Method and device for switching operation mode of offshore wind power true bipolar flexible DC system

Abstract

The present disclosure proposes a method and device for switching the operation mode of an offshore wind power true bipolar flexible DC system, the method comprising detecting whether a converter fails, generating a locking instruction if one converter fails or two positive / negative converters fail; locking four converters based on the locking instruction, disconnecting the incoming line switches of all connecting transformers; closing the neutral bus switch of the failed converter and the same positive / negative converter, the remaining two converters include the machine-side target converter and the grid-side target converter, closing the incoming line switch of the connecting transformer connected to the grid-side target converter; obtaining the DC line voltage of the flexible DC system and the AC voltage of the machine-side target converter in real time, controlling the unlocking of the two target converters based on the DC line voltage, and controlling the closing of the incoming line switch of the connecting transformer connected to the machine-side target converter based on the AC voltage. According to the method disclosed in the present disclosure, the time for the DC system to switch from bipolar to unipolar operation can be shortened.

Description

Technical Field

[0001] The present disclosure relates to the field of flexible direct current power transmission in offshore wind farms, and in particular to a method and device for switching operating modes of an offshore wind power true bipolar flexible direct current system. Background Art

[0002] With the rapid development of new energy power generation, wind power generation has gradually occupied a large proportion in the power system. Wind power generation includes onshore wind power generation and offshore wind power generation. Among them, for offshore wind power generation, flexible direct current transmission technology is currently the mainstream way to transmit large-scale wind power in deep sea.

[0003] The flexible direct current transmission systems for offshore wind power that have been built so far are all symmetrical unipolar topologies. The disadvantage is that if the converter fails, the entire system will not be able to deliver power. Therefore, there is a true bipolar topology transmission solution for large-capacity offshore wind power direct current transmission application scenarios. Under the true bipolar topology, when one pole converter fails, the bipolar system can be converted to a unipolar system to ensure that half of the wind farm power is delivered. However, the existing bipolar system takes a long time to convert to a unipolar system when one pole converter fails, which is not conducive to the rapid recovery of power transmission. Summary of the invention

[0004] The present disclosure aims to solve one of the technical problems in the related art at least to some extent.

[0005] To this end, the first purpose of the present disclosure is to propose a method for switching the operating mode of an offshore wind power true bipolar flexible DC system, the main purpose of which is to shorten the time it takes for the DC system to switch from bipolar to unipolar operation.

[0006] The second objective of the present disclosure is to propose an offshore wind power true bipolar flexible DC system operation mode switching device.

[0007] The third objective of the present disclosure is to propose an offshore wind power true bipolar flexible DC system operation mode switching device.

[0008] To achieve the above-mentioned purpose, the first embodiment of the present disclosure proposes a method for switching the operation mode of an offshore wind power true bipolar flexible DC system. The offshore wind power true bipolar flexible DC system includes four converters, and the four converters include two positive converters and two negative converters. The two positive converters are a machine-side positive converter and a grid-side positive converter, and the two negative converters are a machine-side negative converter and a grid-side negative converter. Each converter is connected to a grid connection point on the corresponding side via a connecting transformer. The method includes:

[0009] Detecting whether the four converters fail, and generating a blocking instruction if one converter fails or two positive / negative converters fail;

[0010] Based on the locking instruction, the four converters are controlled to be locked, and the incoming line switches of all connected transformers are controlled to be disconnected;

[0011] Controlling the neutral bus switch of the faulty converter and the converter with the same positive / negative pole to close, so that the remaining two converters form a loop, the remaining two converters include a machine-side target converter and a grid-side target converter, and controlling the incoming line switch of the coupling transformer connected to the grid-side target converter to close, so as to charge the remaining two converters;

[0012] The DC line voltage of the flexible DC system and the AC voltage of the target converter on the machine side are obtained in real time, the two target converters are unlocked based on the DC line voltage, and the incoming switch of the connecting transformer connected to the target converter on the machine side is closed based on the AC voltage, thereby completing the switching.

[0013] In one embodiment of the present disclosure, the unlocking of two target converters based on the DC line voltage control includes: when the DC line voltage rises to a first set voltage range, first controlling the grid-side target converter to unlock; when the DC line voltage rises to a second set voltage range, then controlling the machine-side target converter to unlock, and the maximum value of the first set voltage range is less than the minimum value of the second set voltage range.

[0014] In one embodiment of the present disclosure, the second set voltage range is ±5% of the DC voltage rated value; the DC voltage rated value is multiplied by 0.707 to obtain the first set voltage, and the first set voltage range is ±5% of the first set voltage.

[0015] In one embodiment of the present disclosure, the closing of the incoming switch of the connecting transformer connected to the target converter on the machine side based on the AC voltage control includes: when the AC voltage of the target converter on the machine side is within a third set voltage range, controlling the closing of the incoming switch of the connecting transformer connected to the target converter on the machine side.

[0016] In one embodiment of the present disclosure, the third set voltage range is ±5% of the rated value of the AC voltage of the target converter on the generator side.

