[0062] Perform PI control on the error and output a voltage adjustment amount;

[0063] Subtract the voltage adjustment amount from the change amount of the additional voltage in the previous moment to obtain the change amount of the additional voltage in the current moment;

[0064] Perform dq decoupling on the change amount of the additional voltage in the current moment to obtain the quadrature-axis component and the direct-axis component corresponding to the change amount of the additional voltage in the current moment;

[0065] Perform voltage conversion on the quadrature-axis component and the direct-axis component corresponding to the change amount of the additional voltage in the current moment to obtain the change amount of the DC voltage in the current moment and the change amount of the valve-side voltage in the current moment;

[0066] Subtract the change amount in the current moment from the change amount of the DC voltage in the previous moment to obtain the DC voltage corresponding to the current moment; subtract the change amount in the current moment from the change amount of the valve-side voltage in the previous moment to obtain the valve-side voltage corresponding to the current moment;

[0067] Input the valve-side voltage and the DC voltage corresponding to the current moment into the voltage-current double closed loop to generate corresponding AC voltage commands and DC voltage commands.

[0068] In an optional implementation manner, the voltage adjustment amount is obtained by adjusting three system parameters in the PI control, and all three system parameters are calculated based on the S2 and the S3.

[0069] In an alternative embodiment, the accessory voltage control loop further includes a valve-side voltage enabling element and a DC voltage enabling element;

[0070] The S4 further includes:

[0071] When the current stage is the first AC voltage independent regulation stage or the second AC voltage independent regulation stage, set the DC voltage enabling element to 0;

[0072] When the current stage is the first DC voltage independent regulation sub-stage or the second DC voltage independent regulation sub-stage, set the valve-side voltage enabling element to 0.

[0073] In a second aspect, the present invention provides a voltage polarity inversion system for a subsea observation network DC power supply system, including: an onshore base station, a downstream junction box; the onshore base station includes a matrix converter and a control module; the control module includes an instruction issuing unit, a signal acquisition unit, a voltage instruction calculation unit, and a variable inductor adjustment unit;

[0074] The instruction issuing unit is electrically connected to the matrix converter and the downstream junction box respectively, and is used for sending a voltage polarity inversion instruction to the matrix converter and the downstream junction box when a submarine cable fault is detected or a subsea electrode needs to be replaced;

[0075] The matrix converter is provided with a variable inductor on the AC side, and is used for receiving the voltage polarity inversion instruction and performing a voltage polarity inversion operation according to the voltage polarity inversion instruction;

[0076] The downstream junction box is electrically connected to the subsea electrode and the submarine cable respectively, and is used for receiving the voltage polarity inversion instruction and putting the subsea electrode into or out of operation, connecting or disconnecting the submarine cable according to the voltage polarity inversion instruction;

[0077] The signal acquisition unit is electrically connected to the instruction issuing unit, and is used for real-time collecting the grid-side voltage, valve-side voltage, AC current, DC voltage, and additional voltage of the matrix converter during the voltage polarity inversion operation of the matrix converter; the additional voltage is the total voltage on the AC filter inductor, variable inductor, and AC line resistance;

[0078] The dq decoupling unit is electrically connected to the signal acquisition unit, and is used for obtaining the AC current, valve-side voltage, and additional voltage, and performing dq decoupling on the AC current, valve-side voltage, and additional voltage to obtain the direct-axis component and quadrature-axis component of the valve-side voltage, the direct-axis component and quadrature-axis component of the additional voltage, and the direct-axis component and quadrature-axis component of the AC current;

[0079] A voltage command calculation unit, electrically connected to the dq decoupling unit and the signal acquisition unit respectively, is configured to determine the stage that the matrix converter is in during the execution of the voltage polarity reversal operation according to the data collected by the signal acquisition unit and the components decoupled by the dq decoupling unit; and generate a corresponding AC voltage command or DC voltage command according to the current stage; the stages include: a first AC voltage independent regulation stage, a polarity reversal stage, and a second AC voltage independent regulation stage; the polarity reversal stage further includes: a first DC voltage independent regulation sub-stage, a first AC-DC voltage parallel regulation sub-stage, a second AC-DC voltage parallel regulation sub-stage, and a second DC voltage independent regulation sub-stage;

[0080] A variable inductor regulation unit, electrically connected to the variable inductor, is configured to perform SPWM control on the matrix converter according to the AC voltage command or DC voltage command corresponding to the current stage, so as to regulate the valve side voltage or the DC voltage.

[0081] The present invention has the following beneficial effects:

[0082] In the embodiment of the present invention, the influencing factors of overcurrent and reversal speed during the polarity reversal process of the matrix converter are qualitatively analyzed. By regulating the size of the variable inductor in real time to control the changes of the valve side voltage (i.e., AC voltage) and the DC voltage, the arm overcurrent during the voltage polarity reversal process is effectively suppressed. At the same time, according to the switching logic between different reversal stages, the valve side voltage and the DC voltage are alternately regulated, thereby minimizing the DC voltage reversal time and reducing the system outage time. In the embodiment of the present invention, during the DC voltage polarity reversal process, the arm current is always limited within 0.7 kA, and the overcurrent is also effectively suppressed during the switching process of each reversal stage. Moreover, the embodiment of the present invention can complete the non-overcurrent DC voltage polarity reversal within nearly 1 s, realize the rapid transfer of the standby loop, take into account the dual requirements of overcurrent suppression and rapid reversal, and will not affect the converter or the power supply system at the same time. Description of the Drawings

[0083] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to these drawings.

