Converter

Abstract

According to the converter provided by the invention, the frequency of the current output by the power main loop to the low-frequency power grid is lower than the power frequency, and the power main loop needs to be connected with the low-frequency power grid through the intelligent fusing unit, so that when the current flowing through the intelligent fusing unit is too large, the current is not too large; the connection between the converter and the low-frequency power grid can be cut off through the disconnection of the intelligent fusing unit; furthermore, during low-frequency power transmission, a frame circuit breaker in the prior art can not be adopted any more, and the model selection problem of the frame circuit breaker is solved; besides, the low-frequency current has a longer period than the power-frequency current, the rise rate of the fault current during short circuit is relatively slower, and the number of sampling points of the intelligent fusing unit in one period is more than that of the power-frequency current, so that the judgment is more accurate, and the intelligent fusing unit can be disconnected quickly and timely when the current is too large to avoid fault expansion. Therefore, a fuse in the grid-side power unit in the prior art can be omitted.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a converter. Background Art

[0002] As the use of offshore wind farm resources approaches saturation, large-capacity offshore wind turbines are moving to deep sea, becoming an inevitable trend in the development of wind power. Deep sea power generation brings about the problem of too long transmission lines and cables between the generator sets and the onshore booster stations. Too long transmission cables will cause excessive line losses at the traditional power frequency of 50Hz, reducing the power generation efficiency of the entire power generation system.

[0003] Low-frequency transmission and high-voltage flexible direct current transmission technologies provide solutions for long-distance offshore wind power generation. Among them, the cost of low-frequency transmission technology is relatively low, and at the same time it can improve the efficiency of the entire wind power generation system, which is more conducive to application.

[0004] For the converter, low-frequency power transmission technology is to change the grid-side power unit from outputting industrial frequency current to outputting low-frequency current; and the biggest obstacle brought by the reduction in frequency is the selection of frame circuit breakers in its grid-connected unit. The breaking capacity of the currently used frame circuit breakers under low-frequency conditions does not meet the low-frequency short-circuit breaking capacity requirements of large-power offshore units. In addition, when low-frequency long-distance power transmission is carried out, the system impedance is large, and the short-circuit current is smaller and rises slower than that during industrial frequency transmission. It is impossible to ensure that the fuse in the grid-side power unit can be quickly disconnected in time to avoid the expansion of the fault. Utility Model Content

[0005] In view of this, the present application provides a converter to solve the problem that the breaking capacity of its frame circuit breaker is insufficient under low-frequency conditions and the problem that the fuse in the grid-side power unit cannot be relied upon to avoid fault expansion.

[0006] To achieve the above objectives, this application provides the following technical solutions:

[0007] The present application provides a converter, comprising: a control unit, at least one power main circuit and at least one intelligent fuse unit; wherein:

[0008] The power main circuit is connected to the low-frequency power grid through the intelligent fuse unit;

[0009] The main power circuit is controlled by the control unit;

[0010] The frequency of the current output by the power main circuit to the low-frequency power grid is lower than the power frequency.

[0011] Optionally, the intelligent fuse unit comprises: a control module, a current detection module and a fuse device; wherein,

[0012] The fuse device is arranged in a power transmission branch corresponding to the power main circuit connected to the low-frequency power grid;

[0013] The current detection module is arranged in the power transmission branch;

[0014] The control module controls the fuse device to disconnect when the current detected by the current detection module is greater than a preset current threshold.

[0015] Optionally, the intelligent fuse unit is also communicatively connected to the control unit.

[0016] Optionally, the signal sent by the control module to the control unit includes:

[0017] An electromagnetic disconnection indication signal is issued when the current detected by the current detection module is greater than the preset current threshold;

[0018] A mechanical disconnection indication signal issued after the fuse device is disconnected; and

[0019] A status feedback indication signal issued after a self-check of the status of the intelligent fuse unit;

[0020] The signal received by the control module from the control unit includes: a control signal for controlling the on / off state of the fuse device.

[0021] Optionally, the control module receives power from an auxiliary power supply circuit in the converter.

[0022] Optionally, the number of the intelligent fuse unit is 1;

[0023] When the number of the main power circuits is greater than 1, the main power circuits are connected in parallel at one side close to the low-frequency power grid and then connected to the low-frequency power grid through the same intelligent fuse unit.

[0024] Optionally, the number of the intelligent fuse units is the same as the number of the main power circuits;

[0025] Each of the intelligent fuse units corresponds to each of the main power circuits one by one, and each of the main power circuits is respectively connected to the low-frequency power grid through the corresponding intelligent fuse unit.

