Application Direction of Frequency Control Technology in Industry

Most industrial motor frequency converters (hereinafter referred to as VFD) are electrical devices that convert industrial frequency AC power into frequency and voltage adjustable AC power to achieve AC motor speed regulation, and have been widely used in various fields of industrial and agricultural production. Therefore, the application knowledge of VFD is one of the necessary skills for mechanical and electrical engineering technicians.

VFD adopts high-performance U/f control and vector control technology, provides low-speed high-torque output, has good dynamic characteristics and overload capacity, and innovative internal interconnection function has unparalleled flexibility. VFD can work in the default factory setting state. It is an ideal variable frequency drive for powering a large number of simple motor variable speed drive systems. Users can set relevant parameters according to their needs, make full use of VFD’s comprehensive and complete control functions, and serve complex motor control systems that require multiple functions. VFD is an electrical device that converts industrial frequency AC power into three-phase AC power with adjustable frequency and voltage, and is used to drive AC asynchronous motors to achieve frequency conversion and speed regulation.

1. Motor variable frequency drive

(1) Using VFD can realize AC motor speed regulation. Since the VFD can be regarded as a frequency-adjustable AC power supply, for the existing constant-speed motor, only the VFD and its corresponding equipment need to be connected between the power supply and the motor to realize the speed regulation of the motor. Any equipment modifications to the motor and its system.

(2) The speed regulation range is large and the speed regulation precision is high. The speed range of ordinary VFD can reach 1:10, and the speed range of high-performance vectorVFD can reach 1:1000. In addition, using VFD, this vector control method to control the speed of the induction motor, can also control the output torque of the motor.

(3) The starting current of the motor is reduced. When the motor is started directly, the starting current of the power frequency motor is 4-7 times the rated current, which will greatly increase the electrical stress of the motor coil and generate heat, thereby shortening the service life of the motor. When the VFD is used for speed regulation, it can start from zero speed and zero voltage, and accelerate according to the law of the slope function, thereby limiting the starting current of the motor.

(4) High-speed, high-voltage, high-current control; now the output frequency of high-frequency VFD can reach 3000KHz, and high-speed VFD can drive a two-pole asynchronous motor to a high speed of 180,000 rpm. With the continuous development of frequency conversion technology, the output frequency of high-frequency VFD is also increasing, and the high-speed drive of VFD is a major advantage of its speed regulation.

2. Energy saving

Using frequency conversion speed regulation, fans, water pumps and other loads, the energy saving rate can reach 10%-30%, up to 60%. Because the actual power consumption of fans and pumps is approximately proportional to the third power of the speed. The application of energy-saving VFDs has developed rapidly in recent decades. According to relevant statistics, the negative shear capacity of fans and water pumps that have undergone frequency conversion transformation in my country only accounts for about 5% of the total capacity, and there is still a lot of room for transformation. In this regard, fans, pumps, etc. The frequency conversion speed regulation can save a lot of electric energy, and the investment can be recovered in a short time, so it is the most widely used. Successful applications include constant pressure water supply, various types of fans, central air conditioning, hydraulic pump frequency control, etc.

3. Precise control

With the development of control technology, in addition to the basic speed control, VFD also adds a variety of computing and intelligent control functions, and the output accuracy is between 0.1% and 0.01%. VFD is also equipped with complete detection and protection links, so it is widely used in automation systems such as printing, elevators, textiles, machine tools, and speed control on production lines.

4. Improve the craft level and product quality.

VFD is also widely used in the field of control of various mechanical equipment such as conveying, lifting, extrusion, and machine tools. , can improve the process level and product quality, reduce the impact and noise of the equipment, and prolong the service life of the equipment. After these machines are controlled by frequency conversion, the mechanical equipment can be simplified, and the operation control is more humanized. Some can change the original process specification, so as to improve the function of the whole equipment.

5. New energy power generation

With the increase of the power of wind turbines, the blades of wind turbines have weighed several tons or dozens of tons. It is quite difficult to control such a large moment of inertia to keep up with the change of wind speed in response to the speed demand. In recent years, variable pitch wind turbines have been put into operation. On the one hand, the blade angle is controlled by pitch; on the other hand, the rotor current of the generator is controlled by fanVFD. Pitch control is a relatively slow process, and the action time is calculated in seconds. It is not ideal for the situation where the wind speed and power output change rapidly. But the action time of VFD to control the generator rotor current frequency is below the millisecond level.

Therefore, when the high-frequency wind speed changes, the generator rotor current frequency can be instantaneously changed by the high-power and high-load VFD, which can ensure that the generator set keeps up with the frequent changes in wind speed, stabilize the power output of the generator set, reduce the adverse impact on the power grid, and reduce the The operating frequency of the pitch control mechanism is improved, and the service life of the pitch control mechanism is extended.