Diode rectifier based offshore converter platform and control method, apparatus and device thereof

Abstract

This application relates to the field of wind power generation technology, and provides an offshore converter platform based on a diode rectifier and its control method, apparatus, and equipment. The method includes acquiring the operating conditions of the wind farm; determining a control strategy for the offshore converter platform based on the operating conditions; and controlling the operation of the offshore converter platform according to the control strategy. If the operating conditions are black-start or no-wind conditions, the control strategy is to close the tie switch and control the auxiliary converter to operate in active power mode, providing active power support to the wind farm through the active power output of the power equipment. If the operating conditions are rated power operating conditions, the control strategy is to open the tie switch and control the auxiliary converter to operate in reactive power mode. This method determines the control strategy for the offshore converter platform based on the operating conditions of the wind farm, and controls the operation of the offshore converter platform according to the control strategy, enabling the auxiliary converter to operate in either reactive power mode or active power mode.

Description

Technical Field

[0001] This application relates to the field of wind power generation technology, and in particular to an offshore converter platform based on a diode rectifier and its control method, device and equipment. Background Technology

[0002] Offshore wind power is a renewable energy source, and deep-sea wind power, due to its abundant energy reserves and high utilization rate, is becoming a new type of renewable energy power generation system. Currently, the development of deep-sea wind power is gradually shifting from independent development of gigawatt (GW)-level wind farms to clustered development of 10GW-level ultra-large-scale wind farms. Areas rich in offshore wind resources are often planned to have multiple adjacent offshore wind farms. Under the background of clustered development, the transmission method of deep-sea wind power needs to shift from the currently widely used point-to-point DC transmission to a multi-terminal DC grid connection method.

[0003] In the selection of topologies for offshore wind power converters, modular multilevel converters (MMCs) are the mainstream choice for offshore wind power projects. However, their large size and weight lead to high costs and construction difficulties for offshore converter platforms, necessitating a more compact and lightweight topology. Replacing MMCs with diode rectifiers (DRs) is currently a research hotspot. Compared to MMCs, DRs offer significant advantages such as lower cost, smaller size, lighter weight, and higher reliability.

[0004] However, replacing the modular multilevel converter (MMC) on offshore converter platforms with diode rectifiers (DRs) also brings many problems to wind farms. The most prominent include a lack of active power reverse transmission capability, the inability to construct an offshore AC grid, and significant reactive power demand and harmonic pollution. Regarding active power reverse transmission, under conditions such as black start and zero-power operation in windless conditions, the offshore converter platform needs to provide a certain amount of power to the wind farm to maintain the operation of necessary auxiliary equipment and maintain the AC collector system voltage. In constructing the AC grid, the uncontrolled nature of the diode rectifier (DR) makes it difficult for it to directly participate in the AC voltage and frequency control of the offshore wind power generation system. Regarding reactive power demand and harmonic current issues, the diode rectifier (DR) consumes a large amount of reactive power while transmitting active power during the rectification process, and generates a large amount of harmonic current during commutation.

[0005] Regarding the active power feedback problem in wind farms using diode rectifiers (DR), two solutions exist. One solution involves configuring energy storage, diesel generators, and other electrical equipment within the wind farm to serve as backup power during no-wind and black-start conditions. The other solution combines the DR with a small-capacity voltage source converter (VSC) to form a hybrid converter, with the VSC serving as temporary power during black-start and near-zero wind operation. In terms of the specific hybrid converter configuration, various schemes exist, including parallel and series connection with the DR main converter at the DC end. Regarding the grid-connected control of wind farms within the AC grid, two types of solutions also exist. One type involves constructing an internal AC grid through distributed grid-connected wind turbines, including reactive power / frequency and active power / frequency droop grid construction similar to synchronous machines. Another type is the centralized grid construction method, such as using the Global Positioning System (GPS) or high-speed communication lines to send the reference phase of each wind turbine, or using additional auxiliary converters with grid construction functions, etc.

[0006] Currently, harmonic issues in AC power grids are typically addressed by configuring passive filter banks on offshore converter platforms or simply adding active filtering functionality to auxiliary converters. Reactive power issues in AC power grids are usually addressed as an adjunct to other issues such as grid construction. For example, in a distributed grid construction strategy, the reactive power demand of an offshore wind power system is distributed among each wind turbine. For some schemes using a centralized grid construction strategy, the reactive power demand of the wind farm may need to be handled by auxiliary converters.

[0007] As mentioned above, for several solutions to active power feedback from offshore converter platforms, energy storage generator sets and diesel generator sets cannot meet the long-term active power requirements of offshore wind power systems during windless operation; the parallel auxiliary converter scheme has a large number of components and is too costly; the series auxiliary converter scheme has overly complex black-start process control and cannot be used in multi-terminal transmission scenarios. In the grid construction scheme of offshore converter platforms, large-scale distributed wind turbine grid construction has potential oscillation and instability risks, and there are no engineering precedents for grid-type wind turbines, which also poses challenges to existing mature wind turbine production and design specifications. Secondly, existing solutions address some issues in diode rectifier (DR) wind farms but lack integrated comprehensive design solutions. This leads to feasibility issues when solving other problems. On the other hand, whether solving individual problems of offshore wind power systems in isolation or simply physically superimposing various individual technologies, the interaction and coupling between multiple objectives such as active power feedback, grid construction, reactive power, and harmonics are ignored. Such a lack of overall system design will result in excessively large and expensive auxiliary converters, significantly weakening or even negating the inherent size and cost advantages of diode rectifiers (DRs). Summary of the Invention

[0008] This application provides an offshore converter platform based on diode rectifiers and its control method, device and equipment. The switching of the auxiliary converter operation mode in the control strategy of the offshore converter platform is used to achieve compact and low-cost design of the auxiliary converter, and to solve the technical problems of active power back-feeding, grid construction and harmonic current filtering in the existing DR wind farm of offshore wind power generation system.

[0009] To achieve the above objectives, this application provides the following technical solution: On one hand, a control method for an offshore converter platform based on a diode rectifier is provided, applied to an offshore converter platform. The offshore converter platform includes a wind farm and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to the diode rectifier via a tie switch and a tie line. The diode rectifier is connected to power equipment for providing active power. The control method for the offshore converter platform includes the following steps: Obtain the operating conditions of the wind farm; Based on the operating conditions, determine the control strategy for the offshore converter platform; control the operation of the offshore converter platform according to the control strategy; If the operating condition is a black start condition or a windless condition, the control strategy is to control the connection switch to close, control the auxiliary converter to operate in active power mode, and provide active power support to the wind farm through the active power output of the power equipment. If the operating condition is the rated power operating condition, then the control strategy is to control the interconnection switch to open and control the auxiliary converter to operate in reactive power mode. The active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid construction control on the AC side of the auxiliary converter; the reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, and constant output terminal voltage control and grid construction control on the AC side of the auxiliary converter.

[0010] Optionally, the control method for the offshore converter platform based on diode rectifiers further includes: if the operating condition is switching from the black start condition or the windless condition to the rated power operating condition, the control strategy is to first control the AC side operating mode of the auxiliary converter to switch from active power control to constant output terminal voltage control, and at the same time set the voltage reference value of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line so that the current of the tie line drops to zero; secondly, control the tie switch to open, and switch the DC side operating mode of the auxiliary converter to open-loop given DC voltage control operation, then the auxiliary converter operates according to the reactive power mode.

