Offshore wind power delivery system and control method thereof

Abstract

The invention discloses an offshore wind power sending-out system and a control method thereof, a converter of an offshore sending-end converter station is of a six-pulse-bridge topological structure, one half bridge of the converter is composed of thyristors, the other half bridge of the converter is composed of diodes, when a direct-current side fault occurs in the system, the trigger angles of the thyristors are adjusted, and the direct-current side fault occurs in the system. A thyristor is converted into an inversion state, the forward conduction characteristic of a diode is combined, a rectifier and a current converter do not output fault current outwards, then direct-current voltage is rapidly reduced through control over an inverter of a land receiving end converter station, and therefore the direct current of a fault point is reduced, and fault clearing is carried out. The technical problem that direct current side faults of an offshore wind power sending-out system with a sending end adopting a unidirectional current type uncontrolled rectification converter based on a diode element cannot be eliminated in time is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of offshore wind power, and in particular to an offshore wind power transmission system and a control method thereof. Background Art

[0002] At present, offshore wind power mainly adopts the transmission mode of nearshore AC and offshore DC, and the capacity of a single project is about one million kilowatts. The AC transmission scheme cannot meet the needs of large-scale deep-sea offshore wind power development, while the traditional DC transmission scheme is costly and difficult to meet the needs of large-scale offshore wind power economic development. It is necessary to explore new low-cost transmission schemes to provide new technical options for deep-sea offshore wind power development. At present, in practical applications, the mainstream scheme for DC transmission is flexible DC transmission technology based on MMC (Modular Multilevel Converter) topology, but its platform is large in size and weight, and the cost is relatively high. The use of unidirectional current-type uncontrolled rectifier converters based on diode elements at the sending end helps to achieve lightweight offshore platforms. Its topology structure is as follows: Figure 1 As shown. However, due to the unidirectional current characteristics, this solution continues to inject fault current into the fault point when a fault occurs on the DC side, resulting in the inability to clear the DC fault in time, thus limiting the practical application of this topology. Therefore, how to solve the technical defect that the offshore wind power transmission system using a unidirectional current-type uncontrolled rectifier converter based on diode elements at the sending end cannot clear the DC side fault in time on the basis of low cost and small volume is a technical problem that needs to be solved urgently by technical personnel in this field. Summary of the invention

[0003] The present invention provides an offshore wind power transmission system and a control method thereof, which are used to solve the technical problem that the offshore wind power transmission system using a unidirectional current-type uncontrolled rectifier converter based on diode elements at the sending end cannot clear the DC side fault in time on the basis of low cost and small volume.

[0004] In view of this, a first aspect of the present invention provides an offshore wind power transmission system, comprising an offshore sending-end converter station and an onshore receiving-end converter station, wherein the offshore sending-end converter station is connected to the onshore receiving-end converter station via a DC line, and the converter of the offshore sending-end converter station is a six-pulse bridge topology structure, wherein one half-bridge of the converter is entirely composed of thyristors, and the other half-bridge of the converter is entirely composed of diodes.

[0005] Optionally, the upper half bridge of the converter is entirely composed of thyristors, and the lower half bridge of the converter is entirely composed of diodes.

[0006] Optionally, the lower half bridge of the converter is entirely composed of thyristors, and the upper half bridge of the converter is entirely composed of diodes.

[0007] Optionally, a normal operation trigger angle of the thyristor is 0-90°, and a trigger angle of the thyristor when a DC side fault occurs in the offshore wind power transmission system is 140°-160°.

[0008] Optionally, a trigger angle of the thyristor when a DC side fault occurs in the offshore wind power transmission system is 150°.

[0009] A second aspect of the present invention provides a control method for an offshore wind power transmission system as described in any one of the first aspects, comprising:

[0010] When the offshore wind power transmission system is operating normally, adjusting the trigger angle of the thyristor within the normal operating trigger angle range of the thyristor according to the operating requirements of the offshore wind power transmission system;

[0011] When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted so that the thyristor is converted into an inverter state, and a DC voltage signal is transmitted to the onshore receiving-end converter station;

[0012] After receiving the DC voltage signal, the onshore receiving end converter station controls the DC voltage signal to And after maintaining the second preset time, the DC voltage signal is controlled to zero, wherein K is the control voltage coefficient, is the DC rated voltage.

