SOWAKAM
  Usually, the blowers and induced draft fans on the boiler have motors running at a fixed speed, and the air volume is adjusted by changing the baffle opening at the fan inlet; the characteristic of the fan is that the load torque is proportional to the square of the rotational speed, and the shaft Power is proportional to the cube of rotational speed and is a square torque load. For square torque loads such as fans, the power consumption accounts for about 70% of the total industrial power consumption. Using variable frequency speed regulation technology, the power consumption can generally be reduced to 60%-70% of the rated power on average, and the energy saving effect is remarkable. .
1. Principle of VFD Inverter speed regulation
  VFD Inverter is produced with the development and integration of microelectronic technology and applied variable frequency technology. The most important function of VFD Inverter is to change the power frequency of the transmission system under normal working conditions, adjust the working power supply and voltage, and realize the Control of the running state of the motor.

  VFD Inverter generally consist of rectifiers, filters, drive circuits, protection circuits and controllers (MCU/DSP). Under normal working conditions, the AC output from the motor power supply passes through the rectifier and is filtered by a capacitor to form a DC voltage with a basically fixed amplitude and apply it to the inverter. A rectangular pulse waveform of a certain shape is obtained at the end. Here, the voltage amplitude is controlled by changing the width of the rectangular pulse; the output frequency is controlled by changing the modulation period, so that the output voltage and frequency can be controlled simultaneously on the inverter to meet the requirements of frequency control for coordinated control. Capable of generating AC power for a wide variety of motor power supplies.

2. Analysis of wind turbine modification plan

  According to the electric transmission theory, the energy-saving effect of frequency conversion is different for different types of loads, and the energy-saving effect of frequency conversion for square torque loads is very obvious.

  The load of the fan belongs to the quadratic law load, and its mechanical characteristics are as follows.

 There are many methods for speed regulation of asynchronous motors, such as pole-changing speed regulation, variable slip speed regulation and variable frequency speed regulation. The first two have large slip losses, low efficiency, and have certain limitations on motor characteristics. Variable frequency speed regulation achieves motor speed regulation by changing the frequency of the stator power supply to change the synchronous frequency. During the entire process of speed regulation, a limited slip rate can be maintained from high speed to low speed, so it has the performance of high efficiency, wide speed regulation range (10~100%) and high precision, and the power saving effect can reach 20~30%. 

  To improve the working efficiency of the motor and save electric energy, a speed regulating device can be installed on the corresponding fan motor. Adjusting the speed regulator according to the working conditions can meet the requirements of the working conditions. According to the fact that when the fan is running at low speed, the resistance torque is very small, and there is no problem of being unable to carry the load at low frequency, so the control method can be used. In addition, it is not necessary to make major changes to the original system by using a frequency converter to transform the fan. During the variable frequency transformation process, the VFD Inverter can be adjusted as needed to meet working requirements.

3 Conclusion

After the VFD Inverter is used, not only many tedious manual operations are eliminated, but also many unsafe hidden dangers are eliminated. And the system is always running in an energy-saving state, and the reasonable rotation of the motor prolongs the service life of the equipment and better adapts to the production needs. At the same time, the fan can start and stop softly, reducing the mechanical impact of the equipment, extending the service life of the equipment, and reducing the maintenance costs of the equipment. Moreover, the inverter's rich internal control functions can easily achieve closed-loop automatic control with other control systems or equipment. Using AC VFD Inverter to carry out energy-saving transformation of fans has the advantages of simple structure, convenient transformation, obvious energy-saving effect and short investment recovery period, so it is worthy of promotion.