[0026] Optionally, the power main circuit includes: a machine-side switch unit, a machine-side filter unit, a machine-side power unit, a DC load unit, a grid-side power unit, a grid-side filter unit and a grid-side switch unit; wherein,

[0027] One side of the machine-side switch unit is connected to the wind turbine set;

[0028] The other side of the machine-side switch unit is connected to the AC side of the machine-side power unit through the machine-side filter unit;

[0029] The DC side of the machine-side power unit is connected to the DC side of the grid-side power unit via a DC bus;

[0030] The DC load unit is connected between the positive and negative electrodes of the DC bus;

[0031] The AC side of the grid-side power unit is connected to one side of the grid-side switch unit through the grid-side filter unit;

[0032] The other side of the grid-side switch unit is connected to the corresponding intelligent fuse unit;

[0033] The AC sides of the two power units are respectively provided with corresponding current detection units, and the output end of each current detection unit is connected to the control unit.

[0034] Optionally, the power main circuit includes: a stator contactor, a machine-side filter unit, a machine-side power unit, a DC load unit, a grid-side power unit, a grid-side filter unit and a grid-side switch unit; wherein,

[0035] One side of the stator contactor is connected to the stator side of the wind turbine;

[0036] The input end of the machine-side filter unit is connected to the rotor side of the wind turbine;

[0037] The output end of the machine-side filter unit is connected to the AC side of the machine-side power unit;

[0038] The DC side of the machine-side power unit is connected to the DC side of the grid-side power unit via a DC bus;

[0039] The DC load unit is connected between the positive and negative electrodes of the DC bus;

[0040] The AC side of the grid-side power unit is connected to the input end of the grid-side filter unit;

[0041] The output end of the grid-side filter unit is connected in parallel with the other side of the stator contactor, and then connected to one side of the grid-side switch unit;

[0042] The other side of the grid-side switch unit is connected to the corresponding intelligent fuse unit;

[0043] The AC sides of the two power units are respectively provided with corresponding current detection units, and the output end of each current detection unit is connected to the control unit.

[0044] Optionally, when the number of the main power circuits is greater than 1, each of the main power circuits is connected to the same wind turbine set.

[0045] The converter provided in the present application has a power main circuit whose current frequency output to the low-frequency power grid is lower than the power frequency, and its power main circuit needs to be connected to the low-frequency power grid through an intelligent fuse unit. Therefore, when the current flowing through the intelligent fuse unit is too large, the connection between the converter and the low-frequency power grid can be cut off by disconnecting the intelligent fuse unit; further, the frame circuit breaker in the prior art can no longer be used during low-frequency power transmission, which solves the problem of frame circuit breaker selection; in addition, since the low-frequency current has a longer cycle than the power frequency current, the rising rate of the fault current during a short circuit is relatively slower, and the number of sampling points of the intelligent fuse unit in one cycle is relatively more than that of the power frequency, so the judgment is more accurate, and it can be quickly and timely disconnected when the current is too large to avoid the expansion of the fault, and the fuse in the grid-side power unit in the prior art can be eliminated. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] In order to more clearly illustrate the embodiments of the utility model or the technical solutions in the prior art, the drawings to be used in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only embodiments of the utility model. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0047] Figure 1 A schematic diagram of the structure of a converter provided by the prior art;

[0048] Figure 2 A schematic diagram of the structure of a converter provided in an embodiment of the present application;

[0049] Figure 3 Another structural schematic diagram of the converter provided in the embodiment of the present application;

[0050] Figure 4 for Figure 2 A specific structural schematic diagram of the converter shown;

[0051] Figure 5 for Figure 4 A circuit diagram of the converter shown;

[0052] Figure 6 for Figure 3 A circuit diagram of the converter shown;

[0053] Figure 7 Another circuit diagram of a converter provided in an embodiment of the present application;

[0054] Figure 8A schematic diagram of the voltage / current waveforms of the intelligent fuse unit in the converter provided in an embodiment of the present application during operation. DETAILED DESCRIPTION

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

[0056] In this application, the terms "comprises", "comprising" or any other variation thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of more restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0057] Figure 1 The figure shows a typical structure diagram of a high-power converter. Among them, the grid-connected unit 107 plays the role of switching the circuit on and off, and has three-stage protection functions of long delay, short delay and instantaneous. It is required to have the ability to actively disconnect the circuit when a short circuit and large current occur, and has an arc extinguishing function, which is generally undertaken by the frame circuit breaker; the grid-side filter unit 106 converts the high-frequency DC switching voltage into the required low-frequency sinusoidal AC voltage; the grid-side power unit 105 includes a DC / AC power conversion power unit and a fast fuse, etc.; the machine-side power unit 103 includes an AC / DC machine-side power conversion power unit; the machine-side filter unit 102 mainly suppresses the reflection peak caused by the long-line transmission from the converter port to the motor port value voltage; the machine-side switch unit 101 is generally undertaken by an isolating switch, which plays the role of opening and closing the circuit between the motor winding and the converter, and does not have an active short-circuit protection function; the DC load unit 104 plays the role of energy storage, voltage stabilization, and shutdown discharge to a safe voltage; the braking unit 108 is used to quickly discharge energy under transient conditions to protect the grid-side power unit 105 and the machine-side power unit 103 to avoid failure caused by fault expansion; the soft start unit 109 is used when starting the machine to prevent the grid-connected unit 107 from directly closing the DC load unit 104, causing an excessive current change rate di / dt and causing the DC load unit 104 to fail.

