A method for configuring the capacity of offshore new energy stations connected to the grid via diode rectification

Abstract

The present invention discloses a method for configuring the capacity of an offshore new energy station connected to the grid via diode rectification, which belongs to the field of marine renewable energy and new energy power generation technology. The method comprises setting variables, combining meteorological data, establishing a wind turbine output model and a photovoltaic output model, and obtaining photovoltaic configuration capacity; establishing a steady-state model, combining the photovoltaic configuration capacity, obtaining the wind turbine output current, verifying and adjusting the photovoltaic configuration capacity with the wind turbine current limit as a static stability constraint condition, and obtaining the photovoltaic preliminary configuration capacity; establishing an impedance model, based on the Nyquist criterion, combining the photovoltaic preliminary configuration capacity, obtaining a stability margin, verifying and adjusting the photovoltaic preliminary configuration capacity with the margin setting value as a dynamic stability constraint condition, and obtaining the photovoltaic optimal configuration capacity. The present invention can realize the capacity configuration of a wind-solar hybrid offshore new energy station, significantly improve the utilization rate of transmission lines, and ensure static stability and dynamic stability in the diode rectification and grid connection scenario.

Description

Technical Field

[0001] The present invention relates to the field of marine renewable energy and new energy power generation technology, and in particular 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 economics of connecting deep-sea wind farms to the grid, lightweight HVDC transmission technology based on diode rectifiers has attracted widespread attention. Diode rectifiers offer advantages such as small size and weight on offshore platforms, low construction costs, and high operational reliability. However, they are uncontrollable and cannot form a stable offshore grid through closed-loop control like modular multilevel converters. Therefore, offshore wind turbines must operate in a grid-building control mode.

[0003] On the one hand, grid-type wind turbines suitable for diode rectifier units are still in the theoretical research stage and have not yet been put into practical engineering applications. Large-scale commercialization still faces problems such as high investment costs, low operational reliability, and lack of engineering experience. On the other hand, due to the wake effect and non-continuous rated operating characteristics, 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 limited land space, the construction of photovoltaic stations has been stalled. Lower sea level temperatures can improve the efficiency of photovoltaic modules, and offshore floating photovoltaics have garnered widespread attention in recent years.

[0004] Therefore, installing floating photovoltaic systems in offshore wind farms not only leverages the negative correlation between wind and solar resources to smooth site output fluctuations and improve transmission line utilization, but also reduces costs and increases efficiency by sharing power equipment and construction and maintenance resources. However, allocating the capacity of grid-connected photovoltaic systems is a key issue in the planning and design phase. Allocating photovoltaic capacity presents two conflicting objectives: increasing cable utilization and minimizing power generation losses. Furthermore, in diode rectifier grid-connected scenarios, an excessively high proportion of grid-connected photovoltaic systems can lead to turbine current limit violations and small-disturbance stability issues.

[0005] At present, invention patents have proposed methods for site selection and sizing of grid-type energy storage or new energy stations, methods for optimizing the configuration of wind-solar complementary power stations, and methods for capacity planning of grid-type converters. However, they are all aimed at scenarios of AC grid connection, conventional DC, and flexible DC transmission. The system operating characteristics are quite different from those of uncontrolled diode rectifier units. The proposed methods cannot be directly transplanted and applied to offshore new energy DC transmission systems via diode rectification. There is still a lack of capacity configuration methods for hybrid offshore new energy stations connected to the grid via diode rectification. Summary of the Invention

[0006] To this end, 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] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A method for configuring the capacity of an offshore renewable energy station connected to the grid via diode rectification comprises the following steps:

[0009] Step S1: Set variables and, in combination with meteorological data, establish wind turbine output models and photovoltaic output models, with the goal of improving the transmission line capacity factor and reducing the power generation loss of the site, and obtain the photovoltaic configuration capacity;

[0010] Step S2: Based on the circuit dynamics of the grid-connected photovoltaic system, the grid-connected wind turbine, and the diode rectifier unit, a steady-state model of the grid-connected photovoltaic system, the grid-connected wind turbine, and the diode rectifier unit is established. Combined with the photovoltaic configuration capacity, the wind turbine output current is obtained. The photovoltaic configuration capacity is verified and adjusted using the wind turbine current limit as a static stability constraint to obtain the preliminary photovoltaic configuration capacity.