[0011] Optionally, the control method for the offshore converter platform based on diode rectifier further includes: if the operating condition is switching from the rated power operating condition to the black start operating condition or the windless operating condition, the control strategy is to set the output voltage of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line, and then control the tie switch to close; and then switch the operating mode of the auxiliary converter to the active power mode.

[0012] Optionally, the specific harmonic filtering control is used to filter or cancel the harmonic current generated by the diode rectifier through the auxiliary converter, and the specific harmonic filtering control includes: The grid connection frequency of the offshore converter platform, the AC side current of the main converter, and the harmonic order of the output current of the diode rectifier are obtained. Integrating the meshing frequency and the harmonic order yields a harmonic meshing reference phase corresponding to the harmonic order. Based on the harmonic meshing reference phase and the AC side current, Parker transformation and low-pass filtering are performed to obtain the dq axis current control reference value of the subharmonic corresponding to the harmonic meshing reference phase. The dq-axis current control reference value is processed by using harmonic current inner loop control to obtain the harmonic compensation voltage corresponding to the subharmonic of the dq-axis current control reference value; The harmonic compensation voltage is superimposed on the fundamental voltage modulation wave of the active power mode.

[0013] Optionally, the grid connection control is used to dynamically adjust the reactive current injected into the grid connection point of the wind farm by the auxiliary converter, and the content of the grid connection control includes: The grid connection frequency of the offshore converter platform, the target value of the q-axis voltage of the auxiliary converter, and the three-phase voltage and three-phase current of the auxiliary converter at the grid connection point of the wind farm are obtained. Integrating the network frequency yields the network reference phase; Parker transformation is performed based on the network reference phase, the three-phase voltages, and the three-phase currents to obtain the q-axis voltage. A PI controller is used to process the q-axis voltage and the target value of the q-axis voltage to obtain the dynamically adjusted q-axis injection current of the auxiliary converter; The q-axis injected current is used as the q-axis current reference value in the AC side control mode of the auxiliary converter.

[0014] On the other hand, a diode rectifier-based offshore converter platform is provided, including a control module, a wind farm, and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to the diode rectifier via a tie switch and a tie line. The diode rectifier is connected to power equipment for providing active power. The control module is used to control the operation of the offshore converter platform according to the control method of the diode rectifier-based offshore converter platform described above.

[0015] Optionally, the main converter is a 12-pulse or dual 12-pulse cascaded diode rectifier, and the auxiliary converter includes a first reactive power compensation module and a second reactive power compensation module connected in parallel. Both the first reactive power compensation module and the second reactive power compensation module include several sub-modules connected in series.

[0016] On another front, a control device for an offshore converter platform based on a diode rectifier is provided, which is applied to the offshore converter platform. The offshore converter platform includes a wind farm and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to the diode rectifier through a tie switch and a tie line. The diode rectifier is connected to power equipment for providing active power. The control device for the offshore converter platform includes: a data acquisition module and a control strategy determination module. The data acquisition module is used to acquire the operating conditions of the wind farm; The control strategy determination module is used to determine the control strategy of the offshore converter platform based on the operating conditions; and to control the operation of the offshore converter platform according to the control strategy. Wherein, if the operating condition is a black start condition or a windless condition, the control strategy is to control the connection switch to close, control the auxiliary converter to operate in active power mode, and provide active power support to the wind farm through the active power output of the power equipment; the active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid connection control on the AC side of the auxiliary converter; If the operating condition is the rated power operating condition, then the control strategy is to control the interconnection switch to open and control the auxiliary converter to operate in reactive power mode; the reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, constant output terminal voltage control on the AC side of the auxiliary converter, and grid construction control. If the operating condition is switching from the black start condition or the windless condition to the rated power operating condition, the control strategy is as follows: First, control the AC side operating mode of the auxiliary converter to switch from active power control to constant output terminal voltage control, and at the same time set the voltage reference value of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line so that the current of the tie line drops to zero; second, control the tie switch to open, and switch the DC side operating mode of the auxiliary converter to open-loop given DC voltage control operation, then the auxiliary converter operates according to the reactive power mode. If the operating condition is switching from the rated power operating condition to the black start operating condition or the windless operating condition, the control strategy is to set the output voltage of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line, and then control the tie switch to close; then switch the operating mode of the auxiliary converter to the active power mode.

[0017] Optionally, the specific harmonic filtering control is used to filter or cancel the harmonic current generated by the diode rectifier through the auxiliary converter, and the specific harmonic filtering control includes: The grid connection frequency of the offshore converter platform, the AC side current of the main converter, and the harmonic order of the output current of the diode rectifier are obtained. Integrating the meshing frequency and the harmonic order yields a harmonic meshing reference phase corresponding to the harmonic order. Based on the harmonic meshing reference phase and the AC side current, Parker transformation and low-pass filtering are performed to obtain the dq axis current control reference value of the subharmonic corresponding to the harmonic meshing reference phase. The dq-axis current control reference value is processed by using harmonic current inner loop control to obtain the harmonic compensation voltage corresponding to the subharmonic of the dq-axis current control reference value; The harmonic compensation voltage is superimposed on the fundamental voltage modulation wave of the active power mode.

[0018] On the other hand, a terminal device is provided, including a processor and a memory; The memory is used to store program code and transmit the program code to the processor; The processor is used to execute the control method for the offshore converter platform based on the diode rectifier as described above, according to the instructions in the program code.

[0019] This invention relates to a diode rectifier-based offshore converter platform and its control method, apparatus, and equipment. The control method for the diode rectifier-based offshore converter platform includes acquiring the operating conditions of the wind farm; determining a control strategy for the offshore converter platform based on the operating conditions; and controlling the operation of the offshore converter platform according to the control strategy. If the operating conditions are black-start or windless, the control strategy involves closing the tie switch and controlling the auxiliary converter to operate in active power mode, providing active power support to the wind farm through the active power output of the power equipment. If the operating conditions are rated power operation, the control strategy involves opening the tie switch and controlling the auxiliary converter to operate in reactive power mode. The active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid connection control on the AC side of the auxiliary converter. The reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, and constant output terminal voltage control and grid connection control on the AC side of the auxiliary converter.

[0020] As can be seen from the above technical solutions, this application has the following advantages: The control method of the offshore converter platform based on diode rectifier determines the control strategy of the offshore converter platform through the operating conditions of the wind farm, and controls the operation of the offshore converter platform according to the control strategy. It can realize the control of the auxiliary converter to operate in reactive power mode or active power mode, and solves the technical problems of active power back-feeding, grid construction, and harmonic current filtering in the existing offshore wind power generation system DR wind farm.