[0084] Figure 1 is a single-pole transmission topology diagram composed of a seawater circuit and a single submarine cable according to an embodiment of the present invention;

[0085] Figure 2 is a flowchart of a method for reversing the voltage polarity of a DC power supply system of a submarine observation network according to an embodiment of the present invention;

[0086] Figure 3 is the topology diagram of the matrix converter according to an embodiment of the present invention;

[0087] Figure 4 is the curve diagram showing the effective values of the valve-side voltage and the DC voltage varying with time during the voltage polarity inversion according to an embodiment of the present invention;

[0088] Figure 5 is the structural schematic diagram of the additional voltage control loop according to an embodiment of the present invention;

[0089] Figure 6 is the flowchart executed by a machine for a voltage polarity inversion method of a DC power supply system for a submarine observation network according to an embodiment of the present invention;

[0090] Figure 7 is the structural schematic diagram of a voltage polarity inversion system of a DC power supply system for a submarine observation network according to an embodiment of the present invention;

[0091] Figure 8 is the curve diagram showing the DC voltage varying with time during the voltage polarity inversion according to an embodiment of the present invention;

[0092] Figure 9 is the curve diagram showing the valve-side voltage varying with time during the voltage polarity inversion according to an embodiment of the present invention;

[0093] Figure 10 is the curve diagram showing the effective value of the AC current varying with time during the voltage polarity inversion according to an embodiment of the present invention. Detailed implementation manners

[0094] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0095] Figure 2 Illustrates a voltage polarity inversion method of a DC power supply system for a submarine observation network according to an embodiment of the present invention. As Figure 2 shown, the process includes the following steps:

[0096] S1. When a submarine cable fault is detected or a seawater electrode needs to be replaced, control the matrix converter to perform a voltage polarity inversion operation.

[0097] Among them, the topological structure diagram of the matrix converter (MC for short) is as Figure 3 shown. Among them, U g is the grid-side voltage, U c is the valve-side voltage, I ac is the AC current, L s is the AC filter inductor, L v is the variable inductor (the adjustable inductor newly added on the AC line), R is the AC line resistance, L sum is the total inductor on the AC line (that is, the total inductor of the AC filter inductor and the variable inductor), U LR is the additional voltage (that is, the total voltage of the AC filter inductor, the variable inductor and the AC line resistance). In order to achieve bipolar voltage output, the converter at the shore base station uses a matrix rectifier, and each phase bridge arm has two IGBTs connected in reverse series. During normal operation, the forward IGBT uses SPWM modulation, and the reverse IGBT conducts continuously. At this time, the matrix rectifier outputs a positive-polarity voltage. When operating in reverse, the control logic of the forward and reverse IGBTs is exchanged. The reverse IGBT uses SPWM modulation, and the forward IGBT conducts continuously. The matrix rectifier outputs a negative-polarity voltage. When the converter at the shore base station is a matrix rectifier, the system will have the ability to supply bipolar DC voltage, meeting the requirement of polarity reversal during the power supply restoration process.

[0098] In an optional manner, the detection process of the system fault in step S1 includes:

[0099] S11. Obtain the positive DC line voltage U dcp and the negative DC line voltage U dcn of the matrix converter.

[0100] S12. Compare the ratio of the absolute value of the positive DC line voltage and the absolute value of the negative DC line voltage with the first preset value and the second preset value respectively.

[0101] Before the fault occurs, the DC voltage amplitudes of the bipolar submarine cable are the same, the polarities are opposite, and it operates in a symmetric state. Construct a judgment basis according to the characteristics of the single-pole ground fault as the protection action criterion, and judge the polarity of the faulty submarine cable.

[0102] Specifically, the judgment basis is expressed as:

[0103]

[0104] Among them, U dcp is the positive DC line voltage, U dcn is the negative DC line voltage, K setp is the set protection action setting value (that is, the first preset value), K setnis the set protection operation setting value (i.e., the second preset value). When the positive / negative pole fault criterion is met, it is determined that the submarine cable of the corresponding pole has failed. Preferably, K setp = 0.8, K setn = 1.2.

[0105] S13. When the ratio is less than or equal to the first preset value, it is determined that the submarine cable at the positive pole of the matrix converter has failed; when the ratio is greater than the second preset value, it is determined that the submarine cable at the negative pole of the matrix converter has failed.

[0106] S2. During the voltage polarity inversion operation of the matrix converter, the grid-side voltage U g , valve-side voltage U c , AC current I ac , DC voltage U dc , and additional voltage U LR of the matrix converter are collected in real time; the additional voltage U LR is the total voltage across the AC filter inductor L s , variable inductor L v and the AC line resistance R.

[0107] It should be noted that the AC filter inductor L s , AC line resistance R, and load resistance R load of the matrix converter are fixed values and are known during the circuit design of the matrix converter. The grid-side voltage U g , valve-side voltage U c , AC current I ac , DC voltage U dc , and additional voltage U LR of the matrix converter are quantities that change dynamically with time (instantaneous values) and need to be collected in real time to provide data support for the subsequent dynamic generation of command values.

[0108] S3. Perform dq decoupling on the AC current I ac , valve-side voltage U c and additional voltage U LR to obtain the direct-axis component U cd and quadrature-axis component U cq of the valve-side voltage, the direct-axis component U LRd and quadrature-axis component U LRq of the additional voltage, as well as the direct-axis component i d and quadrature-axis component i q of the AC current.

