阅读说明：本技术 一种混合式海上风场变流器拓扑结构及其使用方法 (Hybrid offshore wind field converter topological structure and application method thereof ) 是由 谢宁 赵伟 王伟 谢志文 岳菁鹏 曾杰 张威 徐琪 于 2020-07-30 设计创作，主要内容包括：本申请公开了一种混合式海上风场变流器拓扑结构及其使用方法,二极管整流器的交流侧与风场内网电连接,二极管整流器的直流侧与高压直流输电线一端电连接；并联换流器包括电力电子变压器,电力电子变压器的交流侧与风场内网输出变压器电连接,电力电子变压器的直流侧第一输出端连接半桥模块串的第一端,半桥模块串的第二端和电力电子变压器的直流侧第二输出端通过LC滤波电路与所述高压直流输电线另一端电连接。可以大幅降低拓扑结构成本,能够在风场启动阶段主动建立风场内网电压,提供风风场的启动功率,实现风场的黑启动。电力电子变压器能在风场稳定发送阶段提供无功补偿与谐波电流补偿,改善了基于二极管整流器系统的性能。(The application discloses a topological structure of a hybrid offshore wind field converter and a using method thereof, wherein the alternating current side of a diode rectifier is electrically connected with a wind field inner network, and the direct current side of the diode rectifier is electrically connected with one end of a high-voltage direct-current transmission line; the parallel converter comprises a power electronic transformer, the alternating current side of the power electronic transformer is electrically connected with the wind farm intranet output transformer, the first output end of the direct current side of the power electronic transformer is connected with the first end of the half-bridge module string, and the second end of the half-bridge module string and the second output end of the direct current side of the power electronic transformer are electrically connected with the other end of the high-voltage direct-current transmission line through an LC filter circuit. The cost of the topological structure can be greatly reduced, the network voltage in the wind farm can be actively established in the starting stage of the wind farm, the starting power of the wind farm is provided, and the black start of the wind farm is realized. The power electronic transformer can provide reactive compensation and harmonic current compensation in the stable sending stage of a wind field, and the performance of a diode rectifier system is improved.)

1. A hybrid offshore wind farm converter topology, comprising: the wind power station comprises a diode rectifier and a parallel converter, wherein the alternating current side of the diode rectifier is electrically connected with a grid in a wind farm, and the direct current side of the diode rectifier is electrically connected with one end of a high-voltage direct-current transmission line; the parallel converter comprises a power electronic transformer, the alternating current side of the power electronic transformer is electrically connected with an output transformer in a wind farm, the first output end of the direct current side of the power electronic transformer is connected with the first end of the half-bridge module string, and the second end of the half-bridge module string and the second output end of the direct current side of the power electronic transformer are electrically connected with the other end of the high-voltage direct-current transmission line through an LC filter circuit.

2. A hybrid offshore wind farm converter topology according to claim 1, wherein the electronic power transformer comprises: the wind power plant comprises a conveying unit and an isolation unit, wherein the first end of the conveying unit is electrically connected with an output transformer in a wind farm, the second end of the conveying unit is electrically connected with the first end of the isolation unit, and the second end of the isolation unit is electrically connected with one end of a half-bridge module string.

3. The hybrid offshore wind farm converter topology according to claim 2, wherein the transport unit comprises a three-phase transport circuit, the transport circuit comprises a first H-bridge module and a first voltage stabilization capacitor, the first H-bridge module is connected in parallel with the first voltage stabilization capacitor, the first H-bridge module in the three-phase transport circuit is respectively electrically connected with a secondary winding of a wind farm internal network output transformer, different first H-bridge modules are cascaded with each other, and an absorption capacitor is arranged in each first H-bridge module.

4. The hybrid offshore wind farm converter topology of claim 3, wherein the isolation unit comprises a three-phase isolation circuit, the isolation circuit comprises a second H-bridge module, a third H-bridge module and a high frequency transformer, a first end of the second H-bridge module is electrically connected to the voltage stabilizing capacitor, two ends of the high frequency transformer are electrically connected to a second end of the second H-bridge module and a first end of the third H-bridge module, respectively, and a second end of the third H-bridge module is electrically connected to one end of the half-bridge module string; and DC blocking capacitors are arranged between the second H-bridge module and the high-frequency transformer, the third H-bridge module is connected with a second voltage stabilizing capacitor in parallel, and absorption capacitors are arranged in the second H-bridge module and the third H-bridge module.

