Abstract: This paper introduces the process adaptability and technical characteristics of variable frequency speed control in the electrical control of the cleaning and combing unit. It briefly introduces the advantages of several variable frequency speed control methods and illustrates the specific applications of variable frequency speed control in process adjustment, energy saving and consumption reduction based on the control currently used in the cleaning and combing unit.
Keywords: Variable frequency speed control, Vector control, V/F control, Process adjustment, Energy saving and consumption reduction
Application of Frequency conversion speed control
in Blowing-carding System
Yang Ruibiao
(Qingdao Hongda Textile Machinery CO.,LTD)
Abstract Technology characteristic and superiority of frequency conversion speed control are introduced. According to blowing-carding system control mode to expound application of Frequency conversion speed control in cotton spinning technology regulate and reduce waste and losses, improve quality.
Key Words Frequency conversion speed control, Vector control, V/F control, technology regulation, reduce waste and losses, improve quality.
1. Requirements of the textile industry for control systems
my country's textile industry is accelerating its internationalization process, but there is still a gap compared to international standards. With increasing automation and rising competitiveness in cotton yarn quality, more demands are being placed on cotton spinning equipment: increasing output while maintaining stability, improving and stabilizing yarn quality, saving energy and reducing consumption, and adapting to multi-variety, small-batch production, among others. As a pre-spinning stage, the quality indicators of the carding and combing system have a significant impact on the final yarn quality. The continuous increase in costs has led many textile mills to place higher demands on cost, efficiency, the precision and stability of electrical control, and the applicability of the process. The emergence of control methods such as frequency converter control and servo control has provided solutions to these problems. While servo control systems offer precise control, their cost is too high. Compared to servo control, frequency converter control offers a higher cost-performance ratio, which is why it is widely used in the cotton spinning industry.
2. Comparison of Variable Frequency Drive Control Methods
2.1 V/F (Constant Voltage-Frequency Ratio) Control and its Characteristics
V/F control, as the name suggests, ensures that the output voltage is proportional to the frequency. The torque of an asynchronous motor is generated by the interaction between the motor's magnetic flux and the current flowing through the rotor. At the rated frequency, if the voltage is constant and only the frequency is reduced, the magnetic flux will be too large, causing magnetic circuit saturation, which can burn out the motor in severe cases. Therefore, the frequency and voltage must change proportionally; that is, the inverter's output voltage is controlled while the frequency is changed to keep the motor's magnetic flux constant, avoiding weak magnetic flux and magnetic saturation. This control method is often used in energy-saving inverters for fans and pumps. V/F control circuits have a simple structure, low cost, and good mechanical rigidity, meeting the smooth speed regulation requirements of general drives, and have been widely used in various industrial fields. The disadvantages are that at low frequencies, the rated torque output of the motor cannot be met, and V/F control makes the inverter operate according to a pre-set compensation level, which cannot change with load variations.
2.2 VC (Vector) Control and its Characteristics
Vector control achieves torque control by measuring and controlling the stator current vector of an asynchronous motor, and controlling the excitation current and torque current of the asynchronous motor separately based on the principle of field orientation. Specifically, the stator current vector of the asynchronous motor is decomposed into a current component that generates the magnetic field (excitation current) and a current component that generates torque (torque current), which are controlled separately. The amplitude and phase of the two components are also controlled simultaneously, hence the name vector control. Because vector control allows the frequency converter to change the output frequency and voltage in real time according to the frequency and load conditions, its dynamic performance is relatively complete. It features precise torque control, fast system response, wide speed range, and good acceleration and deceleration performance. In applications with high torque control requirements, its superior control performance is highly praised by users. Vector control is divided into two types: sensorless vector control and closed-loop vector control.
2.2.1 Sensorless vector control
Because vector inverters can detect and control the motor's flux and torque current separately, automatically changing the voltage and frequency to ensure consistency between the commanded value and the actual detected value, vector control is achieved. Although it is an open-loop control system, it significantly improves static accuracy and dynamic performance, achieving a speed accuracy of up to 5%. The speed response is also relatively fast. This scheme is very suitable for applications with less demanding requirements, offering a simple control structure and high reliability. Figure 1 shows the system block diagram of sensorless vector control:
Figure 1
2.2.2 Vector Control (Closed Loop)
The former control method adds a feedback loop. Vector closed-loop variable frequency speed regulation is the most ideal control method, similar to servo and DC closed-loop speed regulation, but with a significantly better cost-performance ratio. This scheme has the following advantages: speed control can start from zero speed, meaning it can operate even at very low speeds; the speed range can reach 100:1 or 1000:1; fast dynamic response and high speed accuracy; good acceleration characteristics and strong resistance to sudden load changes. Its disadvantages are: higher price; the speed sensor must be installed coaxially with the motor; and the added feedback loop increases the technical difficulty of installation and maintenance. Therefore, for applications where speed accuracy requirements are not particularly high and load changes are not drastic, an open-loop vector variable frequency speed regulation system is recommended. Figure 2 shows the control block diagram of the vector control variable frequency speed regulation system.
