CN106600459B - Optimization method for solving voltage deviation of photovoltaic access point - Google Patents
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Abstract
The invention discloses an optimization method for solving the problem of voltage deviation of a photovoltaic access point, which is used for researching the distribution characteristics of distributed photovoltaic in different areas, establishing a distributed photovoltaic power generation model, a load model and a primary network topological structure, researching the voltage deviation rule of the photovoltaic power supply access point from three aspects of space, time and different voltage grades, and respectively discussing the internal relation between the voltage deviation and the distribution characteristics of the distributed power supply under different power return scenes. On the premise of ensuring the requirements of various aspects of safe and stable operation of a power grid and a power station, the invention provides a technical scheme comprising the steps of additionally arranging a power distribution network transformer on-load voltage regulation device, reconstructing a primary grid structure, adjusting the active and reactive outputs of a photovoltaic inverter, additionally arranging a reactive compensation device and an energy storage device under the framework of meeting technical regulations and standard standards. Based on a voltage deviation rule and a photovoltaic power feedback scene, an optimal scheme for solving the voltage deviation is provided from the technical and economic aspects.
Description
The technical field is as follows:
the invention belongs to the technical field of power system dispatching automation, and particularly relates to an optimization method for solving the problem of voltage deviation of a photovoltaic access point.
Background art:
with the improvement of the living consumption level of residents and the accelerated promotion of constructing a resource-saving and environment-friendly society, the requirements of novel urbanization development roads on environmental protection inevitably become stricter. Under the dual pressure of resources and environment, new energy power generation is developed, and the method has extremely important significance for optimizing an energy structure, protecting the ecological environment and promoting the sustainable development of the economic society. The rapid development of new energy sources and the test of the safe operation of the power grid are provided. Due to the characteristics of unevenness, randomness, volatility, intermittence and the like of solar radiation change, the output power of the photovoltaic power supply fluctuates greatly and is difficult to predict, the large-scale access of the photovoltaic power supply can certainly impact a power grid, the peak load of the power grid is aggravated, and the complexity of safety and stability control measures is greatly increased.
Photovoltaic generation systems (PVGS) usually implement grid-connected operation via low-voltage or medium-voltage distribution networks by means of inverters. The traditional power system transmission and distribution network is designed to be a unidirectional power transmission and distribution system from a power generation unit to a load, and a large-scale photovoltaic power generation system is operated in a grid-connected mode, so that the problem of backflow of tide can be caused, and the voltage of a Point of Common Coupling (PCC) of the photovoltaic power generation system is increased or over-voltage is caused. The voltage rise not only affects the power supply quality of local loads, but also increases the loss of power transmission and distribution equipment such as lines and transformers, causes system overload, and limits the access of PCC to more photovoltaic power generation systems, thereby affecting the permeability of the photovoltaic power generation systems. It is therefore necessary to control the PCC voltage. However, the PCC voltage rise cannot be solved completely and economically by simply relying on the voltage regulation method of the conventional power system.
Distributed photovoltaic power generation is rapidly developed in China, the permeability of distributed photovoltaic power generation is continuously improved, and power return scenes of a power distribution network appear in many areas. However, the increasing capacity of the distributed power supply is increasing, a certain impact is already caused on the power distribution network, and the grid connection pressure is getting larger and larger. In particular, many distributed generation facilities are installed in relatively remote rural areas where local grid conditions are more limited. Due to the characteristics of the distributed photovoltaic power generation, negative influences are often brought to a power grid, the distributed photovoltaic power generation is connected to a power distribution system, and influences are brought to power supply economy, node voltage, tide, short-circuit current, network power supply reliability and the like of the power distribution network, and the situation that the voltage deviation exceeds the limit is the most common and important. The grid connection of the distributed photovoltaic changes the original structure of a single power supply and a radiation type power supply network, and the phenomenon of tidal current backflow is caused, so that the influence of the distributed photovoltaic grid connection on the safety of maintainers, the protection automation of the power distribution network and the influence on the power quality of the power distribution network need to be improved. At present, no unified solution is provided for the voltage deviation problem of the public node of the power distribution network in China, and the voltage deviation can be continuously increased or even out of limit along with the continuous increase of the permeability of the distributed power generation in view of the leading foreign practical experience of the distributed power generation grid connection technology of the power distribution network, so that the power supply quality is influenced, the disconnection of the distributed power supply is caused, and the like. In this situation, it is not easy to study the technology for solving the voltage deviation problem. On the other hand, different pressure regulating methods have different investment costs and running costs. Therefore, how to find the optimal solution from both technical and economic aspects is the key to reasonably solve the voltage deviation problem.