5. The hybrid offshore wind farm converter topology of claim 1, wherein the string of half-bridge modules comprises a plurality of half-bridge modules, the plurality of half-bridge modules connected in series.

6. A hybrid offshore wind farm converter topology according to claim 1, wherein the LC filter circuit comprises a filter inductor and a filter capacitor, wherein a first end of the filter inductor is electrically connected to a second end of the half bridge module string and a first end of the filter capacitor, respectively, a second end of the filter inductor is electrically connected to the hvdc line, and a second end of the filter capacitor is electrically connected to the dc side second output of the power electronic transformer and the hvdc line, respectively.

7. A hybrid offshore wind farm converter topology according to claim 6, wherein the HVDC lines comprise a positive high voltage DC line electrically connected to the second end of the filter inductor and a negative HVDC line electrically connected to the second end of the filter capacitor and the second end of the power electronic transformer respectively.

8. The hybrid offshore wind farm converter topology of claim 1, wherein the diode current converter is a multiplexed diode rectifier.

9. A method of using a hybrid offshore wind farm converter topology, using the hybrid offshore wind farm converter topology of any of claims 1-8, the method comprising:

in the wind field starting stage, a power electronic transformer in the parallel current converter transmits electric energy on a high-voltage direct current side to a wind field internal network through an inversion function, establishes alternating-current voltage of the wind field internal network, and controls the voltage of the wind field internal network to be lower than the rectification threshold voltage of a diode rectifier so that the diode rectifier does not work;

the wind turbine generator starts to generate power, a wind field is converted from a load to a power supply, and at the moment, an internal network of the wind field starts to transmit active power to a high-voltage direct-current side through a parallel converter;

after the wind field is started, the voltage of an AC port is boosted by a power electronic transformer, and the voltage in the wind field is boosted to reach the rectification threshold voltage of a diode rectifier;

then the power electronic transformer gradually reduces to transmit active power to the direct current side, so that the output power of the wind field is transferred to the diode rectifier from the parallel converter, and the parallel converter gradually operates under the condition of zero active power;

when the wind field enters a stable power generation operation stage, the parallel converter does not transmit active power to the power grid any more, and all modules of the sub module string in the parallel converter are locked to be removed from the system.

Technical Field

The application relates to the technical field of flexible direct-current transmission equipment, in particular to a hybrid offshore wind field converter topological structure and a using method thereof.

Background

The voltage source converter structure adopted in the existing flexible direct current engineering mainly has three structures, including a two-level topological structure, a three-level topological structure and a modular multi-level topological structure. The two-level and three-level structures have fewer output levels and poorer output voltage waveforms, and high-frequency PWM is required to improve the quality of the output voltage waveforms, so that high requirements on the switching consistency and voltage-sharing performance of switching devices are provided, and the problems are more serious along with the increase of the number of the series devices, so that the two-level and three-level structures are difficult to popularize in the field of high-voltage flexible direct-current transmission.

The existing high-voltage flexible direct-current transmission technology adopts a plurality of sub-modules to construct a high-capacity high-voltage direct-current converter, has the advantages of simple manufacture, good waveform quality and low loss, and has the defects that a plurality of offshore wind farm transmission projects adopting the modular multi-level converter technology are successfully put into operation, but the number of used devices is increased along with the increase of voltage grades, the size is huge, the balance control of sub-module capacitor voltage and the difficulty of circulation control among bridge arms are increased, and the cost of the converter is increased. For a direct current transmission system of an offshore wind field, the construction cost of an offshore platform is high, so that the system cost is multiplied.

Because the wind field only outputs power when in steady-state operation, the diode rectification topological structure has low cost and does not need to be controlled, the cost, the volume and the weight can be greatly reduced, but a series of problems can be caused by only adopting diode rectification, and firstly, the diode rectifier cannot independently establish the voltage of a wind field internal network; secondly, a certain return power is needed in the starting stage of the wind turbine generator, and the diode rectifying structure has no inversion function and cannot meet the black starting requirement of a wind field; in addition, diode rectifiers introduce a large amount of current harmonics and there is no way to provide reactive compensation for the wind farm.