[0109] S4. Determine the stage in which the matrix converter is during the voltage polarity inversion operation according to Steps S2 and S3; and generate corresponding AC voltage commands or DC voltage commands according to the current stage; the stages include: the first AC voltage independent regulation stage, the polarity inversion stage, and the second AC voltage independent regulation stage; the polarity inversion stage further includes: the first DC voltage independent regulation sub-stage, the first AC-DC voltage parallel regulation sub-stage, the second AC-DC voltage parallel regulation sub-stage, and the second DC voltage independent regulation sub-stage.

[0110] In Step S4, according to the data collected in Step S2 and the decoupled components in Step S4, the stage in which the matrix converter is during the voltage polarity inversion operation can be determined. For example, as Figure 4 shown, the abscissa is time and the ordinate is the RMS value of the valve side voltage U crms and the RMS value of the DC voltage U dcrms . The first AC voltage independent regulation stage corresponds to the U c regulation process (t1→t2), the polarity inversion stage corresponds to the polarity inversion process (t2→t6), and the second AC voltage independent regulation stage corresponds to the U c regulation process (t6→t7). Among them, the polarity inversion stage is further divided into four sub-stages, namely the first DC voltage independent regulation sub-stage (t2→t3), the first AC-DC voltage parallel regulation sub-stage (t3→t4), the second AC-DC voltage parallel regulation sub-stage (t4→t5), and the second DC voltage independent regulation sub-stage (t5→t6).

[0111] It should be noted that the matrix rectifier adopts constant DC voltage control under normal operating conditions. When starting to perform the voltage polarity inversion operation, the q-axis control loop switches from constant reactive power control to constant AC voltage control and performs voltage polarity inversion according to the control method as Figure 4 shown. There is a switching logic between each stage during the voltage polarity inversion operation, and the control commands for each stage are different. For example, there is a certain switching logic between the first AC voltage independent regulation stage and the first DC voltage independent regulation sub-stage. When the switching logic is satisfied, the command generated in the first AC voltage independent regulation stage is switched to the command generated in the first DC voltage independent regulation sub-stage.

[0112] In an optional implementation manner, determining the stage in which the matrix converter is during the voltage polarity inversion operation according to Steps S2 and S3 includes:

[0113] 1) The determination process of the first AC voltage independent regulation stage (t1→t2) is as follows:

[0114] According to the grid-side voltage U g and the valve-side voltage U cand alternating current I ac , calculate the variable inductor L v ;

[0115] When the variable inductor L v does not meet the first condition, determine the current stage as the first alternating voltage independent regulation stage;

[0116] The first condition is:

[0117] L v = L max

[0118] where, L max is the maximum inductance allowed for the variable inductor, L v is the variable inductor;

[0119] The maximum inductance L allowed for the variable inductor max is:

[0120]

[0121] where, L max is the maximum inductance allowed for the variable inductor, U g is the grid-side voltage; I ac max is the maximum current allowed for the AC line; R is the resistance of the AC line; L s is the AC filter inductor; ω is the angular frequency.

[0122] Specifically, as Figure 4 shown, during the first alternating voltage independent regulation stage t1 → t2, control the valve-side voltage U c to decrease, while the DC voltage U dc is maintained constant to extend the rated power transmission time. During this stage, the alternating voltage is regulated independently, and the variable inductor L v gradually increases. When the valve-side voltage U c equals the first preset voltage U c.t2 , the variable inductor L v will increase to the maximum value (the maximum inductance L allowed for the variable inductor max ), so raising the variable inductor L v to L max is used as the start criterion for the first DC voltage independent regulation sub-stage.

[0123] The first preset voltage is:

[0124]

[0125]

[0126] where, U g is the grid-side voltage; L maxThe maximum inductance allowed for the variable inductor; L s is the AC filtering inductor; ω is the angular frequency; U LRq is the quadrature axis component of the additional voltage.

[0127] 2) The determination process of the first DC voltage independent regulation sub-phase (t2→t3) is as follows:

[0128] When the variable inductor L v satisfies the first condition and the DC voltage U dc and the valve side voltage U c do not satisfy the second condition, it is determined that the current phase is the first DC voltage independent regulation sub-phase.

[0129] The second condition is:

[0130] |U dc | - |U c | ≤ δ

[0131] where U dc is the DC voltage; U c is the valve side voltage; δ is the maximum measurement error of the voltage sensor.

[0132] Specifically, as Figure 4 shown, in the first DC voltage independent regulation sub-phase t2→t3, the DC voltage U dc is controlled to decrease while the valve side voltage U c is maintained constant. When the effective value of the valve side voltage U crms is equal to the effective value of the DC voltage U dcrms (i.e., there is a maximum measurement error of a voltage sensor between the DC voltage U dc and the valve side voltage U c ), the tracking of the DC voltage U dc is completed. Therefore, the second condition can be used as the starting criterion for the first AC-DC voltage parallel regulation sub-phase.

[0133] 3) The determination process of the first AC-DC voltage parallel regulation sub-phase (t3→t4) is as follows:

[0134] When the DC voltage U dc and the valve side voltage U c satisfy the second condition and the DC voltage U dc does not satisfy the third condition, it is determined that the current phase is the first AC-DC voltage parallel regulation sub-phase;

[0135] The third condition is:

[0136] |U dc | ≤ δ

[0137] where U dcis the DC voltage; δ is the maximum measurement error of the voltage sensor.

