Diode hybrid converter dc transmission system, method, apparatus, and storage medium

Abstract

The application provides a diode hybrid converter DC transmission system, method, device and storage medium, the system comprises: a DC input end of a fan grid side converter is connected with a DC bus capacitor of a machine side converter, an AC output end is connected with an AC collection network of a wind power plant, and a DC-AC inverter for obtaining wind power is arranged; an AC input end of a hybrid rectifier is connected with a public coupling point of the AC collection network of the wind power plant, a DC output end is connected with positive and negative ends of a DC transmission line, and AC-DC conversion of wind power plant power is realized; a DC input end of a modular multilevel converter is used for receiving wind power rectified by the hybrid rectifier through the DC transmission line, performing DC-AC inversion, and connecting an AC output end with a receiving end power grid to realize wind power grid connection. The application improves the reliability of the fan AC network system, can well solve the problem of additional reactive power provided by the fan, reduces the reactive power transmission in the line, better realizes AC voltage control of the wind power plant, and improves the system stability.

Description

Technical Field

[0001] This invention relates to the field of DC power transmission from wind farms, and particularly to DC power transmission systems, methods, equipment, and storage media using diode hybrid converters. Background Technology

[0002] Large-scale centralized grid connection of wind power is an important means for my country to promote its dual-carbon goals and achieve clean energy and sustainable development. Among these, wind power connected to the grid via DC transmission enables large-scale, long-distance transmission of wind power, particularly suitable for offshore wind power transmission. However, traditional modular multilevel converter platforms based on fully controlled devices suffer from high costs, large size, and heavy weight, which are even more pronounced in offshore wind power applications with stringent size and weight requirements. Therefore, a new type of wind power grid connection scheme based on diode-based DC transmission has emerged.

[0003] For wind power diode-based DC transmission schemes, the first key issue is the grid connection control of AC wind farms. Since diodes themselves do not have grid connection capabilities, the control strategy of the wind turbine converter needs to be modified to become a grid-connected turbine. This grid-connected turbine will be responsible for establishing the AC voltage and frequency of the wind farm, while also fulfilling functions such as active power output control and reactive power distribution. Grid connection control of wind farms using diode-based DC transmission is a problem that still needs to be researched and solved.

[0004] The second problem with wind turbine diode DC transmission solutions is the need for additional reactive power compensation and filtering devices. Traditional modular multilevel converters do not consume reactive power themselves, and due to their high level number and low harmonic content, they do not require additional reactive power compensation and filtering devices. However, diodes themselves generate significant reactive power, reaching approximately 30% of the active power. Furthermore, twelve-pulse rectifiers generate 11th and 13th harmonic currents, thus requiring additional reactive power compensation and filtering devices. These devices occupy a large area, which is a key factor in their suitability for offshore wind power applications.

[0005] In existing wind farm grid-connected diode DC transmission systems, the AC grid connection method primarily utilizes grid control technology to control the voltage and frequency of the wind farm's AC system. Since the active power output of the diodes is achieved by controlling the AC grid connection point voltage, it is necessary to control the turbine terminal voltage to regulate the active power output. One approach is active-voltage and reactive-frequency droop control, where controlling the turbine terminal voltage controls active power, and controlling the turbine terminal frequency controls reactive power distribution. However, this method creates strong active-reactive coupling because, as in traditional AC systems, active power flow between turbines is frequency-dependent, while reactive power flow is voltage-dependent. Another method employs active-frequency and reactive-voltage droop control, where the turbine terminal frequency is measured and a voltage command is added via a PI controller. This added value is used to adjust the AC voltage at the diode grid connection point to control the diode's active power output. While this method reduces the coupling between active and reactive power, the different turbine terminal frequencies mean that reactive and active power still exhibit coupling, and the PI integrator introduces errors in reactive power distribution.