[0017] To achieve the above-mentioned purpose, the second aspect of the present disclosure proposes an offshore wind power true bipolar flexible DC system operation mode switching device, the offshore wind power true bipolar flexible DC system includes four converters, the four converters include two positive converters and two negative converters, the two positive converters are the machine side positive converter and the grid side positive converter, the two negative converters are the machine side negative converter and the grid side negative converter, each converter is connected to the grid connection point on the corresponding side via a connecting transformer, and the device includes:

[0018] A detection unit, used for detecting whether the four converters fail, and generating a blocking instruction if one converter fails or two positive / negative converters fail;

[0019] A first control unit, configured to control the four converters to be locked based on the locking instruction, and to control the inlet switches of all connected transformers to be disconnected;

[0020] The second control unit is used to control the neutral bus switch of the faulty converter and the same positive / negative converter to close, so that the remaining two converters form a loop, the remaining two converters include a machine-side target converter and a grid-side target converter, and control the incoming line switch of the coupling transformer connected to the grid-side target converter to close, so as to charge the remaining two converters;

[0021] The third control unit is used to obtain the DC line voltage of the flexible DC system and the AC voltage of the target converter on the machine side in real time, control the two target converters to unlock based on the DC line voltage, and control the closing of the incoming switch of the connecting transformer connected to the target converter on the machine side based on the AC voltage, thereby completing the switching.

[0022] In one embodiment of the present disclosure, the third control unit is specifically used to: when the DC line voltage rises to a first set voltage range, first control the grid-side target converter to unlock; when the DC line voltage rises to a second set voltage range, then control the machine-side target converter to unlock, and the maximum value of the first set voltage range is less than the minimum value of the second set voltage range.

[0023] In one embodiment of the present disclosure, the third control unit is specifically used to control the incoming line switch of the coupling transformer connected to the machine-side target converter to close when the AC voltage of the machine-side target converter is within a third set voltage range.

[0024] In one embodiment of the present disclosure, in the third control unit, the second set voltage range is ±5% of the DC voltage rated value; the DC voltage rated value is multiplied by 0.707 to obtain the first set voltage, and the first set voltage range is ±5% of the first set voltage; the third set voltage range is ±5% of the AC voltage rated value of the machine-side target converter.

[0025] To achieve the above-mentioned purpose, the third aspect embodiment of the present disclosure proposes an offshore wind power true bipolar flexible DC system operation mode switching device, comprising: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the offshore wind power true bipolar flexible DC system operation mode switching method of the first aspect embodiment of the present disclosure.

[0026] In one or more embodiments of the present disclosure, an offshore wind power true bipolar flexible DC system includes four converters, the four converters include two positive converters and two negative converters, the two positive converters are a machine-side positive converter and a grid-side positive converter, the two negative converters are a machine-side negative converter and a grid-side negative converter, each converter is connected to a grid connection point on a corresponding side via a connecting transformer, and a switching method includes: detecting whether the four converters fail, if one converter fails or two positive / negative converters fail, generating a locking instruction; controlling the four converters to lock based on the locking instruction, and controlling all connecting transformers to lock. The incoming line switch of the converter is disconnected; the neutral bus switch of the faulty converter and the converter with the same positive / negative pole is controlled to be closed to form a loop for the remaining two converters, the remaining two converters include the machine-side target converter and the grid-side target converter, and the incoming line switch of the connecting transformer connected to the grid-side target converter is controlled to be closed to charge the remaining two converters; the DC line voltage of the flexible DC system and the AC voltage of the machine-side target converter are obtained in real time, the two target converters are controlled to be unlocked based on the DC line voltage, and the incoming line switch of the connecting transformer connected to the machine-side target converter is controlled to be closed based on the AC voltage, thereby completing the switching. In this case, when a converter fails or two positive / negative converters fail, all converters are locked first, the incoming line switches of all connecting transformers are disconnected, and then the neutral busbar of the faulty converter and the same positive / negative converter is closed to form a loop for the remaining two converters. For the formed loop, the incoming line switch of the connecting transformer connected to the grid-side target converter is closed in turn, the two target converters are unlocked, and the incoming line switch of the connecting transformer connected to the machine-side target converter is closed, so as to quickly isolate the faulty converter, shorten the time for the DC system to switch from bipolar to unipolar operation, realize rapid switching of the operating mode, and facilitate rapid recovery of power transmission.

