Capacity configuration method for offshore new energy station through diode rectification grid connection

Abstract

The invention discloses a capacity configuration method for an offshore new energy station through diode rectification grid connection, and belongs to the technical field of ocean renewable energy and new energy power generation, and the method comprises the steps: setting variables, combining meteorological data, building a fan output model and a photovoltaic output model, and obtaining a photovoltaic configuration capacity; establishing a steady-state model, obtaining a fan output current in combination with the photovoltaic configuration capacity, and verifying and adjusting the photovoltaic configuration capacity by taking fan current amplitude limiting as a static stability constraint condition to obtain a photovoltaic preliminary configuration capacity; and establishing an impedance model, obtaining a stability margin based on a Nyquist criterion and in combination with the photovoltaic preliminary configuration capacity, and verifying and adjusting the photovoltaic preliminary configuration capacity by taking a margin set value as a dynamic stability constraint condition to obtain the photovoltaic optimal configuration capacity. According to the invention, the capacity configuration of the wind-solar hybrid offshore new energy station can be realized, the utilization rate of the power transmission line can be obviously improved, and the static stability and the dynamic stability in a diode rectification grid-connected scene can be ensured.

Description

Technical Field

[0001] The present invention relates to the technical field of marine renewable energy and new energy power generation, and specifically relates to a method for configuring the capacity of an offshore new energy station connected to the grid through diode rectification. Background Art

[0002] To improve the economy of grid connection for deep - sea and far - sea wind farms, the lightweight high - voltage direct - current (HVDC) transmission technology based on diode rectifier units has attracted wide attention. Diode rectifier units have the advantages of small volume, light weight, low construction cost, and high operation reliability on offshore platforms. However, they have uncontrollable characteristics and cannot construct a stable offshore power grid through closed - loop control like modular multilevel converters. Therefore, offshore wind turbines need to operate in a grid - forming control mode.

[0003] On the one hand, currently, the grid - forming wind turbines applicable to diode rectifier units are still in the theoretical research stage, without actual engineering applications. Large - scale commercialization still has problems such as high investment costs, low operation reliability, and lack of engineering experience. On the other hand, limited by the wake effect and the non - continuous rated operating conditions, the actual power generation of wind farms is less than the theoretical installed capacity, resulting in underutilization of transmission lines. In addition, due to the shortage of land space, the construction of photovoltaic power stations has stagnated. The lower sea - level temperature can improve the efficiency of photovoltaic modules, and floating photovoltaic power generation offshore has received wide attention in recent years.

[0004] Therefore, building floating photovoltaics in an offshore wind farm can not only utilize the negative correlation of wind and light resources to smooth the output fluctuations of the power station and improve the utilization rate of transmission lines, but also reduce costs and increase efficiency by sharing power equipment and construction, operation, and maintenance resources. However, how to achieve the capacity configuration of grid - following photovoltaics is the core issue in the planning and design stage. There are two conflicting goals when configuring the photovoltaic capacity, namely, improving the utilization rate of cables and reducing power generation losses. At the same time, in the scenario of diode rectification and grid connection, too high a proportion of grid - following photovoltaics will cause problems such as over - limit of the fan current and small - signal stability.

[0005] Currently, existing invention patents have proposed methods for site selection and capacity determination of grid - forming energy storage or new energy stations, optimization methods for wind - solar hybrid power stations, and capacity planning methods for grid - following and grid - forming converters. However, they are all for scenarios of AC grid connection, conventional DC, and flexible DC transmission. The system operation characteristics are quite different from those of uncontrolled diode rectifier units, and the proposed methods cannot be directly transplanted and applied to the offshore new energy DC transmission system with diode rectification. The method for configuring the capacity of a hybrid offshore new energy station connected to the grid through diode rectification is still blank. Summary of the Invention

[0006] Therefore, the present invention provides a method for configuring the capacity of an offshore new energy station connected to the grid through diode rectification to solve the problems in the prior art.