[0011] Step S3: Impedance models of grid-following photovoltaics, grid-connected wind turbines, and diode rectifier units are established respectively. Based on the Nyquist criterion and combined with the initial photovoltaic configuration capacity, the stability margin is obtained. The initial photovoltaic configuration capacity is verified and adjusted using the margin setting value as a dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity.

[0012] Furthermore, in step S1, variables are set and meteorological data are combined to establish wind turbine and photovoltaic output models, with the goal of improving the transmission line capacity factor and reducing the power generation loss of the station, to obtain the photovoltaic configuration capacity, specifically including:

[0013] Step S11: Set variables, including the rated capacity of the fan S wt , Rated capacity of electrical equipment S r , PV rated capacity S pv and configurable maximum photovoltaic capacity S pvmax Typical annual meteorological data with hourly resolution, including actual wind speed V w(h) , actual light intensity R s(h) and the actual temperature T (h) ; where h represents the number of hours;

[0014] Step S12: Based on the rated capacity S of the fan wt and actual wind speed V w(h) , establish a wind turbine output model; based on the photovoltaic rated capacity S pv , actual light intensity R s(h) and the actual temperature T (h) , establish the photovoltaic output model; based on the wind turbine output model and the photovoltaic output model, obtain the wind turbine annual power generation E wt(h) and annual photovoltaic power generation E pv(h) ;

[0015] Step S13: Based on the annual power generation E of the wind turbine wt(h) , annual photovoltaic power generation E pv(h) and rated capacity S of electrical equipment r , we get the power generation loss rate ce and cable utilization rate cf, and use the power generation loss rate ce and cable utilization rate cf to get the objective function;

[0016] Step S14: Based on the objective function, in (0, S pvmax ) traverse the photovoltaic rated capacity S in step size ε within the range pv And calculate the corresponding objective function value ob, and set the minimum value of the objective function ob min The corresponding photovoltaic rated capacity S pv As photovoltaic configuration capacity.

[0017] Furthermore, the wind turbine output model is:

[0018] ;

[0019] Among them, P wt(h) Indicates the fan output power, 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, α, β, and γ are the characteristic parameters 1, 2, and 3 of the wind turbine power curve, respectively.

[0020] Furthermore, the photovoltaic output model is:

[0021] ;

[0022] 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 ambient temperature coefficient, T (h) is the actual temperature, T STC is the standard ambient temperature, e pv For power loss.

[0023] Furthermore, the objective function is:

[0024] ;

[0025] Where ob is the objective function value, ce is the power generation loss rate, cf is the cable utilization rate, a and b are weighted coefficients 1 and 2 respectively, and norm represents normalization processing.

[0026] Furthermore, in step S2, the photovoltaic configuration capacity is verified and adjusted using the wind turbine current limit as a static stability constraint condition to obtain the preliminary photovoltaic configuration capacity, which specifically includes:

[0027] 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;

[0028] 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 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.

[0029] Furthermore, in step S2, the wind turbine output current is obtained, specifically by establishing a steady-state model of the grid-following photovoltaic, grid-forming wind turbine and diode rectifier unit in the dq coordinate system, and solving the steady-state model of the wind turbine and photovoltaic within the full power range under the given wind turbine rated capacity and photovoltaic configuration capacity to obtain the wind turbine output current.

[0030] Furthermore, in step S3, the initial photovoltaic configuration capacity is verified and adjusted using the margin setting value as a dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity, specifically including:

[0031] Step S31: If the stability margin is greater than or equal to the margin setting value, the photovoltaic preliminary configuration capacity passes the dynamic stability check, and the photovoltaic preliminary configuration capacity is used as the photovoltaic optimal configuration capacity;

[0032] Step S32: If the stability margin is less than the margin setting value, the photovoltaic preliminary configuration capacity fails the dynamic stability check, and the photovoltaic preliminary configuration capacity is updated in decreasing step size ε until the updated photovoltaic preliminary configuration capacity passes the dynamic stability check. The updated photovoltaic preliminary configuration capacity is used as the photovoltaic optimal configuration capacity.

[0033] Furthermore, in step S3, a stability margin is obtained, specifically: based on the impedance models of grid-following photovoltaics, grid-connected wind turbines and diode rectifier units, an impedance model is established under a given power scenario with a given wind turbine rated capacity and photovoltaic preliminary configuration capacity, and the stability margin is obtained based on the Nyquist criterion.