[0058] from Figure 1It can be seen that the grid-connected unit 107 is the core device that connects the converter to the power grid, and plays a vital role in the normal and stable operation of the converter. The current frame circuit breakers are all designed according to the power frequency of 50Hz / 60Hz. When the low-frequency power grid is connected, that is, the power grid frequency becomes low frequency, such as 20Hz or 16.7Hz, the energy increases sharply due to the longer power signal cycle; in this case, the simulation of the low-frequency arc of the frame circuit breaker shows that the breaking capacity of the same model of frame circuit breaker under low-frequency conditions is reduced from 65kA to 20kA, which is about 0.3 capacity reduction; obviously, this result does not meet the requirement that the low-frequency short-circuit breaking capacity of offshore large-power units should be at least 50kA.

[0059] In addition, during low-frequency long-distance power transmission, especially high power such as above 10MW, the system impedance is relatively large. When a short circuit occurs on the DC side, the short-circuit current flowing through the bridge arm fuse in the grid-side power unit 105 may be less than the minimum breaking capacity of the fuse; and, under low-frequency conditions, the rising rate of the short-circuit current is obviously less than the rising rate of the short-circuit current under power frequency conditions; therefore, when the DC side of the machine-side power unit 103 fails, the fuse in the grid-side power unit 105, which would have quickly cut off the grid-side fault current under power frequency conditions, may no longer be able to quickly cut off the grid-side fault current, causing the grid-side power unit 105 to also fail; at this time, the frame circuit breaker on the grid side is at risk of contact erosion and damage due to excessive temperature under low-frequency conditions.

[0060] Therefore, the present application provides a converter to solve the problem that the frame circuit breaker thereof has insufficient breaking capacity under low-frequency conditions and cannot rely on the fuse in the grid-side power unit to avoid fault expansion.

[0061] See also Figure 2 The converter comprises: a control unit 10, at least one ( Figure 2 Two are shown as examples) power main circuit 20 and at least one ( Figure 2 Two are shown as examples) intelligent fuse units 30; wherein:

[0062] The power main circuit 20 is connected to the low-frequency power grid through the intelligent fuse unit 30. The intelligent fuse unit 30 can be disconnected when the current is too large, that is, the fault current is cut off. The number and corresponding relationship of the intelligent fuse unit 30 and the power main circuit 20 can be determined according to the actual application environment, but any power main circuit 20 needs to be connected to the low-frequency power grid through the corresponding intelligent fuse unit 30, for example:

[0063] In one example, the number of intelligent fuse units 30 is the same as the number of main power circuits 20; moreover, each intelligent fuse unit 30 corresponds to each main power circuit 20 one by one, and each main power circuit 20 is respectively connected to the low-frequency power grid through the corresponding intelligent fuse unit 30; specifically, each main power circuit 20 is respectively connected to one side of the corresponding intelligent fuse unit 30, and the other sides of each intelligent fuse unit 30 are connected in parallel and connected to the low-frequency power grid together; that is, a combination of multiple main power circuits 20 + intelligent fuse units 30 is arranged in parallel. Figure 2 In the example, the number of the intelligent fuse units 30 and the number of the power main circuits 20 are both two. At this time, each power main circuit 20 is respectively equipped with a corresponding intelligent fuse unit 30 to connect to the low-frequency power grid.

[0064] In another example, the number of intelligent fuse units 30 is 1; and the number of main power circuits 20 can be 1 or greater than 1; when the number of main power circuits 20 is greater than 1, each main power circuit 20 is close to one side of the low-frequency power grid, such as the output end of each main power circuit 20 in a wind power generation system, and is connected in parallel through the same intelligent fuse unit 30. Figure 3 In the example, two power main circuits 20 are used for demonstration. At this time, the output ends of the two power main circuits 20 are connected in parallel and share the same intelligent fuse unit 30 to connect to the low-frequency power grid. Figure 2 One group of intelligent fuse units 30 is omitted, and the remaining group of intelligent fuse units 30 is moved between the parallel connection point of the output ends of the two power main circuits 20 and the low-frequency power grid, and the other settings remain unchanged.

[0065] In actual applications, there will be a corresponding transformer between the intelligent fuse unit 30 and the low-frequency power grid, and multiple intelligent fuse units 30 can share the same transformer. In the wind power generation system, the wind turbine is connected to the low-frequency power grid through the corresponding main power circuit 20, the intelligent fuse unit 30 and the transformer in turn. In addition, when the number of main power circuits 20 is greater than 1, the input ends of each main power circuit 20 can be connected to the same wind turbine, thereby achieving the sharing of the output power of the wind turbine, which can be applied to the scenario of high-power low-frequency power transmission; the number of main power circuits 20 can be set according to the power demand of the wind turbine, which is not limited here and is within the scope of protection of this application.