Disclosure of Invention

In order to solve the technical problems, the following technical scheme is provided:

in a first aspect, an embodiment of the present application provides a hybrid offshore wind farm converter topology, including: the wind power station comprises a diode rectifier and a parallel converter, wherein the alternating current side of the diode rectifier is electrically connected with a grid in a wind farm, and the direct current side of the diode rectifier is electrically connected with one end of a high-voltage direct-current transmission line; the parallel converter comprises a power electronic transformer, the alternating current side of the power electronic transformer is electrically connected with an output transformer in a wind farm, the first output end of the direct current side of the power electronic transformer is connected with the first end of the half-bridge module string, and the second end of the half-bridge module string and the second output end of the direct current side of the power electronic transformer are electrically connected with the other end of the high-voltage direct-current transmission line through an LC filter circuit.

By adopting the implementation mode, the cost of the topological structure can be greatly reduced, the network voltage in the wind farm can be actively established in the starting stage of the wind farm, the starting power of the wind farm is provided, and the black start of the wind farm is realized. The power electronic transformer can provide reactive compensation and harmonic current compensation in the stable sending stage of a wind field, and the performance of a diode rectifier system is improved.

With reference to the first aspect, in a first possible implementation manner of the first aspect, the electronic power transformer includes: the wind power plant comprises a conveying unit and an isolation unit, wherein the first end of the conveying unit is electrically connected with an output transformer in a wind farm, the second end of the conveying unit is electrically connected with the first end of the isolation unit, and the second end of the isolation unit is electrically connected with one end of a half-bridge module string.

With reference to the first possible implementation manner of the first aspect, in a second possible implementation manner of the first aspect, the conveying unit includes a three-phase conveying circuit, the conveying circuit includes a first H-bridge module and a first voltage-stabilizing capacitor, the first H-bridge module is connected in parallel with the first voltage-stabilizing capacitor, the first H-bridge module in the three-phase conveying circuit is respectively electrically connected with a secondary winding of the wind farm internal network output transformer, different first H-bridge modules are cascaded with each other, and an absorption capacitor is disposed in the first H-bridge module.

With reference to the second possible implementation manner of the first aspect, in a third possible implementation manner of the first aspect, the isolation unit includes a three-phase isolation circuit, and the isolation circuit includes a second H-bridge module, a third H-bridge module, and a high-frequency transformer, where a first end of the second H-bridge module is electrically connected to the voltage-stabilizing capacitor, two ends of the high-frequency transformer are electrically connected to a second end of the second H-bridge module and a first end of the third H-bridge module, respectively, and a second end of the third H-bridge module is electrically connected to one end of the half-bridge module string; and DC blocking capacitors are arranged between the second H-bridge module and the high-frequency transformer, the third H-bridge module is connected with a second voltage stabilizing capacitor in parallel, and absorption capacitors are arranged in the second H-bridge module and the third H-bridge module.

With reference to the first aspect, in a fourth possible implementation manner of the first aspect, the half-bridge module string includes a plurality of half-bridge modules, and the plurality of half-bridge modules are connected in series.

With reference to the first aspect, in a fifth possible implementation manner of the first aspect, the LC filter circuit includes a filter inductor and a filter capacitor, a first end of the filter inductor is electrically connected to a second end of the half-bridge module string and a first end of the filter capacitor, respectively, a second end of the filter inductor is electrically connected to the high-voltage direct-current power transmission line, and a second end of the filter capacitor is electrically connected to a second output end on the direct-current side of the power electronic transformer and the high-voltage direct-current power transmission line, respectively.

With reference to the fifth possible implementation manner of the first aspect, in a sixth possible implementation manner of the first aspect, the high-voltage direct current power transmission line includes a positive high-voltage direct current power transmission line and a negative high-voltage direct current power transmission line, the positive high-voltage direct current power transmission line is electrically connected to the second end of the filter inductor, and the negative high-voltage direct current power transmission line is electrically connected to the second end of the filter capacitor and the second output end of the power electronic transformer on the direct current side, respectively.