[0034] The present invention has the following advantages:

[0035] (1) The method proposed in the present invention can optimize the configuration of floating photovoltaic power generation for offshore wind farms connected to the grid with diode rectification, thereby realizing the utilization of the sea space within the wind farm area, improving the capacity factor of the transmission line and the utilization rate of electrical equipment such as converters, smoothing the daily and seasonal fluctuations of the station output, and sharing the construction and operation and maintenance costs to improve economic efficiency.

[0036] (2) The method proposed in the present invention can comprehensively consider the two indicators of cable utilization and power generation loss, avoid excessive configuration of photovoltaics that leads to the inability to transmit electricity and bring about large economic losses, and achieve coordinated balance and comprehensive optimization of cable utilization and power generation loss within a certain range.

[0037] (3) The method proposed in the present invention is based on the operating characteristics of the system in the diode rectifier grid-connected scenario, and adds static and dynamic stability verification processes. This can avoid the triggering of wind turbine current limiting and the resulting system frequency instability when the proportion of grid-connected 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-connected photovoltaics is too high. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0039] The structures, proportions, sizes, etc. illustrated in this specification are intended only to complement the contents disclosed herein and to facilitate understanding and reading by persons familiar with the art. They are not intended to limit the conditions under which the present invention may be implemented and therefore have no substantive technical significance. Any structural modifications, changes in proportions, or adjustments in sizes, without affecting the efficacy and objectives of the present invention, shall still fall within the scope of the technical contents disclosed herein.

[0040] Figure 1 A flow chart of a method for configuring the capacity of an offshore renewable energy station connected to the grid via diode rectification provided by the present invention;

[0041] Figure 2 A distribution diagram of meteorological data of light, temperature, and wind speed provided by an embodiment of the present invention;

[0042] Figure 3 Monthly power generation statistics for offshore wind farms, photovoltaic farms, and hybrid farms provided by the present invention;

[0043] Figure 4A graph showing the cable utilization rate and power generation loss rate as a function of photovoltaic configuration capacity, provided by the present invention;

[0044] Figure 5 A graph showing the objective function ob provided by the present invention changing with the photovoltaic configuration capacity;

[0045] Figure 6 This is a topological diagram of the grid-connected system of the hybrid offshore new energy station provided by the present invention via a diode rectifier unit;

[0046] Figure 7 The present invention provides a distribution diagram of wind turbine output current within the full power range under the configuration capacity of 800MW wind turbine and 850MW photovoltaic;

[0047] Figure 8 The Nyquist curve and system stability margin diagram based on the impedance model under different photovoltaic configuration capacities provided by the present invention are shown. DETAILED DESCRIPTION

[0048] The following describes the implementation of the present invention using specific embodiments. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. Obviously, the embodiments described are only a portion of the present invention, not all of it. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are intended to fall within the scope of protection of the present invention.

[0049] A method for configuring the capacity of offshore renewable energy stations connected to the grid via diode rectification, such as Figure 1 As shown, the following steps are included:

[0050] Step S1: Set variables and, in combination with meteorological data, establish wind turbine output models and photovoltaic output models. With the goal of increasing the transmission line capacity factor and reducing power generation losses at the site, the photovoltaic configuration capacity is obtained, specifically:

[0051] Step S11: Set variables, including the rated capacity of the fan S wt , Rated capacity of electrical equipment S r , PV rated capacity S pv and configurable maximum photovoltaic capacity S pvmax Typical annual meteorological data with hourly resolution, including actual wind speed V w(h) , actual light intensity R s(h) and the actual temperature T (h) ; where h represents the number of hours.

[0052] In the specific implementation, the rated capacity of wind turbines is set to 800MW, the rated capacity of electrical equipment such as converter stations and cables is set to 800MW, the rated capacity of photovoltaic power generation is set as the optimization variable, and the maximum configurable photovoltaic capacity is set to 1500MW. Meteorological data is obtained from the EAR5 public database of the European Center for Medium-Range Weather Forecasts. The time resolution is selected as hourly, and the geographical location is selected as a certain place in Jiangsu Province, my country. The year 2016 is used for analysis, which is a total of 366 days and 8784 hours. The meteorological data is as follows: Figure 2 shown.