[0138] Specifically, as Figure 4 shown, in the first AC-DC voltage parallel regulation sub-phase t3→t4, control the DC voltage U dc and the valve-side voltage U c to decrease in parallel. When the DC voltage U dc drops to 0, that is, when the DC voltage U dc meets the third condition, the reverse IGBT can be turned on to ensure zero crossing of the voltage during the polarity inversion stage and avoid irreversible damage to the matrix converter caused by hard polarity switching.

[0139] At the same time, after the reverse IGBT is turned on, the DC voltage U dc continues to decrease, and the valve-side voltage U c rises in the reverse direction, entering the second AC-DC voltage parallel regulation sub-phase. Therefore, the third condition can be used as the start criterion for the second AC-DC voltage parallel regulation sub-phase.

[0140] 4) The determination process of the second AC-DC voltage parallel regulation sub-phase (t4→t5) is as follows:

[0141] When the DC voltage U dc meets the third condition and the valve-side voltage U c does not meet the fourth condition, determine the current stage as the second AC-DC voltage parallel regulation sub-phase;

[0142] The fourth condition is:

[0143] |U c |-|U c.t3 |≤δ

[0144] where U c is the valve-side voltage; δ is the maximum measurement error of the voltage sensor; U c.t3 is the first preset voltage;

[0145] The first preset voltage is

[0146]

[0147] where U g is the grid-side voltage; L max is the maximum inductance allowed by the variable inductor; L s is the AC filter inductor; ω is the angular frequency; U LRq is the quadrature-axis component of the additional voltage.

[0148] Specifically, in the second AC-DC voltage parallel regulation sub-phase t4→t5, the DC voltage U dc continues to decrease, and the valve-side voltage U cRise in the reverse direction. According to the symmetry of the voltage change, when the valve-side voltage U c equals the first preset voltage U c.t2 again, it enters the second sub-phase of independent regulation of the DC voltage. Therefore, the fourth condition can be used as the starting criterion for the second sub-phase of independent regulation of the DC voltage.

[0149] 5) The determination process of the second sub-phase of independent regulation of the DC voltage (t5→t6) is as follows:

[0150] When the valve-side voltage U c satisfies the fourth condition and the DC voltage U dc does not satisfy the fifth condition, it is determined that the current stage is the second sub-phase of independent regulation of the DC voltage;

[0151] The fifth condition is:

[0152] |U dc |-|U dc.rating |≤δ

[0153] where U dc is the DC voltage; δ is the maximum measurement error of the voltage sensor; U dc.rating is the rated value of the DC voltage.

[0154] Specifically, in the second sub-phase of independent regulation of the DC voltage t5→t6, the valve-side voltage U c is maintained constant, while the DC voltage U dc rises in the reverse direction. When the DC voltage U dc returns to the rated value of the DC voltage U dc.rating it starts the second sub-phase of independent regulation of the AC voltage.

[0155] 6) The determination process of the second sub-phase of independent regulation of the AC voltage t6→t7 is as follows:

[0156] When the DC voltage satisfies the fifth condition and the valve-side voltage does not satisfy the sixth condition, it is determined that the current stage is the second sub-phase of independent regulation of the AC voltage;

[0157] The sixth condition is:

[0158] |U c |-|U c.rating |≤δ

[0159] where U c is the valve-side voltage; δ is the maximum measurement error of the voltage sensor; U c.rating is the rated value of the valve-side voltage;

[0160] Specifically, in the second sub-phase of independent regulation of the AC voltage t6→t7, the DC voltage U dc is maintained constant, and the valve-side voltage U cRise when the valve-side voltage U c rises to the rated value of the valve-side voltage U c.rating . At this time, stop the change of the voltage command value, and the MC changes from constant AC voltage control to constant reactive power control. At this time, the system completes all voltage polarity reversals and enters the power transmission mode of a single submarine cable plus a seawater circuit and continues to operate.

[0161] 7) The determination process for the end of the voltage polarity reversal operation is as follows:

[0162] When the valve-side voltage satisfies the sixth condition, it is determined that the voltage polarity reversal operation of the matrix converter ends.

[0163] S5. According to the command value corresponding to the current stage, perform SPWM control on the matrix converter to regulate the valve-side voltage or the DC voltage.

[0164] In an optional implementation manner, step S4 further includes:

[0165] When the current stage is the first AC voltage independent regulation stage, determine whether the AC current satisfies the seventh condition;

[0166] The seventh condition is:

[0167] I ac =I ac max

[0168] where, I ac is the AC current, and I ac max is the maximum allowable current of the AC line;

[0169] When the AC current satisfies the seventh condition, calculate the total inductance on the AC line according to the grid-side voltage, the valve-side voltage, and the AC current:

[0170]

[0171] where, U g is the grid-side voltage; U c is the valve-side voltage; δ is the angle between the grid-side voltage and the valve-side voltage; I ac is the AC current; ω is the angular frequency; R is the resistance of the AC line;

[0172] Calculate the variable inductance L v according to the total inductance on the AC line:

[0173] L sum =L v +L s

[0174] where, L s is the AC filter inductance, and L v is the variable inductance.

[0175] Specifically, as Figure 3 and Figure 4 shown, during the first AC voltage independent regulation stage (t1 → t2), the voltage U on the control valve side c drops, while the DC voltage U dc remains constant to extend the rated power transmission time.

[0176] At the initial stage of the first AC voltage independent regulation stage, the amplitude of the AC current I ac rapidly rises as U c changes. When I ac rises to I acmax , the variable inductor L v is inserted to limit the current. By controlling the magnitude of the variable inductor L v , the DC side voltage is maintained constant during the continuous drop of the voltage U on the valve side. c

[0177] Moreover, step S5 further includes:

[0178] According to the value corresponding to the variable inductor, the variable inductor L on the AC side of the matrix converter v is adjusted to the corresponding value.

