Wind energy is one of the energy sources without pollution, and it is inexhaustible and inexhaustible. For coastal islands, grassland and pastoral areas, mountainous areas and plateau areas that are short of water, fuel and transportation inconvenient, wind power can be used according to local conditions. As a clean and renewable energy, wind energy has been paid more and more attention by countries all over the world.

Converting the kinetic energy of the wind into mechanical energy, and then converting the mechanical energy into electrical energy, is wind power generation. Wind power generation technology is a multi-disciplinary, sustainable, green and comprehensive technology. The devices required for wind power generation are called wind turbines. The wind turbine is mainly composed of two parts: the wind turbine part converts wind energy into mechanical energy; the generator part converts mechanical energy into electrical energy.

1. Classification of small wind turbines
The small wind power generation system is very efficient, but it is not composed of only one generator, but a small system with certain technological content: wind turbine + wind generator + controller + energy storage device. A wind turbine consists of a nose, a swivel, a tail, and blades. Each part is very important, and the functions of each part are: the blades are used to receive the wind and turn into electrical energy through the nose; the tail makes the blades always face the direction of the incoming wind to obtain the maximum wind energy; the swivel can make the nose flexibly rotate to achieve The function of adjusting the direction of the tail; the rotor of the nose is a permanent magnet, and the stator windings cut the magnetic lines of force to generate electricity.

Small-scale wind power generation can be divided into vertical axis wind turbine (VAWT) and horizontal axis wind turbine (HAWT) according to its design and structure. The rotation axis of the horizontal axis wind turbine is parallel to the wind direction. Most of the horizontal axis wind turbines have their blades continuously adjusted with the wind direction, so they are more susceptible to the influence of terrain and features. The rotation of the vertical axis wind turbine The axis is perpendicular to the wind direction. The advantage of this type is that the design is relatively simple, because it is not necessary to adjust the direction with the change of the wind direction, it can be divided into egg-beating rotor (Darrieus) and barrel rotor (Savonius), etc. Invented in 1931 by engineer Georges Jean Marie Darrieus. The barrel rotor (Savonius) was invented by the Dutch engineer Sigurd J.Savonius in 1922]. The comparison between the vertical axis wind turbine and the horizontal axis wind turbine is shown in Table 1.

ProjectVAWT (Vertical Axis Wind Turbine)HAWT (Horizontal axis wind turbine)
Design conceptGyroscopic rotation, does not change the axis with the wind directionNeed to have fins to turn the windmill with the wind
AdvantageLow starting wind speed, power generation is not affected by terrain wind, low noise, safety, and long service lifeHigher power generation efficiency at high wind speeds
ShortcomingRelatively slow speed, complex design, high manufacturing costHigh requirements for starting wind speed, high noise, sensitive to terrain wind, inability to overcome the problem of uncertain wind direction, easy damage to the tail shaft with the change of wind direction, and high installation cost
Accessories materialTreated with no Mingdacro anti-corrosion and environmental protection technologyHot dip galvanized
Applicable placesApplicable to urban areas, suburban areas, coastal areas and mountainous areasMostly suitable for large spaces with no shelter
SummaryThe vertical axis wind turbine is not affected by the change of wind direction and can receive wind from all directions at any time.Generally, the horizontal axis wind turbine must rotate continuously with the change of wind direction
Table 1 Comparison of vertical axis wind turbine and horizontal axis wind turbine

2. horizontal axis wind turbines
A wind turbine whose installation position of the axis of the wind rotor and the horizontal plane is not more than 15 degrees is called a horizontal axis wind turbine. The horizontal axis wind turbine blades are shown in Figure 1.

What are the characteristics of small wind turbines?
Figure 1 Horizontal axis wind turbine blade

The horizontal axis wind turbine can be a lift device (that is, the lift drives the wind wheel), or it can be a resistance device (the resistance drives the wind wheel). Most horizontal axis wind turbines have an opposite wind device. . There are three types of horizontal axial wind turbines: traditional windmills, low-speed wind turbines and high-speed wind turbines. The main technical parameters of the horizontal axis wind turbine are:
(1) The diameter of the wind wheel, usually the larger the power of the wind turbine, the larger the diameter.
(2) The number of blades, the wind turbine for high-speed power generation is 2~4 pieces, and the low-speed wind turbine is more than 4 pieces.
(3) Blade materials, modern small wind turbine blades use high-strength and low-density composite materials.
(4) The wind energy utilization coefficient is generally between 0.15 and 0.5.
(5) Start wind speed, generally 3~5m/s
(6) Shutdown wind speed, usually 15~35m/s
(7) The output power of modern small wind turbines is generally several hundred watts to several kilowatts.
(8) Generator, divided into DC generator and AC generator.
(9) Tower height, etc.