[0066] The main power circuit 20 is controlled by the control unit 10. In the wind power generation system, the structure of the main power circuit 20 may include Figure 2 and Figure 3As shown in: the machine side switch unit 201, the machine side filter unit 202, the machine side power unit 203, the DC load unit 204, the grid side power unit 205, the grid side filter unit 206 and the grid side switch unit 207, other specific implementation forms described below may also be adopted; in actual applications, the power main circuit 20 may further include Figure 1 Other components shown in the dashed box are not described here.

[0067] The frequency of the current output by the power main circuit 20 to the low-frequency grid is consistent with the frequency of the low-frequency grid, and both are lower than the industrial frequency. In practical applications, the industrial frequency specifically refers to 50 Hz or 60 Hz, and a fluctuation of ±10% is allowed. Specifically, the frequency of the current output by the power main circuit 20 to the low-frequency grid can be 16.7 Hz or 20 Hz, and a fluctuation of ±10% is also allowed, depending on the frequency of the low-frequency grid to which it is connected. At this time, the converter can use low-frequency power transmission technology to realize the transmission of electric energy and connect to the low-frequency grid through a corresponding low-frequency transformer.

[0068] Since any power main circuit 20 needs to be connected to the low-frequency power grid through the corresponding intelligent fuse unit 30, when the current flowing through the intelligent fuse unit 30 is too large, it is no longer necessary to rely on the frame circuit breaker in the power main circuit 20 for disconnection, or rely on the fuse of the grid-side power unit in the power main circuit 20 to cut off the grid-side fault current and avoid the expansion of the fault. Instead, the connection between the converter and the low-frequency power grid can be cut off by disconnecting the intelligent fuse unit 30 to achieve protection. Therefore, the frame circuit breaker in the prior art can no longer be used, and the fuse in the grid-side power unit can also be cancelled.

[0069] The converter provided in this embodiment, through the above principle, can cut off the connection between the converter and the low-frequency power grid by disconnecting the intelligent fuse unit 30 during low-frequency power transmission; therefore, the frame circuit breaker in the prior art need not be used, thereby solving the problem of selecting the frame circuit breaker; in addition, since the low-frequency current has a longer cycle than the power frequency current, the rising rate of the fault current during a short circuit is relatively slower, and the number of sampling points of the intelligent fuse unit 30 in one cycle is relatively greater than that of the power frequency, so the judgment is more accurate, and the fuse can be quickly and timely disconnected when the current is too large to avoid the expansion of the fault, thereby eliminating the fuse in the grid-side power unit in the prior art.

[0070] Based on the previous embodiment, this embodiment provides some optional examples for the specific structure of the power main circuit 20, such as:

[0071] like Figure 4As shown in the figure, the main power circuit 20 includes: a machine-side switch unit 201, a machine-side filter unit 202, a machine-side power unit 203, a DC load unit 204, a grid-side power unit 205, a grid-side filter unit 206 and a grid-side switch unit 207; wherein, one side of the machine-side switch unit 201, as the input end of the main power circuit 20, is used to connect the wind turbine G; the other side of the machine-side switch unit 201 is connected to the AC side of the machine-side power unit 203 through the machine-side filter unit 202; the DC side of the machine-side power unit 203 The DC side of the grid-side power unit 205 is connected to the DC side through a DC bus; the DC load unit 204 is connected between the positive and negative poles of the DC bus; the AC side of the grid-side power unit 205 is connected to one side of the grid-side switch unit 207 through the grid-side filter unit 206; the other side of the grid-side switch unit 207, as the output end of the main power loop 20, is used to connect the corresponding intelligent fuse unit 30; the AC sides of the two power units are respectively provided with corresponding current detection units, and the output end of each current detection unit is connected to the control unit 10.

[0072] It should be noted that Figure 4 exist Figure 2 Based on the above, three-phase AC power is taken as an example for demonstration, in which one of the power main circuits 20: the machine side switch unit 201 is QS3, the machine side filter unit 202 is Dudt1, the machine side power unit 203 includes an AC / DC power conversion power unit, and the current detection unit on the AC side of the AC / DC power conversion power unit includes three bridge arm current sensors TA7 to TA9, the grid side power unit 205 includes a DC / AC power conversion power unit, and the current detection unit on the AC side of the DC / AC power conversion power unit includes three bridge arm current sensors TA1 to TA3, the grid side filter unit 206 is PFC1, and the grid side switch unit 207 is QS1. In another power main circuit 20: the machine side switch unit 201 is QS4, the machine side filter unit 202 is Dudt2, the machine side power unit 203 includes an AC / DC power conversion power unit, and the current detection unit on the AC side of the AC / DC power conversion power unit includes three bridge arm current sensors TA10 to TA12, the grid side power unit 205 includes a DC / AC power conversion power unit, and the current detection unit on the AC side of the DC / AC power conversion power unit includes three bridge arm current sensors TA4 to TA6, the grid side filter unit 206 is PFC2, and the grid side switch unit 207 is QS2.