[0021] The control device for the offshore converter platform based on diode rectifiers acquires the operating conditions of the wind farm through a data acquisition module and a control strategy determination module, determines the control strategy for the offshore converter platform, and controls the operation of the offshore converter platform according to the control strategy. It can control the auxiliary converter to operate in reactive power mode or active power mode. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating the steps of the control method for an offshore converter platform based on a diode rectifier as described in an embodiment of this application. Figure 2 This is a schematic diagram of the topology of the offshore converter platform based on diode rectifiers described in the embodiments of this application; Figure 3This is a schematic diagram of the operating mode topology of the auxiliary converter in the offshore converter platform based on a diode rectifier, as described in the embodiments of this application. Figure 4 This is a schematic diagram of the control framework of the auxiliary converter in the control method of the offshore converter platform based on diode rectifier described in the embodiments of this application; Figure 5 This is a schematic diagram of the control device for an offshore converter platform based on a diode rectifier, as described in another embodiment of this application. Figure 6 This is a schematic diagram of the terminal device described in an embodiment of this application. Detailed Implementation

[0024] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0025] In the description of the embodiments of this application, 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 indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified.

[0026] In the embodiments of this application, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of this application according to the specific circumstances.

[0027] Patent terminology used in this application: The Global Positioning System (GPS) is a high-precision radio navigation positioning system based on artificial Earth satellites. GPS provides accurate geographic location, vehicle speed, and precise time information anywhere in the world and in near-Earth space.

[0028] Offshore wind power transmission systems are key infrastructure for efficiently and stably transmitting electricity generated by offshore wind turbines to onshore power grids. The core system consists of three parts: a data collection system, a step-up / converter station, and submarine cables. With development extending into deeper and more remote sea areas, flexible direct current transmission (VSC-HVDC) has become the mainstream technology for large-capacity, long-distance transmission.

[0029] The Parker transformation is a commonly used coordinate transformation method in motors and power systems. The coordinate system transformation of the Parker transformation is to transform the three-phase stationary coordinate system (a, b, c) to the synchronous rotating coordinate system (d, q axis).

[0030] The core objective of harmonic current inner-loop control is to enable the actual current to track the command current containing harmonic components quickly and without steady-state error. Traditional PI control has limited gain at high-frequency harmonics, requiring improved strategies such as proportional resonant control (PR) or repetitive control (RC). PR sets infinite gain at the fundamental frequency and specific harmonic frequencies (e.g., 5th, 7th, and 11th harmonics) to achieve zero steady-state error tracking of sinusoidal commands. RC utilizes an internal model principle to memorize and compensate for periodic errors within one fundamental cycle; it offers extremely high gain for any integer harmonic order, but its dynamic response is slow (delayed by one cycle). It is often combined with PI or PR to form a composite control to balance steady-state accuracy and dynamic speed.

[0031] A power module is an industrial product that combines and packages power semiconductor devices such as IGBTs and MOSFETs according to specific circuit functions. Its core function is to realize the conversion and control of electrical energy.

[0032] CHB is an abbreviation for Cascaded H-Bridge multilevel converter. CHB is a topology that synthesizes high-voltage, high-quality AC waveforms by connecting multiple independent DC power supply H-bridge power units in series.

[0033] This application provides an offshore converter platform based on a diode rectifier and its control method, device and equipment, which solves the technical problems of active power back-feeding, grid construction and harmonic current filtering in the existing DR wind farm of offshore wind power generation system.

[0034] Example 1: Figure 1 This is a flowchart illustrating the steps of the control method for an offshore converter platform based on a diode rectifier as described in an embodiment of this application. Figure 2 This is a topology diagram of the offshore converter platform based on diode rectifiers as described in an embodiment of this application.

[0035] In the embodiments of this application, the diode rectifier-based offshore converter platform includes a control module, a wind farm 10, and a main converter 20 and an auxiliary converter 30 connected to the grid connection point PCC of the wind farm 10. The auxiliary converter 30 is connected to the diode rectifier 40 through a tie switch HSS and a tie line. The diode rectifier 40 is connected to the power equipment 50 for providing active power. The control module is used to control the operation of the offshore converter platform according to the control method of the diode rectifier-based offshore converter platform.

[0036] It should be noted that the power equipment 50 can be other wind farms or active power sources, such as generators, energy storage converters, frequency converters, rectifiers, etc. The main converter 20 can be selected as a diode rectifier. In this embodiment, the offshore converter platform based on diode rectifiers is a hybrid offshore converter station topology composed of the main converter 20 and a small-capacity auxiliary converter 30. The wind farm 10 converges at the point of common connection (PCC) of the offshore converter platform via the offshore medium-voltage AC system. At the PCC, the main converter 20 and the auxiliary converter 30 of the offshore converter platform are connected separately. The DC end of the main converter 20 is connected to the multi-terminal DC grid in the wind farm cluster. The DC terminal of the auxiliary converter 30 is connected to a small-capacity DC tie line via a fast switching device (HSS). The other end of the DC tie line is connected to other wind farms or active power sources within the cluster via a small-capacity diode rectifier 40. The diode rectifier 40 is selected as a small-capacity diode rectifier.

[0037] Figure 3 This is a schematic diagram of the operating mode topology of the auxiliary converter in the offshore converter platform based on the diode rectifier described in the embodiments of this application.

[0038] In the embodiments of this application, the main converter 20 is a 12-pulse or dual 12-pulse cascaded diode rectifier, and the auxiliary converter 30 includes a first reactive power compensation module and a second reactive power compensation module connected in parallel. Both the first reactive power compensation module and the second reactive power compensation module include several sub-modules connected in series.

[0039] It should be noted that both the first and second reactive power compensation modules can be selected as static synchronous var compensators (SSCs). The submodule is a full-bridge power module (FBSM).

[0040] In this embodiment, the working principle of the offshore converter platform based on diode rectifiers is as follows: the wind power generated by wind farm 10 is transmitted from the DC bus through the main converter 20, and the auxiliary converter 30 provides grid support for the offshore AC system while simultaneously solving the current harmonic problem of the diode rectifier 40. When wind farm 10 requires an external active power source due to windless conditions or black start conditions, the auxiliary converter provides active power support to the wind farm connected to the DR through a small-capacity DC tie line. The reactive power demand of the system is divided into steady-state and transient parts. The steady-state demand is distributed to each wind turbine through a centralized reactive power distribution link, while the transient demand during disturbances is handled by the auxiliary converter according to the grid control principle.

[0041] like Figure 2 and Figure 3 As shown in the embodiments of this application, the submodule topology design of the auxiliary converter 30, while simple half-bridge submodules can meet all functional requirements, suffers from size and cost issues that render it essentially infeasible in engineering. Based on the traditional half-bridge submodule topology, a series of modifications and optimizations have been made to form... Figure 2 The topology shown. Where, according to... Figure 3 As shown, the Static Synchronous Var Compensator (STATCOM) is not an additional device, but rather an operating state of the auxiliary converter 30. When the tie switch HSS is closed, the auxiliary converter 30 operates in active power mode (such as MMC mode), transmitting active power; when the tie switch HSS is open, the auxiliary converter 30 switches to the first and second reactive power compensation modules of a cascaded full-bridge converter topology, operating as two independent STATCOMs connected to the grid connection point PCC.