[0006] For reactive power compensation and filtering in diode DC power transmission systems, current solutions all employ additional reactive power compensation and filtering devices. However, this significantly increases the footprint of the offshore converter platform. Furthermore, since the reactive power consumption of the diode rectifier varies with active power, the wind turbines will bear this variable reactive power when using fixed parallel compensation devices. The flow of reactive power in the lines may have some impact on the system's voltage control and stable operation.

[0007] Existing methods cannot effectively achieve decoupled active and reactive power control in wind farm grids. The fundamental reason is that wind turbines need to handle the regulation characteristics of traditional AC grids based on active power-frequency and reactive power-voltage, while the presence of diodes as rectifiers necessitates AC voltage regulation for overall active power control. These three control dimensions are difficult to simultaneously achieve in wind farm grid converters. Currently, modular multilevel converters are commonly used at the receiving end of diode DC transmission systems. However, these converters employ constant DC voltage control to maintain a constant DC system voltage. In this case, the active power output of the diode rectifier is achieved by the wind turbine controlling the AC grid voltage of the wind farm. In reality, diode active power control can also be achieved by adjusting the DC voltage. In this case, the AC voltage of the wind farm grid AC system does not need to be changed, and the wind farm grid converter can be simplified to a traditional grid control design, naturally achieving active and reactive power decoupling. To achieve DC voltage regulation, a modular multilevel converter with series-connected variable DC voltage diodes can be used as a rectifier station. Active power output can be regulated by adjusting the DC voltage of the modular multilevel converter. Simultaneously, this modular multilevel converter can provide dynamic reactive power compensation and filtering functions. Summary of the Invention

[0008] The present invention aims to at least partially solve one of the technical problems in the related art.

[0009] To address this, the first aspect of this invention proposes a wind turbine grid-diode hybrid converter DC power output system. The rectifier side employs a hybrid converter composed of a twelve-pulse diode series voltage-variable modular multilevel converter. This hybrid converter can control the active power output of the wind farm through active DC voltage control. Combined with the grid control design of the wind turbine converter, it achieves decoupling control of active and reactive power in the wind turbine grid AC system. Furthermore, this variable voltage modular multilevel converter can simultaneously provide reactive power compensation and filtering functions, thus eliminating the need for additional reactive power compensation and filtering devices and significantly reducing the footprint.

[0010] The second aspect of this invention proposes a control method for a wind power grid diode hybrid converter DC power transmission system.

[0011] A third aspect of the present invention provides a computer device.

[0012] A fourth aspect of the present invention provides a storage medium.

[0013] A first aspect of the present invention provides a wind turbine grid-side diode hybrid converter DC power output system, comprising: a wind turbine grid-side converter, a hybrid rectifier, and a DC voltage variable modular multilevel converter, wherein the DC input terminal of the wind turbine grid-side converter is connected to the DC bus capacitor of the turbine-side converter, and the AC output terminal is connected to the AC collection network of the wind farm for obtaining DC-AC inversion of wind power;

[0014] The AC input terminal of the hybrid rectifier is connected to the common coupling point of the AC collection network of the wind farm, and the DC output terminal is connected in series to the positive and negative terminals of the DC transmission line to realize the AC-DC conversion of the main power. The DC input terminal of the modular multilevel converter is used to receive the wind power rectified by the hybrid rectifier through the DC transmission line. After the DC-AC inverter, the AC output terminal is connected to the receiving end grid to realize the grid connection of wind power.

