Capacity optimization configuration method, device and equipment of DRU-MMC series hybrid converter and medium

Abstract

The invention relates to the technical field of electric power systems, in particular to a capacity optimization configuration method, device and equipment for a DRU-MMC series hybrid converter and a medium, and the method comprises the steps: building a topological structure of an offshore wind power delivery system, configuring a reactive power support function of a wind turbine generator, and adopting a constant power factor to control a dynamic compensation reactive power demand; configuring an auxiliary MMC to execute active filtering and dynamic compensation functions, absorbing harmonic current generated by the DRU, and compensating incompletely compensated reactive power of the wind turbine generator; the rated capacity of the auxiliary MMC is optimally calculated according to the residual reactive power demand after compensation of the wind turbine generator and the filtering demand of the auxiliary MMC; by utilizing the reactive power regulation capability of the wind turbine generator, the auxiliary MMC only needs to process a small amount of dynamic reactive power and reduce the capacity demand and the direct current voltage distribution proportion, so that on the premise of ensuring reactive power balance and electric energy quality, the equipment investment, the operation loss and the occupied area of an offshore platform are reduced, and the economical efficiency and the applicability of the system are improved.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a method, apparatus, equipment and medium for capacity optimization configuration of a DRU-MMC series hybrid converter. Background Technology

[0002] With the global energy transition and the development of offshore wind power towards deep-sea and large-capacity applications, high-voltage direct current (HVDC) transmission has become the preferred solution for long-distance offshore wind power transmission. Among them, the DRU-MMC series hybrid converter scheme significantly reduces the number of MMC sub-modules on the offshore platform by connecting a low-cost, high-reliability diode rectifier unit in series with a fully controlled MMC on the DC side, effectively reducing the equipment cost and footprint of the offshore converter station, and showing good application prospects. However, in this hybrid converter scheme, the reactive power balance and harmonic suppression requirements of the offshore AC system directly determine the capacity configuration of the auxiliary MMC, and the capacity of the MMC is a key factor affecting the economics of the system.

[0003] Currently, there are two main approaches to traditional capacity configuration methods, both of which have significant limitations. The first approach is to have the MMC handle all reactive power compensation and active filtering. This approach requires the auxiliary MMC to simultaneously compensate for the full reactive power required for DRU operation and actively suppress the characteristic harmonics generated by the DRU. While this approach avoids the use of passive filters, it requires the auxiliary MMC to have extremely high capacity to simultaneously meet both functional requirements. This results in not only huge initial equipment investment but also high operating losses, significantly reducing the overall system's economic efficiency. The second approach combines MMC reactive power compensation with passive filters. In this scheme, the auxiliary MMC is primarily responsible for reactive power compensation, while passive filters are configured to absorb harmonics. Although this reduces the capacity pressure on the MMC for active filtering, the passive filters themselves are large and bulky, greatly increasing the weight and footprint of the offshore platform. This contradicts the design goals of lightweight and compact offshore platforms. More problematic is that passive filters output fixed capacitive reactive power under different operating conditions, requiring the MMC to additionally compensate for the excess reactive power, especially under low wind speed and light load conditions. This leads to poor system operational flexibility, and the overall economic efficiency remains unsatisfactory.

[0004] The information disclosed in this background section is intended only to enhance the understanding of the general background of the invention and should not be construed as an admission or in any way implying that the information constitutes prior art known to those skilled in the art. Summary of the Invention

[0005] This invention provides a method, apparatus, equipment, and medium for optimizing the capacity configuration of a DRU-MMC series hybrid converter, thereby effectively solving the problems in the background art.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a capacity optimization configuration method for a DRU-MMC series hybrid converter, comprising the following steps:

[0007] Establish the topology of the DRU-MMC series hybrid converter offshore wind power transmission system, and analyze the reactive power demand and characteristic harmonic current of the DRU in the topology.

[0008] Based on the analysis of the reactive power demand, the reactive power support function of the wind turbine is configured, and constant power factor control is adopted to enable the reactive power output of the wind turbine to dynamically compensate the main reactive power demand of the DRU.

[0009] Based on the analysis of the characteristic harmonic current, the active filtering and dynamic compensation functions of the auxiliary MMC are configured, and the auxiliary MMC is controlled to perform active filtering to absorb the characteristic harmonic current generated by the DRU, and to compensate for the dynamic reactive power demand of the wind turbine that is not fully compensated.

[0010] Based on the residual reactive power demand of the wind turbine after compensation and the active filtering demand to be undertaken by the auxiliary MMC, the rated capacity of the auxiliary MMC is calculated and optimized.

[0011] Furthermore, the topology of the DRU-MMC series hybrid converter offshore wind power transmission system includes 12 pulse DRUs and an auxiliary half-bridge MMC connected in series on the DC side, and both of their AC sides are connected to the AC collection point of the offshore wind farm to form an offshore converter station.

[0012] Furthermore, by performing Fourier decomposition on the AC side current of the DRU, its characteristic harmonic set is determined to be 12k±1, where k is a positive integer; and the amplitude of each harmonic is estimated at no more than 1 / (12k±1) of the fundamental amplitude, as input parameters for subsequent filtering and capacity configuration.