Figure 2
3. Application of Variable Frequency Speed Regulation in the Cotton Spinning Industry
3.1 Application in process adjustment
1. The cylinder motor has a large power and a very large starting current. The frequency conversion speed regulation realizes the soft start of the cylinder motor and eliminates the large current surge, thus extending the service life of the motor and equipment.
2. The use of frequency converters for the Doffer motor and the large pressure roller motor (three-roller section) greatly facilitates process adjustments, such as output, process draw ratio, and applicability to different products.
3. Due to rising labor costs, more and more lap-type carding machines are being converted to tin-type machines. This places higher demands on the control of cotton feeding at the rear of the carding machine. During low-speed yarn raising, the feeding motor operates at a low frequency, and insufficient torque leads to the "sleeping" phenomenon of the feeding roller. Unexpected drafting during the transition from slow to fast speed and the "jerking" caused by wear on the gearbox gears result in uneven sliver weight and severely excessive CV% (volume percentage), often leading to a significant drop in yarn grade or even rendering the yarn unqualified. The application of variable frequency speed control solves these problems.
4. The textile market is developing towards high productivity and high quality. The application of vector frequency conversion control in wide-width carding machines not only meets the torque requirements of carding machines when running at low speeds, but also avoids the impact of accidental drafting on cotton slivers during speed increases due to its good acceleration and deceleration performance. At the same time, it also has good dynamic performance at high speeds.
3.2 Energy saving and consumption reduction
1. The application of frequency converters eliminates the gearbox, inertia flywheel, brushed electromagnetic clutch, and dual-speed motor, thus reducing the most troublesome and time-consuming problems for maintenance workers, such as gearbox oil leaks, gear wear and replacement, and clutch failure. Due to the variety of product types, there are correspondingly many process wheels; reducing some of these process wheels reduces costs for enterprises to some extent.
2. Variable frequency speed control of fans and air conditioners offers considerable energy savings. As fluid mechanics shows, air volume Q is directly proportional to the first power of the rotational speed, and pressure h is directly proportional to the square of the rotational speed.
As can be seen from the formula, if the fan power is constant, when the required air volume is reduced, the rotational speed can be reduced proportionally.
At this point, the output power of the fan decreases in a cubic relationship. Fans are widely used in cotton spinning equipment.
Its transmission system primarily consists of high-power AC motors, including dust filter fans and stand-alone fans, consuming a significant amount of electricity.
This is a major user of cotton spinning equipment. Dust filter fans typically adjust airflow by changing the size of the pulley; single unit...
The fan regulates the airflow by adjusting the damper. While this method is simple, it relies on increasing...
Pipeline network losses come at the cost of consuming a large amount of energy. Using variable frequency speed control can fundamentally prevent this energy loss.
The waste is obvious, judging solely from formula (3.3), the electricity savings are considerable. Air conditioning is essential for cotton mills...
The preferred equipment for keeping the system off is the inverter air conditioner, which minimizes temperature fluctuations and avoids frequent on/off cycles.
It extends the compressor's lifespan and features high efficiency and energy saving. It also avoids the stress on the motor caused by frequent starts.
And damage to the power grid. It also ensured that the workshop temperature and humidity met the standard requirements, providing assurance for yarn quality.
Prerequisites.
4. Conclusion
The advantages and advanced nature of the control method, as well as its application in the cleaning and combing system, have verified the advantages of variable frequency speed regulation in terms of process adjustment, energy saving and consumption reduction in the cleaning and combing system.
References:
[1] Li Liangren. Variable Frequency Speed Control Technology and Application. Electronic Industry Press, 2009.
[2] Yuan Chi. Application of variable frequency speed regulation technology in automatic ventilation and temperature control system of cotton mill [J]. Machine Tool & Hydraulics. 2004, No. 5
[3] Li Qi. Speed regulation of frequency converters and their application in textile enterprises. Heilongjiang Textile. 2000, No. 4.
[4] Chu Xiaojiang, Zhou Lianxiu. Comparison of several AC speed regulation methods and application of frequency conversion speed regulation in our factory. Jiangxi Energy. 1995, No. 4
About the author: Yang Ruibiao (1984-), male, engineer, Qingdao, 266042
Mobile phone: 18853273711