[0073] In practical applications, the AC / DC power conversion power unit and the DC / AC power conversion power unit can be specifically used Figure 5The NPC (Neutral Point Clamped, neutral point clamped) topology shown in the figure, and the neutral point of the DC / AC power conversion power unit can be connected to the midpoint O of the DC load unit 204; the DC load unit 204 can specifically include an upper half bus capacitor (such as Figure 5 C1 or C3) and the lower half bus capacitor (as shown in Figure 5 C2 or C4 shown in ), both are connected to the midpoint O; the machine-side filter unit 202 can specifically adopt an LCR filter, and the grid-side filter unit 206 can specifically adopt an LCL filter; the machine-side switch unit 201 and the grid-side switch unit 207 can respectively adopt suitable types of isolating switches. Figure 5 The DC+ refers to the positive pole of the DC bus, and the DC- refers to the negative pole of the DC bus.

[0074] Figure 5 A specific internal circuit structure diagram of a full-power wind turbine single cabinet non-shared bus model is shown, but it is not limited to this. The specific topology of each internal unit can also adopt other forms in the prior art, all of which are within the protection scope of this application.

[0075] in addition, Figure 6 is Figure 3 Based on the three-phase alternating current, an exemplary display of the circuit structure is given. Figure 5 The difference is that Figure 3 and Figure 2 The difference is that different power main circuits 20 are no longer equipped with independent intelligent fuse units 30 (such as Figure 5 Instead of S-FU1 and S-FU2 shown in FIG, the output terminals are connected in parallel and share the same intelligent fuse unit 30 (such as Figure 6 S-FU1 shown in ); other structural settings are the same as Figure 5 Of course, the specific topology of each unit inside the power main circuit 20 can also adopt other forms in the prior art, which will not be repeated here.

[0076] like Figure 7As shown in, the power main circuit 20 can also adopt a double-fed conversion structure, specifically including: a stator contactor KM1, a machine-side filter unit 202, a machine-side power unit 203, a DC load unit 204, a grid-side power unit 205, a grid-side filter unit 206 and a grid-side switch unit 207; wherein, one side of the stator contactor KM1 is connected to the stator side of the wind turbine G; the input end of the machine-side filter unit 202 is connected to the rotor side of the wind turbine G; the output end of the machine-side filter unit 202 is connected to the AC side of the machine-side power unit 203; the DC side of the machine-side power unit 203 The DC side of the grid-side power unit 205 is connected to the DC side through a DC bus; the DC load unit 204 is connected between the positive and negative poles of the DC bus; the AC side of the grid-side power unit 205 is connected to the input end of the grid-side filter unit 206; the output end of the grid-side filter unit 206 is connected in parallel with the other side of the stator contactor, and then connected to one side of the grid-side switch unit 207; the other side of the grid-side switch unit 207 is connected to the corresponding intelligent fuse unit 30; the AC sides of the two power units are respectively provided with corresponding current detection units, and the output end of each current detection unit is connected to the control unit 10.

[0077] Figure 7 Only one power main circuit 20 is taken as an example for demonstration, wherein the machine side filter unit 202 is Dudt, and specifically an LCR filter can be used; the machine side power unit 203 includes an AC / DC power conversion power unit, and specifically an NPC topology can be used; the current detection unit on the AC side of the AC / DC power conversion power unit includes three bridge arm current sensors TA4 to TA6; the DC load unit 204 can specifically include an upper half bus capacitor (such as Figure 7 C1) and the lower half bus capacitor (as shown in Figure 7 C2 shown in ), both are connected at the midpoint O; the grid-side power unit 205 includes a DC / AC power conversion power unit, which can also adopt an NPC topology, and the neutral point thereof can be connected to the midpoint O of the DC load unit 204; the current detection unit on the AC side of the DC / AC power conversion power unit includes three bridge arm current sensors TA1 to TA3; the grid-side filter unit 206 is a PFC, which can specifically adopt an LCL filter; the grid-side switch unit 207 is QS1; the grid-side filter unit 206 and the grid-side switch unit 207 can adopt an isolating switch of a suitable type; Figure 7 The DC+ refers to the positive pole of the DC bus, and the DC- refers to the negative pole of the DC bus.

[0078] Compared to Figure 5 , Figure 7 The grid-connected device in the topology shown has an additional stator contactor KM1 to connect the stator side of the generator in the wind turbine with the low-frequency grid, playing the role of switching the circuit on and off.

[0079] It is worth noting that the above structures provided in this embodiment are only some optional examples of the main power circuit 20 and are not limited thereto in practical applications. Other structures in the prior art are also within the protection scope of this application.

[0080] On the basis of the above embodiments, this embodiment provides some examples for the implementation of the intelligent fuse unit 30, for example, it may specifically include: a control module ( Figures 4 to 7 Not shown), current detection module ( Figures 4 to 7 not shown) and fuses (such as Figures 4 to 7 (as shown in the dotted box indicated by 30); where:

[0081] The fuse device is arranged in the power transmission branch corresponding to the power main circuit 20 connected to the low-frequency power grid. For the application scenario of three-phase alternating current, the fuse device can be as follows: Figures 4 to 7 As shown in , it includes three smart fuses (Smart Fuse, referred to as S-FU) respectively arranged in each phase transmission branch, so that when a phase-to-phase short circuit or any phase-to-ground short circuit occurs, effective protection can be achieved by timely disconnecting the corresponding smart fuse. In practical applications, the fuse device may also only include corresponding smart fuses arranged in any two-phase transmission branches, and can also be disconnected for protection when a phase-to-phase short circuit occurs. The structural setting of the fuse device depends on its specific application environment, and is not limited here, and is within the protection scope of this application.