[0007] To achieve the above object, the present invention provides the following technical solutions: A method for configuring the capacity of an offshore new energy power station with grid connection through diode rectification, comprising the following steps: Step S1: Set variables, combine meteorological data, establish a wind turbine output model and a photovoltaic output model, and take improving the transmission line capacity factor and reducing the power generation loss of the power station as the goal to obtain the photovoltaic configured capacity; Step S2: Based on the circuit dynamics of the grid-following photovoltaic, grid-forming wind turbine and diode rectifier unit, establish a steady-state model of the grid-following photovoltaic, grid-forming wind turbine and diode rectifier unit, and combine the photovoltaic configured capacity to obtain the output current of the wind turbine. Check and adjust the photovoltaic configured capacity with the wind turbine current limit as the static stability constraint condition to obtain the preliminary photovoltaic configured capacity; Step S3: Respectively establish impedance models of the grid-following photovoltaic, grid-forming wind turbine and diode rectifier unit, and based on the Nyquist criterion, combine the preliminary photovoltaic configured capacity to obtain the stability margin. Check and adjust the preliminary photovoltaic configured capacity with the margin set value as the dynamic stability constraint condition to obtain the optimal photovoltaic configured capacity.

[0008] Further, in step S1, setting variables, combining meteorological data, establishing wind turbine and photovoltaic output models, and taking improving the transmission line capacity factor and reducing the power generation loss of the power station as the goal to obtain the photovoltaic configured capacity specifically includes: Step S11: Set variables, including the rated capacity S of the wind turbine wt , the rated capacity S of the electrical equipment r , the rated capacity S of the photovoltaic pv and the maximum configurable photovoltaic capacity S pvmax ; Given typical annual meteorological data with hourly resolution, including the actual wind speed V w(h) , the actual light intensity R s(h) and the actual temperature T (h) ; where h represents the number of hours; Step S12: Based on the rated capacity S of the wind turbine wt and the actual wind speed V w(h) , establish a wind turbine output model; based on the rated capacity S of the photovoltaic pv , the actual light intensity R s(h) and the actual temperature T (h) , establish a photovoltaic output model; based on the wind turbine output model and the photovoltaic output model, obtain the annual power generation E of the wind turbine wt(h) and the annual power generation E of the photovoltaic pv(h) ; Step S13: Based on the annual power generation E of the wind turbine wt(h) , the annual power generation E of the photovoltaic pv(h) and the rated capacity S of the electrical equipment r, the power generation loss rate ce and the cable utilization rate cf are obtained, and the objective function is obtained by using the power generation loss rate ce and the cable utilization rate cf; Step S14: Based on the objective function, traverse the photovoltaic rated capacity S within the range of (0, S pvmax ) with a step size of ε pv and calculate the corresponding objective function value ob, and use the photovoltaic rated capacity S corresponding to the minimum objective function value ob min as the photovoltaic configuration capacity. pv As the photovoltaic configuration capacity.

[0009] Furthermore, the fan output power model is: ; Among them, P wt(h) represents the fan output power, S wt is the fan rated capacity, V w(h) is the actual wind speed, V in is the cut-in wind speed, V off is the cut-out wind speed, V r is the rated wind speed, and α, β, and γ are the characteristic parameter one, characteristic parameter two, and characteristic parameter three of the fan power curve respectively.

[0010] Furthermore, the photovoltaic output power model is: ; Among them, P pv(h) is the photovoltaic output power, S pv is the photovoltaic rated capacity, R s(h) is the actual light intensity, R STC is the light intensity under standard test conditions, η T is the environmental temperature coefficient, T (h) is the actual temperature, T STC is the standard ambient temperature, e pv is the power loss.

[0011] Furthermore, the objective function is: ; Among them, ob is the objective function value, ce is the power generation loss rate, cf is the cable utilization rate, a and b are the weighting coefficient one and weighting coefficient two respectively, and norm represents normalization processing.

[0012] Furthermore, in step S2, the photovoltaic configuration capacity is verified and adjusted with the fan current limit as the static stability constraint condition to obtain the preliminary photovoltaic configuration capacity, which specifically includes: Step S21: If the fan output current is less than or equal to the fan current limit threshold, the photovoltaic configuration capacity passes the static stability verification, and the photovoltaic configuration capacity is used as the preliminary photovoltaic configuration capacity; Step S22: If the output current of the wind turbine is greater than the current limit threshold of the wind turbine, the configured PV capacity fails the static stability check. Update the configured PV capacity in decreasing order by step size ε until the updated configured PV capacity passes the static stability check. The updated configured PV capacity is used as the preliminary configured PV capacity.

