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The application of independent photovoltaic and simulation technology in wind power generation system

Abstract: This paper briefly introduces the application of simulation technology in wind power generation system, and focuses on the modeling methods and model structures of wind speed, wind turbine and wind farm. Finally, combined with the actual development of wind power system in China, it explains the significance of using wind farm simulator to solve the problem of operator training

key words: wind power generation, wind farm, simulation, model, modeling method, simulator

Introduction

for the consideration of environmental protection and the current situation of global energy shortage, wind power generation has developed rapidly all over the world. With the technological progress of the wind power industry, the cost of wind power generation has been gradually reduced, and it has been able to compete with nuclear power generation and hydropower generation economically. At present, China is facing the situation of power shortage. In China's power industry, where coal power plays a leading role, the development of coal power is restricted due to the limitation of environmental carrying capacity and the coal shortage caused by various factors. China is rich in wind energy resources, and the use of wind energy has been supported by the government policy. The wind power industry is facing unprecedented development opportunities. In recent years, China's wind power industry has a good momentum of development, and many large-scale wind farms are in the construction or planning stage

there are still many restrictive factors in the development of China's wind power industry. In terms of technology, the production technology of large-scale wind power generation equipment is not qualified, and most of them are purchased or imported from abroad, with a weak R & D foundation; The research on the operation characteristics of wind turbines or wind farms is insufficient, because the materials can be compacted, vented, ground and plasticized in a very short space, the operation management level needs to be improved. The extensive application of simulation technology in the design, test, operation analysis and other aspects of wind power generation equipment will help to speed up the development of wind power generation technology in China, and is a shortcut to narrow the technological gap with developed countries

1 overview of the application of simulation technology in wind power generation system

with the wide application of wind power generation in the world, in order to reduce the cost of wind power generation and improve the efficiency of wind energy utilization, the single machine capacity of wind power generation equipment is increasing, and at the same time, more research topics are put forward for the design and manufacture of wind turbines, the design and operation of control systems and other aspects. The traditional physical test research methods can not meet the development needs. Simulation technology has been increasingly widely used in the field of wind turbine research and testing because it is not limited by meteorological conditions and has the advantages of low investment

simulation is to select some behavior characteristics of a physical or abstract system and express their process with a mathematical model. If the mathematical model is solved by computer, it is called computer simulation. Generally speaking, simulation refers to a comprehensive technology that uses instruments and equipment, models, multimedia technology, and the layout of the site and environment to imitate the working characteristics and environment of the real system, and then used for scientific research, industrial design, prediction, teaching and training purposes. If the simulation is limited to the purpose of design and research, there is no need to simulate the environment of the object system, and there is no need for real-time simulation. Simulation research can be carried out with the help of a mainstream microcomputer and commercial simulation software

in the early 1980s, foreign scholars began to apply simulation methods to the performance research of wind turbine [1]. Since then, the application scope of simulation technology in wind power generation system has gradually expanded. At present, simulation technology is applied in the design, manufacture, performance test and research of key wind power equipment and control system, and the operation analysis of wind turbine or wind farm. The application of simulation technology has largely replaced the traditional means of design inspection using actual equipment. The main research directions are summarized as follows

1) wind energy characteristic simulation, reflecting the location distribution and time variation characteristics of wind energy. The simulation results of wind characteristics will be used in the simulation analysis of wind turbine or wind farm, which is the basis of wind power simulation research

2) wind turbine simulation, which simulates the change law of the output electric energy of a specific wind turbine under the change of wind energy, analyzes its characteristics, looks for the shortcomings of the equipment itself, and provides suggestions for improvement. The parameters characterizing electric energy characteristics mainly include active power, reactive power, voltage and frequency

3) control system simulation, establish the simulation model of the control system to be tested and the simulation model of the control object, and establish the relationship between the models. Change the wind energy parameters or working state of the simulated wind turbine, test the action characteristics and working effects of the control system under various operation modes, find the problems in the design of the control system, and modify the simulation model for further verification after improving the design until the control system meets the design and operation requirements

4) wind farm simulation, establish the simulation model of the whole wind farm according to the specific wind energy characteristics of a specific wind farm and the actual (or planning and Design) installed wind turbines. Study the impact of wind energy change, wind turbine intervention or withdrawal system on the power characteristics of wind farms, and then analyze the feasibility of wind farm construction, analyze the impact of wind farms on power systems under different operation modes, or use it for operator training to improve the operation and management level of wind farms

domestic research on wind power system using simulation technology started late, and there are few published simulation research results, which has not yet formed a climate. In recent years, the situation has changed. More researchers have introduced simulation technology into the research of wind power system. It is believed that more high-level simulation research results will be published in the near future, which can effectively promote the technological progress of wind power industry