[0015] The wind farm grid-connected diode hybrid converter DC power transmission system of this invention has two key features. First, the overall power output of the wind farm is regulated by changing the DC voltage using a variable DC voltage modular multilevel converter (MMC) within the hybrid converter. In this case, the AC grid voltage of the diode rectifier does not need to be adjusted, and the wind farm grid-connected converter is simplified to a classic grid control strategy, completely achieving decoupling of active and reactive power. This improves control performance and simplifies controller design. Simultaneously, the characteristics of the wind farm AC system using this method are similar to those of a traditional AC grid-connected system, improving reliability, and the corresponding classic analysis methods can be directly used to guide the analysis and design. Since a large range of power control can be achieved with a relatively small DC voltage variation range in the diode rectifier DC system, the variable DC voltage modular multilevel converter can use a smaller number of MMC modules, resulting in minimal cost increase. Second, it enables reactive power compensation and wind farm AC voltage control. The modular multilevel converter in the hybrid converter can inject reactive power, thus dynamically compensating for the reactive power generated by the diodes. On the one hand, it eliminates the land occupation problem caused by installing additional reactive power compensation devices; on the other hand, dynamic reactive power compensation can effectively solve the problem of additional reactive power required by wind turbines, reduce reactive power transmission in the lines, better achieve AC voltage control of wind farms, and improve system stability. Thirdly, it enables active filtering, thus eliminating the need for additional passive filtering devices and reducing land occupation.

[0016] A second aspect of the present invention provides a control method for a wind power grid diode hybrid converter DC transmission system, comprising:

[0017] The DC input terminal of the wind turbine grid-side converter is connected to the DC bus capacitor of the turbine-side converter, and the AC output terminal is connected to the AC collection network of the wind farm to obtain DC-AC inversion of wind power; the AC input terminal of the hybrid rectifier is connected to the common coupling point of the AC collection network of the wind farm, and the DC output terminal is connected in series to the positive and negative terminals of the DC transmission line to realize AC-DC conversion of main power; the DC input terminal of the modular multilevel converter receives the wind power rectified by the hybrid rectifier through the DC transmission line, and after DC-AC inversion, the AC output terminal is connected to the receiving-end grid to realize wind power grid connection.

[0018] The control method of the wind turbine grid diode DC power transmission system of the present invention realizes the active and reactive power decoupling control of the wind turbine grid AC system, improves the reliability of the wind turbine AC grid system, and makes the classical AC system control theory applicable to the wind turbine grid diode power transmission system.

[0019] A third aspect of the present invention provides a computer device including a processor and a memory; wherein the processor runs a program corresponding to the executable program code by reading executable program code stored in the memory, for implementing a control method for the wind power grid diode hybrid converter DC transmission system.

[0020] A fourth aspect of the present invention provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements a control method for a wind power grid diode hybrid converter DC power transmission system as described above.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0023] Figure 1 This is a schematic diagram of a wind power grid diode hybrid converter DC power transmission system according to an embodiment of the present invention;

[0024] Figure 2 This is a schematic diagram of a wind turbine grid-side converter according to an embodiment of the present invention;

[0025] Figure 3 This is a schematic diagram of a DC power transmission twelve-pulse thyristor converter according to an embodiment of the present invention;

[0026] Figure 4 This is a schematic diagram of a DC voltage variable modular multilevel converter structure in a hybrid converter according to an embodiment of the present invention;

[0027] Figure 5 This is a schematic diagram of a full-bridge submodule of a DC voltage variable submodule according to an embodiment of the present invention;

[0028] Figure 6 This is a schematic diagram of a single-current unidirectional H-bridge submodule of a DC voltage variable submodule according to an embodiment of the present invention;

[0029] Figure 7 A flowchart of a control method for a wind power grid diode hybrid converter DC power transmission system according to an embodiment of the present invention;

[0030] Figure 8 This is a schematic diagram of a wind turbine grid-side converter control method according to an embodiment of the present invention;

[0031] Figure 9This is a schematic diagram of a DC voltage variable modular multilevel converter control method in a hybrid converter according to an embodiment of the present invention;

[0032] Figure 10 A computer device according to an embodiment of the present invention. Detailed Implementation

[0033] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0034] The following description, with reference to the accompanying drawings, describes a wind power grid diode hybrid converter DC transmission system, method, apparatus, and storage medium according to embodiments of the present invention.

[0035] Figure 1 This is a schematic diagram of the structure of the wind power grid diode hybrid converter DC power transmission system provided in an embodiment of the present invention.