[0082] The current detection module is arranged in the power transmission branch and is used to detect the current between the corresponding power main circuit 20 and the low-frequency power grid. It can specifically include three sensors respectively arranged in each phase transmission branch, and its specific setting position can be at the front end or the rear end of the fuse device. It is not limited here and depends on its specific application environment.

[0083] The control module controls the fuse device to disconnect when the current detected by the current detection module is greater than a preset current threshold.

[0084] In this case, the intelligent fuse unit 30 can realize the protection of the passive mode by working independently. Figure 8 The specific working process is described as follows:

[0085] 1) The intelligent fuse unit 30 initially sets a preset current threshold αIsc according to the actual requirement of the whole machine for breaking the short-circuit current Isc; wherein α is a correction coefficient, α≤1.

[0086] 2) During the period from t1 to t2, the current detection module detects the current i flowing through the fuse device and starts to determine whether the current i exceeds the preset current threshold αIsc.

[0087] After the current detection module detects that the current i is greater than the preset current threshold αIsc, in order to avoid misjudgment, it can automatically perform multiple judgments in succession, with a judgment frequency of tens of microseconds; if the judgment results are all abnormal, the control module triggers a disconnection signal to control the fuse device to disconnect.

[0088] 3) During the period from t2 to t3, the judgment is effective and the control module sends the disconnection signal to the fuse device.

[0089] The fuse device starts to break after a delay of several hundred microseconds. Figure 8 The u shown in is the voltage across the fuse device.

[0090] 4) During the period t4, the fuse device is completely disconnected, that is, the intelligent fuse unit 30 is completely disconnected, and the short-circuit rapid protection is completed.

[0091] Preferably, Figures 2 to 7 As shown in , in the converter, the intelligent fuse unit 30 can also be communicatively connected with the control unit 10 .

[0092] In this case, the signal sent by the control module to the control unit 10 may include: an electromagnetic disconnection indication signal issued when the current detected by the current detection module is greater than the preset current threshold; and a mechanical disconnection indication signal issued after the fuse device is disconnected. That is, when the current i detected by the current detection module is greater than the preset current threshold αIsc, that is, for the above-mentioned period t2 to t3, the control module not only sends the disconnection signal to the fuse device to control the disconnection of the fuse device, but also feeds back the electromagnetic disconnection indication signal to the control unit 10, so that the control unit 10 can know that the current is too large and the fuse device is disconnected. In addition, after the fuse device is disconnected, that is, in the above-mentioned period t4, after the fuse device is completely disconnected, the control module can feed back the mechanical disconnection indication signal to the control unit 10, so that the control unit 10 can know that the fuse device has been disconnected.

[0093] Furthermore, the control module can receive power from the corresponding auxiliary power supply circuit in the converter; in addition, the signal sent by the control module to the control unit 10 may also include: a status feedback indication signal, which is sent after the control module performs a self-check on the status of the intelligent fuse unit 30 to indicate whether all devices of the intelligent fuse unit 30 including itself are normal; furthermore, the control module can also receive the control signal sent by the control unit 10.

[0094] In this case, the intelligent fuse unit 30 can be controlled by the control unit 10 to implement active mode protection. The specific working process is described below:

[0095] 1) The control module receives power supply, that is, the control power 24V is powered on, the intelligent fuse unit 30 starts self-checking, and sends a status feedback indication signal to the control unit 10.

[0096] 2) After the control unit 10 receives the status feedback indication signal, if the status feedback indication signal is abnormal, the startup is prohibited; if the status feedback indication signal is normal, the startup is allowed.

[0097] 3) After the power is allowed to be loaded after starting, the bridge arm sensors TA4 to TA6 will detect the three-phase bridge arm low-frequency currents Ia, Ib, and Ic of the grid-side power unit 205 in real time, and the bridge arm sensors TA10 to TA12 will detect the three-phase bridge arm low-frequency currents Iu, Iv, and Iw of the machine-side power unit 203 in real time. Each sensor at the two locations will then upload the corresponding detection results to the control unit 10 respectively.

[0098] 4) The control unit 10 determines the three-phase currents Ia, Ib, and Ic on the grid side (e.g. Figures 5 to 7 If the maximum value of the DC load unit 204 (the dotted line with arrows on the left side shown in the figure) is greater than the first current threshold βIn, a control signal, i.e., a disconnection instruction, is immediately sent to the intelligent fuse unit 30; the intelligent fuse unit 30 immediately enters the above-mentioned t2 to t3 period, triggering its control module to send the disconnection signal to the fuse device, and feedback the electromagnetic disconnection indication signal to the control unit 10. After the intelligent fuse unit 30 is quickly cut off, the mechanical disconnection indication signal is fed back to the control unit 10 to protect the grid-side power unit 205 from failure due to fault expansion. β is the grid-side overcurrent correction coefficient, β>1, In is the rated current of the grid-side bridge arm of the converter, and βIn≤αIsc.