[0179] In an alternative embodiment, step S5 further includes: at the initial moment when the DC voltage satisfies the third condition, controlling the reverse IGBT of the matrix converter to adopt SPWM modulation, and the forward IGBT remains continuously conducting.

[0180] Specifically, the initial moment when the DC voltage satisfies the third condition is the moment corresponding to the first time the DC voltage satisfies the third condition, that is, corresponding to Figure 4 the t4 moment in. At this moment, the reverse IGBT is inserted, which can ensure the voltage zero-crossing during the polarity inversion stage and avoid irreversible damage to the matrix converter caused by hard polarity switching.

[0181] In an alternative embodiment, the AC voltage command or the DC voltage command is generated based on an additional voltage control loop: the additional voltage control loop includes: an overcurrent suppression control loop, voltage conversion, a reverse rate control loop, and a voltage-current double closed loop, as Figure 5 shown.

[0182] Among them, the generation process of the AC voltage command or the DC voltage command is as follows:

[0183] Step a: Input the AC current I ac into the overcurrent suppression control loop to calculate the error between the AC current I ac and the reference current I acref .

[0184] It should be noted that, Figure 5All subscripts with "ref" represent the instruction values corresponding to each numerical value in the computer. In the embodiments of the present invention, only specific numerical values are used to describe the generation process. As for the instruction values corresponding to the specific numerical values, they are only a form of representation in the computer and are not specifically limited herein.

[0185] Among them, the reference current I acref is a pre-set current value, which can ensure that the arm current always remains within the pre-set current value. Preferably, the reference current I acref is 0.7 kA.

[0186] Step b: Perform PI control on the error and output the voltage adjustment amount;

[0187] Step c: Subtract the voltage adjustment amount from the change amount ΔU LR (t - Δt) of the additional voltage in the previous moment to obtain the change amount ΔU LR (t) of the additional voltage in the current moment;

[0188] Step d: Perform dq decoupling on the change amount ΔU LR (t) of the additional voltage in the current moment to obtain the quadrature-axis component ΔU LRq (t) and the direct-axis component ΔU LRd (t) corresponding to the change amount of the additional voltage in the current moment;

[0189] Step e: Perform voltage conversion on the quadrature-axis component ΔU LRq (t) and the direct-axis component ΔU LRd (t) corresponding to the change amount of the additional voltage in the current moment to obtain the change amount ΔU dc (t) of the DC voltage in the current moment and the change amount ΔU c (t) of the valve-side voltage in the current moment.

[0190] Specifically, the voltage conversion can be expressed as:

[0191]

[0192] Among them, ΔU c is the change amount of the valve-side voltage per unit time, U LRd is the direct-axis component of the additional voltage, U LRq is the quadrature-axis component of the additional voltage, ΔU LRd is the direct-axis component corresponding to the change amount of the additional voltage per unit time, ΔU LRq is the quadrature-axis component corresponding to the change amount of the additional voltage per unit time.

[0193] Step f: Subtract the change amount ΔU dc of the DC voltage U LR(t - Δt) minus the change ΔU within the current moment dc (t), to obtain the DC voltage U corresponding to the current moment dc (t); subtract the change ΔU of the valve-side voltage within the previous moment c (t - Δt) from the change ΔU within the current moment c (t), to obtain the valve-side voltage U corresponding to the current moment c (t);

[0194] Step g: Input the valve-side voltage U corresponding to the current moment c (t) and the DC voltage U dc (t) into the voltage-current double closed-loop to generate corresponding AC voltage instructions and DC voltage instructions.

[0195] In an alternative embodiment, the voltage adjustment amount is obtained by adjusting three system parameters in the PI control, and the three system parameters are all calculated based on Step S2 and Step S3. Specifically, the three system parameters are N1, N2, and N3 respectively, and the specific calculation formulas are shown in Table 1:

[0196] Table 1

[0197]

[0198]

[0199] Among them, A L is an intermediate parameter and can be expressed as:

[0200]

[0201] The meaning of each letter involved in the above system parameters has been explained previously and will not be elaborated here.

[0202] In the initial stage of voltage polarity inversion in the embodiment of the present invention, the reference current I acref is set in the accessory voltage control loop, so that the reference current I acref and the AC current at the current moment adjust the error between the two in real time through the three parameters of the PI link, and then through voltage conversion, reverse rate control loop and voltage-current double closed-loop, the AC voltage instructions and DC voltage instructions corresponding to when the arm current can always be kept within the preset reference current I acref can be obtained. Finally, the valve-side voltage and DC voltage are respectively subjected to SPWM control according to the AC voltage instructions and DC voltage instructions, so that the waveforms corresponding to the valve-side voltage and DC voltage are controlled in the manner shown in Figure 4 shown.

[0203] In an alternative embodiment, as Figure 5As shown, the accessory voltage control loop further includes a valve-side voltage enabling element and a DC voltage enabling element.

[0204] S4 further includes:

[0205] When the current stage is the first AC voltage single regulation stage or the second AC voltage single regulation stage, set the DC voltage enabling element to 0;

[0206] When the current stage is the first DC voltage single regulation sub-stage or the second DC voltage single regulation sub-stage, set the valve-side voltage enabling element to 0.