[0036] like Figure 1 As shown, the wind turbine grid-side diode DC power transmission system includes: a wind turbine grid-side converter 100, a hybrid rectifier 200, and a modular multilevel converter 300, wherein,

[0037] The DC input terminal of the wind turbine grid-side converter 100 is connected to the DC bus capacitor of the turbine-side converter, and the AC output terminal is connected to the AC collection network of the wind farm to obtain DC-AC inversion of wind power.

[0038] The AC input terminal of the hybrid rectifier 200 is connected to the common coupling point of the AC collection network of the wind farm, and the DC output terminal is connected in series to the positive and negative terminals of the DC transmission line to realize the AC-DC conversion of the main power.

[0039] The DC input terminal of the modular multilevel converter 300 is used to receive wind power rectified by the hybrid rectifier 200 through a DC transmission line. After DC-AC inversion, the AC output terminal is connected to the receiving end grid to realize wind power grid connection.

[0040] Furthermore, the twelve-pulse thyristor converter in the wind turbine grid-side converter 100 and the hybrid rectifier 200 of the present invention, and the DC voltage variable modular multilevel converter in the hybrid converter 200, are respectively as follows: Figure 2 , Figure 3 and Figure 4 As shown.

[0041] Specifically, the wind turbine grid-side converter 100 of this embodiment realizes DC-AC inversion of wind power captured by each wind turbine. Its DC input terminal is connected to the DC bus capacitor of the turbine-side converter, and its AC output terminal is connected to the AC collector network of the wind farm. Then, a twelve-pulse diode rectifier is connected in series with a DC voltage variable modular multilevel converter as the sending-end hybrid rectifier 200. The AC input terminals of both are connected to the common coupling point (PCC) of the wind farm's AC collector network, and the DC output terminals are connected in series to the positive and negative terminals of the DC transmission line. In the hybrid rectifier 200, the twelve-pulse diode rectifier realizes the AC-DC conversion of the main power. The series DC voltage variable modular multilevel converter is used on the AC side to compensate for and filter the AC reactive power and harmonics of the twelve-pulse diode rectifier; on the DC side, the system power output is changed by adjusting the variable DC voltage. After being rectified by the hybrid rectifier 200, the wind power is connected to the receiving-end modular multilevel converter 300 via a DC transmission line. After being converted from DC to AC, the AC output is connected to the receiving-end power grid, thus achieving grid connection of the wind power.

[0042] Furthermore, DC voltage variable modular multilevel converters, such as Figure 4 As shown, each phase includes an upper bridge arm and a lower bridge arm. Each bridge arm is composed of N identical fully controllable submodules that can output positive and negative capacitor voltages cascaded together. For example, a full-bridge submodule such as... Figure 5 As shown, or a unidirectional current H-bridge submodule, such as Figure 6 As shown. The lower end of the upper bridge arm and the upper end of the lower bridge arm of each phase are connected together through an inductor L. The midpoint of the inductor becomes the AC output terminal of that phase. The upper ends of the upper bridge arms of all phases are connected together to form the DC positive terminal, and the lower ends of the lower bridge arms of all phases are connected together to form the DC negative terminal.

[0043] The wind farm grid-connected diode hybrid converter DC power transmission system of this invention has two key features. First, the overall power output of the wind farm is regulated by changing the DC voltage using a variable DC voltage modular multilevel converter (MMC) within the hybrid converter. In this case, the AC grid voltage of the diode rectifier does not need to be adjusted, and the wind farm grid-connected converter is simplified to a classic grid control strategy, completely achieving decoupling of active and reactive power. This improves control performance and simplifies controller design. Simultaneously, the characteristics of the wind farm AC system using this method are similar to those of a traditional AC grid-connected system, improving reliability, and the corresponding classic analysis methods can be directly used to guide the analysis and design. Since a large range of power control can be achieved with a relatively small DC voltage variation range in the diode rectifier DC system, the variable DC voltage modular multilevel converter can use a smaller number of MMC modules, resulting in minimal cost increase. Second, it enables reactive power compensation and wind farm AC voltage control. The modular multilevel converter in the hybrid converter can inject reactive power, thus dynamically compensating for the reactive power generated by the diodes. On the one hand, it eliminates the land occupation problem caused by installing additional reactive power compensation devices; on the other hand, dynamic reactive power compensation can effectively solve the problem of additional reactive power required by wind turbines, reduce reactive power transmission in the lines, better achieve AC voltage control of wind farms, and improve system stability. Thirdly, it enables active filtering, thus eliminating the need for additional passive filtering devices and reducing land occupation.