There are many styles of horizontal axis wind turbines, some have wind rotors with reversing blades, and some horizontal axis wind turbines generate vortices around the wind rotor to concentrate the airflow and increase the airflow speed. The FD series small horizontal axis wind turbine designed with innovative technology has the following advantages
(1) The starting resistance of the wind turbine is greatly reduced, and the wind speed can be started when the wind speed is 2m/s. The best level in various countries is 3.5~4m/s start-up.
(2) The horizontal axis technology is adopted to reduce various mechanical losses and electromagnetic losses in the operation of the motor, so that the power generation under the same wind speed is increased by nearly 20%, especially the power generation at low wind speed is significantly improved.
(3) After using the horizontal axis technology to reduce various losses of the motor, the service life is also greatly extended.
(4) The shell of the wind turbine is made of high-strength aluminum alloy by precision die-casting process, light weight, high strength, no rust, corrosion resistance and salt spray resistance,
(5) The generator adopts high-efficiency and high-temperature resistant materials, and the stator components are treated by vacuum dipping process, which greatly improves the insulation performance and service life.
(6) The wind wheel is carefully designed by aerodynamic optimization software, with high utilization rate of wind energy and low operating noise. The impeller is dynamically balanced to ensure quiet and smooth operation. The blades are made of advanced polymer composite materials, which have good strength and toughness, light weight and no deformation. Its tensile strength, service life and consistency are much higher than wood blades, fiberglass and plastic blades.
(7) The whole machine adopts anti-rust treatment, and all external fasteners of the motor are made of stainless steel. The service life is greatly improved in rainy and salt spray areas.
(8) The structure is simple, no professional knowledge is required, and the installation and debugging work can be completed with simple operations with ordinary tools.
(9) The controller of the FD series wind turbine adopts intelligent control, and has the indication function and automatic protection function for the normal charging, overcharging, overdischarging and other states of the battery. And automatically brake when the wind turbine is no-load to prevent accidental speeding.

3. Vertical Axis Wind Turbines
The wind wheel of the vertical axis wind turbine does not adjust its direction with the change of the wind direction. The wind wheel of the vertical axis wind turbine rotates around a vertical axis, and the axis of the wind wheel is perpendicular to the wind direction. The advantage is that it can accept wind from any direction, so when the wind direction changes, there is no need to face the wind. Since no direction adjusting device is required, its structural design is simplified. Another advantage of vertical axis wind turbines is that the gearbox and generator can be installed on the ground, which is very easy to maintain.

Although the vertical axis wind turbine has not yet been commercialized in large quantities, it has many characteristics, such as no need for large towers, generators can be installed on the ground, easy maintenance, and easy blade manufacturing. Vertical axis wind turbine.

There are three common structures of vertical axis wind turbines: S-type wind rotor, Darieu type wind rotor and rotor type wind rotor, as shown in Figure 2. The s-type wind rotor is composed of two semi-cylindrical blades whose axes are staggered. For larger wind turbines, it is more difficult to adopt this structure because of the limitation of deflection and safety limit stress.

What are the characteristics of small wind turbines?
Figure 2 Vertical axis wind turbine

The Darrieu type wind turbine, which uses the lift of the airfoil to do work, is the main competitor of the horizontal axis wind turbine. Darieu wind turbines come in many forms, basically straight blades and curved blades.

When the wind direction changes, the vertical axis wind turbine does not need to face the wind direction. In this regard, it is a big advantage compared to the horizontal axis wind turbine, which simplifies the structure and reduces the gyroscopic force when the wind rotor is opposite to the wind direction.

In theory, the rotary-wing wind turbine does not require a windward device like the horizontal-axis wind turbine, but it also has the problem of speed limit exceeding the working speed. In order to limit the speed, its mechanism must be complicated, and the advantages of its simple structure no longer exist. The wind turbine has not yet entered the stage of popularization and application due to some technical difficulties that have not yet been resolved.

The earliest vertical axis wind turbine is a circular arc-shaped double-blade structure (Φ type or called Darryl), which has not been vigorously developed due to its small wind receiving area and high corresponding starting wind speed. H-shaped wind turbines are closely related to the development of science and technology, especially the development of computer technology. Since the design of H-shaped vertical axis wind turbines requires a large number of air-hole mechanics calculations and digital simulation calculations, it takes at least a few Years, and not one calculation can get the correct result, so in the age when computers were not very developed, people could not complete this design idea at all.

The H-type vertical axis wind turbine adopts the principle of air tunnel mechanics. For the wind tunnel simulation of vertical axis rotation, the blade adopts the shape of an aircraft wing. When the wind rotor rotates, it will not be deformed and change its efficiency; it is composed of vertical straight lines. It consists of 4-5 blades, the blades are fixed by a 4- or 5-angled wheel hub, and the wind wheel is composed of a connecting rod connecting the blades.

According to the principle of the H-type wind turbine, the speed of the rotor speed rises faster (the torque rises quickly), and the power generation rate of the generator it drives increases correspondingly faster, and the power generation curve becomes full. Under the same power, the rated wind speed of the vertical axis wind turbine is smaller than that of the existing horizontal axis wind turbine, and the power generation is also larger when the wind speed is low.