[0053] Step S12: Based on the rated capacity S of the fan wt and actual wind speed V w(h) , establish a wind turbine output model; based on the photovoltaic rated capacity S pv , 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 photovoltaic output model P pv(h) =f(R s(h) ,T (h) ), and the annual power generation of the wind turbine E is obtained wt(h) and annual photovoltaic power generation E pv(h) ;

[0054] Among them, the fan output model is:

[0055] ;

[0056] Among them, P wt(h) Indicates the fan output power, 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 characteristic parameters 1, 2, and 3 of the wind turbine power curve, respectively. This embodiment takes a single offshore wind turbine with a rated power of 10 MW as an example. 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.

[0057] α, β, and γ are used to fit the nonlinear interval between the cut-in wind speed and the rated wind speed. The specific calculation method is as follows:

[0058] ;

[0059] The photovoltaic output model is:

[0060] ;

[0061] Among them, Ppv(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 ambient temperature coefficient, T (h) is the actual temperature, T STC is the standard ambient temperature, e pv Power loss caused by AC and other links.

[0062] This embodiment takes the N-type double-sided double-glass module suitable for offshore photovoltaic power stations as an example. The maximum power of a single module is 630W, and the ambient temperature coefficient η T Up to 0.29% / ℃, light intensity R under standard test conditions STC and ambient temperature T STC 1000W / m 2 and 25℃, power loss e pv Take 5%.

[0063] Based on meteorological data and output model, the annual power generation sequence of wind turbines and photovoltaics can be calculated. In this embodiment, taking the configuration of wind turbines and photovoltaics with 800MW each as an example, the following can be obtained after monthly statistics and aggregation: Figure 3 The monthly power generation histogram shown in the figure shows that when wind turbines and photovoltaics are deployed separately, power generation exhibits significant seasonal fluctuations. For example, wind turbine power generation shows a significant decline from June to August, while photovoltaic power generation, in contrast, increases significantly during this period. Due to the negative correlation between wind and photovoltaic output on a temporal scale, power generation fluctuations are smaller when wind and solar power are deployed together.

[0064] Step S13: Based on the annual power generation E of the wind turbine wt(h) , annual photovoltaic power generation E pv(h) and rated capacity S of electrical equipment r , we get the power generation loss rate ce and cable utilization rate cf, and use the power generation loss rate ce and cable utilization rate cf to get the objective function;

[0065] The objective function is:

[0066] ;

[0067] Where ob is the objective function value, ce is the power generation loss rate, cf is the cable utilization rate, a and b are weighted coefficients 1 and 2 respectively, and norm represents normalization processing.

[0068] Where ce is the power generation loss rate, that is, the proportion of power generation that cannot be transmitted due to cable capacity limitations to the total power generation. The specific calculation method is as follows:

[0069] ;

[0070] cf The cable utilization rate is the ratio of the cable's full-load operation time to the total time. The specific calculation method is as follows:

[0071] ;

[0072] In this embodiment, taking the wind turbine configuration of 800MW and the maximum photovoltaic configuration capacity of 1500MW as an example, the changes of the power generation loss rate and cable utilization rate with the photovoltaic configuration capacity are calculated. Figure 4 As shown in the figure, it can be seen that with the increase of photovoltaic configuration capacity, both ce and cf show a nonlinear increasing trend. When 1500MW floating photovoltaic is configured, the annual average cable utilization rate can be increased from 18% to 42%. However, at this time, 11.6% of the generated electricity cannot be transmitted, causing a certain degree of economic loss.

[0073] Step S14: Based on the objective function, in (0, S pvmax ) traverse the photovoltaic rated capacity S in step size ε within the range pv And calculate the corresponding objective function value ob, and set the minimum value of the objective function ob min The corresponding photovoltaic rated capacity S pv As photovoltaic configuration capacity.

[0074] In this embodiment, the calculation results are as follows Figure 5 As shown in the figure, the minimum value of the objective function ob occurs when the photovoltaic configuration capacity is 850MW, accounting for 51.5% of the total installed capacity of the hybrid station. At this time, only 3.2% of the electricity cannot be transmitted, and the cable utilization rate is 33.3%, which is about doubled compared with before the photovoltaic configuration. A good balance can be achieved between the power loss rate and the cable utilization rate.