[0013] Furthermore, the wind turbine is configured to use constant power factor control. By adjusting the reactive power output of its converter, the wind turbine provides reactive power that is compatible with the active power output of the turbine group, thereby dynamically tracking and compensating for the main reactive power demand of the DRU under different operating conditions.

[0014] Furthermore, the active filtering function of the auxiliary MMC is implemented through a harmonic extraction strategy based on synchronous rotating coordinate transformation, the harmonic extraction strategy including:

[0015] The current signal on the AC side of the DRU is transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system;

[0016] The DC component of the current signal is extracted, and high-frequency components are filtered out using a low-pass filter;

[0017] The difference between the obtained DC component and the reference value is input into the proportional-integral controller to generate a differential-mode voltage reference value for controlling the auxiliary MMC;

[0018] Based on the differential mode voltage reference value, the auxiliary MMC is controlled to actively absorb the characteristic harmonic current generated by the DRU.

[0019] Furthermore, the differential mode voltage reference value is superimposed on the fundamental voltage command after being transformed by the inverse synchronous rotating coordinate system, so as to control the auxiliary MMC to output a harmonic compensation current with the same amplitude and opposite phase as the DRU harmonic current.

[0020] Furthermore, the rated capacity of the auxiliary MMC is determined by the following formula:

[0021] ;

[0022] ;

[0023] In the formula, S MMC For the required capacity of MMC, P MMC Q represents the active power transmitted by the MMC. MMC P represents the total reactive power output of the MMC. w S represents the active power output of the wind farm. f δ represents the harmonic capacity occupied by the active filter, and δ represents the target power factor value for constant power factor control of the wind turbine.

[0024] Furthermore, it also includes:

[0025] Electromagnetic transient simulation was used to verify the capacity of the optimized auxiliary MMC, ensuring that it meets the requirements of reactive power balance and power quality when the system operating conditions change.

[0026] The present invention also includes a capacity optimization configuration device for a DRU-MMC series hybrid converter, using the method described above, comprising:

[0027] The system modeling and analysis unit is used to establish the topology of the DRU-MMC series hybrid converter offshore wind power transmission system and analyze the reactive power demand and characteristic harmonic current of the DRU in the topology.

[0028] The wind turbine control configuration unit is used to configure the reactive power support function of the wind turbine based on the analysis of the reactive power demand, and to use constant power factor control to enable the reactive power output of the wind turbine to dynamically compensate the main reactive power demand of the DRU.

[0029] The auxiliary MMC control configuration unit is used to configure the active filtering and dynamic compensation functions of the auxiliary MMC based on the analysis of the characteristic harmonic current, control the auxiliary MMC to perform active filtering to absorb the characteristic harmonic current generated by the DRU, and compensate for the dynamic reactive power demand of the wind turbine that is not fully compensated.

[0030] The capacity calculation and optimization unit is used to calculate and optimize the rated capacity of the auxiliary MMC based on the residual reactive power demand of the wind turbine after compensation and the active filtering demand to be undertaken by the auxiliary MMC.

[0031] The present invention also includes a computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the computer program, implements the method as described above.

[0032] The present invention also includes a storage medium having a computer program stored thereon, which, when executed by a processor, implements the method as described above.

[0033] The beneficial effects of this invention are as follows: By establishing a system topology and analyzing the characteristics of the DRU, the main reactive power support function of the wind turbine and the small-capacity active filtering and dynamic compensation function of the auxiliary MMC are configured in a coordinated manner. Based on this coordinated configuration, the rated capacity of the auxiliary MMC is accurately calculated. By making full use of the reactive power regulation capability of the wind turbine itself to undertake the main reactive power compensation, the auxiliary MMC can focus on the core task of active filtering and only needs to supplement a small amount of dynamic reactive power. This significantly reduces the rated capacity requirement of the auxiliary MMC and the DC voltage distribution ratio. Compared with traditional solutions, this invention can reduce the capacity of the auxiliary MMC while ensuring system reactive power balance and power quality. This effectively reduces equipment investment, operating losses and offshore platform footprint, and greatly improves the economy and engineering applicability of the DRU-MMC series hybrid converter offshore wind power transmission system. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention 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 recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 A flowchart illustrating the capacity optimization configuration method for a DRU-MMC series hybrid converter;

[0036] Figure 2Topology diagram of a DRU-MMC series hybrid converter offshore wind power DC transmission system;

[0037] Figure 3 Block diagram for auxiliary MMC harmonic suppression control strategy;

[0038] Figure 4 This is a simulated wind speed variation curve.

[0039] Figure 5 The active power waveforms of MMC and DRU when using strategy 1 are shown.

[0040] Figure 6 The waveforms of reactive power of MMC and DRU when using strategy 1 are shown.

[0041] Figure 7 The waveform of voltage harmonic components at the PCC point of the marine AC system when strategy 1 is adopted;

[0042] Figure 8 The waveform of harmonic components of AC current in an offshore wind farm when strategy 1 is adopted;

[0043] Figure 9 The active power waveforms of MMC and DRU when using strategy 2 are shown.

[0044] Figure 10 The waveforms of reactive power of MMC and DRU when using strategy 2 are shown.