The method is based on the characteristics of the power distribution network, analyzes the distribution characteristics of the distributed photovoltaic power supply and the characteristics of the power distribution network of each voltage class, and establishes a correlation model of the voltage deviation and the distribution characteristics of the distributed photovoltaic power supply by combining the physical principle of the voltage deviation. Various voltage regulating means in the power distribution network are analyzed, and technical characteristics of the voltage regulating means are analyzed. The economy of various pressure regulating means is analyzed according to market conditions, construction costs and the like. Different distributed photovoltaic power sources are distributed for different power grids to provide an appropriate solution to the voltage deviation.
The invention content is as follows:
in order to overcome the defects of the prior art, the invention comprehensively considers a distribution network model and each voltage regulating means on the basis of fully considering the characteristics of a power grid and the grid-connected rule of the distributed photovoltaic power supply, calculates the actual investment of each voltage regulating scheme in the life cycle by using a net present value method, aims at minimizing the comprehensive cost, and optimizes a control strategy to improve the effect of solving the voltage deviation of a photovoltaic access point.
An optimization method for resolving photovoltaic access point voltage deviations, the method comprising the steps of:
(1) weather prediction is carried out, and a traditional power distribution network element model, a distributed power generation model, a load model and a primary network topological structure model are established;
(2) the method comprises the steps of equivalence is carried out on a photovoltaic power generation system connected to a power distribution network, an equivalent circuit is established, and public node voltage variation caused by the fact that the photovoltaic system is connected is obtained;
(3) determining main factors causing the voltage change of the photovoltaic grid-connected common node according to the voltage change of the common node;
(4) analyzing a change rule between the voltage deviation and the photovoltaic distribution characteristics, and selecting a voltage adjustment strategy according to the characteristics of the photovoltaic power generation system;
(5) constructing a target function of an economic evaluation model, carrying out detailed analysis on the comprehensive cost, namely the abandoned photovoltaic power generation punishment, the voltage out-of-limit punishment, the power supply operation and power distribution network operation and maintenance cost, the line reconstruction investment cost and the peripheral voltage regulating equipment investment and operation maintenance cost on the basis of considering the technical characteristics of different voltage regulating schemes and the service life of equipment, and selecting the voltage regulating scheme with the minimum comprehensive cost by using a net present value method, wherein the net present value method comprises the following steps:
NPV: net present value
I: fixed investment cost
O & M: fixed year operation and maintenance cost
V: variable annual operating costs
E: reward mechanism
x, n: investment equipment number and corresponding service life of equipment
K: annual percentage of interest
(6) And determining the capacity and the working strategy of the voltage regulating equipment, and further solving the voltage deviation of the photovoltaic access point.
In the step (1), the specific method for weather prediction is as follows: analyzing all meteorological factors influencing photovoltaic output, wherein the ratio of average output under the same weather type to average output in the sunny day is a corresponding day type index, non-stationarity of photovoltaic power supply hourly output power distribution when the weather is suddenly changed is considered, historical hourly output data of the photovoltaic power supply are divided into two categories according to the weather type, one category is data under the non-sudden change weather, the other category is data under the sudden change weather, only the highest temperature in the day is considered when the data under the non-sudden change weather is used for prediction, and the day type indexes of the highest temperature in the day, the morning and the afternoon are considered when the data under the sudden change weather is used for prediction.