With reference to the first aspect, in a seventh possible implementation manner of the first aspect, the diode current transformer is a multiple diode rectifier.

In a second aspect, an embodiment of the present application provides a method for using a hybrid offshore wind farm converter topology, where the hybrid offshore wind farm converter topology described in the first aspect or any implementation manner of the first aspect is adopted, and the method includes: in the wind field starting stage, a power electronic transformer in the parallel current converter transmits electric energy on a high-voltage direct current side to a wind field internal network through an inversion function, establishes alternating-current voltage of the wind field internal network, and controls the voltage of the wind field internal network to be lower than the rectification threshold voltage of a diode rectifier so that the diode rectifier does not work; the wind turbine generator starts to generate power, a wind field is converted from a load to a power supply, and at the moment, an internal network of the wind field starts to transmit active power to a high-voltage direct-current side through a parallel converter; after the wind field is started, the voltage of an AC port is boosted by a power electronic transformer, and the voltage in the wind field is boosted to reach the rectification threshold voltage of a diode rectifier; then the power electronic transformer gradually reduces to transmit active power to the direct current side, so that the output power of the wind field is transferred to the diode rectifier from the parallel converter, and the parallel converter gradually operates under the condition of zero active power; when the wind field enters a stable power generation operation stage, the parallel converter does not transmit active power to the power grid any more, and all modules of the sub module string in the parallel converter are locked to be removed from the system.

Drawings

Fig. 1 is a schematic diagram of a hybrid offshore wind farm converter topology according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of an electronic power transformer according to an embodiment of the present disclosure;

fig. 3 is a schematic flow chart of a method for using a hybrid offshore wind farm converter topology according to an embodiment of the present application;

in fig. 1-3, the symbols are represented as: the power supply comprises a 1-diode rectifier, a 2-parallel converter, a 3-power electronic transformer, a 4-half bridge module string, a 5-LC filter circuit, a 6-transmission unit, a 7-isolation unit, a 8-first H bridge module, a 9-second H bridge module, a 10-third H bridge module, a 11-high-frequency transformer, a 12-half bridge module, a 13-positive high-voltage direct-current power transmission line, a 14-negative high-voltage direct-current power transmission line, a C1-first voltage-stabilizing capacitor, a C2-blocking capacitor, a C3-second voltage-stabilizing capacitor, an L1-filter inductor and a C4-filter capacitor.

Detailed Description

The present invention will be described with reference to the accompanying drawings and embodiments.

Fig. 1 is a schematic diagram of a hybrid offshore wind farm converter topology according to an embodiment of the present application, and referring to fig. 1, the hybrid offshore wind farm converter topology according to the embodiment includes: a diode rectifier 1 and a parallel inverter 2. The alternating current side of the diode rectifier 1 is electrically connected with the grid in the wind farm, the direct current side of the diode rectifier 1 is electrically connected with one end of the high-voltage direct-current transmission line, and the diode rectifier is a multiple diode rectifier 1. The parallel converter 2 comprises a power electronic transformer 3, the alternating current side of the power electronic transformer 3 is electrically connected with an output transformer in a wind farm, the first output end of the direct current side of the power electronic transformer 3 is connected with the first end of a half-bridge module string 4, and the second end of the half-bridge module string 4 and the second output end of the direct current side of the power electronic transformer 3 are electrically connected with the other end of the high-voltage direct-current transmission line through an LC filter circuit 5.

Referring to fig. 2, the electronic power transformer includes: conveying unit 6 and isolation unit 7, conveying unit 6 first end with wind farm intranet output transformer electricity is connected, conveying unit 6 second end with isolation unit 7 first end electricity is connected, isolation unit 7 second end and half-bridge module cluster 4 one end electricity are connected.

The transmission unit 6 comprises a three-phase transmission circuit, the transmission circuit comprises a first H-bridge module 8 and a first voltage-stabilizing capacitor C1, the first H-bridge module 8 is connected in parallel with the first voltage-stabilizing capacitor C1, and the first voltage-stabilizing capacitor C1 is used for smoothing and filtering voltage and preventing overvoltage from affecting devices. The first H-bridge modules 8 in the three-phase conveying circuit are respectively and electrically connected with secondary windings of the grid output transformers in the wind farm, different first H-bridge modules 8 are mutually cascaded, and absorption capacitors are arranged in the first H-bridge modules and used for suppressing transient overvoltage of device switches.