[0045] Figure 11 The waveform of voltage harmonic components at the PCC point of the marine AC system when strategy 2 is adopted;

[0046] Figure 12 The waveform of harmonic components of AC current in offshore wind farms when using strategy 2 is shown.

[0047] Figure 13 The active power waveforms of MMC and DRU when using strategy 3 are shown.

[0048] Figure 14 The waveforms of reactive power of MMC and DRU when using strategy 3 are shown.

[0049] Figure 15 The waveform of voltage harmonic components at the PCC point of the marine AC system when strategy 3 is adopted;

[0050] Figure 16 The waveform of harmonic components of AC current in an offshore wind farm when strategy 3 is adopted;

[0051] Figure 17 A schematic diagram of the capacity optimization configuration device for a DRU-MMC series hybrid converter;

[0052] Figure 18 This is a schematic diagram of the structure of a computer device. Detailed Implementation

[0053] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0054] like Figures 1 to 16 As shown: A method for optimizing the capacity configuration of a DRU-MMC series hybrid converter includes the following steps:

[0055] S10: Establish the topology of the offshore wind power transmission system of DRU-MMC (Diode Rectifier Unit-Modular Multilevel Converter) series hybrid converter, and analyze the reactive power demand and characteristic harmonic current of DRU (Diode Rectifier Unit) in the topology.

[0056] S20: Based on the analysis of reactive power demand, configure the reactive power support function of the wind turbine, and adopt constant power factor control to enable the reactive power output of the wind turbine to dynamically compensate the main reactive power demand of the DRU.

[0057] S30: Based on the analysis of characteristic harmonic currents, the active filtering and dynamic compensation functions of the auxiliary MMC (modular multilevel converter) are configured. The auxiliary MMC is controlled to perform active filtering to absorb the characteristic harmonic currents generated by the DRU and to compensate for the dynamic reactive power demand of the wind turbine that is not fully compensated.

[0058] S40: Based on the residual reactive power demand after compensation of the wind turbine and the active filtering demand to be undertaken by the auxiliary MMC, the rated capacity of the auxiliary MMC is calculated and optimized. Through the coordinated configuration of the main reactive power support function of the wind turbine and the small-capacity active filtering and dynamic compensation function of the auxiliary MMC, the rated capacity of the auxiliary MMC can be significantly reduced compared with the configuration method of the auxiliary MMC performing all reactive power compensation and active filtering alone.

[0059] First, a topology model of the DRU-MMC system was established using power system simulation software, and detailed modeling of each component was performed to accurately analyze the reactive power demand and characteristic harmonic currents in the offshore wind power system. Based on this, constant power factor control technology was implemented to ensure that the wind turbines could dynamically adjust according to actual reactive power demand, providing real-time reactive power compensation. Furthermore, by rationally configuring the auxiliary MMC, effective absorption of harmonic currents generated in the wind power system was achieved, while simultaneously compensating for reactive power demands not fully covered by the wind turbines. In the later stages of the design, a comprehensive evaluation of the remaining reactive power demand after wind turbine compensation and the active filtering function of the auxiliary MMC was conducted. An optimization algorithm was used to accurately calculate the optimal rated capacity of the auxiliary MMC, thereby minimizing unnecessary equipment investment and energy consumption. This optimization process ensures efficient operation under different operating conditions, not only improving power quality but also avoiding potential equipment overload and over-design risks, providing strong support for the stable operation and economic efficiency of the offshore wind power system.

[0060] By precisely optimizing the reactive power compensation function of the wind turbine and the active filtering and dynamic compensation capabilities of the auxiliary MMC, a highly efficient and flexible design is achieved, significantly improving economy and operating efficiency. Compared with existing technologies, the solution of this invention has the following main advantages:

[0061] The capacity requirements of the auxiliary MMC have been optimized: by rationally allocating the functions of the wind turbine and the auxiliary MMC, it is ensured that the wind turbine can effectively and dynamically compensate for reactive power. At the same time, the auxiliary MMC is mainly responsible for filtering and compensating for characteristic harmonic currents, avoiding the problem of the auxiliary MMC having to bear excessive capacity load in the traditional solution. In this way, not only is the initial investment of the equipment reduced, but also the operating loss is reduced, significantly improving the overall economy.

[0062] Improving system flexibility and stability: This invention enables the system to flexibly cope with reactive power fluctuations and harmonic currents under different operating conditions by coordinating the control of the wind turbine and the auxiliary MMC. Especially under low wind speed and light load conditions, it can still operate stably and maintain a high power factor, thus improving the system's flexibility and operational stability.

[0063] Reduced equipment size and footprint: By optimizing the configuration and removing redundant passive filters, this invention significantly reduces the equipment size and footprint of offshore platforms, meeting the design requirements of lightweight and compact offshore wind power platforms. This not only improves reliability but also enhances the platform's adaptability.

[0064] In summary, this invention can significantly reduce system costs and improve operating efficiency while ensuring system power quality and stability, and meets the stringent requirements of offshore wind power transmission systems for equipment size and floor space, thereby significantly enhancing economic competitiveness.