[0042] It should be noted that, as Figure 3As shown, the auxiliary converter 30 exhibits an asymmetry between AC and DC power: the DC side of the auxiliary converter 30 only needs to transmit the active power required by the wind farm, resulting in a very low power demand. However, the AC side of the auxiliary converter 30, in addition to transmitting the same active power, also has a greater reactive power output requirement due to grid connection requirements. Conventional half-bridge MMCs have a fixed coupling relationship between their DC-side voltages. If a higher AC voltage is configured based on the high reactive power demand on the AC side, the DC-side voltage will be forced to rise. For the DC side, which only transmits active power, an excessively high DC voltage will cause the tie line to enter an inefficient high-voltage, low-current operating state, resulting in idle cable current-carrying capacity and redundant insulation costs. Therefore, a hybrid submodule MMC can be used to reduce the DC-side voltage, improving the economy of the auxiliary converter 30 and the tie line. The hybrid submodule can reduce the number of submodules without changing the total number of switching devices. Because the grid connection function places significant reactive power pressure on the auxiliary converter 30, a control method based on diode rectifiers for offshore converter platforms is adopted. This utilizes the slower-responding wind turbines to handle the system's steady-state reactive power requirements, while the auxiliary converter 30 only provides temporary support when the wind farm 10 is disturbed. The auxiliary converter 30 outputs almost no reactive power in steady state, only rapidly compensating for reactive power imbalances and providing some control capability during transient processes, significantly reducing capacity requirements. Considering the temporary nature of the auxiliary converter 30's reactive power output, further optimization is possible by combining it with techniques such as active power mode MMC short-term overload operation. Regarding the issue of excessively high arm voltage requirements caused by the filtering function, specific harmonic filtering control using the control method of the offshore converter platform based on diode rectifiers reduces the harmonic current voltage drop by eliminating the need for transformers, alleviating arm voltage pressure and thus saving on submodule usage. To further reduce the arm voltage requirements, based on the operating characteristics of the diode rectifier 40 in the wind farm, the auxiliary converter 30 is modified to a 100% full-bridge power module. A control strategy for switching operation of the auxiliary converter 30 is proposed, which can flexibly switch between active power mode (such as MMC mode) and reactive power mode (such as static synchronous var compensator STATCOM).

[0043] Figure 4 This is a schematic diagram of the control framework for the auxiliary converter in the control method for an offshore converter platform based on a diode rectifier, as described in an embodiment of this application. Figure 4 middle, V abc and I abc These represent the three-phase voltage and three-phase current at the grid connection point of the auxiliary converter, respectively. P i and Q i These represent the active power and reactive power injected into the wind farm by the auxiliary converter, respectively. ω0 represents the network frequency given in the open-loop configuration of the offshore converter platform, generated by integration. θ This represents a given mesh reference phase in an open loop. I d , I q , V d and V q They represent I abc and V abc The corresponding d-axis current component, q-axis current component, d-axis voltage component, and q-axis voltage component after Park transformation. I d，ref and I q，ref This represents the d-axis current control reference value and q-axis current control reference value generated by the controller. I DRac This represents the AC side current of the main converter in an offshore converter platform. I DRdc This represents the DC-side current of the diode converter in an offshore converter platform. DRdc This represents the minimum DC current of the diode converter in an offshore converter platform. U cavg This represents the average value of the output terminal voltage of the submodule in the auxiliary converter. cavg This indicates the target voltage value at the output terminal of the submodule in the auxiliary converter. V dc 、I dc These represent the DC-side voltage and DC-side current of the auxiliary converter, respectively. I dc，ref This indicates the control reference value for DC current. θ k This represents the reference phase for the harmonic network formed under the kth harmonic. I dq，ref 、I dq（k），ref This represents the dq-axis current control reference value generated by the controller and the dq-axis current control reference value corresponding to the kth harmonic. V acref 、V dcref 、V h（k），ref These represent the AC voltage reference value of the AC side control input, the DC voltage reference value of the DC side control input, and the harmonic compensation voltage of the specific harmonic filtering control input, respectively. V acref 、Vh（k），ref The calculation process is based on the current inner loop control that is already maturely applied in engineering, and the voltage is calculated based on the current reference value obtained from the previous stage.

[0044] like Figure 1 As shown in the figure, this application provides a control method for an offshore converter platform based on a diode rectifier, including the following steps: S1. Obtain the operating conditions of the wind farm.

[0045] It should be noted that in the control process of an offshore converter platform based on a diode rectifier, such as Figure 2 As shown, the offshore converter platform based on diode rectifiers obtains the operating conditions of the wind farm through step S1, providing data for subsequent steps to determine the control strategy of the offshore converter platform based on diode rectifiers. In this embodiment, the operating conditions of the wind farm include black start condition, no wind condition, and rated power operating condition. No wind condition refers to the wind farm's operating condition where it cannot output wind power due to excessively low wind speeds, which frequently occurs during wind farm operation. At this time, all wind turbines in the wind farm cannot generate or can only generate very little active power, and the wind farm lacks a source of active power to meet the power needs of various internal auxiliary equipment. Therefore, an auxiliary converter is needed to inject active power. Black start condition refers to the process where, after the entire power system is shut down due to a fault, the system gradually resumes operation without relying on external network assistance, starting through generator sets with self-starting capabilities or through external power supply, driving other units. Rated power operating condition refers to the maximum power value that electrical equipment (such as a wind farm) can stably output for a long period under normal operating conditions; it is the safe threshold for continuous operation of the equipment.

[0046] In this embodiment of the application, the control method for the offshore converter platform based on diode rectifiers can determine the operating conditions of the wind farm based on the operating data of the offshore converter platform.

[0047] S2. Determine the control strategy for the offshore converter platform based on the operating conditions; control the operation of the offshore converter platform according to the control strategy.

[0048] It should be noted that, to address the time-independent nature of active power transmission and harmonic filtering in extreme operating conditions of wind farms, step S2 determines the control strategy for the offshore converter platform based on preset rules according to the wind farm's operating conditions obtained in step S1, and controls the operation of the offshore converter platform according to the control strategy. In this embodiment, the control method for the offshore converter platform based on diode rectifiers determines the control strategy for controlling the operation of the offshore converter platform by obtaining the wind farm's operating conditions in step S1. This control method for the offshore converter platform based on diode rectifiers is compatible with the optimized topology and operating mode of the offshore converter platform based on diode rectifiers. It can integrate and solve the overall control strategy for the diode rectifier problem of the offshore converter platform, and can also achieve a control mode that allows for rapid zero-current smooth switching between active power mode and reactive power mode, avoiding the need for DC circuit breakers caused by load switching.

[0049] In this embodiment, the control method for an offshore converter platform based on diode rectifiers, combined with the operating characteristics of wind farms, optimizes the compact and low-cost design of auxiliary converters that integrate solutions to diode rectifier problems. The problems addressed include a hybrid bridge topology designed to address AC / DC power asymmetry, optimization of the reactive power capacity of the auxiliary converter under time-scale decoupling, elimination of the direct-connection transformer scheme, and the control strategy of this diode rectifier-based offshore converter platform control method enabling the auxiliary converter to switch between active and reactive power modes, as well as accurately determining the bridge arm voltage design optimization based on the harmonic current components of the diode rectifier.