[0207] Specifically, when in the first AC voltage single regulation stage or the second AC voltage single regulation stage, the corresponding DC voltage U dc Remains constant. At this time, only need to set the DC voltage enabling element to 0, omitting the calculation steps before the DC voltage enabling element to improve the system operation efficiency.

[0208] When in the first DC voltage single regulation sub-stage or the second DC voltage single regulation sub-stage, the corresponding valve-side voltage U c Remains constant. At this time, only need to set the valve-side voltage enabling element to 0, omitting the calculation steps before the valve-side voltage enabling element to improve the system operation efficiency.

[0209] It should be noted that when in the first AC voltage single regulation stage or the second AC voltage single regulation stage, the valve-side voltage is controlled according to the corresponding AC voltage command output by the additional voltage control loop; when in the first DC voltage single regulation sub-stage or the second DC voltage single regulation sub-stage, the DC voltage is controlled according to the corresponding DC voltage command output by the additional voltage control loop; when in the first AC-DC voltage parallel regulation sub-stage or the second AC-DC voltage parallel regulation sub-stage, both the valve-side voltage and the DC voltage are controlled according to the corresponding DC voltage command and AC voltage command output by the additional voltage control loop. The control flow of the entire system is as Figure 6 shown.

[0210] In the embodiments of the present invention, the influencing factors of overcurrent and inversion speed during the polarity inversion process of the matrix converter are qualitatively analyzed. By regulating the magnitude of the variable inductor in real time to control the valve-side voltage (i.e., the AC voltage) and the DC voltage change, the arm overcurrent during the voltage polarity inversion process is effectively suppressed. At the same time, according to the switching logic between different inversion stages, the valve-side voltage and the DC voltage are alternately regulated, thereby minimizing the DC voltage inversion time and reducing the system outage time. In the embodiments of the present invention, during the DC voltage polarity inversion process, the arm current is always limited within 0.7 kA, and the overcurrent is also effectively suppressed during the switching process of each inversion stage. Moreover, the embodiments of the present invention can complete the DC voltage polarity inversion without overcurrent within nearly 1 s, realize the rapid transfer of the standby circuit, take into account the dual requirements of overcurrent suppression and rapid inversion, and will not affect the converter or the power supply system at the same time.

[0211] The embodiments of the present invention also provide a voltage polarity inversion system for a DC power supply system of a submarine observation network, as Figure 7 shown, including: an onshore base station and a lower-level connection box; the onshore base station includes a matrix converter and a control module; the control module includes an instruction issuing unit, a signal acquisition unit, a voltage instruction calculation unit, and a variable inductor adjustment unit;

[0212] The instruction issuing unit 701 is electrically connected to the matrix converter and the lower-level connection box respectively, and is used for sending a voltage polarity inversion instruction to the matrix converter and the lower-level connection box when a submarine cable fault is detected or a seawater electrode needs to be replaced;

[0213] The matrix converter is provided with a variable inductor on the AC side, and is used for receiving the voltage polarity inversion instruction and performing a voltage polarity inversion operation according to the voltage polarity inversion instruction;

[0214] The lower-level connection box is electrically connected to the seawater electrode and the submarine cable respectively, and is used for receiving the voltage polarity inversion instruction and putting the seawater electrode into or out of operation, connecting or disconnecting the submarine cable according to the voltage polarity inversion instruction;

[0215] The signal acquisition unit 702 is electrically connected to the instruction issuing unit, and is used for real-time acquisition of the grid-side voltage, valve-side voltage, AC current, DC voltage, and additional voltage of the matrix converter during the voltage polarity inversion operation of the matrix converter; the additional voltage is the total voltage on the AC filter inductor, variable inductor, and AC line resistance;

[0216] The dq decoupling unit 703 is electrically connected to the signal acquisition unit, and is used for obtaining the AC current, valve-side voltage, and additional voltage, and performing dq decoupling on the AC current, valve-side voltage, and additional voltage to obtain the direct-axis component and quadrature-axis component of the valve-side voltage, the direct-axis component and quadrature-axis component of the additional voltage, and the direct-axis component and quadrature-axis component of the AC current;

[0217] The voltage command calculation unit 704 is electrically connected to the dq decoupling unit and the signal acquisition unit respectively, and is used to determine the stage that the matrix converter is in during the execution of the voltage polarity reversal operation according to the data collected by the signal acquisition unit and the components decoupled by the dq decoupling unit; and generate corresponding AC voltage commands or DC voltage commands according to the current stage; the stages include: the first AC voltage independent regulation stage, the polarity reversal stage, and the second AC voltage independent regulation stage; the polarity reversal stage further includes: the first DC voltage independent regulation sub-stage, the first AC-DC voltage parallel regulation sub-stage, the second AC-DC voltage parallel regulation sub-stage, and the second DC voltage independent regulation sub-stage;

[0218] The variable inductor regulation unit 705 is electrically connected to the variable inductor, and is used to perform SPWM control on the matrix converter according to the AC voltage command or DC voltage command corresponding to the current stage, so as to regulate the valve side voltage or the DC voltage.

[0219] To verify the technical effects of the embodiments of the present invention, a single-end submarine observation network power supply system based on a matrix rectifier is built in PSCAD / EMTDC. In the normal operation state, the matrix converter adopts constant DC voltage control, and the DC submarine cable adopts the frequency-dependent phase domain model. The simulation parameters of this submarine observation network power supply system are shown in Table 1:

[0220] Table 1

[0221]

[0222] Then, at t = 2s, it starts to enter the voltage polarity reversal stage. The waveforms of each signal in this stage are as Figures 8 - 10 shown. It can be seen that whether it is switching the zero vector or the process of switching from the DC voltage polarity reversal control to the traditional constant DC voltage control, the current flowing through the three-phase bridge arm does not generate a large overcurrent and remains within the allowable range. The entire process of DC voltage polarity reversal lasts for about 1.03s. During this period, the output power and output current on the DC side fluctuate briefly, and then the system quickly and smoothly transitions to the operation of the reorganized single submarine cable plus seawater loop, and the power supplied by the system resumes normal.