[0044] Secondly, a control method for a wind power grid diode hybrid converter DC power transmission system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0045] Figure 7 This is a flowchart of a control method for a wind turbine grid diode DC power transmission system according to an embodiment of the present invention.

[0046] like Figure 7 As shown, the method includes:

[0047] S1, connect the DC input terminal of the wind turbine grid-side converter to the DC bus capacitor of the turbine-side converter, and connect the AC output terminal to the AC collection network of the wind farm to obtain the DC-AC inverter of the wind power;

[0048] S2 connects the AC input terminal of the hybrid rectifier to the common coupling point of the AC collection network of the wind farm, and connects the DC output terminal in series to the positive and negative terminals of the DC transmission line to realize the AC-DC conversion of the main power.

[0049] S3 receives wind power rectified by a hybrid rectifier through a DC transmission line at the DC input terminal of the modular multilevel converter. After DC-AC inversion, the AC output terminal is connected to the receiving-end power grid to achieve wind power grid connection.

[0050] Specifically, the methods of the embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0051] like Figure 8 The diagram illustrates a control method for a wind turbine grid-side converter according to an embodiment of the present invention, comprising the following steps:

[0052] (1) Set the reference value P of the active power output of the grid-side converter of the wind turbine. ref (This reference value is usually obtained from the outer loop of the DC capacitor voltage control of the wind turbine converter.) Collect the active power P output by the grid-side converter of the wind turbine and calculate the power deviation signal ΔP = P. ref -P;

[0053] (2) The power deviation signal ΔP above is passed through a proportional controller and summed with the reference frequency ω0 to obtain the frequency reference value ω;

[0054] (3) The phase reference value θ is obtained by integrating the frequency reference value ω of the wind turbine grid-side converter over time. u ;

[0055] (4) Set the reference value Q of the reactive power output of the grid-side converter of the wind turbine. ref (This reference value can be set to 0), collect the reactive power Q output by the grid-side converter of the wind turbine, and calculate the reactive power deviation signal ΔQ = Q. ref -Q;

[0056] (5) The power deviation signal ΔQ above is passed through the proportional controller and summed with the reference voltage u0 to obtain the voltage reference value u;

[0057] (6) The voltage and phase reference values ​​of the above wind turbine grid-side converter are passed through the current limiting and damping control inner loop to obtain the final converter internal potential amplitude e and phase θ. e ;

[0058] (7) The reference value of the three-phase internal potential e of the grid-side converter of the wind turbine is calculated. a e b e c :

[0059]

[0060] (8) The reference voltage e of the three-phase internal potential of the above-mentioned wind turbine grid-side converter. a e b e c The signal is fed into the pulse width modulation stage to obtain the control pulse signal for the grid-side converter of the wind turbine.