In the step (2), the voltage variation of the common node caused by the connection of the photovoltaic system is
Because in the power return scene, the node load is less than the output of the photovoltaic system, and
much less than
The second term in the above equation is much smaller than the first term, so the variation of the common node voltage is
Wherein, the voltages of the grid-connected common node and the bus node of the power distribution network are U, U respectivelysWhen the photovoltaic power generation system is not connected to the grid, the voltage of the common node is U0After the photovoltaic power generation system is connected to the grid and when a tide return scene is generated, the voltage of the common node is U1The resistance component and reactance component R + jX of the overhead line exist between the two nodes, the output P + jQ of the photovoltaic system is obtained, and the nodePoint load PL+jQL。
The photovoltaic power supply mathematical modeling step comprises the steps of firstly dispersing the radiation quantity received by a representative daily horizontal plane per hour according to the cosine law of solar radiation, and adopting the following formula in order to facilitate the conversion of sunrise and sunset time:
S′P＝S′Dsin α
of formula (II) S'PThe direct radiation dose of the horizontal plane; s'DIs the degree of direct radiation; for the same place, the radiation quantity directly received by the ground is mainly influenced by the solar altitude and is in a sine relationship, so that the direct ground radiation quantity obtained from a meteorological department can be dispersed into the direct ground received radiation quantity of each hour according to the sine relationship, and the method comprises the following steps:
a. calculating the sunrise and sunset time of the representative day, and respectively corresponding to the intersection points 0 and pi of the sine curve and the horizontal axis;
b. converting each integral point time of the representative day into a radian corresponding to the sine curve;
c. calculating the area enclosed on the sinusoidal curve every hour by integration to obtain the direct radiation quantity at the moment;
after the direct radiation quantity at a certain moment is known, the power generation quantity of the solar cell can be calculated, and the calculation formula is as follows:
G＝ηPNT
in the formula, eta is the photovoltaic system efficiency, and is generally 70%; pNIs the peak power; t is the output efficiency corresponding to the sunshine duration, and the calculation formula is as follows:
wherein Z is total radiation quantity received by the square matrix, and direct radiation quantity S 'of available horizontal plane'PInstead, 3.6 are the reduced coefficients of MJ and kWh; r is the standard irradiation intensity, i.e. 1000W/m2. Therefore, the power generation amount per hour of the solar cell can be obtained:
in the formula, zβ(tm) And m months represents the total amount of radiation received at the solar cell inclination angle.
In the step (3), the main factors causing the voltage change of the photovoltaic grid-connected common node are the bus voltage of the power distribution network, the impedance parameter of the power transmission line and the output power of the photovoltaic power generation system.
The voltage regulation strategy in the step (4) comprises regulating the voltage of a bus of the power distribution network through an on-load tap changer or installing a voltage regulator in the power distribution network to regulate the voltage in the bus or a line; adjusting a primary grid structure and improving impedance parameters of the power transmission line; utilizing active and reactive power regulation of the distributed photovoltaic inverter; reactive compensation equipment is additionally arranged at the public node; and the energy storage equipment is additionally arranged at the common node to smooth the active output of the distributed power system.
The modes of adjusting the primary grid structure comprise equipment upgrading and replacing, capacity increasing, overhead line replacing by a cable and power grid topological structure changing.
The control strategy for the self-regulation of the inverter comprises: constant power factor control, active power factor control curve control and reactive voltage control curve control.
The reactive compensation equipment adopts a static compensator.
The energy storage equipment is selected to be energy storage battery to still include energy storage system controller, it is according to the change of sunshine intensity and load, constantly switch over and adjust energy storage battery's operating condition, on the one hand directly send the electric energy after the adjustment to direct current or exchange load, on the other hand reduces the biggest power of distributing type photovoltaic, stores unnecessary electric energy, thereby has avoided the rising of node voltage.
The optimization method of the capacity and the working strategy of the voltage regulating equipment can be optimized by using a double-layer nesting mode, input data comprise meteorological data such as illumination and the like, a grid topological structure, power load data and technical and economic parameters of each voltage regulating equipment in a simulation platform, a random system model is generated, simulation is carried out through active and reactive power regulation of each voltage regulating equipment, economic evaluation is carried out on the randomly generated system model while all technical requirements are met, then population is generally optimized through an evolution theory, and a final optimization result is generated through repeated iteration.
Analyzing a change rule between the voltage deviation and the photovoltaic distribution characteristics from three dimensions of time, space and voltage grade; in the aspect of time dimension, annual time sequence data are analyzed according to the acquired input data, influence factors comprise the output of a single photovoltaic device, the capacity of each node photovoltaic device and the change of a primary network structure in the considered time, the time sequence data are analyzed, the power grid state at each moment, namely the voltage state of each node, the season and the moment of voltage out-of-limit easy to occur are judged in advance, and the change rule between voltage deviation and time is obtained. In the aspect of spatial dimension, as the installation capacity and the installation place of the photovoltaic equipment are different, the output power of the space is different, namely, part of the areas are frequently generated all the year round due to large installation capacity or relatively rich photovoltaic resources, while some areas are rarely generated all the year round due to small installation capacity or relatively poor photovoltaic resources, and the output difference between the areas is analyzed to obtain the change rule between the voltage deviation and the space; in the aspect of voltage grade dimensionality, the capacity scales of photovoltaic power generation systems connected into power distribution networks with different voltage grades are greatly different, the requirements for the voltage grades are different, and the grid connection conditions of other distributed power supplies in each voltage grade are different, so that the change rule between the voltage deviation and the voltage grade is obtained.