2 wind energy and wind turbine simulation model

compared with conventional generating units (such as thermal power, hydropower, nuclear power), the outstanding feature of wind turbine is that the input energy is not controlled, which leads to the composition of wind turbine is very different from conventional generating units and presents diversified characteristics. We know that synchronous generators are widely used in the mechanical energy to electric energy conversion devices of conventional generator sets, while the generators used in parallel wind turbines are diverse, such as constant speed and constant frequency synchronous/asynchronous generators, AC/DC/AC generators, field modulation generators, AC excitation doubly fed generators, etc. Due to the different types of generators used, the corresponding control systems are very different, and the characteristics of electric energy parameters changing with wind energy are also very different

simulation researchers need to develop targeted simulation model software according to the characteristics of wind turbine. Limited by space, this paper mainly introduces the simulation of common parts

2.1 the overall structure of the simulation model of typical wind turbine

the constant speed wind turbine, which is widely used in the wind farm, is shown in Figure 1 [2]. The asynchronous generator converts the mechanical energy absorbed by the wind turbine into electrical energy, and the generator speed changes within a certain range with the change of power generation. Because the speed change range is very small (about 1%), it is usually called a constant speed system. Stall type regulation mode is usually used for constant speed system

a typical variable-speed wind turbine generator set is shown in Figure 2, which adopts doubly fed asynchronous generator (DFIG). The stator coil of the generator is directly connected with electricity, and the rotor coil is connected with electricity through slip ring and power electronic inverter. Therefore, when the change of wind speed causes the change of generator speed, by controlling the frequency of rotor current, the stator frequency can be kept constant, and then the variable speed operation of wind turbine can be realized. Under the condition of high wind speed, the output power of the wind turbine is limited by adjusting the blade pitch

the overall structure of the simulation models of the above two kinds of wind turbines are shown in Figure 3 and Figure 4 respectively [3]. The control system of variable-speed wind turbine is much more complex than the constant speed system, and its simulation model correspondingly adds the controller sub model of pitch angle, speed, terminal voltage and the simulation model of frequency converter

2.2 wind energy characteristic model

the parameters describing wind energy characteristics mainly include wind speed, wind direction and wind density. The density of wind mainly depends on the geographical location of the fan, and climate change will also have a certain impact. For a specific fan, the wind density can be directly obtained from the measured data, and the change of density can be ignored; For research-based simulation applications, the change of wind direction can be ignored, that is, it is assumed that the wind turbine has been tracking the change of wind direction. Therefore, we mainly focus on the variation characteristics of wind speed

wind is formed by atmospheric circulation, and wind speed is a typical random variable. If not, we still need to face a long-standing problem: what is the cost-effectiveness of "reducing the plastic consumption of vehicles by adding graphene"? Dr Deakin said, "we expect to consider the directionality of the wind. The wind speed is a function of its spatial coordinate position and time, that is, v=f (x, y, Z, t). We will describe the spatial and temporal distribution and variation characteristics of the wind speed in a certain region, which is also known as the wind field model." 。 Strictly speaking, the wind speed at each spatial location is different due to the randomness of the wind, the terrain of the wind field and other factors. Therefore, it is almost impossible to establish an accurate wind field model, which needs to be simplified

if the terrain of the wind farm is relatively flat and the surrounding is open, it can be basically considered that the wind speed at all points in the whole wind farm is the same at the same height. In this way, the three-dimensional space model of the wind farm wind speed can be simplified into a one-dimensional model that changes along the height direction

for large-scale wind farms with wide spatial distribution and complex terrain, the whole wind farm can be divided into several regions, and a simplified one-dimensional space model can be established according to the characteristics of wind energy in different regions to form a segmented lumped one-dimensional model. The spatial model of wind speed is transformed into the study of the variation law of wind speed along the height of ground level. With the help of aerodynamic theory and wind field measurement data, the model is not difficult to establish

in the time dimension, the wind speed variation range of large period scale (hour, day) is large, and there is no rule to follow, so the wind speed variation model can only be fitted according to the wind field monitoring record data. For the vast majority of simulation applications, we don't care much about the changes of wind speed on a large time scale, but focus on the characteristics of wind speed changes on a small time scale. On a small time scale, the change of wind speed with time shows the characteristics of fluctuating change, that is, the mean value of wind speed is basically unchanged for a period of time, and the wind speed fluctuates near the mean value. Domestic and foreign scholars have proposed various methods to describe the wind frequency distribution, such as probability distribution model, Rayleigh distribution model, lognormal distribution model, etc. [1]

it should be noted that when establishing the simulation model of each wind turbine in the wind farm, the wake effect of the wind turbine needs to be taken into account, that is, the influence of the upstream wind turbine on the inflow wind speed of the downstream wind turbine. The relationship and degree of influence depend on the wind direction, wind speed and the relationship between the installation position of the wind turbine. At this time, the output mechanical energy of the wind turbine is usually corrected by the wake coefficient

2.3 wind turbine model [4]

the actual mechanical power output that wind turbines can obtain is:

3 wind farm simulation model

3.1 lumped modeling method

wind farms are usually composed of hundreds or even thousands of wind turbine units, involving a variety of wind turbine models and generator types that continue to expand. It is also necessary to consider the interaction between wind turbines, making the wind farm simulation very complex

according to the normal idea, to establish the simulation model of wind farm, we need to aim at