[0027] Additional aspects and advantages of the present disclosure will be given in part in the following description and in part will be obvious from the following description or learned through practice of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the specific implementation of the present disclosure or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the specific implementation or prior art description. Obviously, the drawings described below are some implementations of the present disclosure. For ordinary technicians in this field, other drawings can also be obtained based on these drawings without creative work. The above and / or additional aspects and advantages of the present disclosure will become obvious and easy to understand from the following description of the embodiments in conjunction with the drawings, in which:

[0029] Figure 1 A schematic diagram of the topological structure of an offshore wind power true bipolar metal-free loop flexible DC transmission system provided by an embodiment of the present disclosure;

[0030] Figure 2 A schematic flow chart of a method for switching an operating mode of an offshore wind power true bipolar flexible DC system provided in an embodiment of the present disclosure;

[0031] Figure 3 A block diagram of an offshore wind power true bipolar flexible DC system operation mode switching device provided by an embodiment of the present disclosure;

[0032] Figure 4 It is a block diagram of an offshore wind power true bipolar flexible DC system operation mode switching device used to implement the offshore wind power true bipolar flexible DC system operation mode switching method of the embodiment of the present disclosure. DETAILED DESCRIPTION

[0033] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the embodiments of the present disclosure. Instead, they are merely examples of devices and methods consistent with some aspects of the embodiments of the present disclosure as detailed in the appended claims.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0035] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of the features. In the description of the present disclosure, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. It should also be understood that the term "and / or" used in the present disclosure refers to and includes any or all possible combinations of one or more associated listed items.

[0036] Embodiments of the present disclosure are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present disclosure, and should not be construed as limiting the present disclosure.

[0037] The present invention provides a method and device for switching the operation mode of an offshore wind power true bipolar flexible DC system, the main purpose of which is to shorten the time it takes for a DC system to switch from bipolar to unipolar operation.

[0038] The offshore wind power true bipolar flexible DC system disclosed in the present invention is an offshore wind power true bipolar flexible DC transmission system without a metal loop topology structure. It is easy to understand that the offshore wind power true bipolar flexible DC system includes four converters, four connecting transformers, a machine-side grid connection point and a grid-side grid connection point. The four converters include two positive converters and two negative converters. The two positive converters are the machine-side positive converters and the grid-side positive converters. The two negative converters are the machine-side negative converters and the grid-side negative converters. Each converter is connected to the grid connection point on the corresponding side via a corresponding connecting transformer. Among them, the positive converter on the machine side and the positive converter on the grid side are the same positive converter, the negative converter on the machine side and the negative converter on the grid side are the same negative converter, the positive converter on the machine side and the negative converter on the grid side are the same negative converter, the positive converter on the machine side and the negative converter on the machine side are the same machine side converter, and the positive converter on the grid side and the negative converter on the grid side are the same grid side converter.

[0039] The offshore wind power true bipolar flexible DC system disclosed in the present invention also includes four neutral bus switches, and each converter is grounded via a corresponding neutral bus switch.

[0040] The offshore wind power true bipolar flexible DC system disclosed in the present invention also includes a DC transmission line, four circuit breakers and multiple inductors. The DC transmission line includes a positive line and a negative line. The positive converter on the machine side is connected to the positive converter on the grid side via the positive line. An inductor and a circuit breaker are respectively arranged at the positive converters on the machine side and the grid side on the positive line. The negative converter on the machine side is connected to the negative converter on the grid side via the negative line. An inductor and a circuit breaker are respectively arranged at the negative converters on the machine side and the grid side on the negative line.

[0041] The machine-side positive converter and the machine-side negative converter of the present disclosure may adopt a wind farm side modular multilevel converter (WFMMC). The grid-side positive converter and the grid-side negative converter may adopt a grid-side modular multilevel converter (GSMMC). The circuit breaker may adopt a DC circuit breaker (DCCB).

[0042] Figure 1 A schematic diagram of the topological structure of an offshore wind power true bipolar non-metal loop flexible DC transmission system provided by an embodiment of the present disclosure. An offshore wind farm includes n wind turbine generator sets G, namely, a first wind turbine generator set G1, ..., an nth wind turbine generator set Gn.

[0043] like Figure 1 As shown, the offshore wind power true bipolar flexible DC system includes a machine-side positive converter, a grid-side positive converter, a machine-side negative converter, a grid-side negative converter, a positive machine-side connection transformer, a positive grid-side connection transformer, a negative machine-side connection transformer, and a negative grid-side connection transformer. One end of the positive machine-side connection transformer and the negative machine-side connection transformer are connected to the offshore wind farm via the machine-side grid connection point, and the other ends of the positive machine-side connection transformer and the negative machine-side connection transformer are respectively connected to the AC side of the corresponding converter, one end of the positive grid-side connection transformer and the negative grid-side connection transformer are connected to the onshore AC power grid via the grid-side grid connection point, and the other ends of the positive grid-side connection transformer and the negative grid-side connection transformer are respectively connected to the AC side of the corresponding converter. The offshore wind power true bipolar flexible DC system includes multiple neutral bus switches. The positive converter on the machine side is grounded through the first neutral bus switch (NBS1), the positive converter on the grid side is grounded through the third neutral bus switch (NBS3), the negative converter on the machine side is grounded through the second neutral bus switch (NBS2), and the negative converter on the grid side is grounded through the fourth neutral bus switch (NBS4). In addition, a first incoming line switch is provided between the positive machine side connection transformer and the machine side grid connection point. A third incoming line switch is provided between the positive grid side connection transformer and the grid side grid connection point. A second incoming line switch is provided between the negative machine side connection transformer and the machine side grid connection point. A fourth incoming line switch is provided between the negative grid side connection transformer and the grid side grid connection point.