[0013] Further, in step S2, to obtain the output current of the wind turbine, specifically: establish a steady-state model of the grid-connected PV, grid-forming wind turbine, and diode rectifier unit in the dq coordinate system. Given the rated capacity of the wind turbine and the configured PV capacity, solve the steady-state model of the wind turbine and PV within the full power range to obtain the output current of the wind turbine.

[0014] Further, in step S3, check and adjust the preliminary configured PV capacity with the margin set value as the dynamic stability constraint condition to obtain the optimal configured PV capacity, specifically including: Step S31: If the stability margin is greater than or equal to the margin set value, the preliminary configured PV capacity passes the dynamic stability check, and the preliminary configured PV capacity is used as the optimal configured PV capacity; Step S32: If the stability margin is less than the margin set value, the preliminary configured PV capacity fails the dynamic stability check. Update the preliminary configured PV capacity in decreasing order by step size ε until the updated preliminary configured PV capacity passes the dynamic stability check. The updated preliminary configured PV capacity is used as the optimal configured PV capacity.

[0015] Further, in step S3, to obtain the stability margin, specifically: based on the impedance models of the grid-connected PV, grid-forming wind turbine, and diode rectifier unit, given the rated capacity of the wind turbine and the preliminary configured PV capacity, establish an impedance model under a given power scenario, and obtain the stability margin based on the Nyquist criterion.

[0016] The present invention has the following advantages: (1) The method proposed by the present invention can optimize the configuration of floating PV for an offshore wind farm with diode rectifier grid connection, thereby realizing the utilization of the internal sea area space of the wind farm area, improving the capacity factor of the transmission line and the utilization rate of electrical equipment such as converters, smoothing the intra-day and seasonal fluctuations of the station output, and sharing the construction and operation and maintenance costs to improve the economy.

[0017] (2) The method proposed by the present invention can comprehensively consider two indicators of cable utilization rate and power generation loss, avoid excessive PV configuration resulting in a large amount of economic loss due to the inability to send out electric energy, and achieve the coordinated balance and comprehensive optimization of cable utilization rate and power generation loss within a certain range.

[0018] (3) The method proposed in the present invention targets the operating characteristics of the system in the scenario of diode rectifier grid connection, and adds static and dynamic stability verification processes. It can avoid the triggering of the current limit of the wind turbine and the resulting system frequency instability when the proportion of grid-forming wind turbines is small and a large amount of reactive power needs to be balanced. It can also avoid the small disturbance stability problem caused by insufficient system damping when the proportion of grid-following PV is too high. Description of the Drawings

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary. For those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained based on the provided drawings.

[0020] The structures, ratios, sizes, etc. illustrated in this specification are only used to cooperate with the content disclosed in the specification for those familiar with this technology to understand and read, and are not used to limit the limited conditions under which the present invention can be implemented. Therefore, they do not have technical substance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope that can be covered by the technical content disclosed in the present invention.

[0021] Figure 1 It is a flowchart of a method for configuring the capacity of an offshore new energy station connected to the grid through a diode rectifier provided by the present invention; Figure 2 It is a meteorological data distribution diagram of light, temperature, and wind speed provided by an embodiment of the present invention; Figure 3 It is a monthly power generation statistical chart of an offshore wind farm, a PV power station, and a hybrid power station provided by the present invention; Figure 4 It is a curve graph showing the changes of two indicators, namely, cable utilization rate and power generation loss rate, with the change of PV configuration capacity provided by the present invention; Figure 5 It is a curve graph showing the change of the objective function ob with the change of PV configuration capacity provided by the present invention; Figure 6 It is a topological structure diagram of a hybrid offshore new energy station grid-connected system through a diode rectifier unit provided by the present invention; Figure 7 It is a distribution diagram of the output current of the wind turbine within the full power range under the PV configuration capacity of 800MW wind turbines and 850MW provided by the present invention; Figure 8 It is a schematic diagram of the Nyquist curve and system stability margin based on the impedance model under different PV configuration capacities provided by the present invention. Detailed Embodiments

[0022] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0023] A method for configuring the capacity of an offshore new energy power station connected to the grid through diode rectification, as Figure 1 shown, includes the following steps: Step S1: Set variables, combine meteorological data, establish a wind turbine output model and a photovoltaic output model, and aim to improve the transmission line capacity factor and reduce the power generation loss of the power station to obtain the configured photovoltaic capacity. Specifically: Step S11: Set variables, including the rated capacity S wt of the wind turbine, the rated capacity S r of the electrical equipment, the rated capacity S pv of the photovoltaic, and the maximum configurable photovoltaic capacity S pvmax ; Given the typical annual meteorological data with an hourly resolution, including the actual wind speed V w(h) , the actual light intensity R s(h) , and the actual temperature T (h) ; where h represents the number of hours.