[0050] In this embodiment, if the operating condition is a black-start condition or a windless condition, the control strategy is to close the tie switch and control the auxiliary converter to operate in active power mode, providing active power support to the wind farm through the active power output of the power equipment. If the operating condition is a rated power operating condition, the control strategy is to open the tie switch and control the auxiliary converter to operate in reactive power mode. The active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid connection control on the AC side of the auxiliary converter. The reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, and constant output terminal voltage control and grid connection control on the AC side of the auxiliary converter.

[0051] It should be noted that under black-start or no-wind operating conditions, the auxiliary converter 30 operates in active power mode to transmit active power, but harmonic currents are low and filtering requirements are low. Under rated power operating conditions, filtering requirements reach their peak, but the wind farm is already self-sufficient in active power and does not require active power input. When the wind farm has sufficient active power, to avoid the wind farm switching back and forth at the power critical point, the critical condition for "sufficient active power" is set to when the wind farm's active power exceeds 0.2 pu. At this point, the auxiliary converter does not need to absorb active power from the tie line and can disconnect the DC tie line, smoothly switching to operation of two independent first and second reactive power compensation modules. In reactive power mode, the arm voltage of the auxiliary converter drops to zero due to the bias of the DC voltage, and the released margin can be used to offset the voltage drop caused by the large amount of harmonic current under full load. Compared with the non-switching operating mode, this control method for offshore converter platforms based on diode rectifiers can typically reduce the DC voltage requirement of the arm voltage, significantly reducing the number of submodules required. pu is the per-unit value of power. During black start or low-power phases (such as black start or no-wind conditions), the auxiliary converter operates in active power mode to provide active power support. The lower filtering requirements eliminate the need for a large number of additional bridge arm submodules. Low power can be understood as black start, zero-power operation in no-wind conditions, and the risky condition where the wind farm is already at a low active power level and may enter no-wind operation. During this phase, the auxiliary converter needs to enter active power mode to prepare for potential active power support. The specific numerical range of low power depends on the assessment of the potential risk of entering no-wind operation during wind farm operation. Low power refers to the wind farm's active power output being below 0.15pu, where pu is the per-unit value of power. During periods of sufficient active power, it can be considered that the wind farm is above this power level and there is no risk of a rapid drop to zero-power operation in no-wind conditions. Therefore, it can be guaranteed that no active power transmission is required from the auxiliary converter. Thus, the auxiliary converter can be switched to operate in two reactive power modes (such as the Static Var Compensator STATCOM). The Static Var Compensator STATCOM operating in CHB topology has no active power transmission capability at all.

[0052] In the embodiments of this application, such as Figure 4 As shown, specific harmonic filtering control is used to filter or cancel harmonic currents generated by the diode rectifier through an auxiliary converter. The specific harmonic filtering control includes: Obtain the grid connection frequency of the offshore converter platform, the AC side current of the main converter, and the harmonic order of the output current of the diode rectifier; By integrating the meshing frequency and harmonic order, the harmonic meshing reference phase corresponding to the harmonic order is obtained; Based on the harmonic network reference phase and AC side current, Parker transformation and low-pass filtering are performed to obtain the dq axis current control reference value of the subharmonic corresponding to the harmonic network reference phase. Harmonic current inner loop control is used to process the dq axis current control reference value to obtain the harmonic compensation voltage corresponding to the subharmonic of the dq axis current control reference value; The harmonic compensation voltage is superimposed on the fundamental voltage modulation wave of the active power mode.

[0053] It should be noted that the specific harmonic filtering control achieves full local compensation of the harmonic current by accurately canceling the harmonic current of the diode rectifier 40 through the auxiliary converter 30. In this embodiment, the fundamental voltage modulation wave is set in the valve-level control.

[0054] like Figure 4 As shown in this embodiment, valve-level control involves the specific control of each internal converter by the auxiliary converter 30. The auxiliary converter 30 converts the voltage reference value generated by the upper-level control into a voltage signal on each arm of the auxiliary converter, and generates control signals for each switching device on one arm accordingly. In valve-level control, the data input to the valve-level control includes the AC voltage reference value of the AC side control input, the DC voltage reference value of the DC side control input, and the harmonic compensation voltage of the specific harmonic filtering control input; the data output by the valve-level control is the control signal controlling the first reactive power compensation module and the second reactive power compensation module in the auxiliary converter 30, such as a certain phase j The control signal for the first reactive power compensation module is a voltage signal. V jp The control signal for the second reactive power compensation module is a voltage signal. V jn It can be calculated according to the first formula, which is: ; In the formula, V jp for j Mutually( j The control signals for the first reactive power compensation module (phases a, b, and c) are... V jn for j Mutually( j The control signal for the second reactive power compensation module (phases a, b, and c) is given.

[0055] In the embodiments of this application, such as Figure 4 As shown, grid-connected control is used to dynamically adjust the reactive current injected into the grid connection point of the wind farm by the auxiliary converter. The content of grid-connected control includes: Obtain the grid connection frequency of the offshore converter platform, the target value of the q-axis voltage of the auxiliary converter, and the three-phase voltage and three-phase current at the grid connection point of the auxiliary converter to the wind farm; Integrating the network frequency yields the network reference phase; Parker transformation is then performed based on the network reference phase, three-phase voltages, and three-phase currents to obtain the q-axis voltage. A PI controller is used to process the q-axis voltage and the target q-axis voltage value to obtain the dynamically adjusted q-axis injection current of the auxiliary converter; The q-axis injection current is used as the reference value for the q-axis current in the AC side control mode of the auxiliary converter.

[0056] It should be noted that the q-axis current reference value is denoted as... I q，ref In active power mode, the q-axis current reference value will also be... I q，ref Input current inner-loop control. In this embodiment, grid control dynamically adjusts the reactive current injected into the grid-connected PCC by the auxiliary converter to stabilize the frequency and phase of the diode-rectifier-based offshore converter platform. The deviation of the grid-connected PCC voltage vector from the reference phase generates a q-axis voltage component. V q At that time, the reactive power grid control loop will respond quickly and dynamically adjust the q-axis current control reference value of the auxiliary converter. I q，ref This causes the PCC voltage vector to re-align with the d-axis of the given reference phase (i.e., V q =0), thus maintaining frequency stability.

[0057] In the embodiments of this application, such as Figure 4 As shown, in active power mode, the active power control on the AC side of the auxiliary converter can be understood as: based on the minimum DC current value DRdc With DC side current I DRdc Subtraction yields the DC current difference on the DC side of the diode converter; this DC current difference is then processed by a PI controller and a filter to obtain the target active power value injected into the wind farm by the auxiliary converter. i ; target value of active power i Active power injected into the wind farm with the auxiliary converter P i The difference between the two values ​​yields the active power difference; this difference is then processed by a PI controller to generate a reference value for d-axis current control. I d，ref In reactive power mode, the constant output voltage control on the AC side of the auxiliary converter can be understood as: the target value of the output voltage. cavg Average voltage at the output terminal U cavg Subtraction yields the voltage difference at the output terminals of the submodules in the auxiliary converter; this voltage difference is then processed by a PI controller to generate a reference value for d-axis current control. I d，ref .

[0058] In the embodiments of this application, such as Figure 4 As shown, the inner current loop control can control the reference value based on the input d-axis current. I d，ref and q-axis current reference value I q，ref The AC voltage reference value for the AC side control input is obtained using the second formula and the Parker inverse transform formula. V acref The second formula is: ; The formula for the inverse Parker transform is: ; In the formula, L External equivalent reactance is used to assist the converter. v acref( d )and v acref ( q The reference AC voltage value for the three-phase AC side control input is obtained after Parker inverse transformation. V acref .

