Application of analytical encoder in wind power control system

With the gradual depletion of conventional energy such as coal and oil, human beings pay more and more attention to the development and utilization of new energy (unconventional energy). New energy refers to various forms of energy other than traditional energy, such as solar energy, geothermal energy, wind energy, ocean energy, biomass energy and nuclear fusion energy. Among them, wind energy is favored for its unique advantages. Compared with other new energy sources, wind energy has three major advantages: first, large reserves and wide distribution; Second, the availability is strong, the cost is relatively low; Third, green energy, does not pollute the environment.

As a kind of clean energy using wind energy, wind power is playing an increasingly important role in environmental protection today. In recent years, the global wind energy market has been developing rapidly at an annual rate of more than 40%, and China has become the world's most important wind energy market after Europe and the United States with its rich wind farm resources and the government's strong support for new energy development, which has brought development opportunities to China's wind energy equipment manufacturing industry. China is rich in wind energy resources, with theoretical reserves of 1.6 billion kilowatts and actual utilizable amounts of 250 million kilowatts, which has great development potential. At the same time, in the national new energy development plan, the wind power generation as a key support industry, so that China's wind power industry has a broader development prospects.

Therefore, wind power has maintained double growth in recent years, the growth rate of wind turbines in 2008 was affected by GDP, but it also exceeded 80%, and the ratio of localization has exceeded 70%. If the wind energy industry wants healthy and sustainable growth, it is necessary to complete the construction of the industrial system and the construction of the industrial chain. The company seized the opportunity, timely development of product routes and solutions to meet the needs, and has been successfully applied in a number of wind farms.

1, horizontal axis wind turbine composition

Based on the more efficient acquisition and utilization of wind energy, the current wind power industry mainly uses horizontal axis wind turbines, whose composition is shown in the figure on the right:

Rotor blades: capture wind energy and convert it into rotational energy for a rotating shaft;

Rotating shaft: converts the rotating energy into the kinetic energy of the generator;

Gearbox: used to increase the shaft speed between the rotor center and the generator;

Generator: using the rotating energy of the rotating shaft to generate electricity through the electromagnetic principle;

Yaw controller (not shown) : Move the rotor to align it with the wind direction;

Braking device: stop the shaft rotation in case of power overload or system failure;

Tower: support the rotor and engine case, and raise the position of the entire device;

2, wind power generation control system

Wind power generation system is the core link in the field of wind power generation, and its technological innovation is very important. At present, the main use of constant speed constant frequency and variable speed constant frequency wind turbine system two categories. In wind power generation, when the wind turbine is connected to the grid, the frequency of the wind power is required to be consistent with the frequency of the grid, that is, constant frequency. Constant speed constant frequency that is, in the process of wind power generation, keep the speed of the windmill (that is, the speed of the generator) unchanged, so as to obtain constant frequency of electric energy. In the process of wind power generation, the speed of the windmill changes with the wind speed, and the method of obtaining constant frequency electric energy through other control methods is called variable speed constant frequency.

Because the wind energy is proportional to the third power of the wind speed, when the wind speed changes in a certain range, if the windmill is allowed to do variable speed movement, it can achieve the purpose of better use of wind energy. The efficiency with which a windmill converts wind energy into mechanical energy can be expressed by the output power coefficient CP, which reaches its maximum value at a certain turbine velocity ratio λ(the ratio of blade tip speed to wind speed). The windmill speed of the constant speed constant frequency unit remains the same, and the wind speed is often changing, obviously CP cannot be maintained at the optimal value. The characteristic of variable speed constant frequency unit is that the speed of the windmill and generator can be changed in a wide range without affecting the frequency of the output power. Due to the variable speed of the windmill, the cycle speed ratio of the windmill can be at or close to the optimal value through proper control, so as to maximize the use of wind power generation. Therefore, the variable speed constant frequency wind power generation system is more and more popular in the wind power generation industry because of its high wind energy utilization coefficient, which can absorb the energy fluctuation caused by the sudden change of wind speed to avoid the spindle and transmission mechanism to bear too much torque and stress, and can improve the power factor of the system.