[0024] In specific implementation, the rated capacity of the wind turbine is set to 800 MW, the rated capacity of the electrical equipment such as the converter station and the cable is set to 800 MW, the rated capacity of the photovoltaic is an optimization variable, and the maximum configurable photovoltaic capacity is 1500 MW. The meteorological data is obtained from the public database EAR5 of the European Centre for Medium-Range Weather Forecasts, with a time resolution of hours, and the geographical location is selected as a certain place in Jiangsu Province, China. Taking 2016 as an example for analysis, there are 366 days and 8784 hours in total, and the meteorological data is as Figure 2 shown.

[0025] Step S12: Based on the rated capacity S wt of the wind turbine and the actual wind speed V w(h) , establish a wind turbine output model; based on the rated capacity S pv of the photovoltaic, the actual light intensity R s(h) , and the actual temperature T (h) , establish a photovoltaic output model; based on the wind turbine output model P wt(h) =f(V w(h) ) and the photovoltaic output model P pv(h) =f(R s(h) ,T (h) ), obtain the annual power generation E of the wind turbinewt(h) and the annual power generation of the photovoltaic power generation E pv(h) ; Among them, the output model of the wind turbine is: ; Among them, P wt(h) represents the output power of the wind turbine, S wt is the rated capacity of the wind turbine, V w(h) is the actual wind speed, V in is the cut-in wind speed, V off is the cut-out wind speed, V r is the rated wind speed, and α, β, and γ are the characteristic parameter one, characteristic parameter two, and characteristic parameter three of the power curve of the wind turbine respectively. In this embodiment, a single 10 MW rated offshore wind turbine is taken as an example, and the cut-in / cut-out wind speeds are 3.5 m / s and 25 m / s respectively, and the rated wind speed is 13 m / s.

[0026] α, β, and γ are used to fit the non-linear interval between the cut-in wind speed and the rated wind speed, and the specific calculation method is as follows: ; The output model of the photovoltaic power generation is: ; Among them, P pv(h) is the output power of the photovoltaic power generation, S pv is the rated capacity of the photovoltaic power generation, R s(h) is the actual light intensity, R STC is the light intensity under standard test conditions, η T is the environmental temperature coefficient, T (h) is the actual temperature, T STC is the standard environmental temperature, e pv is the power loss caused by AC and other links.

[0027] In this embodiment, an N-type double-sided double-glass module applicable to an offshore photovoltaic power station is taken as an example. The maximum power of a single piece is 630 W, and the environmental temperature coefficient η T can reach 0.29% / °C. The light intensity R STC and the environmental temperature T STC under standard test conditions are 1000 W / m 2 and 25 °C respectively, and the power loss e pv is taken as 5%.

[0028] Based on the meteorological data and the output model, the annual power generation sequences of the wind turbine and the photovoltaic power generation can be calculated. In this embodiment, taking 800 MW of wind turbines and photovoltaic power generation as an example for each, after summarizing them by month, the following can be obtained as Figure 3The monthly power generation bar chart shown indicates that when the wind turbines and photovoltaic systems are deployed separately, there are significant seasonal fluctuations in power generation. For example, the power generation of the wind turbines shows an obvious decline from June to August, while on the contrary, the power generation of the photovoltaic systems increases significantly during this period. Due to the negative correlation between the power outputs of wind power and photovoltaic power on the time scale, the power generation fluctuations are smaller when they are operated jointly.

[0029] Step S13: Based on the annual power generation E of the wind turbines wt(h) , the annual power generation E of the photovoltaic systems pv(h) and the rated capacity S of the electrical equipment r , the power generation loss rate ce and the cable utilization rate cf are obtained, and the objective function is obtained by using the power generation loss rate ce and the cable utilization rate cf; The objective function is: ; where ob is the objective function value, ce is the power generation loss rate, cf is the cable utilization rate, a and b are the first weighting coefficient and the second weighting coefficient respectively, and norm represents the normalization process.