[0013] Optionally, when a DC side fault occurs in the offshore wind power transmission system, adjusting the trigger angle of the thyristor so that the thyristor is converted to an inverter state, and transmitting the DC voltage signal to the onshore receiving-end converter station, comprises:

[0014] When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is smoothly changed to 150° within a third preset time, so that the thyristor is converted into an inverter state and transmits a DC voltage signal to the onshore receiving converter station.

[0015] Optionally, when a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted so that the thyristor is converted into an inverter state, and a DC voltage signal is transmitted to the onshore receiving-end converter station, and the method further includes:

[0016] The DC side current of the offshore wind power transmission system is detected, and when the rising rate of the DC side current is greater than or equal to 1 kA / ms, it is determined that a DC side fault occurs in the offshore wind power transmission system.

[0017] Optionally, the control voltage coefficient is 0.2~0.5.

[0018] Optionally, the first preset time is 10 ms, and the second preset time is 20 ms.

[0019] Optionally, the third preset time is 10 ms.

[0020] It can be seen from the above technical solutions that the offshore wind power transmission system provided by the present invention has the following advantages:

[0021] The offshore wind power transmission system provided by the present invention has a converter of a six-pulse bridge topology structure at the offshore sending-end converter station. One half-bridge of the converter is entirely composed of thyristors, and the other half-bridge is entirely composed of diodes. When a DC side fault occurs in the system, the trigger angle of the thyristor is adjusted to convert the thyristor into an inverter state. Combined with the forward conduction characteristics of the diode, the rectifier converter does not output the fault current to the outside, and then the DC voltage is rapidly reduced through the control of the inverter of the onshore receiving-end converter station, thereby reducing the DC current at the fault point to clear the fault. The control of the fault current by thyristors not only solves the problem that a pure diode system cannot clear the DC side fault, but also maintains the technical characteristics of the diode system in terms of low cost and small size. On the basis of low cost and small size, the technical problem that the offshore wind power transmission system using a unidirectional current-type uncontrolled rectifier converter based on diode elements at the sending end cannot clear the DC side fault in time is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 A schematic diagram of the topological structure of an offshore wind power transmission system in which a unidirectional current-type uncontrolled rectifier converter based on diode elements is used at the sending end in the prior art;

[0024] Figure 2 A schematic diagram of the topological structure of an offshore wind power transmission system provided in an embodiment of the present invention;

[0025] Figure 3 It is a flow chart of a control method of an offshore wind power transmission system provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] For easier understanding, see Figure 2 The present invention provides an embodiment of an offshore wind power transmission system, including an offshore sending-end converter station and an onshore receiving-end converter station, wherein the offshore sending-end converter station is connected to the onshore receiving-end converter station via a DC line, and the converter of the offshore sending-end converter station is a six-pulse bridge topology structure, wherein one half-bridge of the converter is entirely composed of thyristors, and the other half-bridge of the converter is entirely composed of diodes.

[0028] It should be noted that if Figure 2 As shown, converter A and converter B are converters of the offshore sending-end converter station. Converter A and converter B adopt a six-pulse bridge topology structure, one half-bridge is entirely composed of thyristors, and the other half-bridge is entirely composed of diodes. Specifically, the converter of the offshore sending-end converter station can be a converter in which the upper half-bridge is entirely composed of thyristors, and the lower half-bridge is entirely composed of diodes. The converter of the offshore sending-end converter station can also be a converter in which the lower half-bridge is entirely composed of thyristors, and the upper half-bridge of the converter is entirely composed of diodes. The cost of diodes is much lower than that of thyristors, and the volume is much smaller than that of MMC. If the six-pulse bridge is entirely composed of diodes, it is impossible to quickly clear the fault on the DC side. In the present invention, one half-bridge of the six-pulse bridge is entirely composed of thyristors, and thyristors are used to control the fault current and clear the fault on the DC side. The other half-bridge is entirely composed of diodes, which maintains the technical characteristics of low cost and small volume of the diode system.