The function of variable speed constant frequency control is to ensure the quality of online power, so the speed of the generator must be measured and fed back to the controller to achieve closed-loop control. At present, the rotating encoder is used to detect the generator speed. At the same time, due to the large power of the generator, the shaft current will be generated, if the encoder and the generator are not insulated, the shaft current will be introduced into the encoder, and then damage the encoder. Eke's EV88P series encoders adopt a unique mechanical design concept to ensure the vibration and shock resistance of the product, and adopt advanced European electrical design technology to ensure the reliable output of the product under the temperature condition of -40~85℃. At the same time, advanced insulation treatment technology is used to effectively prevent shaft current damage to the encoder. The EV88P series encoder, with its excellent performance characteristics and stable operation, has been successfully applied in a wind power equipment manufacturer in North China, and its stable operation in the wind farm has been recognized by customers.

3. Variable pitch control system for wind power generation

In terms of wind power technology development, the single capacity of wind turbines is developing towards large-scale, and megawatt wind turbines have become the mainstream products in the wind power market. At present, variable pitch control technology is widely used in large wind turbines. Variable pitch control is to control the blade rotation along the longitudinal axis of the blade, adjust the pitch Angle at any time according to the change of wind speed, control the energy absorption of the wind wheel, and maintain a certain output power. The advantages of variable pitch control are to ensure the rated power of high wind speed, stable output above the rated power point, high wind energy utilization coefficient at the rated point, improve the starting performance and braking performance of the wind turbine, improve the overall flexibility of the fan, and reduce the force condition of the whole machine and blade. In the grid-connection process, the variable pitch control can also realize fast and shock-free grid-connection. The combination of variable pitch control system and variable speed constant frequency technology finally improves the power generation efficiency and power quality of the whole wind power generation system.

There are two kinds of actuator in pitch control system, hydraulic pitch actuator and electric pitch actuator. Among them, the motor variable propeller actuator is the use of motor to control the blade, compact structure, flexible control, reliable action, there is no nonlinear hydraulic actuator, oil leakage, jam and other phenomena. The motor pitch control mechanism can adjust each blade individually using a servo motor. The servo motor directly controls the pitch Angle of the blade by meshing with the inner tooth ring of the impeller hub through the driving gear. The rotary encoder feeds back the change of pitch Angle to the controller, and then performs closed-loop PID negative feedback control on the motor.

EB58 series incremental encoders, EAS58 series analog output absolute encoders and EAM58 series SSI output absolute encoders provide cost-effective sensor solutions for wind power customers with excellent mechanical vibration resistance and stable electrical output performance under -40℃ temperature conditions. Among them, the EB58 series encoder is used for servo motor signal feedback in the variable pitch system to control blade Angle control, and the use of EAS58 or EAM58 series encoder to give absolute position information feedback to the variable pitch Angle. EB58 and EAS58 series encoders have been successfully applied in a wind power equipment manufacturer in North China, and have been greatly recognized by customers.

4. Concluding remarks

Wind power generation technology has become increasingly mature, occupies a prominent position in the field of renewable green energy development, and has important development and utilization value. Especially in remote mountainous areas, pastoral areas and island areas, wind power generation can provide clean energy for the life and production of local residents, and alleviate the shortage of energy supply.

In the past, investors and operators paid more attention to the price of the product, and in the whole life cycle, the maintenance cost accounted for 40% to 70%, mainly depending on the quality of the product. More and more wind power users are shifting their focus to how to improve product quality and enhance reliability while reducing maintenance costs. With a strong technical accumulation and excellent product quality, a company like Ike can enrich and improve China's wind power industry chain, help wind power equipment manufacturers improve product quality and minimize maintenance costs.