[0044] like Figure 1As shown, the offshore wind power true bipolar flexible DC system includes a DC transmission line and an inductor and a DC circuit breaker arranged on the DC transmission line. The DC transmission line includes a positive line and a negative line. The machine-side positive converter is connected to the grid-side positive converter via the positive line. A first inductor L1 and a first DC circuit breaker DCCB1 are arranged near the machine-side positive converter on the positive line. A third inductor L3 and a third DC circuit breaker DCCB3 are arranged near the grid-side positive converter on the positive line. The machine-side negative converter is connected to the grid-side negative converter via the negative line. A second inductor L2 and a second DC circuit breaker DCCB2 are arranged near the machine-side negative converter on the negative line. A fourth inductor L4 and a fourth DC circuit breaker DCCB4 are arranged near the grid-side negative converter on the negative line.

[0045] In a first embodiment, Figure 2 The flowchart of the method for switching the operation mode of the offshore wind power true bipolar flexible DC system provided by the embodiment of the present disclosure is as follows. Figure 2 As shown, the method for switching the operation mode of the offshore wind power true bipolar flexible DC system includes the following steps:

[0046] Step S11, detecting whether the four converters fail. If one converter fails or two positive / negative converters fail, a blocking instruction is generated.

[0047] Specifically, in step S11, it is detected whether the positive converter on the machine side, the positive converter on the grid side, the negative converter on the machine side, and the negative converter on the grid side are faulty, wherein there are two types of fault conditions for generating a locking instruction, the first type of fault condition is that one of the four converters, namely, the positive converter on the machine side, the positive converter on the grid side, the negative converter on the machine side, and the negative converter on the grid side, fails; the second type of fault condition is that a same-pole converter (i.e., the same positive / negative converter) fails, i.e., the two positive converters, namely, the positive converter on the machine side and the positive converter on the grid side, fail, or the two negative converters, namely, the negative converter on the machine side and the negative converter on the grid side, fail.

[0048] In step S11, if no converter failure is detected, the bipolar normal operation of the offshore wind power true bipolar flexible DC system is carried out, and the offshore wind power true bipolar flexible DC system is in bipolar operation mode at this time; if a converter fails or two positive / negative converters fail, it is necessary to switch the offshore wind power true bipolar flexible DC system from bipolar operation mode to unipolar operation mode, and the controller of the faulty converter generates a locking instruction.

[0049] Step S12: Based on the locking instruction, the four converters are controlled to be locked, and the incoming line switches of all connected transformers are controlled to be disconnected.

[0050] In step S12, considering that long-term sea-flow current is not allowed for offshore engineering, any two of the four converters communicate with each other, and each converter needs to receive a signal from other converters to indicate whether to lock. Therefore, if a locking signal (i.e., a locking command) is received, the converter is controlled to lock.

[0051] Taking the failure of the positive converter on the machine side as an example, when the positive converter on the machine side fails, the controller of the positive converter on the machine side generates a locking instruction, and based on the locking instruction, the positive converter on the machine side is locked through the converter area protection action. After the controllers of the remaining three converters, the positive converter on the grid side, the negative converter on the machine side, and the negative converter on the grid side, receive the locking instruction from the positive converter on the machine side, they lock their respective converters through their respective converter area protection actions.

[0052] In step S12, the incoming line switches of all the connection transformers are controlled to be disconnected based on the locking instruction. Specifically, based on the locking instruction, the first incoming line switch between the positive machine-side connection transformer and the machine-side grid connection point is controlled to be disconnected, the third incoming line switch between the positive grid-side connection transformer and the grid-side grid connection point is controlled to be disconnected, the second incoming line switch between the negative machine-side connection transformer and the machine-side grid connection point is controlled to be disconnected, and the fourth incoming line switch between the negative grid-side connection transformer and the grid-side grid connection point is controlled to be disconnected.

[0053] Step S13, controlling the neutral bus switch of the faulty converter and the converter with the same positive / negative pole to close, so that the remaining two converters form a loop, the remaining two converters include the machine-side target converter and the grid-side target converter, and controlling the incoming line switch of the connecting transformer connected to the grid-side target converter to close, so as to charge the remaining two converters.

[0054] In step S13, taking the fault of the positive converter on the generator side as an example, the first neutral bus switch (NBS 正机 ) is closed, and the third neutral bus switch (NBS) of the positive converter on the grid side is controlled at the same time. 正网 ) is closed, and the remaining machine-side negative converter and grid-side negative converter form a loop with the DC transmission line. Among them, the machine-side negative converter is the machine-side target converter, and the grid-side negative converter is the grid-side target converter. After the loop is formed, the fourth incoming line switch between the negative grid-side connection transformer and the grid-side grid connection point is controlled to be closed, and at this time, the grid-side negative converter and the machine-side negative converter are uncontrolled rectified and charged.

[0055] Step S14, obtaining the DC line voltage of the flexible DC system and the AC voltage of the target converter on the machine side in real time, controlling the two target converters to unlock based on the DC line voltage, and controlling the incoming line switch of the connecting transformer connected to the target converter on the machine side to close based on the AC voltage, thereby completing the switching.