[0075] Step S2: Based on the circuit dynamics of the grid-connected photovoltaic system, the grid-connected wind turbine, and the diode rectifier unit, a steady-state model of the grid-connected photovoltaic system, the grid-connected wind turbine, and the diode rectifier unit is established. Combined with the photovoltaic configuration capacity, the wind turbine output current is obtained. The photovoltaic configuration capacity is verified and adjusted using the wind turbine current limit as a static stability constraint condition to obtain the initial photovoltaic configuration capacity, which is specifically:

[0076] A steady-state model for grid-connected photovoltaics, grid-connected wind turbines, and diode rectifier units is established in the dq coordinate system. Its mathematical expression is a multivariable nonlinear system of equations. Computer software can be used to solve all variables, and the wind turbine output current can be calculated from two of these variables. Given the rated wind turbine capacity and PV configuration capacity, the steady-state model for the wind turbine and PV system is solved over the full power range to determine the wind turbine output current.

[0077] The equivalent circuit of the system is Figure 6 As shown in the figure, due to the large scale of offshore renewable energy stations, which usually include hundreds of wind turbines and hundreds of floating photovoltaic units, they are equivalently reduced to facilitate modeling and calculation. The hybrid station is equivalent to a grid-connected photovoltaic and a grid-connected wind turbine, and they are modeled as controlled current sources and controlled voltage sources respectively according to their control characteristics. The steady-state model of the grid-connected photovoltaic is as follows:

[0078] ;

[0079] Where, C fl and L fl They are the filter capacitor and transformer leakage reactance of grid-following photovoltaic, P wl and Q wl Indicates the active power and reactive power output of the grid-following photovoltaic system. V fl and e are the port voltage and grid connection point voltage of the grid-following photovoltaic converter respectively. i wl and i ol are the output current and grid-connected current of the grid-following photovoltaic converter, respectively. d and q represent the components of the d-axis and q-axis respectively.

[0080] The steady-state model of the grid-type wind turbine is as follows:

[0081] ;

[0082] Where, C fm and L tm They are the filter capacitor and transformer leakage reactance of the grid-type wind turbine, P wm Indicates the active power output of the grid-type wind turbine. V fm is the port voltage of the grid-type wind turbine converter, i wm and i om are the output current and grid-connected current of the grid-connected wind turbine converter, ω and ω 0 represents the system angular frequency and its rated value, k Q is the reactive frequency droop proportional coefficient.

[0083] The steady-state model of the diode rectifier unit is as follows:

[0084] ;

[0085] Where, i dr is the AC side input current of the diode rectifier unit, C Q Indicates the equivalent capacitance 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 Indicates the leakage reactance of the commutation transformer, with a transformation ratio of 1: T dr , T dr Indicates the transformation ratio between the high-voltage side and the low-voltage side of the converter transformer in the diode rectifier station, V dc0 Indicates the DC side voltage of the onshore inverter station. L dc and R dc Indicates the inductance of the smoothing reactor and the resistance of the DC cable, n is the number of diode rectifier platforms.

[0086] If the wind turbine output current is less than or equal to the wind turbine current limit threshold, the PV configuration capacity passes the static stability check and is used as the preliminary PV configuration capacity.

[0087] If the wind turbine output current is greater than the wind turbine current limit threshold, the PV configuration capacity fails the static stability check. The PV configuration capacity is updated in decreasing steps of ε until the updated PV configuration capacity passes the static stability check. The updated PV configuration capacity is used as the preliminary PV configuration capacity.

[0088] In this embodiment, the photovoltaic configuration capacity obtained in step 1 is 850MW. In this scenario, the output current distribution of the grid-type wind turbine with a rated capacity of 800MW in the full power range is solved, and the results are as follows: Figure 7 As shown in the figure, when the wind turbine is running at rated power and the photovoltaic output is 0.1pu, the wind turbine output current reaches its maximum value due to the need to balance the surplus reactive power of the filter group, but it is less than the wind turbine current limit of 1.2pu, indicating that the hybrid system can operate stably within the full power range, that is, the photovoltaic configuration capacity of 850MW can meet the static stability verification conditions.

[0089] Step S3: Impedance models of grid-following photovoltaics, grid-connected wind turbines, and diode rectifier units are established respectively. Based on the Nyquist criterion and combined with the initial photovoltaic configuration capacity, the stability margin is obtained. The initial photovoltaic configuration capacity is verified and adjusted using the margin setting value as a dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity.

[0090] In step S3, the initial photovoltaic configuration capacity is verified and adjusted using the margin setting value as a dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity, specifically including:

[0091] Based on the impedance models of grid-following photovoltaics, grid-connected wind turbines and diode rectifier units, impedance models are established for output power scenarios of 0.1pu and 1pu respectively, given the rated capacity of the wind turbine and the initial configuration capacity of the photovoltaics. The stability margin is obtained based on the Nyquist criterion.