[0061] like Figure 9 The diagram illustrates a control method for a DC-DC hybrid converter according to an embodiment of the present invention, comprising the following steps:

[0062] (1) Collect the instantaneous three-phase voltage u at the common coupling point of the AC collector network of the wind farm.sa u sb u sc The frequency ω is obtained by inputting it into the frequency detection unit;

[0063] (2) Set the frequency reference value ω0 of the AC collector network of the wind farm, and calculate the frequency deviation signal Δω=ω-ω0 based on the obtained frequency measurement value ω;

[0064] (3) After passing the above submodule capacitor voltage deviation signal Δω through the proportional-integral controller, the DC voltage reference value U of the DC voltage variable modular multilevel converter is obtained. dc_ref ;

[0065] (4) Set the capacitor voltage value of the DC voltage variable modular multilevel converter submodule to U. cap_ref The average value u of the capacitor voltage of each submodule in a DC voltage variable modular multilevel converter is calculated by collecting the capacitor voltages of all submodules. cap Calculate the capacitor voltage deviation signal Δu of the submodule. cap =U cap_ref -u cap ;

[0066] (5) The capacitor voltage deviation signal Δu of the above sub-module cap After passing through the proportional controller, the target value I of the active current amplitude of the DC voltage variable modular multilevel converter is obtained. p_ref The reference value i of the three-phase active current of the DC voltage variable modular multilevel converter was calculated. p_a_ref i p_b_ref i p_c_ref :

[0067]

[0068] (6) Set the voltage reference value u0 of the AC collector network of the wind farm, and calculate the voltage deviation signal Δu = u - u0 based on the obtained voltage measurement value u;

[0069] (7) After passing the AC voltage deviation signal Δu through the proportional-integral controller, the target value I of the reactive current amplitude of the DC voltage variable modular multilevel converter is obtained. q_ref ;

[0070] (8) Based on the target value I of the reactive current amplitude of the modular multilevel converter q_ref The reference value i of the three-phase reactive current of the DC voltage variable modular multilevel converter was calculated. q_a_ref i q_b_ref i q_c_ref :

[0071]

[0072] (9) Collect the instantaneous value i of the three-phase AC input current of the twelve-pulse thyristor converter. lcc_a i lcc_b i lcc_c Harmonic components in the three-phase AC input current of a twelve-pulse thyristor converter are detected to obtain the reference value i of the three-phase harmonic compensation current of the DC voltage variable modular multilevel converter. f_a_ref i f_b_ref i f_c_ref ;

[0073] (10) Based on the above reference value i for the three-phase active current of the DC voltage variable modular multilevel converter. p_a_ref i p_b_ref i p_c_ref Three-phase reactive current reference value i q_a_ref i q_b_ref i q_c_ref and the reference value i for three-phase harmonic compensation current f_a_ref i f_b_ref i f_c_ref The three-phase reference current value i of the DC voltage variable modular multilevel converter was calculated. a_ref i b_ref i c_ref :

[0074]

[0075] (11) The three-phase reference current value i of the DC voltage variable modular multilevel converter a_ref i b_ref i c_ref The input is fed into the current control loop to obtain the reference value u of the three-phase AC voltage of the DC voltage variable modular multilevel converter. a_ref u b_ref u c_ref ;

[0076] (12) Based on the above three-phase AC voltage reference value u a_ref u b_ref u b_ref and DC voltage reference value U dc_ref The reference voltage u of the six arms of the series-compensated modular multilevel converter was calculated. ap_ref u an_re f、ub p_re f、ub n_re f、u cp_re f、u cn_re f:

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083] (13) The reference voltage u of the six arms of the above-mentioned series-compensated modular multilevel converter is... ap_ref ,u an_ref ,u bp_ref ,u bn_ref ,u cp_ref ,u cn_ref The signal is fed into the pulse width modulation stage to obtain the control pulse signal for the DC voltage variable modular multilevel converter.