[0030] Among them, ce is the power generation loss rate, that is, the proportion of the power generation that cannot be sent out due to the cable capacity limitation in the total power generation. The specific calculation method is as follows: ; cf cf is the cable utilization rate, that is, the proportion of the full-load operation time of the cable in the total time. The specific calculation method is as follows: ; In this embodiment, taking the wind turbines configured with 800 MW and the maximum capacity of the photovoltaic systems configured with 1500 MW as an example, the changes of the two indexes of the power generation loss rate and the cable utilization rate with the configured capacity of the photovoltaic systems are calculated. As Figure 4 shown, it can be seen from the figure that with the increase of the configured capacity of the photovoltaic systems, both ce and cf show a non-linear increasing trend. When 1500 MW of floating photovoltaic is configured, the annual average cable utilization rate can be increased from 18% to 42%, but at this time, 11.6% of the power generation cannot be sent out, resulting in a certain degree of economic loss.

[0031] Step S14: Based on the objective function, traverse the rated capacity S of the photovoltaic systems pvmax in the range of (0, S pv ) with a step size of ε and calculate the corresponding objective function value ob. The rated capacity S of the photovoltaic systems min corresponding to the minimum value ob of the objective function pv is used as the configured capacity of the photovoltaic systems.

[0032] The calculation results in this embodiment are as Figure 5As shown in the figure, the minimum value of the objective function ob appears when the photovoltaic configuration capacity is 850 MW, accounting for 51.5% of the total installed capacity of the hybrid power station. At this time, only 3.2% of the electric energy cannot be sent out, and the cable utilization rate is 33.3%, which is about twice that before the photovoltaic configuration. A better balance can be achieved between the power loss rate and the cable utilization rate.

[0033] Step S2: Based on the circuit dynamics of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit, establish the steady-state models of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit. Combining the photovoltaic configuration capacity, obtain the output current of the wind turbine. Using the wind turbine current limit as the static stability constraint condition, verify and adjust the photovoltaic configuration capacity to obtain the preliminary photovoltaic configuration capacity, specifically as follows: Establish the steady-state models of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit in the dq coordinate system. Its mathematical expression is a multivariable nonlinear equation set, and the values of all variables can be solved by computer software. The output current of the wind turbine can be calculated from two of the variables. Given the rated capacity of the wind turbine and the photovoltaic configuration capacity, solve the steady-state models of the wind turbine and photovoltaic in the full power range to obtain the output current of the wind turbine.

[0034] The equivalent circuit of the system is as Figure 6 shown. Since the scale of the offshore new energy power station is very large, usually including hundreds of wind turbines and hundreds of floating photovoltaic units, for the convenience of modeling and calculation, it is equivalently reduced in order. The hybrid power station is equivalent to a grid-connected aggregated photovoltaic and a grid-forming aggregated wind turbine, and they are respectively modeled as a controlled current source and a controlled voltage source according to the control characteristics. The steady-state model of the grid-connected photovoltaic is as follows: ; In the formula, C fl and L fl are respectively the filter capacitor and the leakage reactance of the transformer of the grid-connected photovoltaic, P wl and Q wl represent the active power and reactive power output of the grid-connected photovoltaic, V fl and e are respectively the port voltage of the grid-connected photovoltaic converter and the grid connection point voltage, i wl and i ol are respectively the output current of the grid-connected photovoltaic converter and the grid connection current. The subscripts d and q respectively represent the d-axis and q-axis components.

[0035] The steady-state model of the grid-forming wind turbine is as follows: ; In the formula, C fm and L tm are the filter capacitor and the leakage reactance of the transformer of the grid-forming wind turbine respectively, P wm represents the active power output of the grid-forming wind turbine, V fm is the voltage at the converter port of the grid-forming wind turbine, i wm and i om are the output current of the converter and the grid-connected current of the grid-forming wind turbine respectively, ω and ω 0 represent the system angular frequency and its rated value respectively, k Q is the reactive power-frequency droop ratio coefficient.