[0056] In step S14, two target converters are unlocked based on the DC line voltage, including: when the DC line voltage rises to the first set voltage range, the grid-side target converter is first controlled to unlock; when the DC line voltage rises to the second set voltage range, the generator-side target converter is then controlled to unlock, and the maximum value of the first set voltage range is less than the minimum value of the second set voltage range. The second set voltage range is ±5% of the DC voltage rated value; the DC voltage rated value is multiplied by 0.707 to obtain the first set voltage, and the first set voltage range is ±5% of the first set voltage.

[0057] In step S14, the line switch of the connection transformer connected to the target converter on the machine side is controlled to be closed based on the AC voltage, including: when the AC voltage of the target converter on the machine side is within a third set voltage range, the line switch of the connection transformer connected to the target converter on the machine side is controlled to be closed. The third set voltage range is ±5% of the rated value of the AC voltage of the target converter on the machine side. For example, when the rated value of the AC voltage is 1pu, the third set voltage range is 0.95pu to 1.05pu.

[0058] In step S14, taking the fault of the positive converter on the machine side as an example, based on the above, it can be known that the negative converter on the machine side is the target converter on the machine side, and the negative converter on the grid side is the target converter on the grid side. At this time, when the DC line voltage rises to the first set voltage range, the negative converter on the grid side is first controlled to unlock and enter the DC voltage control mode for active charging; then when the DC line voltage rises to the second set voltage range, the negative converter on the machine side is controlled to unlock and enter the AC voltage amplitude / frequency control mode. At this time, the offshore AC grid voltage (that is, the AC voltage of the target converter on the machine side) gradually rises until it reaches the rated AC voltage. When the AC voltage of the negative converter on the machine side is in the third set voltage range (that is, the AC voltage is stably running in the third set voltage range), the second incoming line switch between the negative machine side connection transformer and the machine side grid connection point is controlled to be closed, thereby providing AC voltage for the offshore wind farm to be connected to the grid, and the switching from the bipolar operation mode to the unipolar operation mode is completed at this time.

[0059] In the operating mode switching method of the offshore wind power true bipolar flexible DC system of the embodiment of the present disclosure, the offshore wind power true bipolar flexible DC system includes four converters, the four converters include two positive converters and two negative converters, the two positive converters are the machine-side positive converter and the grid-side positive converter, the two negative converters are the machine-side negative converter and the grid-side negative converter, each converter is connected to the grid connection point on the corresponding side via a connecting transformer, and the switching method includes: detecting whether the four converters fail, if one converter fails or two positive / negative converters fail, generating a locking instruction; controlling the four converters to lock based on the locking instruction. , control the line switches of all connected transformers to be disconnected; control the neutral bus switch of the faulty converter and the same positive / negative converter to be closed, so that the remaining two converters form a loop. The remaining two converters include the machine-side target converter and the grid-side target converter. Control the line switch of the connecting transformer connected to the grid-side target converter to be closed to charge the remaining two converters; obtain the DC line voltage of the flexible DC system and the AC voltage of the machine-side target converter in real time, control the two target converters to be unlocked based on the DC line voltage, and control the line switch of the connecting transformer connected to the machine-side target converter to be closed based on the AC voltage, thereby completing the switching. In this case, when a converter fails or two positive / negative converters fail, all converters are locked first, the incoming line switches of all connecting transformers are disconnected, and then the neutral busbar of the faulty converter and the same positive / negative converter is closed to form a loop for the remaining two converters. For the formed loop, the incoming line switch of the connecting transformer connected to the grid-side target converter is closed in turn, the two target converters are unlocked, and the incoming line switch of the connecting transformer connected to the machine-side target converter is closed, so as to quickly isolate the faulty converter, shorten the time for the DC system to switch from bipolar to unipolar operation, realize rapid switching of the operating mode, and facilitate rapid recovery of power transmission.

[0060] The following are embodiments of the device disclosed herein, which can be used to execute the method embodiments disclosed herein. For details not disclosed in the device embodiments disclosed herein, please refer to the method embodiments disclosed herein.

[0061] The present disclosure relates to an offshore wind power true bipolar flexible DC system operation mode switching device. The offshore wind power true bipolar flexible DC system operation mode switching device can shorten the time for the DC system to switch from bipolar to unipolar operation. The offshore wind power true bipolar flexible DC system includes four converters, and the four converters include two positive converters and two negative converters. The two positive converters are the machine-side positive converter and the grid-side positive converter, and the two negative converters are the machine-side negative converter and the grid-side negative converter. Each converter is connected to the grid connection point on the corresponding side via a connecting transformer.