By adopting the technical scheme, the problem of voltage deviation can be optimally solved from the technical and economic aspects.
Drawings
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the accompanying drawings.
FIG. 1 shows a photovoltaic grid-connected tidal current counter-current equivalent circuit
FIG. 2 is a distribution profile of a distributed photovoltaic power source in different dimensions
FIG. 3 is a double nested pattern frame structure
Detailed Description
According to the requirements in the technical provisions of the distributed power supply access power grid, after the distributed photovoltaic power supply is connected to the grid, the voltage deviation range of the public node meets the provisions of power quality supply voltage allowable deviation (GB/T12325-2008), namely: 35kV or above, the sum of absolute values of positive deviation range and negative deviation range of the node voltage is less than or equal to 10% of the nominal voltage, and the deviation range of the three-phase node voltage of 10kV or below is between-7% and + 7%; the voltage deviation of the 220V single-phase node ranges from-10% to + 7%.
The equivalent circuit of the photovoltaic power generation system connected to the distribution network is shown in fig. 1.
In fig. 1, two nodes respectively refer to a grid-connected common node of a photovoltaic system and a bus node of a power distribution network, and the voltages of the two nodes are U, Us. Between the two nodes, there are a resistance component and a reactance component R + jX of the overhead line. The output P + jQ of the photovoltaic system is greater than the node load PL+jQLThus, a scenario of overall power return to the grid occurs. Firstly, assuming that a photovoltaic power generation system is not connected to the grid, the voltage U of a common node0Is composed of
After the photovoltaic power generation system is connected to the grid, a tide return scene is generated, and the voltage U of the common node1Is composed of
Slave node voltage U1The formula can find that the bus voltage U of the power distribution networkSThe terminal voltage of the distribution network can be directly influenced. The voltage variation of the common node caused by the connection of the photovoltaic system is
Because in the power foldback scene, the node load is smallOutput on the photovoltaic system, and
much less than
The second term in the above equation is much smaller than the first term, so the common node voltage variation is approximated to be
According to the physical principle and the mathematical model, the main factors causing the voltage change of the photovoltaic grid-connected common node are judged to be the influences of the bus voltage of the power distribution network, the impedance parameters of the power transmission line and the output power of the photovoltaic power generation system. According to the characteristics of photovoltaic distribution, different characteristics of dimensions of active power, reactive power, line impedance and transformer node voltage are combined, and influence factors and influence magnitude generated by voltage deviation are quantized.
Establishing a model based on a simulation platform, wherein the model comprises a traditional power distribution network element model, a distributed power generation model and a load model; the traditional power distribution network element model mainly comprises a transformer and a distribution line model; the distributed power generation model is mainly a photovoltaic model, and the load model mainly considers loads of residents and industries and businesses.
Distribution characteristics of distributed photovoltaic in different areas are considered, wherein the distribution characteristics comprise an access mode, a power grid primary grid structure, equipment capacity, access point natural conditions and the like.
The method comprises the steps of performing weather prediction, analyzing various meteorological factors influencing photovoltaic output, wherein the ratio of average output under the same weather type to the average output in the sunny day is a corresponding day type index, the distribution of the photovoltaic power output in hours is closely related to the geographical position of an installation place and meteorological conditions, historical data of photovoltaic power generation comprises the geographical position, the installation angle of a photovoltaic array and the like, considering the non-stationarity of the photovoltaic power output power distribution in the sudden change of weather, dividing the photovoltaic power output data in the historical hours into two categories according to the weather type, wherein one category is data under the non-sudden change weather, the other category is data under the sudden change weather, only the highest temperature in the day is considered when the data under the non-sudden change weather is used for prediction, and the highest temperature in the day, the morning and afternoon day type indexes are considered when the data under the sudden change weather is. The non-abrupt weather comprises sunny days, cloudy days, rainy days or snowy days, and the abrupt weather refers to the transition of the three weather conditions, such as sunny to cloudy and cloudy to rainy.