[0036] The steady-state model of the diode rectifier unit is as follows: ; In the formula, i dr is the input current on the AC side of the diode rectifier unit, C Q represents the equivalent capacitor for reactive power compensation, I dcr and V dcr are the DC current and DC voltage of the diode rectifier unit respectively, µ is the commutation overlap angle, L dr represents the leakage reactance of the commutation transformer, and the turns ratio is 1: T dr , T dr represents the turns ratio between the high-voltage side and the low-voltage side of the commutation transformer in the diode rectifier station, V dc0 represents the DC-side voltage of the onshore inverter station, L dc and R dc represent the inductance of the smoothing reactor and the resistance of the DC cable, n is the number of diode rectifier platforms.

[0037] If the output current of the wind turbine is less than or equal to the wind turbine current limit threshold, the PV configuration capacity passes the static stability check, and the PV configuration capacity is used as the preliminary PV configuration capacity; If the output current of the fan is greater than the fan current limit threshold, the photovoltaic configuration capacity fails the static stability check. The photovoltaic configuration capacity is updated in decreasing steps of ε until the updated photovoltaic configuration capacity passes the static stability check. The updated photovoltaic configuration capacity is used as the preliminary photovoltaic configuration capacity.

[0038] In this embodiment, the photovoltaic configuration capacity obtained in step 1 is 850 MW. In this scenario, the output current distribution of a grid-connected fan with a rated capacity of 800 MW within the full power range is solved, and the result is as Figure 7 shown. It can be seen from the figure that under the condition of the fan operating at rated power and the photovoltaic output being 0.1 pu, due to the need to balance the surplus reactive power of the filter bank, the output current of the fan reaches the maximum value, but is less than the fan current limit of 1.2 pu, indicating that the hybrid system can operate stably within the full power range, that is, the photovoltaic configuration capacity of 850 MW can meet the static stability check conditions.

[0039] Step S3: Establish impedance models for the grid-following photovoltaic, grid-forming fan, and diode rectifier unit respectively. Based on the Nyquist criterion and combined with the preliminary photovoltaic configuration capacity, obtain the stability margin. Use the margin setting value as the dynamic stability constraint condition to check and adjust the preliminary photovoltaic configuration capacity to obtain the optimal photovoltaic configuration capacity.

[0040] In step S3, using the margin setting value as the dynamic stability constraint condition to check and adjust the preliminary photovoltaic configuration capacity to obtain the optimal photovoltaic configuration capacity specifically includes: Based on the impedance models of the grid-following photovoltaic, grid-forming fan, and diode rectifier unit, given the rated capacity of the fan and the preliminary photovoltaic configuration capacity, establish impedance models for the power scenarios of 0.1 pu and 1 pu output power respectively, and obtain the stability margin based on the Nyquist criterion.

[0041] The impedance models of the grid-following photovoltaic, grid-forming fan, and diode rectifier unit can all be uniformly expressed in the following form: ; The impedance modeling is carried out in the frequency domain, where s represents the Laplace operator, and Z a is a 2×2 transfer function matrix, Z dd , Z dq , Z qd , Z qq respectively represent the impedance transfer functions of different channels. When the superscript a is GFL, GFM, DRU, Z GFL , Z GFM and Z DRUrespectively represent the AC-side impedance models of the grid-following PV, grid-forming wind turbine, and diode rectifier unit. In the application of the Nyquist criterion and the quantification of stability margins, since the impedance method is usually used to analyze the interaction stability of two subsystems, and at this time there are three subsystems after system aggregation, namely the grid-following PV, grid-forming wind turbine, and diode rectifier unit, the parallel impedance Z S of the PV and the diode rectifier unit is taken as one subsystem, and the wind turbine impedance is taken as another subsystem. At this time, the wind turbine output current can be expressed as follows: ; In the formula, I L represents the output current of the grid-forming wind turbine, I GFL represents that the grid-following PV is modeled as a controlled current source, V GFM represents that the grid-forming wind turbine is modeled as a controlled voltage source. Therefore, on the premise of ensuring the stability of both the grid-forming wind turbine connected to an ideal current source and the grid-following PV connected to an ideal voltage source, the stability of the system is determined by the following return ratio matrix: ; where, / / represents impedance parallel connection, L represents the return ratio matrix, and it is judged whether the system is stable by whether the eigenvalue curve of L encloses the point (-1, j0) on the complex plane, where j represents the imaginary unit, and the stability margin of the system is calculated through the position of the intersection of the curve and the unit circle.