[0099] Similarly, the control unit 10 determines the three-phase currents Iu, Iv, and Iw on the machine side (such as Figures 5 to 7 If the maximum value of the DC load unit 204 (the dotted line with arrows on the right side shown in the figure) is greater than the second current threshold value γIm, a control signal, i.e., a disconnection instruction, is immediately sent to the intelligent fuse unit 30; the intelligent fuse unit 30 immediately enters the above-mentioned t2 to t3 period, triggering its control module to send the disconnection signal to the fuse device, and feedback the electromagnetic disconnection indication signal to the control unit 10. After the intelligent fuse unit 30 is quickly cut off, the mechanical disconnection indication signal is fed back to the control unit 10 to protect the grid-side power unit 205 in advance from failure due to fault expansion. γ is the machine-side overcurrent correction coefficient, γ>1, and Im is the rated current of the machine-side bridge arm of the converter.

[0100] 5) After receiving the electromagnetic disconnection indication signal and the mechanical disconnection indication signal fed back by the intelligent fuse unit 30, the control unit 10 sends an instruction to disconnect the network-side switch unit 207, completing the entire low-frequency short-circuit disconnection fault protection shutdown process.

[0101] In practical applications, the intelligent fuse unit 30 preferably has both a passive protection mode and an active protection mode; and its built-in sensor supports broadband sampling, and the control module can disconnect the fuse device, feedback the above-mentioned various node information, and receive control signals.

[0102] by Figure 4 or Figure 5 Taking the structure shown in the figure as an example, the power circuit of the low-frequency converter is composed of two independent power main circuits 20, and the core grid-connected device includes: the main device, namely two intelligent fuse units (i.e. S-FU1 and S-FU2 in the figure) 30, two grid-side switch units (i.e. isolating switches QS1 and QS2 in the figure) 207, four current detection units (each current detection unit includes each bridge arm current sensor TA) and a control unit 10. It should be noted that Figure 5 Only the connection relationship between one of the power main circuits 20 and the control unit 10 is shown, and the other circuit is the same and will not be shown one by one. In practical applications, each grid-side switch unit 207 also needs to receive power supply, such as a 24VDC power supply, which can be derived from an auxiliary power supply circuit that already exists in the converter, or a dedicated independent auxiliary power supply circuit can be additionally provided on the basis of the existing circuit structure; depending on the specific application environment, it is within the protection scope of this application.

[0103] The grid-side switch unit 207 is used to cut off the connection between the isolated low-frequency grid and the converter circuit. Figure 1 The grid-connected unit 107 needs to adopt a frame circuit breaker, and the grid-side switch unit 207 can adopt an isolating switch; the current detection unit on the grid side is used to collect the grid-connected current of the converter, and its frequency range is 0 to 25kHz, and feed it back to the control unit 10; the control unit 10 is used to collect the signal fed back by the intelligent fuse unit 30, and send a control signal to the intelligent fuse unit 30, and the control unit 10 can specifically adopt a CPU (Central Processing Unit).

[0104] for Figure 4 or Figure 5 The full-power wind turbine single cabinet non-shared busbar model shown in the figure aims at low-frequency offshore long-distance power transmission. For the difficulties brought by the design of the traditional converter grid-connected unit, this embodiment proposes a design method using an intelligent fuse unit 30+isolating switch+partial auxiliary circuit. These auxiliary circuits may include the original circuits of the converter such as the above-mentioned auxiliary power supply circuit, current detection unit, control unit 10, etc., which solves the problem of insufficient low-frequency breaking capacity of the current 1140V low-voltage frame circuit breaker. At the same time, it solves the problem that the traditional fuse cannot protect the semiconductor module in the grid-side power unit under low frequency because the current rise rate during short circuit is slower than the industrial frequency 50Hz, resulting in the expansion of faults and high subsequent maintenance costs.

[0105] It should be noted that Figure 7 For the double-fed converter structure shown in 5) in the above specific implementation process, the control unit 10 will send a command to disconnect the grid-side switch unit 207 and the stator contactor KM1 after receiving the electromagnetic disconnection indication signal and the mechanical disconnection indication signal fed back by the intelligent fuse unit 30, completing the entire low-frequency short-circuit disconnection fault protection shutdown process. The other implementation process parameter settings remain unchanged.