The isolation unit 7 comprises a three-phase isolation circuit, the isolation circuit comprises a second H-bridge module 9, a third H-bridge module 10 and a high-frequency transformer 11, the first end of the second H-bridge module 9 is electrically connected with a first voltage stabilizing capacitor C1, two ends of the high-frequency transformer 11 are respectively electrically connected with the second end of the second H-bridge module 9 and the first end of the third H-bridge module 10, and the second end of the third H-bridge module 10 is electrically connected with one end of the half-bridge module string 4. And a DC blocking capacitor C2 is arranged between each of the second H-bridge module 9 and the third H-bridge module 10 and the high-frequency transformer 11, and the DC blocking capacitor C2 is used for eliminating DC components in the current or voltage at the outlet of the H-bridge and preventing the DC magnetic bias of the high-frequency transformer. The third H-bridge module is provided with a second voltage-stabilizing capacitor C3 in parallel, the second voltage-stabilizing capacitor C3 is the same as the second voltage-stabilizing capacitor C1, and the second voltage-stabilizing capacitor C3 is also used for smoothing voltage and preventing overvoltage from influencing devices. Absorption capacitors are arranged in the second H-bridge module 9 and the third H-bridge module 10.

The three phases of the delivery unit 6 may each employ a multi-stage H-bridge module series configuration (only one H-bridge module is shown for each phase in the figure) to convert an ac input voltage to a dc voltage or to convert a dc voltage to an ac output voltage. The input or output voltage is divided evenly across each module, thereby reducing the voltage seen by the switching devices on each power module. The isolation unit 7 converts the direct current signal into a high-frequency square wave, the high-frequency square wave is coupled to the secondary side through the high-frequency transformer 11 and then reduced into direct current, and all H-bridge modules on the isolation level direct current side are connected in series, so that the voltage on the direct current side is maximized.

The half-bridge module string 4 comprises a plurality of half-bridge modules 12, a plurality of the half-bridge modules 12 being connected in series. The LC filter circuit comprises a filter inductor L1 and a filter capacitor C4, wherein a first end of the filter inductor L1 is electrically connected with a second end of the half-bridge module string 4 and a first end of the filter capacitor C4 respectively, a second end of the filter inductor L1 is electrically connected with the high-voltage direct-current power transmission line, and a second end of the filter capacitor C4 is electrically connected with a second output end of the power electronic transformer 3 on the direct-current side and the high-voltage direct-current power transmission line respectively.

The LC filter circuit comprises a filter inductor L1 and a filter capacitor C4, wherein a first end of the filter inductor L1 is electrically connected with a second end of the half-bridge module string 4 and a first end of the filter capacitor C4 respectively, a second end of the filter inductor L1 is electrically connected with the high-voltage direct-current power transmission line, and a second end of the filter capacitor C4 is electrically connected with a second output end of the power electronic transformer 3 on the direct-current side and the high-voltage direct-current power transmission line respectively. The LC filter circuit 5 functions to prevent high frequency current inside the parallel converter 2 from entering the high voltage dc line.

The high-voltage direct current transmission line comprises a positive high-voltage direct current transmission line 13 and a negative high-voltage direct current transmission line 14, the positive high-voltage direct current transmission line 13 is electrically connected with the second end of the filter inductor L1, and the negative high-voltage direct current transmission line 14 and the second end of the filter capacitor C4 are electrically connected with the second output end of the power electronic transformer 3 on the direct current side.

According to the embodiment, compared with the traditional voltage-class voltage source converter, the hybrid offshore wind field converter topological structure can greatly reduce the cost of the topological structure, can actively establish the network voltage in the wind field at the starting stage of the wind field, provides the starting power of the wind field, and realizes the black start of the wind field. The power electronic transformer 3 can provide reactive compensation and harmonic current compensation in the stable transmission stage of the wind field, and the performance of the diode rectifier 1-based system is improved.