[0059] In the embodiments of this application, such as Figure 4 As shown, in reactive power mode, the open-loop DC voltage control of the auxiliary converter's DC side refers to controlling the DC voltage reference value of the DC side control input. V dcref Set to 0.

[0060] In the embodiments of this application, such as Figure 4 As shown, in active power mode, the power balance control on the DC side of the auxiliary converter can be understood as: the target value of the output terminal voltage. cavg Average voltage at the output terminal U cavg Subtraction yields the voltage difference at the output terminals of the submodules in the auxiliary converter; this voltage difference is then processed by a PI controller to generate a control reference value for the DC current. I dc，ref Based on the control reference value of DC current I dc，refThe DC voltage reference value for the DC-side control input is calculated using the third formula for DC current control. V dcref The third formula is: ; In the formula, V dc0 This is the DC voltage reference value. k p , k i These are the proportional and integral coefficients of the PI controller, respectively. S For the Laplace operator.

[0061] This application provides a control method for an offshore converter platform based on a diode rectifier, comprising: acquiring the operating conditions of a wind farm; determining a control strategy for the offshore converter platform based on the operating conditions; controlling the operation of the offshore converter platform according to the control strategy; if the operating conditions are black-start or windless, the control strategy is to close the tie switch and control the auxiliary converter to operate in active power mode, providing active power support to the wind farm through the active power output of the power equipment; if the operating conditions are rated power operation, the control strategy is to open the tie switch and control the auxiliary converter to operate in reactive power mode; wherein, the active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid connection control on the AC side of the auxiliary converter; the reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, and constant output terminal voltage control and grid connection control on the AC side of the auxiliary converter. This control method for offshore converter platforms based on diode rectifiers determines the control strategy of the offshore converter platform by analyzing the operating conditions of the wind farm. The method controls the operation of the offshore converter platform according to the control strategy, enabling the auxiliary converter to operate in reactive power mode or active power mode. This solves the technical problems of active power backfeed, grid construction, and harmonic current filtering in existing offshore wind power generation systems' DR wind farms.

[0062] In one embodiment of this application, the control method for the diode rectifier-based offshore converter platform further includes: If the operating condition switches from black start or no-wind operation to rated power operation, the control strategy is as follows: First, the operating mode of the auxiliary converter's AC side is switched from active power control to constant output voltage control. Simultaneously, the reference voltage value on the auxiliary converter's DC side is set higher than the tie-line DC voltage. Due to the unidirectional conduction characteristic of the diode rectifier connected to the tie-line, the tie-line current is reduced to zero. Second, the tie-line switch is smoothly disconnected, and the operating mode of the auxiliary converter's DC side is switched to open-loop given DC voltage control. At this time, the reference DC voltage value input to the auxiliary converter's DC side is...V dcref If the value drops to zero, the auxiliary converter will operate in reactive power mode. If the operating condition is switching from rated power operation to black start or no wind operation, the control strategy is to set the output voltage of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line, and then control the tie switch to close. Due to the unidirectional conduction characteristic of the diode rectifier connected to the tie line, closing the tie switch does not cause a current surge, thus achieving a smooth switching. Then, the operating mode of the auxiliary converter is switched to active power mode.

[0063] It should be noted that the control method for the diode rectifier-based offshore converter platform achieves rapid, zero-current smooth switching between active and reactive power modes through a control strategy. In this embodiment, the control method for the diode rectifier-based offshore converter platform can also optimize the submodule capacitors and arm inductors based on the operating conditions of the wind farm when switching operation modes. When the wind farm has extremely low power and the auxiliary converter operates in active power mode, the reactive power disturbance amplitude in the diode rectifier-based offshore converter platform is limited, and there is no need to design large capacitors for full-load conditions. However, when the wind farm has high power and the auxiliary converter operates in reactive power mode, the capacitor requirement is much lower than that of conventional auxiliary converters (such as modular multilevel converters, MMC) due to reduced arm energy fluctuations. Therefore, the overall capacitor requirement of the control method for the diode rectifier-based offshore converter platform is significantly reduced compared to the non-switching operation mode. On the other hand, since the circulating current of the auxiliary converter arm is smaller under low power conditions, and the circulating current characteristics change under reactive power mode, the selection value of the auxiliary converter arm inductance can also be reduced, further reducing the arm burden caused by harmonic voltage drop.

[0064] In this embodiment, the control method for an offshore converter platform based on a diode rectifier exploits the inherent harmonic distribution characteristics of the diode rectifier, further reducing the requirements of the filtering function on the bridge arm voltage. In conventional filtering design, due to the lack of understanding of the phase characteristics of the harmonic sources, the bridge arm voltage output capability is usually configured by directly superimposing the peak values ​​of the fundamental and each harmonic voltage. However, the commutation characteristics of the diode rectifier constrain the phase relationship of the harmonic current, making conventional active filter design specifications redundant. Therefore, this control method for an offshore converter platform based on a diode rectifier achieves accurate calculation of harmonic voltage drop by finely evaluating the information of each component of the diode rectifier harmonic current, breaking conventional design principles and further reducing the number of sub-modules. The control block diagram corresponding to the auxiliary converter topology and switching operation mode is as follows. Figure 4As shown, the control method of the offshore converter platform based on diode rectifier controls the auxiliary converter to operate in active power mode or reactive power mode according to the operating conditions of the wind farm, so as to solve multi-dimensional problems such as active power back-feedback, grid construction, and harmonic current filtering in the diode rectifier DR wind farm.

[0065] It should be noted that the control method for this diode rectifier-based offshore converter platform, combined with the platform itself, can comprehensively address issues related to active power feedback, grid construction, reactive power balance, and harmonics in diode rectifier DR systems. This control method specifically optimizes the topology and operation of the added auxiliary converter, ensuring that the platform inherits the compact and low-cost advantages of diode rectifier DR systems. It also resolves the feasibility issues of existing diode rectifier DR solutions, significantly improving their economic efficiency. This diode rectifier-based offshore converter platform can serve as an alternative to the existing mainstream modular multilevel converter (MMC) offshore converter platforms, addressing the high cost of existing offshore converter platforms.

[0066] In this embodiment, the control method for the offshore converter platform based on diode rectifiers determines the control strategy of the offshore converter platform based on the operating conditions of the wind farm. The control strategy meets the active power demand within the wind farm under conditions such as black start and near-zero wind operation, while maintaining the energy balance inside the converter. The control strategy needs to be switched to meet different operating modes.