Performing mathematical modeling on a photovoltaic power supply, firstly dispersing the radiation quantity received by a representative daily horizontal plane per hour, wherein the basis of the dispersion is the cosine law of solar radiation, and in order to facilitate the conversion of sunrise and sunset time, the following formula is adopted:
S′P＝S′Dsin α
of formula (II) S'PThe direct radiation dose of the horizontal plane; s'DIs the degree of direct radiation.
For the same place, the radiation quantity directly received by the ground is mainly influenced by the solar altitude and is in a sine relationship, so that the direct ground radiation quantity obtained from a meteorological department can be dispersed into the direct ground received radiation quantity of each hour according to the sine relationship, and the method comprises the following steps:
a. calculating the sunrise and sunset time of the representative day, and respectively corresponding to the intersection points 0 and pi of the sine curve and the horizontal axis;
b. converting each integral point time of the representative day into a radian corresponding to the sine curve;
c. the area enclosed on the sinusoid for each hour is calculated by integration to obtain the amount of direct radiation at that time.
After the direct radiation amount at a certain moment is known, the power generation amount of the solar cell can be calculated by the following calculation formula:
G＝η PNT
in the formula, eta is the photovoltaic system efficiency, and is generally 70%; pNIs the peak power; t is the output efficiency corresponding to the sunshine duration, and the calculation formula is as follows:
wherein Z is total radiation received by the square matrix, and can be direct radiation S 'of horizontal plane'PInstead, 3.6 are the reduced coefficients of MJ and kWh; r is the standard irradiation intensity, i.e. 1000W/m2. Therefore, the power generation amount per hour of the solar cell can be obtained:
in the formula, zβ(tm) And m months represents the total amount of radiation received at the solar cell inclination angle.
Different power return scenes are established from space, time and different voltage levels, and different scenes are classified, such as different voltage levels, power grid topological structures and the like, and the inherent relation between the voltage deviation and the distribution characteristics of the distributed power supply under different scenes is discussed respectively. And aiming at the scale of the returned power of the distributed power supply and different voltage levels, finding out the influence factor and the influence magnitude of the returned power on the voltage deviation.
As shown in fig. 2, a distributed photovoltaic database is established according to the collected information of the distributed photovoltaic system. And analyzing the change rule between the voltage deviation and the photovoltaic distribution characteristics from three dimensions of time, space and voltage grade.
The time dimension is as follows: and analyzing annual time sequence data according to the acquired input data, wherein the influence factors comprise the output of a single photovoltaic device, the capacity of each node of the photovoltaic device and the change of the primary network structure in the considered time. And analyzing the time sequence data to obtain the power grid state at each moment, namely the voltage state of each node, and further prejudging the season and moment when the voltage is out of limit easily to obtain the change rule between the voltage deviation and the time, namely how the voltage deviation changes when the photovoltaic output is different at different moments.
Spatial dimension: because the installation capacity and the installation place of the photovoltaic equipment are different, the output power of the photovoltaic equipment is different in space, namely, the output power of a part of areas is more frequently generated all the year round due to large installation capacity or relatively rich photovoltaic resources, the output power difference between the areas is analyzed to obtain the change rule between the voltage deviation and the space, namely, the installed access points of the same voltage level are different in size of the access capacity, the distances between the installed access points and the bus are different, and the voltage deviation is changed.
Voltage class dimension: the capacity scales of the photovoltaic power generation systems connected to the power distribution networks with different voltage grades are different, the requirements for the voltage grades are different, the grid connection conditions of other distributed power supplies in each voltage grade are different, and the change rule between the voltage deviation and the voltage grade is obtained, namely how the voltage deviation changes after the photovoltaic equipment with certain capacity is connected to the different voltage grades.