[0062] See also Figure 3, Figure 3 A block diagram of an offshore wind power true bipolar flexible DC system operation mode switching device provided by an embodiment of the present disclosure. The offshore wind power true bipolar flexible DC system operation mode switching device 10 includes a detection unit 11, a first control unit 12, a second control unit 13 and a third control unit 14, wherein:

[0063] A detection unit 11 is used to detect whether the four converters fail, and if one converter fails or two positive / negative converters fail, a blocking instruction is generated;

[0064] A first control unit 12 is used to control the four converters to be locked based on the locking instruction, and to control the inlet switches of all connected transformers to be disconnected;

[0065] The second control unit 13 is used to control the neutral bus switch of the faulty converter and the converter with the same positive / negative pole to close, so that the remaining two converters form a loop, the remaining two converters include the machine-side target converter and the grid-side target converter, and control the incoming line switch of the coupling transformer connected to the grid-side target converter to close, so as to charge the remaining two converters;

[0066] The third control unit 14 is used to obtain the DC line voltage of the flexible DC system and the AC voltage of the target converter on the machine side in real time, control the two target converters to unlock based on the DC line voltage, and control the closing of the incoming switch of the connecting transformer connected to the target converter on the machine side based on the AC voltage, thereby completing the switching.

[0067] Optionally, the third control unit is specifically used to: when the DC line voltage rises to a first set voltage range, first control the grid-side target converter to unlock; when the DC line voltage rises to a second set voltage range, then control the machine-side target converter to unlock, and the maximum value of the first set voltage range is less than the minimum value of the second set voltage range.

[0068] Optionally, the third control unit 14 is specifically configured to: when the AC voltage of the target converter on the machine side is within a third set voltage range, control the incoming line switch of the coupling transformer connected to the target converter on the machine side to be closed.

[0069] Optionally, in the third control unit 14, the second set voltage range is ±5% of the DC voltage rated value; the DC voltage rated value is multiplied by 0.707 to obtain the first set voltage, and the first set voltage range is ±5% of the first set voltage; the third set voltage range is ±5% of the AC voltage rated value of the target converter on the machine side.

[0070] It should be noted that the above explanation of the embodiment of the method for switching the operating mode of an offshore wind power true bipolar flexible DC system is also applicable to the operating mode switching device of the offshore wind power true bipolar flexible DC system of this embodiment, which will not be repeated here.

[0071] In the operating mode switching device of the offshore wind power true bipolar flexible DC system of the embodiment of the present disclosure, the detection unit is used to detect whether the four converters fail. If one converter fails or two positive / negative converters fail, a locking instruction is generated; the first control unit is used to control the locking of the four converters based on the locking instruction, and control the incoming line switches of all connecting transformers to be disconnected; the second control unit is used to control the neutral bus switch of the failed converter and the same positive / negative converter to be closed, so that the remaining two converters form a loop, and the remaining two converters include a machine-side target converter and a grid-side target converter, and control the incoming line switch of the connecting transformer connected to the grid-side target converter to be closed to charge the remaining two converters; the third control unit is used to obtain the DC line voltage of the flexible DC system and the AC voltage of the machine-side target converter in real time, control the two target converters to be unlocked based on the DC line voltage, and control the incoming line switch of the connecting transformer connected to the machine-side target converter to be closed based on the AC voltage, thereby completing the switching. In this case, when a converter fails or two positive / negative converters fail, all converters are locked first, the incoming line switches of all connecting transformers are disconnected, and then the neutral busbar of the faulty converter and the same positive / negative converter is closed to form a loop for the remaining two converters. For the formed loop, the incoming line switch of the connecting transformer connected to the grid-side target converter is closed in turn, the two target converters are unlocked, and the incoming line switch of the connecting transformer connected to the machine-side target converter is closed, so as to quickly isolate the faulty converter, shorten the time for the DC system to switch from bipolar to unipolar operation, realize rapid switching of the operating mode, and facilitate rapid recovery of power transmission.

[0072] According to an embodiment of the present disclosure, the present disclosure also provides an offshore wind power true bipolar flexible direct current system operation mode switching device, a readable storage medium and a computer program product.

[0073] Figure 4It is a block diagram of an offshore wind power true bipolar flexible DC system operation mode switching device used to implement the offshore wind power true bipolar flexible DC system operation mode switching method of the embodiment of the present disclosure. The offshore wind power true bipolar flexible DC system operation mode switching device is intended to represent various forms of digital computers, such as laptop computers, desktop computers, workbenches, personal digital assistants, servers, blade servers, mainframe computers, and other suitable computers. The offshore wind power true bipolar flexible DC system operation mode switching device can also represent various forms of mobile devices, such as personal digital processing, cellular phones, smart phones, wearable electronic devices and other similar computing devices. The components shown in the present disclosure, the connections and relationships of the components, and the functions of the components are merely examples and are not intended to limit the implementation of the present disclosure described and / or required in the present disclosure.

[0074] like Figure 4 As shown, the offshore wind power true bipolar flexible DC system operation mode switching device 20 includes a computing unit 21, which can perform various appropriate actions and processes according to a computer program stored in a read-only memory (ROM) 22 or a computer program loaded from a storage unit 28 to a random access memory (RAM) 23. In RAM 23, various programs and data required for the operation of the offshore wind power true bipolar flexible DC system operation mode switching device 20 can also be stored. The computing unit 21, ROM 22 and RAM 23 are connected to each other through a bus 24. An input / output (I / O) interface 25 is also connected to the bus 24.