[0067] It should be noted that in active power mode, the AC side of the auxiliary converter is responsible for controlling the injection of specific active power into the wind farm through active power control and grid connection control. The active power reference value is given according to the wind farm's needs. The DC side of the auxiliary converter is responsible for power balance control to maintain the dynamic balance of power on both the AC and DC sides of the converter and prevent energy accumulation inside the auxiliary converter. In reactive power mode, the AC side of the auxiliary converter is responsible for constant output voltage control and grid connection control, with the control objective changed to maintaining constant energy inside the converter. The DC side of the auxiliary converter is responsible for actively reducing the voltage reference value to zero through open-loop given DC voltage control. When the auxiliary converter operates in reactive power mode, the voltage at the DC terminal of the auxiliary converter, which is equivalent to the voltage between the neutral points of two reactive power compensation modules (such as the first reactive power compensation module and the second reactive power compensation module), needs to be reduced to zero. All operating conditions in the wind farm require grid connection control by the auxiliary converter to provide operating frequency support for the wind turbines in the grid-connected wind farm.

[0068] In this embodiment, the control method for an offshore converter platform based on a diode rectifier, during the determination of the control strategy according to the operating conditions of the wind farm, requires the auxiliary converter to have the ability to flexibly switch between active power mode and reactive power mode to meet the active power demand that may exist in the daily operation of the wind farm, since zero-power operation conditions occur frequently without wind. The switching process between active power mode and reactive power mode in the control method for the offshore converter platform based on a diode rectifier also needs to be as smooth as possible to reduce the impact on power equipment. Specifically: During the switching process from active power mode to reactive power mode of the auxiliary converter, once the wind farm's output power is sufficient to reliably operate independently from the tie line, the system switches from black-start or no-wind operation to rated power operation, and the tie switch is disconnected. First, the AC side of the auxiliary converter switches from active power control to constant output voltage control, while the DC side voltage reference value is raised to slightly higher than the tie line DC voltage. Since the other end of the tie line is a diode rectifier with unidirectional conduction, the tie line current is forced to strictly drop to zero. Subsequently, the connection between the auxiliary converter and the tie line can be safely disconnected using the tie switch (such as a conventional disconnector). Finally, by switching the DC side operating mode of the auxiliary converter to open-loop DC voltage control, the DC terminal voltage of the auxiliary converter is adjusted to zero, and the auxiliary converter enters reactive power mode operation.

[0069] During the switching process from reactive power mode to active power mode of the auxiliary converter, firstly, the DC-side control of the auxiliary converter will increase the output voltage to a level slightly higher than the current tie line DC voltage, and then control the tie switch to close, closing the loop between the power equipment and the wind farm. Since the output voltage of the DC side of the auxiliary converter (meaning the DC side voltage of the converter is slightly higher than the original voltage of the tie line) is slightly higher than the tie line DC voltage at this time, no inrush current will be generated at the moment of closing. Finally, the active power control links of the AC and DC sides of the auxiliary converter are completely switched to the active power mode control strategy, and active power can be transmitted according to the needs of the wind farm, completing the switch from reactive power mode to active power mode.

[0070] Example 2: Figure 5 This is a schematic diagram of the control device for an offshore converter platform based on a diode rectifier, as described in an embodiment of this application.

[0071] like Figure 5As shown, this application embodiment provides a control device for an offshore converter platform based on a diode rectifier, applied to an offshore converter platform. The offshore converter platform includes a wind farm and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to the diode rectifier through a tie switch and a tie line. The diode rectifier is connected to power equipment for providing active power. The control device for the offshore converter platform includes: a data acquisition module 100 and a control strategy determination module 200. The data acquisition module 100 is used to acquire the operating conditions of the wind farm; The control strategy determination module 200 is used to determine the control strategy of the offshore converter platform based on the operating conditions; and to control the operation of the offshore converter platform according to the control strategy. If the operating condition is black start or no wind, the control strategy is to close the control tie switch and control the auxiliary converter to operate in active power mode, so as to provide active power support to the wind farm through the active power output of the power equipment; the active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid construction control on the AC side of the auxiliary converter. If the operating condition is rated power operation, the control strategy is to open the tie switch and control the auxiliary converter to operate in reactive power mode. The reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, constant output terminal voltage control on the AC side of the auxiliary converter, and grid construction control. If the operating condition is switching from black start or no wind to rated power operation, the control strategy is as follows: First, control the AC side of the auxiliary converter to switch from active power control to constant output voltage control, and at the same time set the voltage reference value of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line so that the current of the tie line drops to zero; second, control the tie switch to open and switch the DC side of the auxiliary converter to open-loop given DC voltage control operation, then the auxiliary converter will operate in reactive power mode. If the operating condition is switching from rated power operation to black start or no wind operation, the control strategy is to set the output voltage of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line, then control the tie switch to close; then switch the operating mode of the auxiliary converter to active power mode.

[0072] It should be noted that the content of each module in the device of Embodiment 2 corresponds to the content of each step in the method of Embodiment 1. Therefore, the content of each module of the control device for the offshore converter platform based on diode rectifiers will not be repeated in this embodiment. This control device for the offshore converter platform based on diode rectifiers acquires the operating conditions of the wind farm through a data acquisition module and a control strategy determination module, determines the control strategy for the offshore converter platform, and controls the operation of the offshore converter platform according to the control strategy. This allows the auxiliary converter to operate in either reactive power mode or active power mode.

[0073] In this embodiment, specific harmonic filtering control is used to filter or cancel harmonic currents generated by the diode rectifier through an auxiliary converter. The specific harmonic filtering control includes: Obtain the grid connection frequency of the offshore converter platform, the AC side current of the main converter, and the harmonic order of the output current of the diode rectifier; By integrating the meshing frequency and harmonic order, the harmonic meshing reference phase corresponding to the harmonic order is obtained; Based on the harmonic network reference phase and AC side current, Parker transformation and low-pass filtering are performed to obtain the dq axis current control reference value of the subharmonic corresponding to the harmonic network reference phase. Harmonic current inner loop control is used to process the dq axis current control reference value to obtain the harmonic compensation voltage corresponding to the subharmonic of the dq axis current control reference value; The harmonic compensation voltage is superimposed on the fundamental voltage modulation wave of the active power mode.

[0074] Example 3: Figure 6 This is a schematic diagram of the terminal device described in an embodiment of this application.

[0075] like Figure 6 As shown, this application provides a terminal device, including a processor and a memory; Memory is used to store program code and transfer the program code to the processor; The processor is used to execute the aforementioned control method for an offshore converter platform based on a diode rectifier, according to instructions in the program code.

[0076] It should be noted that the processor is used to execute the steps in the above-described embodiment of a control method for an offshore converter platform based on a diode rectifier, according to the instructions in the program code. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the above-described system / device embodiments.

[0077] For example, a computer program can be divided into one or more modules / units, one or more of which are stored in memory and executed by a processor to complete this application. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in a terminal device.

[0078] Terminal devices can be computing devices such as desktop computers, laptops, handheld computers, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will understand that this does not constitute a limitation on the terminal device, which may include more or fewer components than illustrated, or combinations of certain components, or different components. For example, a terminal device may also include input / output devices, network access devices, buses, etc.

[0079] The processor can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0080] Memory can be an internal storage unit of a terminal device, such as a hard drive or RAM. Memory can also be an external storage device, such as a plug-in hard drive, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used to temporarily store data that has been output or will be output.