[0223] By investing in the variable inductor to dynamically regulate the additional voltage magnitude, the embodiments of the present invention realize the compensation and support for the AC side voltage. During the polarity reversal process, the AC-DC voltage is smoothly reduced to a lower voltage level and then reversed, effectively suppressing the overcurrent problem of the bridge arm of the voltage source converter. Compared with the conventional voltage polarity reversal method in the related technology, its overcurrent suppression ability is increased by 19.55%; at the same time, by adopting the AC voltage - DC voltage alternating regulation method, the polarity reversal time is shortened by 55%, effectively ensuring the power supply continuity.

[0224] Although embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations fall within the scope defined by the appended claims.

Claims

1. A method for voltage polarity inversion of a DC power supply system for a subsea observation network, characterized in that, Including: S1. When a submarine cable fault is detected or a submarine electrode needs to be replaced, control the matrix converter to perform a voltage polarity reversal operation; S2. During the voltage polarity reversal operation of the matrix converter, collect the grid-side voltage, valve-side voltage, AC current, DC voltage, and additional voltage of the matrix converter in real time; the additional voltage is the total voltage across the AC filter inductor, variable inductor, and AC line resistance; S3. Perform dq decoupling on the AC current, valve-side voltage, and additional voltage to obtain the direct-axis component and quadrature-axis component of the valve-side voltage, the direct-axis component and quadrature-axis component of the additional voltage, and the direct-axis component and quadrature-axis component of the AC current; S4. According to S2 and S3, determine the stage in which the matrix converter is during the voltage polarity reversal operation; And generate a corresponding AC voltage command or DC voltage command according to the current stage; The stages include: the first AC voltage independent regulation stage, the polarity reversal stage, and the second AC voltage independent regulation stage; the polarity reversal stage further includes: the first DC voltage independent regulation sub-stage, the first AC-DC voltage parallel regulation sub-stage, the second AC-DC voltage parallel regulation sub-stage, and the second DC voltage independent regulation sub-stage; S5. Perform SPWM control on the matrix converter according to the AC voltage command or DC voltage command corresponding to the current stage to regulate the valve-side voltage or DC voltage.

2. The method according to claim 1, characterized in that, The S4 includes: Calculate the variable inductor according to the grid-side voltage, valve-side voltage, and AC current; When the variable inductor does not meet the first condition, determine that the current stage is the first AC voltage independent regulation stage; The first condition includes: L v = L max Among them, L max is the maximum inductance allowed for the variable inductor, and L v is the variable inductor; The maximum inductance allowed for the variable inductor is: Among them, L max is the maximum inductance allowed for the variable inductor, U g is the grid-side voltage; I ac max is the maximum current allowed for the AC line; R is the AC line resistance; L s is the AC filter inductor; ω is the angular frequency; When the variable inductor meets the first condition and the DC voltage and valve-side voltage do not meet the second condition, determine that the current stage is the first DC voltage independent regulation sub-stage; The second condition is: |U dc |-|U c |≤δ Among them, U dc is the DC voltage; U c is the valve side voltage; δ is the maximum measurement error of the voltage sensor; When the DC voltage and valve-side voltage meet the second condition and the DC voltage does not meet the third condition, determine that the current stage is the first AC-DC voltage parallel regulation sub-stage; The third condition is: |U dc |≤δ where U dc is the DC voltage; δ is the maximum measurement error of the voltage sensor; When the DC voltage meets the third condition and the valve-side voltage does not meet the fourth condition, determine that the current stage is the second AC-DC voltage parallel regulation sub-stage; The fourth condition is: |U c |-|U c.t3 |≤δ Among them, U c is the valve side voltage; δ is the maximum measurement error of the voltage sensor; U c.t3 is the first preset voltage; The first preset voltage is Among them, U g is the grid-side voltage; L max is the maximum inductance allowed by the variable inductor; L s is the AC filter inductor; ω is the angular frequency; U LRq is the quadrature-axis component of the additional voltage; When the valve-side voltage meets the fourth condition and the DC voltage does not meet the fifth condition, determine that the current stage is the second DC voltage independent regulation sub-stage; The fifth condition is: |U dc |-|U dc.rating |≤δ Among them, U dc is the DC voltage; δ is the maximum measurement error of the voltage sensor; U dc.rating is the rated value of the DC voltage; When the DC voltage meets the fifth condition and the valve-side voltage does not meet the sixth condition, determine that the current stage is the second AC voltage independent regulation stage; The sixth condition is: |U c |-|U c.rating |≤δ Among them, U c is the valve-side voltage; δ is the maximum measurement error of the voltage sensor; U c.rating is the rated value of the valve-side voltage; When the valve-side voltage meets the sixth condition, determine that the voltage polarity reversal operation of the matrix converter ends.