Aiming at the characteristics of the photovoltaic power generation system, the voltage regulation strategy adopted by the invention comprises,
1. regulating the bus voltage of the power distribution network through an on-load tap changer or installing a voltage regulator in the power distribution network to regulate the voltage in a bus or a line;
2. the method comprises the steps of adjusting a primary grid structure, improving impedance parameters of a power transmission line, and improving the robustness of the system by means of equipment upgrading replacement, capacity increase, overhead line replacement by cables, power grid topological structure change and the like;
3. the active and reactive power regulation of the distributed photovoltaic inverter considers the limiting factors such as the power factor range, the transformer and the line capacity of the normal operation of the inverter in the regulation process, and the adopted control strategy comprises the following steps: constant power factor control, active power factor control curve control and reactive voltage control curve control;
4. reactive power compensation equipment is additionally arranged at a common node, so that reactive power output of a distributed photovoltaic system is controlled from a source, and in order to overcome the defects that a capacitor serving as a reactive power compensation device can only be used as a power supply and cannot be used as a load and the regulation is discontinuous, a static compensator is adopted to achieve rapid and smooth regulation of reactive power, the power loss is small, and the adaptability to impact load is strong;
5. the energy storage device is additionally arranged at the common node, active power output of the distributed power system is smoothed, and particularly, the energy storage battery is matched with distributed photovoltaic power generation access to realize peak clipping, valley filling and load compensation and improve electric energy quality application. The solar photovoltaic energy storage system is characterized by further comprising an energy storage system controller, wherein the energy storage system controller continuously switches and adjusts the working state of the energy storage system according to the change of the sunlight intensity and the load, on one hand, the adjusted electric energy is directly sent to a direct current or alternating current load, on the other hand, the maximum distributed photovoltaic output can be reduced, and redundant electric energy is stored, so that the node voltage is prevented from rising.
And constructing a target function of an economic evaluation model, carrying out detailed analysis on the comprehensive cost, namely the abandoned photovoltaic power generation punishment, the voltage out-of-limit punishment, the power supply operation and power distribution network operation and maintenance cost, the line reconstruction investment cost, the peripheral voltage regulating equipment investment and operation maintenance cost and the like on the basis of considering the technical characteristics of different voltage regulating schemes and the service life of equipment, and selecting the voltage regulating scheme with the minimum comprehensive cost by using a net present value method. On the basis of economic evaluation research, capacity configuration and optimal calculation on working strategies are carried out on the selected final technical scheme, and the optimal working conditions meeting different time, space and voltage levels at the same time are determined. And determining each component factor of the comprehensive cost, determining an objective function of the optimization scheme, and calculating the configuration capacity and the working strategy of the optimal scheme by combining a corresponding optimization algorithm.
The net present value method takes into account the time value of the capital, takes into account the net cash flow over the entire process, and describes the difference between the present value of the future cash flow generated by an investment and the investment cost of the project. The comprehensive cost is classified and generally divided into fixed investment cost (line reconstruction and voltage regulation equipment commissioning), fixed annual operation maintenance cost, variable annual operation cost (voltage out-of-limit punishment and light abandonment punishment) and reward mechanism. The net present value method is calculated as follows:
NPV: net present value
I: fixed investment cost
O & M: fixed year operation and maintenance cost
V: variable annual operating costs
E: reward mechanism
x, n: investment equipment number and corresponding service life of equipment
K: annual percentage of interest
The optimization method of the capacity and the working strategy of the voltage regulating equipment can use a double-layer nesting mode for optimization and simulation, as shown in figure 3, input data comprise meteorological data such as illumination and the like, a grid topological structure, power load data and technical and economic parameters of each voltage regulating equipment in a simulation platform, a random system model is generated, simulation is carried out through active power regulation and reactive power regulation of each voltage regulating equipment, economic evaluation is carried out on the randomly generated system model while all technical requirements are met, then population is generally optimized through an evolution theory, and a final optimization result is generated through repeated iteration. The purpose of adopting the double-layer nested mode is to independently operate the configuration of the capacity of the voltage regulating equipment and the establishment of the active and reactive power output time and size as much as possible. The optimization method of the capacity and the working strategy of the pressure regulating equipment can also be analyzed by adopting the existing method known by the technical personnel in the field.