[0065] As a preferred embodiment of the above, in step S10, the topology of the DRU-MMC series hybrid converter offshore wind power transmission system includes a 12-pulse DRU and an auxiliary half-bridge MMC connected in series on the DC side, and both of their AC sides are connected to the AC collection point of the offshore wind farm to form an offshore converter station. Specifically, the DC output terminal of the 12-pulse DRU and the DC port of the auxiliary half-bridge MMC are connected in series by a cable to form the DC transmission line of the hybrid converter. The AC ports of both are connected to the same AC bus via transformers. This bus is connected to the AC grid connection point of the wind turbine group through a submarine cable. During operation, the DRU undertakes the main active power transmission task, while the auxiliary MMC achieves dynamic balance of DC side voltage by adjusting its bridge arm voltage. At the same time, it participates in reactive power compensation and harmonic suppression through the AC side port. The setting of the AC collection point makes the AC system of the wind turbine group, DRU and auxiliary MMC form a unified interface, simplifying the electrical structure layout of the offshore platform.

[0066] like Figure 2 As shown in the figure, the DRU-MMC series hybrid converter offshore wind power transmission system topology involved in this invention consists of a 12-pulse DRU and an auxiliary MMC connected in series on the DC side to form a hybrid converter, which together form an offshore converter station. The AC sides of both the DRU and the MMC are connected to the PCC point of the offshore wind farm. The offshore converter station transmits power to the onshore inverter side MMC station through DC transmission lines, and then connects to the onshore AC power grid.

[0067] The DRU absorbs reactive power during operation. The amount of reactive power absorbed, QDRU, is related to parameters such as the active power transmission rate and the leakage reactance of the converter transformer. As the active power increases, the reactive power absorbed by the DRU also increases. This is illustrated in the following formula:

[0068] ;

[0069] In the formula, f is the fundamental frequency of the marine AC system, Ir is the amplitude of the DRU fundamental current, and k is a positive integer.

[0070] In step S10, the characteristic harmonic set of the DRU AC side current is determined by Fourier decomposition to be 12k±1, where k is a positive integer. The amplitude of each harmonic is estimated to be no more than 1 / (12k±1) of the fundamental amplitude, and used as input parameters for subsequent filtering and capacity configuration. For example, the amplitude of the 13th harmonic is no more than 1 / 13 of the fundamental amplitude, and the amplitude of the 25th harmonic is no more than 1 / 25. This estimation method considers both theoretical derivation results and provides a simplified calculation basis for engineering applications. The obtained parameters can be directly used to assist in the calculation of MMC filter capacity and the design of filter parameters. Compared with the existing technology, traditional methods usually only consider characteristic harmonics of fixed orders or use empirical values ​​to estimate harmonic amplitudes, which can easily lead to insufficient or excessive redundancy in filter capacity design. This method accurately identifies the actual harmonic components through Fourier decomposition and establishes amplitude estimation rules in combination with theoretical models, which not only ensures the harmonic suppression effect but also avoids the blindness of capacity configuration.

[0071] In this embodiment, in step S20, the wind turbine is configured to use constant power factor control. By adjusting the reactive power output of its converter, the wind turbine provides reactive power that is compatible with the active power output of the turbine group, thereby dynamically tracking and compensating for the main reactive power demand of the DRU under different operating conditions.

[0072] One of the core aspects of this capacity optimization configuration method lies in fully utilizing the reactive power regulation capabilities of offshore wind turbines. The controller of the offshore wind farm is configured to use CPFC (Constant Power Factor Control). For example, the power factor of the wind farm at the PCC (Point of Common Coupling) can be set to 0.95. Under this configuration, the wind turbine's converter dynamically adjusts its reactive power output according to its current active power output and the set power factor target. This means that the wind farm directly provides reactive power support proportional to its active power output. Through the CPFC of the wind turbine, the main reactive power demand of the 12-pulse DRU under different operating conditions can be dynamically tracked and compensated. This will significantly reduce the burden on the auxiliary MMC to provide reactive power compensation for the DRU. This configuration requires the wind turbine to have a certain reactive power regulation capability.

[0073] Specifically, during wind turbine operation, its active power output fluctuates with wind speed. The reactive power demand of the DRU (Dynamic Reactive Power Receiver) is directly related to the amplitude and phase of the current flowing through its converter valve. By using the overall active power output of the wind turbine group as an input parameter, combined with a preset power factor target value, such as 0.95 (lagging or leading), the required reactive power output can be calculated. The converter adjusts the modulation strategy of its internal inverter based on this calculation result, outputting a reactive current that matches the active power output, thereby compensating for the fundamental reactive power demand of the DRU during steady-state operation. When load changes cause fluctuations in the DRU's reactive power demand, the wind... The generator set corrects its reactive power output in real time through closed-loop control, ensuring that its output reactive power always follows the changes in DRU demand. In traditional solutions, the MMC needs to bear the full reactive power compensation of the DRU, resulting in excessive capacity configuration. However, this solution allows the wind turbine to actively provide reactive power related to its own active power output, so that the auxiliary MMC only needs to compensate for the remaining dynamic reactive power component, thereby significantly reducing its capacity requirement. In addition, existing technologies require additional fixed capacitive reactive power compensation devices when using passive filters, while this solution avoids the rigid reactive power coupling problem introduced by passive equipment through the dynamic adjustment capability of the wind turbine.