3. The method according to claim 2, wherein The S4 further includes: When the current stage is the first AC voltage independent regulation stage, determine whether the AC current meets the seventh condition; The seventh condition is: I ac = I ac max Among them, I ac is the alternating current, and I ac max is the maximum allowable current of the alternating current line; When the AC current meets the seventh condition, calculate the total inductance on the AC line according to the grid-side voltage, valve-side voltage, and AC current: Among them, U g is the grid-side voltage; U c is the valve-side voltage; δ is the angle between the grid-side voltage and the valve-side voltage; I ac is the AC current; ω is the angular frequency; R is the AC line resistance; Calculate the variable inductor L based on the total inductance on the AC line v : L sum = L v + L s Among them, L s is the AC filter inductor, and L v is the variable inductor; And, the S5 further includes: Adjust the variable inductor on the AC side of the matrix converter to the corresponding value according to the value corresponding to the variable inductor.

4. The method according to claim 2 or 3, characterized in that, The S5 further includes: At the initial moment when the DC voltage satisfies the third condition, the reverse IGBT of the matrix converter is controlled by SPWM modulation, and the forward IGBT is continuously turned on.

5. The method according to claim 2 or 3, characterized in that The AC voltage command or DC voltage command is generated based on an additional voltage control loop: the additional voltage control loop includes: an overcurrent suppression control loop, voltage conversion, a reverse rate control loop, and a voltage-current double closed loop; The generation process of the AC voltage command or DC voltage command is as follows: The AC current is input into the overcurrent suppression control loop to calculate the error between the AC current and the reference current; Perform PI control on the error and output a voltage adjustment amount; Subtract the voltage adjustment amount from the change amount of the additional voltage in the previous moment to obtain the change amount of the additional voltage in the current moment; Perform dq decoupling on the change amount of the additional voltage in the current moment to obtain the quadrature axis component and direct axis component corresponding to the change amount of the additional voltage in the current moment; Perform voltage conversion on the quadrature axis component and direct axis component corresponding to the change amount of the additional voltage in the current moment to obtain the change amount of the DC voltage in the current moment and the change amount of the valve side voltage in the current moment; Subtract the change amount in the current moment from the change amount of the DC voltage in the previous moment to obtain the DC voltage corresponding to the current moment; subtract the change amount in the current moment from the change amount of the valve side voltage in the previous moment to obtain the valve side voltage corresponding to the current moment; Input the valve side voltage and DC voltage corresponding to the current moment into the voltage-current double closed loop to generate corresponding AC voltage commands and DC voltage commands.

6. The method according to claim 5, characterized in that, The voltage adjustment amount is obtained by adjusting three system parameters in the PI control, and all three system parameters are calculated based on the S2 and the S3.

7. The method according to claim 5, wherein The additional voltage control loop further includes a valve side voltage enabling element and a DC voltage enabling element; The S4 further includes: When the current stage is the first AC voltage independent regulation stage or the second AC voltage independent regulation stage, set the DC voltage enabling element to 0; When the current stage is the first DC voltage independent regulation sub-stage or the second DC voltage independent regulation sub-stage, set the valve side voltage enabling element to 0.

8. A voltage polarity inversion system for a DC power supply system of a submarine observation network, characterized in that, It includes: An onshore base station and a lower-level connection box; the onshore base station includes a matrix converter and a control module; the control module includes an instruction issuing unit, a signal acquisition unit, a voltage instruction calculation unit, and a variable inductor adjustment unit; The instruction issuing unit is electrically connected to the matrix converter and the lower-level connection box respectively, and is used to send a voltage polarity reversal instruction to the matrix converter and the lower-level connection box when a submarine cable fault is detected or the submarine electrode needs to be replaced; The matrix converter is provided with a variable inductor on the AC side, and is used to receive the voltage polarity reversal instruction and perform a voltage polarity reversal operation according to the voltage polarity reversal instruction; The lower-level connection box is electrically connected to the submarine electrode and the submarine cable respectively, and is used to receive the voltage polarity reversal instruction and connect or disconnect the submarine electrode and connect or disconnect the submarine cable according to the voltage polarity reversal instruction. A signal acquisition unit, electrically connected to the instruction issuing unit, is configured to collect the grid-side voltage, valve-side voltage, AC current, DC voltage, and additional voltage of the matrix converter in real time during the voltage polarity reversal operation of the matrix converter; the additional voltage is the total voltage across the AC filter inductor, variable inductor, and AC line resistance; A dq decoupling unit, electrically connected to the signal acquisition unit, is configured to obtain the AC current, valve-side voltage, and additional voltage, and perform dq decoupling on the AC current, valve-side voltage, and additional voltage to obtain the direct-axis component and quadrature-axis component of the valve-side voltage, the direct-axis component and quadrature-axis component of the additional voltage, and the direct-axis component and quadrature-axis component of the AC current; A voltage instruction calculation unit, electrically connected to the dq decoupling unit and the signal acquisition unit respectively, is configured to determine the stage at which the matrix converter is during the voltage polarity reversal operation according to the data collected by the signal acquisition unit and the components decoupled by the dq decoupling unit; And generate a corresponding AC voltage instruction or DC voltage instruction according to the current stage; The stages include: a first AC voltage independent regulation stage, a polarity reversal stage, and a second AC voltage independent regulation stage; the polarity reversal stage further includes: a first DC voltage independent regulation sub-stage, a first AC-DC voltage parallel regulation sub-stage, a second AC-DC voltage parallel regulation sub-stage, and a second DC voltage independent regulation sub-stage; A variable inductor regulation unit, electrically connected to the variable inductor, is configured to perform SPWM control on the matrix converter according to the AC voltage instruction or DC voltage instruction corresponding to the current stage to regulate the valve-side voltage or DC voltage.

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