[0084] The control method for the DC power transmission system of the wind farm grid-diode hybrid converter in this invention has two key aspects. First, the overall power output of the wind farm is regulated by changing the DC voltage using a variable DC voltage modular multilevel converter (MMC) in the hybrid converter. In this case, the AC grid voltage of the diode rectifier does not need to be adjusted, and the wind farm grid-connected converter is simplified to a classic grid-connected control strategy, completely achieving decoupling of active and reactive power. This improves control performance and simplifies controller design. Simultaneously, the characteristics of the wind farm AC system using this method are similar to those of a traditional AC grid-connected system, improving reliability, and the corresponding classic analysis methods can be directly used to guide the analysis and design. Since a large range of power control can be achieved with a relatively small DC voltage variation range in the diode rectifier DC system, the variable DC voltage modular multilevel converter can use a smaller number of MMC modules, resulting in minimal cost increase. Second, it enables reactive power compensation and wind farm AC voltage control. The modular multilevel converter in the hybrid converter can inject reactive power, thus dynamically compensating for the reactive power generated by the diodes. On the one hand, it eliminates the land occupation problem caused by installing additional reactive power compensation devices; on the other hand, dynamic reactive power compensation can effectively solve the problem of additional reactive power required by wind turbines, reduce reactive power transmission in the lines, better achieve AC voltage control of wind farms, and improve system stability. Thirdly, it enables active filtering, thus eliminating the need for additional passive filtering devices and reducing land occupation.

[0085] To implement the methods of the above embodiments, the present invention also provides a computer device, such as... Figure 10As shown, the computer device 600 includes a memory 601 and a processor 602; wherein, the processor 602 reads executable program code stored in the memory 601 to run a program corresponding to the executable program code, so as to implement the various steps of the method described above.

[0086] To implement the above embodiments, this application also proposes a non-transitory computer-readable storage medium storing a computer program thereon, which, when executed by a processor, implements the control method of the wind turbine grid diode hybrid converter DC power transmission system as described in the foregoing embodiments.

[0087] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0088] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0089] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A control method for a wind power grid diode hybrid converter DC power transmission system, characterized in that, The method includes the following steps: Connect the DC input terminal of the wind turbine grid-side converter to the DC bus capacitor of the turbine-side converter, and connect the AC output terminal to the AC collection network of the wind farm to obtain the DC-AC inverter of the wind power. The AC input terminal of the hybrid rectifier is connected to the common coupling point of the AC collection network of the wind farm, and the DC output terminal is connected in series to the positive and negative terminals of the DC transmission line to realize the AC-DC conversion of the main power. The DC input terminal of the modular multilevel converter receives wind power rectified by the hybrid rectifier through a DC transmission line, and the AC output terminal of the DC-AC inverter is connected to the receiving-end power grid to realize wind power grid connection. The voltage at the common coupling point of the AC collector network of the wind farm is collected, and the frequency is detected to obtain the grid frequency. Set the frequency reference value for the AC collection network of the wind farm, and calculate the frequency deviation signal based on the grid frequency; The frequency deviation signal is converted to obtain the DC voltage reference value of the DC voltage variable modular multilevel converter. Set the capacitor voltage value of the submodule of the DC voltage variable modular multilevel converter, collect the capacitor voltage of all submodules of the DC voltage variable modular multilevel converter, calculate the average value of the submodule capacitor voltage, and calculate the submodule capacitor voltage deviation signal. The submodule capacitor voltage deviation signal is converted to obtain the target value of the active current amplitude of the DC voltage variable modular multilevel converter, and the reference value of the three-phase active current of the DC voltage variable modular multilevel converter is calculated: Set a reference voltage value for the AC collector network of the wind farm, and calculate the voltage deviation signal based on the voltage at the common coupling point of the AC collector network of the wind farm. The voltage deviation signal is converted to obtain the target value of the reactive current amplitude of the DC voltage variable modular multilevel converter. Based on the target value, the reference value of the three-phase reactive current of the DC voltage variable modular multilevel converter is calculated as follows: The instantaneous value of the three-phase AC input current of the twelve-pulse thyristor converter is collected, the harmonic components in the three-phase AC input current of the twelve-pulse thyristor converter are detected, and the reference value of the three-phase harmonic compensation current of the DC voltage variable modular multilevel converter is obtained. Based on the reference values ​​of the three-phase active current, three-phase reactive current, and three-phase harmonic compensation current of the DC voltage variable modular multilevel converter, the three-phase reference current value of the DC voltage variable modular multilevel converter is calculated as follows: The three-phase reference current value of the DC voltage variable modular multilevel converter is input to the current control loop to obtain the three-phase AC voltage reference value of the DC voltage variable modular multilevel converter. Based on the three-phase AC voltage reference value and the DC voltage reference value, the reference voltages of multiple arms of the series-compensated modular multilevel converter are calculated. The reference voltages of the multiple bridge arms are fed into the pulse width modulation stage to obtain the control pulse signal of the DC voltage variable modular multilevel converter.