The platform used for the analysis of the present invention is known to those skilled in the art, and the platform is a professional commercial platform such as Sincal, Neplan, Integral, etc., and an academic research platform such as Matlab, OpenDSS, etc., and the above optimization algorithm is an optimization algorithm known in the art that can generate a stochastic system model.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and it is apparent that those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (12)
1. An optimization method for solving the voltage deviation of a photovoltaic access point is characterized by comprising the following steps: the method comprises the following steps:
(1) weather prediction is carried out, and a traditional power distribution network element model, a distributed power generation model, a load model and a primary network topological structure model are established;
(2) the method comprises the steps of equivalence is carried out on a photovoltaic power generation system connected to a power distribution network, an equivalent circuit is established, and public node voltage variation caused by the fact that the photovoltaic system is connected is obtained;
(3) determining main factors causing the voltage change of the photovoltaic grid-connected common node according to the voltage change of the common node;
(4) analyzing a change rule between the voltage deviation and the photovoltaic distribution characteristics, and selecting a voltage adjustment strategy according to the characteristics of the photovoltaic power generation system;
(5) constructing a target function of an economic evaluation model, carrying out detailed analysis on the comprehensive cost, namely the abandoned photovoltaic power generation punishment, the voltage out-of-limit punishment, the power supply operation and power distribution network operation and maintenance cost, the line reconstruction investment cost and the peripheral voltage regulating equipment investment and operation maintenance cost on the basis of considering the technical characteristics of different voltage regulating schemes and the service life of equipment, and selecting the voltage regulating scheme with the minimum comprehensive cost by using a net present value method, wherein the net present value method comprises the following steps:
NPV: net present value
I: fixed investment cost
O & M: fixed year operation and maintenance cost
V: variable annual operating costs
E: reward mechanism
x, n: investment equipment number and corresponding service life of equipment
K: annual percentage of interest
(6) And determining the capacity and the working strategy of the voltage regulating equipment, and further solving the voltage deviation of the photovoltaic access point.
2. The optimization method according to claim 1, characterized in that:
in the step (1), the specific method for weather prediction is as follows: analyzing all meteorological factors influencing photovoltaic output, wherein the ratio of average output under the same weather type to average output in the sunny day is a corresponding day type index, non-stationarity of photovoltaic power supply hourly output power distribution when the weather is suddenly changed is considered, historical hourly output data of the photovoltaic power supply are divided into two categories according to the weather type, one category is data under the non-sudden change weather, the other category is data under the sudden change weather, only the highest temperature in the day is considered when the data under the non-sudden change weather is used for prediction, and the day type indexes of the highest temperature in the day, the morning and the afternoon are considered when the data under the sudden change weather is used for prediction.
3. The optimization method according to claim 1, characterized in that:
in the step (2), the voltage variation of the common node caused by the connection of the photovoltaic system is
Because in the power return scene, the node load is less than the output of the photovoltaic system, and
much less than
The second term in the above equation is much smaller than the first term, so the variation of the common node voltage is
Wherein, the voltage of the grid-connected common node and the bus node of the power distribution network is divided intoIs otherwise U, UsWhen the photovoltaic power generation system is not connected to the grid, the voltage of the common node is U0After the photovoltaic power generation system is connected to the grid and when a tide return scene is generated, the voltage of the common node is U1The resistance component and reactance component R + jX of the overhead line exist between the two nodes, the output P + jQ of the photovoltaic system and the node load PL+jQL。
4. The optimization method according to claim 1, characterized in that: the photovoltaic power supply mathematical modeling step comprises the steps of firstly dispersing the radiation quantity received by a representative daily horizontal plane per hour according to the cosine law of solar radiation, and adopting the following formula in order to facilitate the conversion of sunrise and sunset time:
S′P＝S′Dsinα
of formula (II) S'PThe direct radiation dose of the horizontal plane; s'DIs the direct radiation dose; for the same place, the radiation quantity directly received by the ground is mainly influenced by the solar altitude and is in a sine relationship, so that the direct ground radiation quantity obtained from a meteorological department can be dispersed into the direct ground received radiation quantity of each hour according to the sine relationship, and the method comprises the following steps:
a. calculating the sunrise and sunset time of the representative day, and respectively corresponding to the intersection points 0 and pi of the sine curve and the horizontal axis;
b. converting each integral point time of the representative day into a radian corresponding to the sine curve;
c. calculating the area enclosed on the sinusoidal curve every hour by integration to obtain the direct radiation quantity at the moment;
after the direct radiation quantity at a certain moment is known, the power generation quantity of the solar cell can be calculated, and the calculation formula is as follows:
G＝ηPNT
in the formula, eta is the photovoltaic system efficiency, and is generally 70%; pNIs the peak power; t is the output efficiency corresponding to the sunshine duration, and the calculation formula is as follows:
wherein Z is total radiation quantity received by the square matrix, and direct radiation quantity S 'of available horizontal plane'PInstead, 3.6 are the reduced coefficients of MJ and kWh; r is the standard irradiation intensity, i.e. 1000W/m2. Therefore, the power generation amount per hour of the solar cell can be obtained:
in the formula, zβ(tm) And m months represents the total amount of radiation received at the solar cell inclination angle.