[0074] As a preferred embodiment of the above, in step S30, the active filtering function of the auxiliary MMC is implemented through a harmonic extraction strategy based on synchronous rotating coordinate transformation. The harmonic extraction strategy includes:

[0075] S31: Transform the current signal on the AC side of the DRU from the three-phase stationary coordinate system to the synchronous rotating coordinate system;

[0076] S32: Extract the DC component of the current signal and filter out high-frequency components using a low-pass filter;

[0077] S33: Input the difference between the obtained DC component and the reference value into the proportional-integral controller to generate a differential mode voltage reference value for controlling the auxiliary MMC;

[0078] S34: Based on the differential mode voltage reference value, control the auxiliary MMC to actively absorb the characteristic harmonic current generated by the DRU, and prevent harmonics from entering the offshore wind farm or onshore power grid.

[0079] Specifically, in the harmonic extraction process, the three-phase current signal is first converted into a DC component in a synchronous rotating coordinate system through coordinate transformation. At this time, the fundamental component exhibits a stable DC signal, while the characteristic harmonic components are converted into AC signals of specific frequencies. Then, a low-pass filter is used to filter the transformed signal, removing high-frequency noise interference and retaining the low-frequency components containing harmonic information. The filtered DC component is compared with a preset reference value, and the resulting error signal is input to a proportional-integral controller for dynamic adjustment, ultimately generating an accurate differential-mode voltage reference value. This reference value is inversely transformed and superimposed on the fundamental voltage command, driving the auxiliary MMC to output a compensation current with the same amplitude but opposite phase as the harmonic current, thus achieving active cancellation of the harmonic current. Traditional solutions rely on passive filters for harmonic absorption, but these suffer from large size and low compensation accuracy. This solution, through a combination of coordinate transformation and closed-loop control, can track the time-varying harmonic components generated by the DRU in real time, achieving accurate filtering without the need for bulky passive equipment. Compared to solutions that rely entirely on the MMC for filtering, this strategy reduces the capacity requirements for harmonic compensation through optimized control algorithms.

[0080] Another core aspect of this capacity optimization configuration method lies in focusing the main functions of the auxiliary MMC on small-capacity active filtering and dynamic compensation. The auxiliary MMC is configured to primarily undertake the active filtering function of the offshore AC system, while supplementing the small amount of dynamic reactive power demand not fully covered by the reactive power support function of the wind turbine. The auxiliary MMC adopts, for example... Figure 3 The diagram shows the block diagram of the auxiliary MMC harmonic suppression control strategy. By using a harmonic extraction method based on synchronous rotating coordinate transformation, the characteristic harmonic current generated on the AC side of the DRU is monitored. The harmonic controller generates a corresponding differential mode voltage reference value, so that the auxiliary MMC actively outputs a harmonic current that is equal in magnitude and opposite in phase to the DRU harmonic current. This achieves active absorption and cancellation of the DRU harmonic current, preventing harmonic pollution of the PCC point voltage and wind farm current. Typically, the capacity required for active filtering by the MMC is about 3% of the DRU transmission capacity.

[0081] Although the wind turbine provides the main reactive power support, the system may still have a small amount of uncompensated dynamic reactive power fluctuations. The auxiliary MMC is configured to use its remaining capacity to supplement the dynamic reactive power demand to maintain the stability of the offshore AC voltage. By focusing the function of the auxiliary MMC on small-capacity active filtering and auxiliary dynamic compensation, its required rated capacity and DC voltage distribution ratio will be significantly reduced.

[0082] In this embodiment, the differential-mode voltage reference value, after undergoing inverse synchronous rotating coordinate transformation, is superimposed on the fundamental voltage command to control the auxiliary MMC output to produce a harmonic compensation current with the same amplitude but opposite phase to the DRU harmonic current. Specifically, during harmonic extraction, the harmonic components of the DRU AC side current signal, after synchronous rotating coordinate transformation, are represented as DC components. After filtering out high-frequency noise through a low-pass filter, the difference between the DC component and the reference value is input to the proportional-integral controller to generate the differential-mode voltage reference value. This reference value, after undergoing inverse synchronous rotating coordinate transformation, is vector-superimposed on the fundamental voltage command in the time domain to form a comprehensive voltage command containing harmonic compensation components. The modulation signal is used to generate a compensation current with the opposite phase to the harmonic current of the DRU through pulse width modulation, thereby achieving active cancellation of the harmonic current. During this process, the amplitude and phase of the fundamental voltage command are tracked in real time by the grid voltage through a phase-locked loop to ensure that the fundamental power transmission is not affected by the harmonic compensation process. The harmonic components are decoupled and controlled in the rotating coordinate system through coordinate transformation, and the compensation command is directly superimposed on the fundamental modulation signal. The fundamental power transmission and harmonic dynamic compensation are realized simultaneously within a single control framework, which avoids the coordination problem of multiple controllers and eliminates the fixed capacitive reactive power problem caused by passive filters.

[0083] Step S40 calculates and optimizes the rated capacity of the auxiliary MMC based on the residual reactive power demand of the wind turbine after compensation and the active filtering demand to be undertaken by the auxiliary MMC.