[0042] If the stability margin is greater than or equal to the margin setting value, the preliminary PV configuration capacity passes the dynamic stability verification, and the preliminary PV configuration capacity is used as the optimal PV configuration capacity; If the stability margin is less than the margin setting value, the preliminary PV configuration capacity fails the dynamic stability verification, and the preliminary PV configuration capacity is updated by decreasing in steps of ε until the updated preliminary PV configuration capacity passes the dynamic stability verification, and the updated preliminary PV configuration capacity is used as the optimal PV configuration capacity.

[0043] In this embodiment, when the PV configuration capacity increases from 100 MW to 1200 MW, the hybrid power station system can maintain stability. As Figure 8 shown, the stability margin decreases from 69° to 38°, and there is a significant negative correlation between the two. In this embodiment, the PV configuration capacity obtained through step 2 verification is 850 MW. At this time, the system stability margin is about 46°, which is greater than the margin setting value of 30°, indicating that the hybrid power station has good stability at this time, that is, the PV configuration capacity of 850 MW can meet the dynamic stability verification conditions.

[0044] In summary, in this embodiment, for the grid-connected system of offshore wind power through diode rectification, a capacity configuration method for a hybrid offshore new energy power station with grid connection through diode rectification is proposed, and the optimal photovoltaic configuration capacity considering the cable utilization rate and the power loss rate is obtained. First, in step 1, the objective function is constructed and the optimal value of the photovoltaic configuration capacity is calculated based on this. Then, in step 2, the steady-state model of the hybrid power station is established and the static stability check is carried out based on the current limit threshold. Finally, in step 3, the impedance model of the hybrid power station is established and the dynamic stability check is carried out based on the stability margin. By using the above method, the capacity configuration of the hybrid onshore and offshore new energy power station with grid connection through diode rectification can be obtained, and the cable utilization rate can be improved and the output fluctuation can be reduced on the basis of ensuring the system stability.

[0045] Although the present invention has been described in detail with general descriptions and specific embodiments above, modifications or improvements can be made to it on the basis of the present invention, which are obvious to those skilled in the art. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of the present invention claimed.

Claims

1. A method for capacity configuration of an offshore new energy power station connected to the grid through diode rectification, characterized in that, It includes the following steps: Step S1: Set variables, combine meteorological data, establish a wind turbine output model and a photovoltaic output model, and aim to improve the transmission line capacity factor and reduce the power generation loss of the power station to obtain the photovoltaic configuration capacity; Step S2: Based on the circuit dynamics of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit, establish a steady-state model of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit. Combine the photovoltaic configuration capacity to obtain the wind turbine output current. Check and adjust the photovoltaic configuration capacity with the wind turbine current limit as the static stability constraint condition to obtain the preliminary photovoltaic configuration capacity; Step S3: Establish impedance models of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit respectively. Based on the Nyquist criterion, combine the preliminary photovoltaic configuration capacity to obtain the stability margin. Check and adjust the preliminary photovoltaic configuration capacity with the margin set value as the dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity.

2. The method for configuring the capacity of an offshore new energy power station connected to the grid through diode rectification according to claim 1, wherein In the step S1, setting variables, combining meteorological data, establishing wind turbine and photovoltaic output models, and aiming to improve the transmission line capacity factor and reduce the power generation loss of the power station to obtain the photovoltaic configuration capacity specifically includes: Step S11: Set variables, including the rated capacity S of the fan wt , the rated capacity S of the electrical equipment r , the rated capacity S of the photovoltaic pv and the configurable maximum capacity S of the photovoltaic pvmax ; Given the typical annual meteorological data with hourly resolution, including the actual wind speed V w(h) , the actual light intensity R s(h) and the actual temperature T (h) ; where h represents the number of hours; Step S12: Based on the rated capacity S of the wind turbine wt and the actual wind speed V w(h) , establish a wind turbine output model; based on the rated capacity S of the photovoltaic system pv , the actual light intensity R s(h) and the actual temperature T (h) , establish a photovoltaic output model; based on the wind turbine output model and the photovoltaic output model, obtain the annual power generation E wt(h) of the wind turbine and the annual power generation E pv(h) of the photovoltaic system; Step S13: Based on the annual power generation E of the fan wt(h) , the annual power generation E of the photovoltaic pv(h) , and the rated capacity S of the electrical equipment r , obtain the power generation loss rate ce and the cable utilization rate cf, and use the power generation loss rate ce and the cable utilization rate cf to obtain the objective function; Step S14: Based on the objective function, traverse the photovoltaic rated capacity S within the range of (0, S pvmax ) with a step size of ε pv and calculate the corresponding objective function value ob, and take the photovoltaic rated capacity S corresponding to the minimum value ob of the objective function min as the photovoltaic configured capacity. pv ​ 3. The method for configuring the capacity of an offshore new energy power station connected to the grid through diode rectification according to claim 2, wherein The wind turbine output model is: ； Among them, P wt(h) represents the output power of the fan, S wt is the rated capacity of the fan, V w(h) is the actual wind speed, V in is the cut-in wind speed, V off is the cut-out wind speed, V r is the rated wind speed, and α, β, and γ are the characteristic parameter one, characteristic parameter two, and characteristic parameter three of the fan power curve, respectively.