5. The optimization method according to claim 1, characterized in that: in the step (3), the main factors causing the voltage change of the photovoltaic grid-connected common node are the bus voltage of the power distribution network, the impedance parameter of the power transmission line and the output power of the photovoltaic power generation system.
6. The optimization method according to claim 1, characterized in that: the voltage regulation strategy in the step (4) comprises regulating the voltage of a bus of the power distribution network through an on-load tap changer or installing a voltage regulator in the power distribution network to regulate the voltage in the bus or a line; adjusting a primary grid structure and improving impedance parameters of the power transmission line; utilizing active and reactive power regulation of the distributed photovoltaic inverter; reactive compensation equipment is additionally arranged at the public node; and the energy storage equipment is additionally arranged at the common node to smooth the active output of the distributed power system.
7. The optimization method according to claim 6, characterized in that: the modes of adjusting the primary grid structure comprise equipment upgrading and replacing, capacity increasing, overhead line replacing by a cable and power grid topological structure changing.
8. The optimization method according to claim 6, characterized in that: the control strategy for the self-regulation of the inverter comprises: constant power factor control, active power factor control curve control and reactive voltage control curve control.
9. The optimization method according to claim 6, characterized in that: the reactive compensation equipment adopts a static compensator.
10. The optimization method according to claim 6, characterized in that: the energy storage equipment is selected to be energy storage battery to still include energy storage system controller, it is according to the change of sunshine intensity and load, constantly switch over and adjust energy storage battery's operating condition, on the one hand directly send the electric energy after the adjustment to direct current or exchange load, on the other hand reduces the biggest power of distributing type photovoltaic, stores unnecessary electric energy, thereby has avoided the rising of node voltage.
11. The optimization method according to claim 1, characterized in that: the optimization method of the capacity and the working strategy of the voltage regulating equipment can be optimized by using a double-layer nesting mode, input data comprise meteorological data such as illumination and the like, a grid topological structure, power load data and technical and economic parameters of each voltage regulating equipment in a simulation platform, a random system model is generated, simulation is carried out through active and reactive power regulation of each voltage regulating equipment, economic evaluation is carried out on the randomly generated system model while all technical requirements are met, then population is generally optimized through an evolution theory, and a final optimization result is generated through repeated iteration.
12. The optimization method according to claim 1, characterized in that: the method further comprises the following steps of analyzing a change rule between the voltage deviation and the photovoltaic distribution characteristics from three dimensions of time, space and voltage grade; in the aspect of time dimension, annual time sequence data are analyzed according to the acquired input data, influence factors comprise the output of a single photovoltaic device, the capacity of each node of the photovoltaic device and the change of a primary network structure in the considered time, the time sequence data are analyzed to obtain the power grid state at each moment, namely the voltage state of each node, the season and the moment of voltage out-of-limit easy to occur are further judged in advance, and the change rule between voltage deviation and time is obtained;
in the aspect of spatial dimension, as the installation capacity and the installation place of the photovoltaic equipment are different, the output power of the space is different, namely, part of the areas are frequently generated all the year round due to large installation capacity or relatively rich photovoltaic resources, while some areas are rarely generated all the year round due to small installation capacity or relatively poor photovoltaic resources, and the output difference between the areas is analyzed to obtain the change rule between the voltage deviation and the space; in the aspect of voltage grade dimensionality, the capacity scales of photovoltaic power generation systems connected into power distribution networks with different voltage grades are greatly different, the requirements for the voltage grades are different, and the grid connection conditions of other distributed power supplies in each voltage grade are different, so that the change rule between the voltage deviation and the voltage grade is obtained.
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| CN108736510B (en) * | 2017-09-08 | 2020-05-12 | 中国南玻集团股份有限公司 | Method for predicting power generation and plant area power utilization ratio of photovoltaic power station |
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| CN109149635B (en) * | 2018-09-03 | 2022-03-11 | 国网江西省电力有限公司电力科学研究院 | Distributed photovoltaic parallel optimization configuration method and system for power distribution network |
| CN110071529B (en) * | 2019-05-16 | 2020-12-29 | 重庆三峡学院 | Method for reducing influence of photovoltaic power generation grid connection on power distribution network |
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