Corresponding to the topology structure of the hybrid offshore wind farm converter provided by the embodiment, the application also provides an embodiment of a method for using the topology structure of the hybrid offshore wind farm converter. Referring to fig. 3, the method includes:

s101, in a wind field starting stage, a power electronic transformer 3 in a parallel converter 2 transmits electric energy on a high-voltage direct current side to a wind field internal network through an inversion function, establishes alternating-current voltage of the wind field internal network, and controls the voltage of the wind field internal network to be lower than the rectification threshold voltage of a diode rectifier 1 to enable the diode rectifier 1 to not work.

The parallel converter 2 is in principle a high-ratio AC/DC converter operating in parallel with the diode rectifier 1 and capable of achieving bidirectional power flow. In the starting stage of the wind farm, the wind turbine generator needs to consume electric energy which accounts for 1% of the generated power when operating, so that the high-voltage direct current is firstly needed to return a certain power to the internal network of the wind farm to enable the wind farm to start operating when the wind turbine generator is started.

Because the diode rectifier valve does not have the inversion function and cannot meet the black start requirement of a wind farm, the power electronic transformer 3 in the parallel converter 2 transmits the electric energy on the high-voltage direct current side to a wind farm internal network through the inversion function and establishes the alternating voltage of the wind farm internal network, and the voltage of the wind farm internal network is controlled to be lower than the rectification threshold voltage of the diode rectifier 1 so that the diode rectifier 1 does not work, and the wind turbine generator can be ensured to start grid connection according to a conventional control strategy. In the starting stage of the wind field, the diode rectifier 1 does not work, the parallel current converter 2 adopts voltage and fixed frequency control, and the behavior of the parallel current converter 2 is equivalent to a point-to-point system of the wind field and the parallel current converter 2.

And S102, the wind turbine generator starts to generate power, the wind farm is converted from a load to a power supply, and at the moment, the internal network of the wind farm starts to transmit active power to the high-voltage direct-current side through the parallel converter 2.

And the active power transmitted by the parallel converter 2 is higher than a certain value as the time changes, the wind field can be considered to be in the starting completion state.

And S103, after the wind field is started, the voltage of the AC port is boosted by the power electronic transformer 3, and the network voltage in the wind field is boosted to reach the rectification threshold voltage of the diode rectifier 1.

And S104, gradually reducing the active power transmitted to the direct current side by the power electronic transformer 3, so that the wind field output power is transferred to the diode rectifier 1 from the parallel converter 2, and the parallel converter 2 gradually operates under the condition of zero active power.

After the wind field enters the power generation starting stage, the converter station and the wind field form a three-terminal system at the moment. The first end is a wind field, and the wind power converter adopts a current control strategy, and the wind turbine generator generally operates with constant power factor, so that the wind field is simplified into a current source with unit power factor in the three ends. The second end is a diode rectifier 1, and the ac line voltage of the diode rectifier 1 is clamped to the dc voltage continuously along with the diode commutation process, so the diode rectifier 1 can be regarded as a load with a unit power factor and a voltage clamping effect. The third end is a power electronic transformer 3, adopts voltage control and has the function equivalent to a controlled voltage source.

And S105, when the wind field enters a stable power generation operation stage, the parallel converter 2 does not transmit active power to the power grid any more, and all the modules of the sub-module string in the parallel converter 2 are locked to be removed from the system.

The submodule string is equivalent to a reverse diode string after being completely locked, and bears a direct current side voltmeter of the original submodule string. Because the direct current in the parallel converter 2 is close to zero before all the modules of the sub-module string are locked, the operation of the parallel converter is not influenced, the parallel converter 2 still controls the voltage at the alternating current side of the wind field, and at the moment, the parallel converter 2 has the function of compensating the reactive power in the wind field and the harmonic wave of the compensation current

It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.

Of course, the above description is not limited to the above examples, and technical features that are not described in this application may be implemented by or using the prior art, and are not described herein again; the above embodiments and drawings are only for illustrating the technical solutions of the present application and not for limiting the present application, and the present application is only described in detail with reference to the preferred embodiments instead, it should be understood by those skilled in the art that changes, modifications, additions or substitutions within the spirit and scope of the present application may be made by those skilled in the art without departing from the spirit of the present application, and the scope of the claims of the present application should also be covered.