4. The method for configuring the capacity of an offshore new energy power station connected to the grid through diode rectification according to claim 2, wherein The photovoltaic output model is: ； Among them, P pv(h) is the photovoltaic output power, S pv is the rated photovoltaic capacity, R s(h) is the actual light intensity, R STC is the light intensity under standard test conditions, η T is the environmental temperature coefficient, T (h) is the actual temperature, T STC is the standard ambient temperature, e pv is the power loss.

5. The method for capacity configuration of an offshore new energy power station connected to the grid through diode rectification according to claim 2, wherein The objective function is: ； Where, ob is the objective function value, ce is the power generation loss rate, cf is the cable utilization rate, a and b are the first weighting coefficient and the second weighting coefficient respectively, and norm represents normalization processing.

6. The capacity configuration method of an offshore new energy power station connected to the grid through diode rectification according to claim 1, wherein In the step S2, checking and adjusting the photovoltaic configuration capacity with the wind turbine current limit as the static stability constraint condition to obtain the preliminary photovoltaic configuration capacity specifically includes: Step S21: If the wind turbine output current is less than or equal to the wind turbine current limit threshold, the photovoltaic configuration capacity passes the static stability check, and the photovoltaic configuration capacity is used as the preliminary photovoltaic configuration capacity; Step S22: If the wind turbine output current is greater than the wind turbine current limit threshold, the photovoltaic configuration capacity fails the static stability check, and the photovoltaic configuration capacity is updated in a decreasing manner by the step size ε until the updated photovoltaic configuration capacity passes the static stability check, and the updated photovoltaic configuration capacity is used as the preliminary photovoltaic configuration capacity.

7. The method for configuring the capacity of an offshore new energy power station connected to the grid through diode rectification according to claim 1, characterized in that, In the step S2, obtaining the wind turbine output current specifically is: Establish a steady-state model of the grid-connected photovoltaic, grid-forming wind turbine, and diode rectifier unit in the dq coordinate system. Given the rated capacity of the wind turbine and the photovoltaic configuration capacity, solve the steady-state model of the wind turbine and the photovoltaic within the full power range to obtain the wind turbine output current.

8. The capacity configuration method of an offshore new energy power station connected to the grid through diode rectification according to claim 1, characterized in that, In the step S3, checking and adjusting the preliminary photovoltaic configuration capacity with the margin set value as the dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity specifically includes: Step S31: If the stability margin is greater than or equal to the margin set value, the preliminary photovoltaic configuration capacity passes the dynamic stability check, and the preliminary photovoltaic configuration capacity is used as the optimal photovoltaic configuration capacity; Step S32: If the stability margin is less than the margin set value, the preliminary photovoltaic configuration capacity fails the dynamic stability check, and the preliminary photovoltaic configuration capacity is updated in a decreasing manner by the step size ε until the updated preliminary photovoltaic configuration capacity passes the dynamic stability check, and the updated preliminary photovoltaic configuration capacity is used as the optimal photovoltaic configuration capacity.

9. The capacity configuration method for an offshore new energy power station connected to the grid through diode rectification according to claim 1, characterized in that, In the step S3, the stability margin is obtained specifically as follows: Based on the impedance models of the grid-connected photovoltaic, the grid-forming wind turbine, and the diode rectifier unit, an impedance model under a given power scenario is established with the rated capacity of the wind turbine and the preliminary configured capacity of the photovoltaic given, and the stability margin is obtained based on the Nyquist criterion.

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