[0075] Multiple components in the offshore wind power true bipolar flexible DC system operation mode switching device 20 are connected to the I / O interface 25, including: an input unit 26, such as a keyboard, a mouse, etc.; an output unit 27, such as various types of displays, speakers, etc.; a storage unit 28, such as a disk, an optical disk, etc., which is communicatively connected to the computing unit 21; and a communication unit 29, such as a network card, a modem, a wireless communication transceiver, etc. The communication unit 29 allows the offshore wind power true bipolar flexible DC system operation mode switching device 20 to exchange information / data with other offshore wind power true bipolar flexible DC system operation mode switching devices through a computer network such as the Internet and / or various telecommunication networks.

[0076] The computing unit 21 may be a variety of general and / or special processing components with processing and computing capabilities. Some examples of the computing unit 21 include, but are not limited to, a central processing unit (CPU), a graphics processing unit (GPU), various dedicated artificial intelligence (AI) computing chips, various computing units running machine learning model algorithms, digital signal processors (DSPs), and any appropriate processors, controllers, microcontrollers, etc. The computing unit 21 performs the various methods and processes described above, such as performing an offshore wind power true bipolar flexible DC system operation mode switching method. For example, in some embodiments, the offshore wind power true bipolar flexible DC system operation mode switching method may be implemented as a computer software program, which is tangibly included in a machine-readable medium, such as a storage unit 28. In some embodiments, part or all of the computer program may be loaded and / or installed on the offshore wind power true bipolar flexible DC system operation mode switching device 20 via ROM 22 and / or communication unit 29. When the computer program is loaded into RAM 23 and executed by the computing unit 21, one or more steps of the offshore wind power true bipolar flexible DC system operation mode switching method described above may be performed. Alternatively, in other embodiments, the computing unit 21 may be configured to execute the method for switching the operating mode of an offshore wind power true bipolar flexible DC system in any other appropriate manner (for example, by means of firmware).

[0077] Various embodiments of the systems and techniques described above in the present disclosure may be implemented in digital electronic circuit systems, integrated circuit systems, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), application specific standard products (ASSPs), systems on chips (SOCs), load programmable logic devices (CPLDs), computer hardware, firmware, software, and / or combinations thereof. These various embodiments may include: being implemented in one or more computer programs that can be executed and / or interpreted on a programmable system including at least one programmable processor, which may be a special purpose or general purpose programmable processor that can receive data and instructions from a storage system, at least one input device, and at least one output device, and transmit data and instructions to the storage system, the at least one input device, and the at least one output device.

[0078] The program code for implementing the method of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general-purpose computer, a special-purpose computer, or other programmable data processing device, so that the program code, when executed by the processor or controller, enables the functions / operations specified in the flow chart and / or block diagram to be implemented. The program code may be executed entirely on the machine, partially on the machine, partially on the machine and partially on a remote machine as a stand-alone software package, or entirely on a remote machine or server.

[0079] In the present disclosure, a machine-readable medium may be a tangible medium that may contain or store a program for use by or in conjunction with an instruction execution system, device, or equipment. A machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. A machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or electronic device, or any suitable combination of the foregoing. A more specific example of a machine-readable storage medium may include an electrical connection based on one or more lines, a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM), an optical storage electronic device, a magnetic storage electronic device, or any suitable combination of the foregoing.

[0080] To provide interaction with a user, the systems and techniques described herein can be implemented on a computer having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to the user; and a keyboard and pointing device (e.g., a mouse or trackball) through which the user can provide input to the computer. Other types of devices can also be used to provide interaction with the user; for example, the feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form (including acoustic input, voice input, or tactile input).

[0081] The systems and techniques described herein can be implemented in a computing system that includes backend components (e.g., as a data server), or a computing system that includes middleware components (e.g., an application server), or a computing system that includes frontend components (e.g., a user computer with a graphical user interface or a web browser through which a user can interact with implementations of the systems and techniques described herein), or a computing system that includes any combination of such backend components, middleware components, or frontend components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: a local area network (LAN), a wide area network (WAN), the Internet, and a blockchain network.

[0082] A computer system may include a client and a server. The client and the server are generally remote from each other and usually interact through a communication network. The relationship between the client and the server is generated by computer programs running on the corresponding computers and having a client-server relationship with each other. The server may be a cloud server, also known as a cloud computing server or cloud host, which is a host product in the cloud computing service system to solve the defects of difficult management and weak business scalability in traditional physical hosts and VPS services ("Virtual Private Server", or "VPS" for short). The server may also be a server of a distributed system, or a server combined with a blockchain.

[0083] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps recorded in this disclosure can be executed in parallel, sequentially or in different orders, as long as the desired results of the technical solutions disclosed in this disclosure can be achieved, and this disclosure is not limited here.