[0106] For offshore wind power high-power generation application scenarios, including but not limited to low-frequency power transmission application scenarios, the converter provided by this application, in view of the technical difficulty in the industry that the grid-side frame circuit breaker, the core equipment of the grid-connected device, has insufficient breaking capacity in this scenario, proposes a solution to protect the corresponding grid-connected device by using an intelligent fuse unit + isolating switch + part of the auxiliary circuit; not only can the traditional frame circuit breaker be eliminated, but also the judgment can be made more accurate with the help of the sensor in the intelligent fuse unit, so that the fuse in the prior art can be omitted in the grid-side power unit. At the same time, the passive protection mode + active protection mode inherent in the intelligent fuse unit is adopted, and the double insurance can judge the short-circuit fault current or low-multiple overload current in advance, and the connection between the converter and the low-frequency power grid can be cut off in advance to protect the grid-side power unit, so as to prevent the fault from being magnified due to the failure of the machine-side power unit, thereby reducing the subsequent maintenance costs.

[0107] The same and similar parts between the various embodiments in this specification can refer to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the system or system embodiment, since it is basically similar to the method embodiment, the description is relatively simple, and the relevant parts can refer to the partial description of the method embodiment. The system and system embodiments described above are only schematic, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative work.

[0108] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of the present utility model.

[0109] With respect to the above description of the disclosed embodiments, the features described in the embodiments in this specification may be replaced or combined with each other, so that professionals in the field can implement or use the present invention. Various modifications to these embodiments will be apparent to professionals in the field, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A converter, characterized in that: include: A control unit, at least one power main circuit and at least one intelligent fuse unit; wherein, The power main circuit is connected to the low-frequency power grid through the intelligent fuse unit; The main power circuit is controlled by the control unit; The frequency of the current output by the power main circuit to the low-frequency power grid is lower than the power frequency.

2. The converter according to claim 1, characterized in that: The intelligent fuse unit comprises: a control module, a current detection module and a fuse device; wherein, The fuse device is arranged in a power transmission branch corresponding to the power main circuit connected to the low-frequency power grid; The current detection module is arranged in the power transmission branch; The control module controls the fuse device to disconnect when the current detected by the current detection module is greater than a preset current threshold.

3. The converter according to claim 2, characterized in that: The intelligent fuse unit is also connected to the control unit for communication.

4. The converter according to claim 3, characterized in that: The signal sent by the control module to the control unit includes: An electromagnetic disconnection indication signal is issued when the current detected by the current detection module is greater than the preset current threshold; A mechanical disconnection indication signal issued after the fuse device is disconnected; and A status feedback indication signal issued after a self-check of the status of the intelligent fuse unit; The signal received by the control module from the control unit includes: a control signal for controlling the on / off state of the fuse device.

5. The converter according to claim 2, characterized in that: The control module receives power from an auxiliary power circuit in the converter.

6. The converter according to any one of claims 1 to 5, characterized in that: The number of the intelligent fuse unit is 1; When the number of the main power circuits is greater than 1, the main power circuits are connected in parallel at one side close to the low-frequency power grid and then connected to the low-frequency power grid through the same intelligent fuse unit.

7. The converter according to any one of claims 1 to 5, characterized in that: The number of the intelligent fuse units is the same as the number of the main power circuits; Each of the intelligent fuse units corresponds to each of the main power circuits one by one, and each of the main power circuits is respectively connected to the low-frequency power grid through the corresponding intelligent fuse unit.

8. The converter according to any one of claims 1 to 5, characterized in that: The power main circuit includes: a machine-side switch unit, a machine-side filter unit, a machine-side power unit, a DC load unit, a grid-side power unit, a grid-side filter unit and a grid-side switch unit; wherein, One side of the machine-side switch unit is connected to the wind turbine set; The other side of the machine-side switch unit is connected to the AC side of the machine-side power unit through the machine-side filter unit; The DC side of the machine-side power unit is connected to the DC side of the grid-side power unit via a DC bus; The DC load unit is connected between the positive and negative electrodes of the DC bus; The AC side of the grid-side power unit is connected to one side of the grid-side switch unit through the grid-side filter unit; The other side of the grid-side switch unit is connected to the corresponding intelligent fuse unit; The AC sides of the two power units are respectively provided with corresponding current detection units, and the output end of each current detection unit is connected to the control unit.

9. The converter according to any one of claims 1 to 5, characterized in that: The power main circuit includes: a stator contactor, a machine-side filter unit, a machine-side power unit, a DC load unit, a grid-side power unit, a grid-side filter unit and a grid-side switch unit; wherein, One side of the stator contactor is connected to the stator side of the wind turbine; The input end of the machine-side filter unit is connected to the rotor side of the wind turbine; The output end of the machine-side filter unit is connected to the AC side of the machine-side power unit; The DC side of the machine-side power unit is connected to the DC side of the grid-side power unit via a DC bus; The DC load unit is connected between the positive and negative electrodes of the DC bus; The AC side of the grid-side power unit is connected to the input end of the grid-side filter unit; The output end of the grid-side filter unit is connected in parallel with the other side of the stator contactor, and then connected to one side of the grid-side switch unit; The other side of the grid-side switch unit is connected to the corresponding intelligent fuse unit; The AC sides of the two power units are respectively provided with corresponding current detection units, and the output end of each current detection unit is connected to the control unit.

10. The converter according to any one of claims 1 to 5, characterized in that: When the number of the main power circuits is greater than 1, each of the main power circuits is connected to the same wind turbine generator set.

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