[0084] After completing the functional configuration of the wind turbine and auxiliary MMC, the present invention proceeds to calculate and optimize the capacity of the auxiliary MMC. Strategy 1 and Strategy 2 represent two traditional MMC capacity configuration methods. Strategy 1 requires the auxiliary MMC to undertake part of the reactive power compensation and cooperate with the passive filter. Strategy 2 requires the auxiliary MMC to undertake all reactive power compensation and active filtering. Based on these functional requirements, the rated capacity required by the auxiliary MMC under these two strategies can be calculated.

[0085] Strategy 1:

[0086] In this strategy, the MMC only participates in reactive power compensation, while the filtering function is entirely undertaken by the passive filter. Since the reactive power demand of the DRU will change with the fluctuation of the active power of the wind farm, the MMC needs to be adjusted in real time to balance the excess reactive power generated by the passive filter, especially under low wind speed conditions. Therefore, the system needs to be configured with a passive filter that meets the requirements of harmonic control. At the same time, the capacity design of the MMC must meet two key conditions: first, to undertake the wind power transmission of the proportional coefficient k; and second, to cover the reactive power compensation demand in the entire operating range. Based on this, the required capacity of the MMC can be calculated and determined by the following formula.

[0087] ;

[0088] ;

[0089] ;

[0090] Among them, Q MMC Q represents the total reactive power output of the MMC. f P is the reactive power output by the passive filter. MMC P represents the active power transmitted by the MMC. w S represents the active power output of the wind farm. MMC The required capacity for MMC.

[0091] Strategy 2:

[0092] This strategy employs offshore MMC to compensate for all reactive power requirements of the DRU and performs active filtering, eliminating the need for passive filters. It also considers the harmonic capacity S occupied by the active filtering. f The required capacity of MMC is calculated using the following formula.

[0093] ;

[0094] ;

[0095] Capacity calculation of the present invention: According to the functional configuration proposed in the present invention, the wind turbine provides the main reactive power support and assists the MMC in performing small-capacity active filtering and dynamic compensation. Based on this, capacity configuration strategy 3 is formed.

[0096] Strategy 3:

[0097] To address the impact of wind farm active power output on the reactive power demand of the DRU (Dynamic Power Unit), optimized system operation is achieved through coordinated control of the wind farm and converter station. In offshore wind farms, constant power factor control is employed to ensure the wind farm provides reactive power support proportionally to its active power output, dynamically compensating for the DRU's reactive power demand. For offshore series converters, a small-capacity MMC (Multi-Mechanical Control Unit) is used for active filtering. Harmonic capacity S is also considered. f The required capacity of the MMC is calculated using the following formula. In step S40, the rated capacity of the auxiliary MMC is determined by the following formula:

[0098] ;

[0099] ;

[0100] In the formula, S MMC For the required capacity of MMC, P MMC Q represents the active power transmitted by the MMC. MMC P represents the total reactive power output of the MMC. wS represents the active power output of the wind farm. f δ represents the harmonic capacity occupied by the active filter, and δ represents the target power factor value for constant power factor control of the wind turbine.

[0101] By combining key parameters such as wind turbine output power, reactive power demand, and active power filter capacity, the optimal capacity of the MMC can be dynamically determined based on actual operating conditions. This avoids the problems of overcapacity or undercapacity caused by relying on experience-based selection or conservative redundancy configuration in traditional designs, thus achieving precise matching between capacity and operational requirements. Precise calculations can effectively reduce the excessive design margin of the auxiliary MMC, decrease the number of sub-modules and the rated capacity requirements of components, thereby reducing equipment procurement, installation, and operating costs. This allows the system to minimize equipment investment while meeting operational requirements, enhancing overall economic competitiveness. Precise modeling of reactive power distribution and power factor control can maintain stable voltage levels and power factors under different wind speeds and load conditions, reducing voltage flicker and energy loss caused by reactive power fluctuations, and enhancing dynamic response performance. The formula includes harmonic capacity S. f By incorporating this into the calculation, the auxiliary MMC can simultaneously meet the functional requirements of harmonic filtering and reactive power compensation during capacity planning, realizing an integrated design of capacity configuration and function allocation, and improving the overall power quality and operating efficiency.

[0102] As a preferred embodiment of the above, after step S40, the method further includes:

[0103] S50: Through electromagnetic transient simulation, the capacity of the optimized auxiliary MMC is verified to ensure that it meets the requirements of reactive power balance and power quality when the system operating conditions change.

[0104] To verify the correctness and effectiveness of the above capacity optimization configuration method, this invention built a model of the DRU-MMC series hybrid converter offshore wind power transmission system on the PSCAD / EMTDC electromagnetic transient simulation platform, and compared the system operation characteristics under three capacity configuration schemes. The main parameters are shown in Table 1.

[0105] Table 1 Main parameters of the simulation system

[0106]

[0107] like Figure 4 The figure shown is a simulated wind speed variation curve. The simulation was set up with various wind speed variation conditions to simulate the actual operation of an offshore wind farm.