[0084] The above specific implementations do not constitute a limitation on the protection scope of the present disclosure. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A method for switching the operation mode of an offshore wind power true bipolar flexible DC system, characterized in that: The offshore wind power true bipolar flexible DC system includes four converters, the four converters include two positive converters and two negative converters, the two positive converters are a machine-side positive converter and a grid-side positive converter, the two negative converters are a machine-side negative converter and a grid-side negative converter, each converter is connected to a grid connection point on the corresponding side via a connecting transformer, and the method includes: Detecting whether the four converters fail, and generating a blocking instruction if one converter fails or two positive converters or negative converters fail; Based on the locking instruction, the four converters are controlled to be locked, and the incoming line switches of all connected transformers are controlled to be disconnected; Controlling the neutral bus switch of the faulty converter and the same positive converter or negative converter to close, so that the remaining two converters form a loop, the remaining two converters include a machine-side target converter and a grid-side target converter, and controlling the incoming line switch of the coupling transformer connected to the grid-side target converter to close, so as to charge the remaining two converters; The DC line voltage of the flexible DC system and the AC voltage of the target converter on the machine side are obtained in real time, the two target converters are unlocked based on the DC line voltage, and the incoming switch of the connecting transformer connected to the target converter on the machine side is closed based on the AC voltage, thereby completing the switching.

2. The method for switching the operation mode of an offshore wind power true bipolar flexible DC system according to claim 1 is characterized in that: The step of controlling the unlocking of two target converters based on the DC line voltage includes: When the DC line voltage rises to a first set voltage range, the target converter on the grid side is first controlled to be unlocked; when the DC line voltage rises to a second set voltage range, the target converter on the machine side is then controlled to be unlocked, and the maximum value of the first set voltage range is less than the minimum value of the second set voltage range.

3. The method for switching the operation mode of an offshore wind power true bipolar flexible DC system according to claim 2 is characterized in that: The second set voltage range is ±5% of the DC voltage rated value; the DC voltage rated value is multiplied by 0.707 to obtain the first set voltage, and the first set voltage range is ±5% of the first set voltage.

4. The method for switching the operation mode of an offshore wind power true bipolar flexible DC system according to claim 3 is characterized in that: The method of controlling the closing of the incoming switch of the connection transformer connected to the target converter on the machine side based on the AC voltage includes: When the AC voltage of the target converter on the machine side is within the third set voltage range, the incoming line switch of the coupling transformer connected to the target converter on the machine side is controlled to be closed.

5. The method for switching the operation mode of an offshore wind power true bipolar flexible DC system according to claim 4 is characterized in that: The third set voltage range is ±5% of the rated value of the AC voltage of the target converter on the generator side.

6. An offshore wind power true bipolar flexible DC system operation mode switching device, characterized in that: The offshore wind power true bipolar flexible DC system includes four converters, including two positive converters and two negative converters, the two positive converters are the machine-side positive converter and the grid-side positive converter, the two negative converters are the machine-side negative converter and the grid-side negative converter, each converter is connected to the grid connection point on the corresponding side via a connecting transformer, and the device includes: A detection unit, used for detecting whether the four converters fail, and generating a blocking instruction if one converter fails or two positive converters or negative converters fail; A first control unit, configured to control the four converters to be locked based on the locking instruction, and to control the inlet switches of all connected transformers to be disconnected; The second control unit is used to control the neutral bus switch of the faulty converter and the same positive converter or negative converter to close, so that the remaining two converters form a loop, the remaining two converters include a machine-side target converter and a grid-side target converter, and control the incoming line switch of the coupling transformer connected to the grid-side target converter to close, so as to charge the remaining two converters; The third control unit is used to obtain the DC line voltage of the flexible DC system and the AC voltage of the target converter on the machine side in real time, control the two target converters to unlock based on the DC line voltage, and control the closing of the incoming switch of the connecting transformer connected to the target converter on the machine side based on the AC voltage, thereby completing the switching.

7. The operating mode switching device of the offshore wind power true bipolar flexible DC system according to claim 6 is characterized in that: The third control unit is specifically used for: When the DC line voltage rises to a first set voltage range, the target converter on the grid side is first controlled to be unlocked; when the DC line voltage rises to a second set voltage range, the target converter on the machine side is then controlled to be unlocked, and the maximum value of the first set voltage range is less than the minimum value of the second set voltage range.

8. The operating mode switching device of the offshore wind power true bipolar flexible DC system according to claim 7 is characterized in that: The third control unit is specifically used for: When the AC voltage of the target converter on the machine side is within the third set voltage range, the incoming line switch of the coupling transformer connected to the target converter on the machine side is controlled to be closed.

9. The operating mode switching device of the offshore wind power true bipolar flexible DC system according to claim 8 is characterized in that: In the third control unit, the second set voltage range is ±5% of the DC voltage rated value; the DC voltage rated value is multiplied by 0.707 to obtain the first set voltage, and the first set voltage range is ±5% of the first set voltage; the third set voltage range is ±5% of the AC voltage rated value of the target converter on the machine side.

10. An offshore wind power true bipolar flexible DC system operation mode switching device, characterized in that: include: at least one processor; as well as a memory communicatively connected to the at least one processor; wherein, The memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the method for switching the operating mode of an offshore wind power true bipolar flexible direct current system according to any one of claims 1-5.

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