[0081] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0082] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0083] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0084] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0085] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0086] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A control method for an offshore converter platform based on a diode rectifier, applied to an offshore converter platform, characterized in that, The offshore converter platform includes a wind farm and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to a diode rectifier via a tie switch and a tie line. The diode rectifier is connected to electrical equipment for providing active power. The control method of the offshore converter platform includes the following steps: Obtain the operating conditions of the wind farm; Based on the operating conditions, determine the control strategy for the offshore converter platform; control the operation of the offshore converter platform according to the control strategy; If the operating condition is a black start condition or a windless condition, the control strategy is to control the connection switch to close, control the auxiliary converter to operate in active power mode, and provide active power support to the wind farm through the active power output of the power equipment. If the operating condition is the rated power operating condition, then the control strategy is to control the interconnection switch to open and control the auxiliary converter to operate in reactive power mode. The active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid construction control on the AC side of the auxiliary converter; the reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, and constant output terminal voltage control and grid construction control on the AC side of the auxiliary converter.

2. The control method for an offshore converter platform based on a diode rectifier according to claim 1, characterized in that, Also includes: If the operating condition is switching from the black start condition or the windless condition to the rated power operating condition, the control strategy is as follows: First, control the AC side of the auxiliary converter to switch from active power control to constant output voltage control, and simultaneously set the voltage reference value of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line so that the current of the tie line drops to zero; second, control the tie switch to open, and switch the DC side of the auxiliary converter to open-loop given DC voltage control operation, then the auxiliary converter operates according to the reactive power mode.

3. The control method for an offshore converter platform based on a diode rectifier according to claim 1, characterized in that, Also includes: If the operating condition is switching from the rated power operating condition to the black start operating condition or the windless operating condition, the control strategy is to set the output voltage of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line, and then control the tie switch to close; then switch the operating mode of the auxiliary converter to the active power mode.

4. The control method for an offshore converter platform based on a diode rectifier according to any one of claims 1-3, characterized in that, The specific harmonic filtering control is used to filter or cancel the harmonic current generated by the diode rectifier through the auxiliary converter. The specific harmonic filtering control includes: The grid connection frequency of the offshore converter platform, the AC side current of the main converter, and the harmonic order of the output current of the diode rectifier are obtained. Integrating the meshing frequency and the harmonic order yields a harmonic meshing reference phase corresponding to the harmonic order. Based on the harmonic meshing reference phase and the AC side current, Parker transformation and low-pass filtering are performed to obtain the dq axis current control reference value of the subharmonic corresponding to the harmonic meshing reference phase. The dq-axis current control reference value is processed by using harmonic current inner loop control to obtain the harmonic compensation voltage corresponding to the subharmonic of the dq-axis current control reference value; The harmonic compensation voltage is superimposed on the fundamental voltage modulation wave of the active power mode.

5. The control method for an offshore converter platform based on a diode rectifier according to any one of claims 1-3, characterized in that, The grid connection control is used to dynamically adjust the reactive current injected into the grid connection point of the wind farm by the auxiliary converter. The content of the grid connection control includes: The grid connection frequency of the offshore converter platform, the target value of the q-axis voltage of the auxiliary converter, and the three-phase voltage and three-phase current of the auxiliary converter at the grid connection point of the wind farm are obtained. Integrating the network frequency yields the network reference phase; Parker transformation is performed based on the network reference phase, the three-phase voltages, and the three-phase currents to obtain the q-axis voltage. A PI controller is used to process the q-axis voltage and the target value of the q-axis voltage to obtain the dynamically adjusted q-axis injection current of the auxiliary converter; The q-axis injected current is used as the q-axis current reference value in the AC side control mode of the auxiliary converter.

6. A marine converter platform based on a diode rectifier, characterized in that, The system includes a control module, a wind farm, and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to a diode rectifier via a tie switch and a tie line. The diode rectifier is connected to power equipment for providing active power. The control module is used to control the operation of the offshore converter platform according to the control method of the offshore converter platform based on the diode rectifier as described in any one of claims 1-5.

7. The offshore converter platform based on a diode rectifier according to claim 6, characterized in that, The main converter is a 12-pulse or dual 12-pulse cascaded diode rectifier. The auxiliary converter includes a first reactive power compensation module and a second reactive power compensation module connected in parallel. Both the first reactive power compensation module and the second reactive power compensation module include several sub-modules connected in series.

8. A control device for an offshore converter platform based on a diode rectifier, applied to an offshore converter platform, characterized in that, The offshore converter platform includes a wind farm and a main converter and an auxiliary converter connected to the grid connection point of the wind farm. The auxiliary converter is connected to a diode rectifier via a tie switch and a tie line. The diode rectifier is connected to power equipment for providing active power. The control device of the offshore converter platform includes a data acquisition module and a control strategy determination module. The data acquisition module is used to acquire the operating conditions of the wind farm; The control strategy determination module is used to determine the control strategy of the offshore converter platform based on the operating conditions; and to control the operation of the offshore converter platform according to the control strategy. Wherein, if the operating condition is a black start condition or a windless condition, the control strategy is to control the connection switch to close, control the auxiliary converter to operate in active power mode, and provide active power support to the wind farm through the active power output of the power equipment; the active power mode includes specific harmonic filtering control, power balance control on the DC side of the auxiliary converter, and active power control and grid connection control on the AC side of the auxiliary converter; If the operating condition is the rated power operating condition, then the control strategy is to control the interconnection switch to open and control the auxiliary converter to operate in reactive power mode; the reactive power mode includes specific harmonic filtering control, open-loop given DC voltage control on the DC side of the auxiliary converter, constant output terminal voltage control on the AC side of the auxiliary converter, and grid construction control. If the operating condition is switching from the black start condition or the windless condition to the rated power operating condition, the control strategy is as follows: First, control the AC side operating mode of the auxiliary converter to switch from active power control to constant output voltage control, and at the same time set the voltage reference value of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line so that the current of the tie line drops to zero; second, control the tie switch to open, and switch the DC side operating mode of the auxiliary converter to open-loop given DC voltage control operation, then the auxiliary converter operates according to the reactive power mode. If the operating condition is switching from the rated power operating condition to the black start operating condition or the windless operating condition, the control strategy is to set the output voltage of the DC side of the auxiliary converter to be higher than the DC voltage of the tie line, and then control the tie switch to close; then switch the operating mode of the auxiliary converter to the active power mode.

9. The control device for an offshore converter platform based on a diode rectifier according to claim 8, characterized in that, The specific harmonic filtering control is used to filter or cancel the harmonic current generated by the diode rectifier through the auxiliary converter. The specific harmonic filtering control includes: The grid connection frequency of the offshore converter platform, the AC side current of the main converter, and the harmonic order of the output current of the diode rectifier are obtained. Integrating the meshing frequency and the harmonic order yields a harmonic meshing reference phase corresponding to the harmonic order. Based on the harmonic meshing reference phase and the AC side current, Parker transformation and low-pass filtering are performed to obtain the dq axis current control reference value of the subharmonic corresponding to the harmonic meshing reference phase. The dq-axis current control reference value is processed by using harmonic current inner loop control to obtain the harmonic compensation voltage corresponding to the subharmonic of the dq-axis current control reference value; The harmonic compensation voltage is superimposed on the fundamental voltage modulation wave of the active power mode.

10. A terminal device, characterized in that, Including the processor and memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the control method for a marine converter platform based on a diode rectifier as described in any one of claims 1-5, according to the instructions in the program code.

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