The application and development prospects of DC speed regulation and AC speed regulation in continuous rolling production
Abstract: With the development of technology, the speed regulatory control of continuous rolling production line has also been continuously optimized and upgraded. At present, both DC speed regulation and AC speed regulation have been widely used in continuous rolling workshop applications. In this paper, based on the analysis of the current application of the two speed regulating methods in continuous rolling production, its advantage and disadvantage, it is concluded that DC speed regulation and AC speed regulation have their own advantages and can be complementary. In the future application of continuous rolling production, the combination of DC speed regulation and AC speed regulation will be the mainstream.
Keywords: Continuous Rolling, DC Speed Regulation, AC Speed Regulation
1 Introduction
Roofing is continuous steel forming. From the initial coiled material to the final qualified plate, different technical instruments and equipment are used in each process to ensure product quality. As the “brain” of the rolling production line, the speed regulation function of the drive system is particularly important. The speed regulation of the roll-shaping drive system is the most basic and core content of the whole production technology and process. Based on the characteristics of the drive system, the appropriate speed regulation mode can improve the production capacity of the rolled product plane to a certain extent and achieve good economic benefits.
At present, the speed regulation of continuous rolling production line mainly uses two kinds of modes, one is DC speed regulation and the other is AC speed regulation. According to the analysis, due to the different application principles and technical characteristics of the two methods, there are great differences in the industrial application of DC speed regulation and AC speed regulation. The former is suitable for large and medium-sized rolling line, and the latter is suitable for small line and production line with small production capacity.
2 The application of DC speed regulation and AC speed regulation in continuous rolling production
2.1 DC speed regulation
DC speed regulation is the kind of speed regulation mode earlier used in roll forming production line. It changes the power frequency to drive motor to regulate the speed by controlling the firing Angle of semiconductor rectifier in the control loop. In the DC speed regulation system, the control circuit is simple and reasonable, and the reliability and speed response are better than those of the AC speed regulation system. In addition, The DC speed regulation system has a wide speed range and can be used in high-speed production lines with large transmission torque.
The traditional DC speed regulating system consists of energy-storing thyristor power supply, speed detecting device, DC motor and speed adjusting controller, as shown in Figure 1. The working principle of the system is that when the speed regulating controller receives the speed instruction, it accurately controls the inlet Angle a of the thyristor, so that the larger the inlet Angle , the larger the DC voltage U, the greater the torque and the faster the motor speed N.
2.2 AC speed regulation
AC speed regulation is a new speed regulating mode which has been widely used in recent years. This speed control system uses frequency conversion, PLC, voltage source converter, AC motor and other technologies. Frequency conversion speed regulating device can be adjusted in the range of 0-50Hz. In addition, it can be divided into vector control and scalar control according to the control mode of AC motor. Compared with DC speed regulation, the system structure of AC speed regulation is relatively complex, but its speed and accuracy of control are very high.
The structure of AC speed regulating system is shown in Fig. 2, which is composed of frequency converter, PLC, AC motor and other components. The frequency converter unit consists of rectifier, DC link, inverter and so on. The control unit outside the frequency converter is composed of a dedicated controller or a programmable logic controller. The working principle of FR speed regulation is based on the output power frequency of the inverter. When the PLC receives the set speed instruction, the drive frequency modulation instruction S is issued to the frequency converter according to the required output speed, and the frequency converter output is changed accordingly.
3 The advantages and disadvantages of DC speed regulation and AC speed regulation
3.1 Advantages of DC speed regulation
First of all, DC speed regulation uses semiconductor components as the main switching elements, which has the advantages of fast dynamic response and low cost. Secondly, the circuit of DC speed control is simple and the driving power is large; Once the speed control mode is selected, the current and voltage of the system will stay in a steady state, so the stability of the system running is very good; In addition, due to its simple structure, the maintenance of DC speed regulation system is simpler than AC speed regulation.
3.2 Advantages of AC speed regulation
First of all, AC speed regulation has a wide range of speed regulation, and the speed regulation accuracy can reach 0.1Hz; Afterwards, the vector speed regulation can make use of the torque capability of the motor itself, so not only can the output torque of the motor be ensured, but also the motor noise can be reduced and the motor life can be extended. In addition, since the speed regulating system is PLC-controlled, the fault diagnosis and diagnosis capability of the system is greatly improved, which greatly reduces the fault handling time.
3.3 Comparative analysis of DC speed regulation and AC speed regulation
Advantages of DC speed regulation advantage: DC speed regulating system has the advantage of simple system structure and good stability. It can respond quickly to speed modulating signals and its dynamic performance is good.
Disadvantage: the cost of the system is relatively high, and its speed control accuracy is not high.
Advantages of AC speed regulation: AC speed regulating system is suitable for small-scale continuous rolling production line. It can accurately control the speed and has wide speed regulating range. In addition, its fault diagnosis and fault handling ability is strong.
Disadvantages: the system circuit is complex and the system responsiveness is slow.
4 Development prospects
At present, DC speed regulation and AC speed regulation are widely used in continuous rolling workshop applications. The two speed regulating methods have their own advantages and can be complementary to each other. In the future application of continuous rolling production, the combination of DC speed regulation and AC speed regulation will be the mainstream, which will realize the optimization and upgrade of continuous rolling production technology, which can obviously improve the production capacity of rollers and reduce the labor intensity of workers, thus improving the economic benefits of continuous rolling enterprises.