[0092] The impedance models of grid-connected photovoltaics, grid-connected wind turbines, and diode rectifier units can all be uniformly expressed as follows:

[0093] ;

[0094] Impedance modeling is performed in the frequency domain, where s represents the Laplace operator, Z a is a 2*2 transfer function matrix, Z dd 、 Z dq 、 Z qd 、 Z qq Represent the impedance transfer functions of different channels, respectively. a When it is GFL, GFM, or DRU, Z GFL 、Z GFM and Z DRU Respectively represent the AC side impedance models of grid-connected photovoltaic, grid-connected wind turbine and diode rectifier unit. In the application of Nyquist criterion and quantification of stability margin, since the impedance method is usually used to analyze the interactive stability of two subsystems, and there are three subsystems after the system is aggregated, namely grid-connected photovoltaic, grid-connected wind turbine and diode rectifier unit, the parallel impedance Z of photovoltaic and diode rectifier unit is used as S As a subsystem, the wind turbine impedance is another subsystem. At this time, the wind turbine output current can be expressed as follows:

[0095] ;

[0096] Where, I L Indicates the output current of the grid-type fan. I GFLIndicates that the grid-connected photovoltaic is modeled as a controlled current source, V GFM The grid-connected wind turbine is modeled as a controlled voltage source. Therefore, under the premise of ensuring that both the grid-connected wind turbine and the grid-connected photovoltaic system maintain stability when connected to an ideal current source and the ideal voltage source, the stability of the system is determined by the following ratio matrix:

[0097] ;

[0098] Where / / represents impedance parallel connection, L represents the back-ratio matrix, and the stability of the system is determined by whether the eigenvalue curve of L surrounds the point (-1, j0) on the complex plane. Where j represents the imaginary unit, and the stability margin of the system is calculated by the intersection of the curve and the unit circle.

[0099] If the stability margin is greater than or equal to the margin setting value, the PV preliminary configuration capacity passes the dynamic stability check and the PV preliminary configuration capacity is used as the PV optimal configuration capacity;

[0100] If the stability margin is less than the margin setting value, the PV preliminary configuration capacity fails the dynamic stability check, and the PV preliminary configuration capacity is updated in decreasing step size ε until the updated PV preliminary configuration capacity passes the dynamic stability check. The updated PV preliminary configuration capacity is used as the optimal PV configuration capacity.

[0101] In this embodiment, when the photovoltaic configuration capacity increases from 100MW to 1200MW, the hybrid station system can maintain stability. Figure 8 As shown, the stability margin decreases from 69° to 38°, showing a significant negative correlation. In this example, the PV configuration capacity obtained after verification in step 2 is 850 MW. At this point, the system stability margin is approximately 46°, which is greater than the set margin value of 30°. This indicates that the hybrid station has good stability. In other words, a PV configuration capacity of 850 MW meets the dynamic stability verification conditions.

[0102] In summary, in this embodiment, for the offshore wind power grid-connected system via diode rectification, a hybrid offshore new energy station capacity configuration method via diode rectification and grid-connected is proposed, and the optimal photovoltaic configuration capacity considering cable utilization and power loss rate is obtained. First, step 1 constructs the objective function and calculates the optimal value of the photovoltaic configuration capacity based on it. Then, step 2 establishes the steady-state model of the hybrid station and performs static stability verification based on the current limiting threshold. Finally, step 3 establishes the impedance model of the hybrid station and performs dynamic stability verification based on the stability margin. The above method can be used to obtain the capacity configuration of wind-solar hybrid offshore new energy station for diode rectification and grid-connected, which can achieve the improvement of cable utilization and the reduction of output volatility on the basis of ensuring system stability.