2. The method according to claim 1, characterized in that, The process of connecting the DC input terminal of the wind turbine grid-side converter to the DC bus capacitor of the turbine-side converter and connecting the AC output terminal to the AC collection network of the wind farm to obtain DC-AC inversion of wind power includes: Set a reference value for the active power output of the wind turbine grid-side converter, collect the active power output of the wind turbine grid-side converter, and calculate the power deviation signal; The power deviation signal is summed with the reference frequency to obtain the frequency reference value; The phase reference value is obtained by integrating the frequency reference value over time. Set a reference value for the reactive power output of the grid-side converter of the wind turbine, collect the reactive power output of the grid-side converter of the wind turbine, and calculate the reactive power deviation signal; The power deviation signal is summed with the reference voltage to obtain the reference voltage of the wind turbine grid-side converter; The reference voltage and phase reference value of the wind turbine grid-side converter are passed through the current limiting and damping control inner loop to obtain the amplitude and phase of the converter internal potential. The reference voltage of the three-phase internal potential of the grid-side converter of the wind turbine is calculated; The reference voltage of the three-phase internal potential of the wind turbine grid-side converter is input into the pulse width modulation circuit to obtain the control pulse signal of the wind turbine grid-side converter.

3. A wind power grid diode hybrid converter DC transmission system according to claim 1, characterized in that, include: Wind turbine grid-side converters, hybrid rectifiers, and modular multilevel converters, among which, The DC input terminal of the wind turbine grid-side converter is connected to the DC bus capacitor of the turbine-side converter, and the AC output terminal is connected to the AC collection network of the wind farm to obtain the DC-AC inversion of wind power. The AC input terminal of the hybrid rectifier is connected to the common coupling point of the AC collection network of the wind farm, and the DC output terminal is connected to the positive and negative terminals of the DC transmission line, which is used to realize the AC-DC conversion of the wind farm power. The DC input terminal of the modular multilevel converter is used to receive wind power rectified by the hybrid rectifier through a DC transmission line. After passing through the DC-AC inverter, the AC output terminal is connected to the receiving-end power grid to realize wind power grid connection. The hybrid rectifier includes: a twelve-pulse diode rectifier connected in series on the DC side with a variable DC voltage modular multilevel converter; The series-connected DC voltage variable modular multilevel converter is used on the AC side to compensate for and filter out the AC reactive power and harmonics of the twelve-pulse diode rectifier, and on the DC side to adjust the variable DC voltage. Each phase of the DC voltage variable modular multilevel converter includes an upper bridge arm and a lower bridge arm, and each bridge arm is composed of multiple identical fully controlled sub-modules cascaded together. The lower end of the upper bridge arm and the upper end of the lower bridge arm of each phase are connected by an inductor. The upper ends of the upper bridge arms of all phases are connected as the positive DC terminal, and the lower ends of the lower bridge arms of all phases are connected as the negative DC terminal.

4. A computer device, characterized in that, Including processor and memory; The processor reads executable program code stored in the memory to run a program corresponding to the executable program code, so as to implement the control method of the wind power grid diode hybrid converter DC transmission system as described in any one of claims 1-2.

5. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by the processor, the program implements the control method for the wind power grid diode hybrid converter DC power transmission system as described in any one of claims 1-2.

Images