[0029] The working principle of the offshore wind power transmission system provided in the present invention is:

[0030] When the offshore wind power transmission system operates normally, the thyristor can adjust the trigger angle within the angle range of 0~90° (that is, the normal operating angle of the thyristor is 0~90°) according to the operating requirements of the offshore wind power transmission system, thereby achieving the requirements of the thyristor converter. When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted to 140°~160°, preferably 150°, so that the thyristor is converted to the inverter state, combined with the forward conduction characteristics of the diode, so that the rectifier converter does not output fault current to the outside. When the inverter of the onshore receiving converter station (that is, the flexible DC inverter composed of the MMC structure) receives the DC voltage signal transmitted by the rectifier converter, it controls the DC voltage signal to drop rapidly, thereby reducing the DC current at the fault point and achieving fault clearing.

[0031] The offshore wind power transmission system provided by the present invention has a converter of a six-pulse bridge topology structure at the offshore sending-end converter station. One half-bridge of the converter is entirely composed of thyristors, and the other half-bridge is entirely composed of diodes. When a DC side fault occurs in the system, the trigger angle of the thyristor is adjusted to convert the thyristor into an inverter state. Combined with the forward conduction characteristics of the diode, the rectifier converter does not output the fault current to the outside, and then the DC voltage is rapidly reduced through the control of the inverter of the onshore receiving-end converter station, thereby reducing the DC current at the fault point to clear the fault. The control of the fault current by thyristors not only solves the problem that a pure diode system cannot clear the DC side fault, but also maintains the technical characteristics of the diode system in terms of low cost and small size. On the basis of low cost and small size, the technical problem that the offshore wind power transmission system using a unidirectional current-type uncontrolled rectifier converter based on diode elements at the sending end cannot clear the DC side fault in time is solved.

[0032] For easier understanding, see Figure 3 The present invention provides an embodiment of a control method applied to any offshore wind power transmission system provided in the present invention, including:

[0033] Step 101: When the offshore wind power transmission system operates normally, the trigger angle of the thyristor is adjusted within the normal operating trigger angle range of the thyristor according to the operating requirements of the offshore wind power transmission system.

[0034] It should be noted that when the offshore wind power transmission system is operating normally, the thyristor can adjust the trigger angle within the angle range of 0~90° according to the operating requirements of the offshore wind power transmission system to achieve the commutation requirements of the thyristor.

[0035] Step 102: When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted so that the thyristor is converted into an inverter state, and the DC voltage signal is transmitted to the onshore receiving converter station.

[0036] It should be noted that the DC side current of the offshore wind power transmission system is detected. When the DC side current rises rapidly, that is, the DC side current rise rate is greater than or equal to 1kA / ms, it is determined that a DC side fault occurs in the offshore wind power transmission system, and the fault clearing program is started to smoothly change the trigger angle of the thyristor from the current operating angle to 140°~160° within the third preset time, preferably 150°, so that the thyristor forms an inverter state and transmits the DC voltage signal to the onshore receiving end converter station. The third preset time is 10ms.

[0037] Step 103: After receiving the DC voltage signal, the onshore receiving converter station controls the DC voltage signal to After maintaining the second preset time, the DC voltage signal is controlled to zero, wherein K is the control voltage coefficient, is the DC rated voltage.

[0038] It should be noted that when the flexible DC inverter of the onshore receiving end converter station receives the DC voltage signal, it controls the DC voltage signal to ,in, is the DC rated voltage, K is the control voltage coefficient, and the value of the control voltage coefficient K is 0.2~0.5. After the state is maintained for a second preset time, the DC voltage signal is controlled to zero. The flexible DC inverter of the onshore receiving-end converter station controls the rapid drop of the DC voltage to reduce the DC current at the fault point and achieve fault clearing. In one embodiment, the first preset time is 10ms and the second preset time is 20ms.