[0108] like Figure 5-8 As shown, the configuration and operation of Strategy 1 (MMC reactive power compensation + passive filter harmonic suppression) are as follows:

[0109] The auxiliary MMC has a rated capacity of 250MVA and a DC voltage of 96kV, and is equipped with a 180Mvar passive dual-tuned filter. Figure 5 The waveforms of active power of MMC and DRU when using strategy 1 are shown. Figure 6 The following are the reactive power waveforms of MMC and DRU when using strategy 1. Figure 7 The waveform of voltage harmonic components at the PCC point of the marine AC system when strategy 1 is adopted. Figure 8 The waveform diagram of the harmonic components of the AC current of the offshore wind farm under strategy 1 shows that the system operates stably under wind speed changes, but the passive filter is large in size, and the MMC still needs to undertake a certain reactive power compensation task.

[0110] like Figure 9-12 As shown, the configuration and operation of Strategy 2 (MMC reactive power compensation + active filtering) are as follows:

[0111] The auxiliary MMC has a rated capacity of 430MVA and a DC voltage of 160kV. The MMC must independently perform all reactive power compensation and active filtering functions. Figure 9 The waveforms of active power of MMC and DRU when using strategy 2 are shown. Figure 10 The following are the reactive power waveforms of MMC and DRU when using strategy 2. Figure 11 The waveform of voltage harmonic components at the PCC point of the marine AC system when strategy 2 is adopted. Figure 12 The waveform diagram of the harmonic components of the AC current of the offshore wind farm when using strategy 2 shows that the system remains stable under wind speed changes, but the MMC capacity requirement and DC voltage level are significantly higher than other schemes, resulting in high costs.

[0112] like Figure 13-16 As shown, the configuration and operation of Strategy 3 (the capacity optimization configuration method of this invention) are as follows:

[0113] This refers to the coordinated configuration of the wind turbine main body reactive power support + small-capacity MMC active filter and dynamic compensation. The auxiliary MMC has a rated capacity of 150MVA and a DC voltage of 64kV. The wind turbine adopts constant power factor control of 0.95. Figure 13 The waveforms of active power of MMC and DRU when using strategy 3 are shown. Figure 14 The following are the reactive power waveforms of MMC and DRU when using strategy 3. Figure 15 The waveform of voltage harmonic components at the PCC point of the marine AC system when using strategy 3. Figure 16The waveform of harmonic components of AC current in offshore wind farms when using strategy 3 is shown. Under wind speed fluctuations, the active / reactive power of the LCC, the harmonic content of the voltage at the PCC point, and the harmonic content of the AC current in the wind farm under this method configuration are all kept at low levels, and the system operates stably. At the same time, the capacity requirement of the auxiliary MMC (150MVA) is significantly lower than that of strategy 1 (250MVA) and strategy 2 (430MVA).

[0114] Simulation results clearly demonstrate that the capacity optimization configuration method proposed in this invention, combined with wind turbine generators providing main reactive power support and auxiliary MMCs for small-capacity active filtering and dynamic compensation, can significantly reduce the capacity requirements of the auxiliary MMCs, the DC voltage distribution ratio, and the equipment footprint. This, in turn, greatly improves the economic efficiency of the DRU-MMC series hybrid converter offshore wind power transmission system while meeting system performance requirements. This provides a superior solution for lightweight offshore wind power transmission.

[0115] The present invention also includes a capacity optimization configuration device for a DRU-MMC series hybrid converter, using the method described above, such as... Figure 17 As shown, it includes:

[0116] The system modeling and analysis unit is used to establish the topology of the DRU-MMC series hybrid converter offshore wind power transmission system and analyze the reactive power demand and characteristic harmonic current of the DRU in the topology.

[0117] The wind turbine control configuration unit is used to configure the reactive power support function of the wind turbine based on the analysis of reactive power demand. It adopts constant power factor control to enable the reactive power output of the wind turbine to dynamically compensate the main reactive power demand of the DRU.

[0118] The auxiliary MMC control configuration unit is used to configure the active filtering and dynamic compensation functions of the auxiliary MMC based on the analysis of characteristic harmonic currents, control the auxiliary MMC to perform active filtering to absorb the characteristic harmonic currents generated by the DRU, and compensate for the dynamic reactive power demand of the wind turbine that is not fully compensated.

[0119] The capacity calculation and optimization unit is used to calculate and optimize the rated capacity of the auxiliary MMC based on the residual reactive power demand after compensation of the wind turbine and the active filtering demand to be undertaken by the auxiliary MMC.

[0120] Please see Figure 18 The diagram shows a structural schematic of a computer device provided in an embodiment of this application. An embodiment of this application provides a computer device 400, including a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it performs the method described above.

[0121] This application embodiment also provides a storage medium 430, on which a computer program is stored, and the computer program is executed by a processor 410 to perform the above method.

[0122] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0123] In the description of this invention, 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. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. "A plurality of" means two or more, unless otherwise explicitly specified.

[0124] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "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 this invention according to the specific circumstances.

[0125] 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. Moreover, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Furthermore, 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.

[0126] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing a particular logical function or process, and the scope of the preferred embodiments of the invention includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of the invention pertain.