[0103] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made thereto. Therefore, such modifications and improvements, without departing from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for configuring the capacity of an offshore new energy station connected to the grid via diode rectification, characterized in that: The following steps are involved: Step S1: Set variables and, in combination with meteorological data, establish wind turbine output models and photovoltaic output models, with the goal of improving the transmission line capacity factor and reducing the power generation loss of the site, and obtain the photovoltaic configuration capacity; The fan output model is: ； Among them, P wt(h) Indicates the fan output power, 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, α, β, and γ are the characteristic parameters 1, 2, and 3 of the wind turbine power curve respectively; The photovoltaic output 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 ambient temperature coefficient, T (h) is the actual temperature, T STC is the standard ambient temperature, e pv is the power loss; Step S2: Based on the circuit dynamics of the grid-connected photovoltaic system, the grid-connected wind turbine, and the diode rectifier unit, a steady-state model of the grid-connected photovoltaic system, the grid-connected wind turbine, and the diode rectifier unit is established. Combined with the photovoltaic configuration capacity, the wind turbine output current is obtained. The photovoltaic configuration capacity is verified and adjusted using the wind turbine current limit as a static stability constraint to obtain the preliminary photovoltaic configuration capacity. Step S3: Impedance models of grid-following photovoltaics, grid-connected wind turbines, and diode rectifier units are established respectively. Based on the Nyquist criterion and combined with the initial photovoltaic configuration capacity, the stability margin is obtained. The initial photovoltaic configuration capacity is verified and adjusted using the margin setting value as a dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity.

2. The method for configuring the capacity of an offshore new energy station connected to the grid through diode rectification according to claim 1, characterized in that: In step S1, variables are set and meteorological data are combined to establish wind turbine and photovoltaic output models, with the goal of improving the transmission line capacity factor and reducing the power generation loss of the site, to obtain the photovoltaic configuration capacity, specifically including: Step S11: Set variables, including the rated capacity of the fan S wt , Rated capacity of electrical equipment S r , PV rated capacity S pv and configurable maximum photovoltaic capacity S pvmax Typical annual meteorological data with hourly resolution, including actual wind speed V w(h) , 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 fan wt and actual wind speed V w(h) , establish a wind turbine output model; based on the photovoltaic rated capacity S pv , actual light intensity R s(h) and the actual temperature T (h) , establish the photovoltaic output model; based on the wind turbine output model and the photovoltaic output model, obtain the wind turbine annual power generation E wt(h) and annual photovoltaic power generation E pv(h) ; Step S13: Based on the annual power generation E of the wind turbine wt(h) , annual photovoltaic power generation E pv(h) and rated capacity S of electrical equipment r , we get 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 get the objective function; Step S14: Based on the objective function, in (0, S pvmax ) traverse the photovoltaic rated capacity S in step size ε within the range pv And calculate the corresponding objective function value ob, and set the minimum value of the objective function ob min The corresponding photovoltaic rated capacity S pv As photovoltaic configuration capacity.

3. The method for configuring the capacity of offshore new energy stations connected to the grid through diode rectification according to claim 2, characterized in that: 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 weighted coefficients 1 and 2 respectively, and norm represents normalization processing.

4. The method for configuring the capacity of offshore new energy stations connected to the grid through diode rectification according to claim 1, characterized in that: In step S2, the wind turbine current limit is used as a static stability constraint to verify and adjust the photovoltaic configuration capacity to obtain the initial photovoltaic configuration capacity, specifically including: 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 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.

5. The method for configuring the capacity of offshore new energy stations connected to the grid through diode rectification according to claim 1, characterized in that: In step S2, the wind turbine output current is obtained by establishing a steady-state model of the grid-following photovoltaic, grid-forming wind turbine, and diode rectifier unit in the dq coordinate system. Given the wind turbine rated capacity and photovoltaic configuration capacity, the steady-state model of the wind turbine and photovoltaic within the full power range is solved to obtain the wind turbine output current.

6. The method for configuring the capacity of offshore new energy stations through diode rectification and grid connection according to claim 1, characterized in that: In step S3, the initial photovoltaic configuration capacity is verified and adjusted using the margin setting value as a dynamic stability constraint condition to obtain the optimal photovoltaic configuration capacity, specifically including: Step S31: If the stability margin is greater than or equal to the margin setting value, the photovoltaic preliminary configuration capacity passes the dynamic stability check, and the photovoltaic preliminary configuration capacity is used as the photovoltaic optimal configuration capacity; Step S32: If the stability margin is less than the margin setting value, the photovoltaic preliminary configuration capacity fails the dynamic stability check, and the photovoltaic preliminary configuration capacity is updated in decreasing step size ε until the updated photovoltaic preliminary configuration capacity passes the dynamic stability check. The updated photovoltaic preliminary configuration capacity is used as the photovoltaic optimal configuration capacity.

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

Images