[0039] The control method of the offshore wind power transmission system provided by the present invention is applied to any offshore wind power transmission system provided by the present invention. When a DC side fault occurs in the system, the trigger angle of the thyristor is adjusted to convert the thyristor into an inverter state. Combined with the forward conduction characteristics of the diode, the rectifier converter does not output the fault current to the outside, and then the DC voltage is rapidly reduced through the control of the inverter of the onshore receiving end converter station, thereby reducing the DC current at the fault point to clear the fault. The control of the fault current by the thyristor not only solves the problem that the pure diode system cannot clear the DC side fault, but also maintains the technical characteristics of the diode system with low cost and small size. On the basis of low cost and small size, it solves the technical problem that the offshore wind power transmission system using a unidirectional current type uncontrolled rectifier converter based on diode elements at the sending end cannot clear the DC side fault in time.

[0040] The terms "first", "second", "third", etc. in the present invention are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products, or devices.

[0041] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An offshore wind power transmission system, characterized in that: It includes an offshore sending-end converter station and an onshore receiving-end converter station. The offshore sending-end converter station is connected to the onshore receiving-end converter station via a DC line. The converter of the offshore sending-end converter station is a six-pulse bridge topology structure. One half-bridge of the converter is entirely composed of thyristors, and the other half-bridge of the converter is entirely composed of diodes.

2. The offshore wind power transmission system according to claim 1, characterized in that: The upper half bridge of the converter is entirely composed of thyristors, and the lower half bridge of the converter is entirely composed of diodes.

3. The offshore wind power transmission system according to claim 1, characterized in that: The lower half bridge of the converter is entirely composed of thyristors, and the upper half bridge of the converter is entirely composed of diodes.

4. The offshore wind power transmission system according to any one of claims 1 to 3, characterized in that: The normal operation trigger angle of the thyristor is 0-90°, and the trigger angle of the thyristor when a DC side fault occurs in the offshore wind power transmission system is 140°-160°.

5. The offshore wind power transmission system according to claim 4, characterized in that: The trigger angle of the thyristor when a DC side fault occurs in the offshore wind power transmission system is 150°.

6. A control method for an offshore wind power transmission system according to any one of claims 1 to 5, characterized in that: include: When the offshore wind power transmission system is operating normally, adjusting the trigger angle of the thyristor within the normal operating trigger angle range of the thyristor according to the operating requirements of the offshore wind power transmission system; When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted so that the thyristor is converted into an inverter state, and a DC voltage signal is transmitted to the onshore receiving-end converter station; After receiving the DC voltage signal, the onshore receiving end converter station controls the DC voltage signal to And after maintaining the second preset time, the DC voltage signal is controlled to zero, wherein K is the control voltage coefficient, is the DC rated voltage.

7. The control method of the offshore wind power transmission system according to claim 6, characterized in that: When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted so that the thyristor is converted into an inverter state, and a DC voltage signal is transmitted to the onshore receiving end converter station, including: When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is smoothly changed to 150° within a third preset time, so that the thyristor is converted into an inverter state and transmits a DC voltage signal to the onshore receiving converter station.

8. The control method for an offshore wind power transmission system according to any one of claims 6 to 7, characterized in that: When a DC side fault occurs in the offshore wind power transmission system, the trigger angle of the thyristor is adjusted so that the thyristor is converted into an inverter state, and a DC voltage signal is transmitted to the onshore receiving end converter station, and the above also includes: The DC side current of the offshore wind power transmission system is detected, and when the rising rate of the DC side current is greater than or equal to 1 kA / ms, it is determined that a DC side fault occurs in the offshore wind power transmission system.

9. The control method of the offshore wind power transmission system according to claim 6, characterized in that: The control voltage coefficient is 0.2~0.

5.

10. The control method of the offshore wind power transmission system according to claim 6, characterized in that: The first preset time is 10 ms, and the second preset time is 20 ms.

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