Because this design structure adopts the special air tunnel mechanics principle, the connection method of the triangle vector method and the direct drive structure, the force of the wind rotor is mainly concentrated on the wheel load, so the wind resistance ability is strong; the characteristics of this design It is also reflected in the impact on the surrounding environment, no noise during operation and small electromagnetic interference, which makes the new vertical axis wind turbine very obvious.

At present, Japan produces the most products of this type of vertical axis wind turbines. At present, the United Kingdom, Canada and other countries are also developing. Most of the products in these countries use parallel connecting rods in the design of wind turbines. The shaft requirements are high, the structure is relatively complex, and there are many on-site installation procedures. In addition, from the mechanical analysis, the larger the power of the H-type vertical axis wind turbine, the longer the blade, the longer the distance between the center point of the parallel rod and the center point of the generator shaft, the worse the wind resistance. Therefore, the triangular vector The connection method of the method can make up for some of the above shortcomings.

4. Wind turbine output characteristics
The torque produced by a horizontal axis rotor with a fixed pitch varies with wind speed and rotational speed. If the rotational speed of the blades is too low, the blades will stall and the torque output by the rotor will drop, so in order to get the maximum power output from the airflow (when the airflow is When the speed is changed) the pitch angle of the blade or the rotational speed of the blade must be changed. Many wind turbine rotors are now designed with variable pitch blades.

A wind turbine can draw maximum power from the air if its rotor speed varies with wind speed, but this is not optimal for a generator driven by the rotor. The solution to the optimal design is to allow the rotor speed to vary with the wind speed, and to use a variable-speed constant-frequency power generation system to obtain electrical energy at the required frequency. The output power curve of the wind turbine is shown in Figure 3, where is the starting wind speed and is the rated wind speed. At this time, the rated power output of the wind turbine is the cut-off wind speed.

What are the characteristics of small wind turbines?
Figure 3 Wind turbine output power curve

When the wind speed is lower than the starting wind speed, the wind turbine cannot rotate. When the wind speed reaches the starting wind speed, the wind turbine starts to rotate, driving the generator to generate electricity. The output power supplies the load and charges the battery. When the terminal voltage of the battery pack reaches the set maximum value, the signal voltage obtained from the voltage detection is switched by the control circuit, so that the system enters the voltage regulation closed-loop control, which not only keeps the battery charged, but also does not cause the battery to be overcharged. When the wind speed exceeds the cut-off wind speed, the wind turbine uses the mechanical speed limiting mechanism to make the wind turbine run at a limited speed or stop running at a certain speed to ensure that the wind turbine will not be damaged.

Ordinary wind turbines need at least a wind speed of 3m/s to start, and a wind speed of 3.5m/s to generate electricity. However, the use of all permanent magnet suspension wind turbines, due to the use of magnetic suspension bearings with micro-friction and small starting torque, can start at a weak wind speed of 1.5m/s, and can generate electricity at a wind speed of 2.5m/s, and the energy efficiency is improved by about 20%. The starting torque of the all permanent magnet suspension wind turbine is reduced to about 1/12 of the national standard, the starting wind speed is reduced by 57.14%, the cut-in wind speed is reduced by 23.81%, and the rated power is increased by 20.57%.

5. Output power of the wind turbine
The rated output power of the wind turbine is determined according to the specific rated wind speed design. Since the energy is proportional to the cube of the wind speed, the power of the wind turbine will vary greatly with the wind speed. Wind turbines of the same construction and rotor diameter can be equipped with generators of different sizes. Therefore, two wind turbines of the same construction and rotor diameter have different rated output power values, depending on whether it is designed for strong wind areas (with larger generators) or weak wind areas (with smaller generators).

The rated power of the generator refers to the power output by the generator at the rated speed. Since the wind speed is not a stable value, the generator speed will change with the wind speed, so the output power will also change with the wind speed. When the wind speed is lower than the design wind speed, the actual output power of the generator will not reach the rated value; when the wind speed is higher than the design wind speed, the actual output power will be higher than the rated value. Of course, due to the limitation of the speed-limiting and speed-regulating device of the wind turbine and the design parameters of the generator itself, the output power of the generator will not increase infinitely, but can only change within a certain range.

When the wind speed is very low, the rotor of the wind turbine will remain stationary. When the cut-in wind speed is reached, the rotor begins to spin and the traction generator begins to generate electricity. As the wind gets stronger, the output power increases. When the wind speed reaches the rated wind speed, the generator will output its rated power. After that, the output power will remain roughly unchanged. When the wind speed further increases and reaches the cut-out wind speed, the wind turbine will brake and no longer output power, so as to avoid damage to the wind turbine. The performance of the wind turbine can be expressed by the power curve, as shown in Figure 4. The power curve shows the output power of the wind turbine at different wind speeds (cut-in wind speed to cut-out wind speed). To select a suitable wind turbine for a specific location, the general method is to use the power curve of the wind turbine and the wind data of the location to estimate the power generation.

What are the characteristics of small wind turbines?
Figure 4 Wind turbine power curve