[0127] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a ordered list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Alternatively, the computer-readable medium may be paper or other suitable media on which the program can be printed, since the program can be obtained electronically, for example, by optically scanning the paper or other medium, followed by editing, interpreting, or otherwise processing as necessary, and then stored in a computer memory.

[0128] It should be understood that various parts of the present invention can be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0129] Those skilled in the art will understand that all or part of the steps of the methods in the above embodiments can be implemented by a program instructing related hardware. The program can be stored in a computer-readable storage medium, and when executed, the program includes one or a combination of the steps of the method embodiments.

[0130] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present invention have been shown and described above, it is to be 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 method for optimizing the capacity configuration of a DRU-MMC series hybrid converter, characterized in that, Includes the following steps: Establish the topology of the DRU-MMC series hybrid converter offshore wind power transmission system, and analyze the reactive power demand and characteristic harmonic current of the DRU in the topology. Based on the analysis of the reactive power demand, the reactive power support function of the wind turbine is configured, and constant power factor control is adopted to enable the reactive power output of the wind turbine to dynamically compensate the main reactive power demand of the DRU. Based on the analysis of the characteristic harmonic current, the active filtering and dynamic compensation functions of the auxiliary MMC are configured, and the auxiliary MMC is controlled to perform active filtering to absorb the characteristic harmonic current generated by the DRU, and to compensate for the dynamic reactive power demand of the wind turbine that is not fully compensated. Based on the residual reactive power demand of the wind turbine after compensation and the active filtering demand to be undertaken by the auxiliary MMC, the rated capacity of the auxiliary MMC is calculated and optimized.

2. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 1, characterized in that, The topology of the DRU-MMC series hybrid converter offshore wind power transmission system includes 12 pulse DRUs and an auxiliary half-bridge MMC connected in series on the DC side, and both of them are connected to the AC collection point of the offshore wind farm on the AC side to form an offshore converter station.

3. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 1, characterized in that, By performing Fourier decomposition on the AC side current of the DRU, its characteristic harmonic set is determined to be 12k±1, where k is a positive integer; and the amplitude of each harmonic is estimated at no more than 1 / (12k±1) of the fundamental amplitude, as input parameters for subsequent filtering and capacity configuration.

4. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 1, characterized in that, The wind turbine is configured to use constant power factor control. By adjusting the reactive power output of its converter, the wind turbine provides reactive power that is compatible with the active power output of the turbine group, thereby dynamically tracking and compensating for the main reactive power demand of the DRU under different operating conditions.

5. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 1, characterized in that, The active filtering function of the auxiliary MMC is implemented through a harmonic extraction strategy based on synchronous rotating coordinate transformation, which includes: The current signal on the AC side of the DRU is transformed from the three-phase stationary coordinate system to the synchronous rotating coordinate system; The DC component of the current signal is extracted, and high-frequency components are filtered out using a low-pass filter; The difference between the obtained DC component and the reference value is input into the proportional-integral controller to generate a differential-mode voltage reference value for controlling the auxiliary MMC; Based on the differential mode voltage reference value, the auxiliary MMC is controlled to actively absorb the characteristic harmonic current generated by the DRU.

6. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 5, characterized in that, The differential mode voltage reference value is superimposed on the fundamental voltage command after being transformed by the inverse synchronous rotating coordinate system, so as to control the auxiliary MMC to output a harmonic compensation current with the same amplitude and opposite phase as the DRU harmonic current.

7. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 1, characterized in that, The rated capacity of the auxiliary MMC is determined by the following formula: ； ； In the formula, S MMC For the required capacity of MMC, P MMC Q represents the active power transmitted by the MMC. MMC P represents the total reactive power output of the MMC. w S represents the active power output of the wind farm. f δ represents the harmonic capacity occupied by the active filter, and δ represents the target power factor value for constant power factor control of the wind turbine.

8. The capacity optimization configuration method for a DRU-MMC series hybrid converter according to claim 1, characterized in that, Also includes: The capacity of the optimized auxiliary MMC was verified through electromagnetic transient simulation to ensure that it meets the requirements of reactive power balance and power quality when the system operating conditions change.

9. A capacity optimization configuration device for a DRU-MMC series hybrid converter, characterized in that, Using the method as described in any one of claims 1 to 8, comprising: The system modeling and analysis unit is used to establish the topology of the DRU-MMC series hybrid converter offshore wind power transmission system and analyze the reactive power demand and characteristic harmonic current of the DRU in the topology. The wind turbine control configuration unit is used to configure the reactive power support function of the wind turbine based on the analysis of the reactive power demand, and to use constant power factor control to enable the reactive power output of the wind turbine to dynamically compensate the main reactive power demand of the DRU. The auxiliary MMC control configuration unit is used to configure the active filtering and dynamic compensation functions of the auxiliary MMC based on the analysis of the characteristic harmonic current, control the auxiliary MMC to perform active filtering to absorb the characteristic harmonic current generated by the DRU, and compensate for the dynamic reactive power demand of the wind turbine that is not fully compensated. The capacity calculation and optimization unit is used to calculate and optimize the rated capacity of the auxiliary MMC based on the residual reactive power demand of the wind turbine after compensation and the active filtering demand to be undertaken by the auxiliary MMC.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the method as described in any one of claims 1-8.

11. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-8.

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