Application of Siemens 6SE70 series VFD (Variable-frequency Drive) in paper machine drive

Core Tips:

Many old paper machines use single DC motor drive, which distributes the speed mechanically. Due to mechanical wear and belt slippage during the production process, speed matching is mismatched, which easily leads to paper breakage and uneven thickness. At the same time, due to the high temperature and humidity on site, the maintenance of the motor increases. In order to optimize product quality and improve labor productivity, many sites have changed it to multi-motor segment drive, that is, the mechanical transmission part of the DC motor and its power is cancelled, and AC motors are installed in each transmission segment, using AC multi-point drive.

1. Requirements for drive control of paper machines

The drive of paper machines includes mesh, press, drying cylinder, sizing, calendering, winding and other segments. Its drive is variable speed drive.

In order to meet the needs of changes in paper characteristics during the production process, the drive of the paper machine must be able to adjust the speed within a certain range, and the speed of each segment can be adjusted separately.

A. The speed of each segment is accurate and easy to adjust.

B. High transmission efficiency, reducing power by 10%-15%.

C. The load control and transmission management of each part are relatively convenient.

D. It is convenient for automatic control and adjustment of the production process, reducing maintenance costs and saving labor.

2. VFD (Variable-frequency Drive) selection

According to the control requirements of the paper machine for transmission, Siemens vector variable frequency speed regulator 6SE70 is selected, with the following features:

A. Industrial VFD (Variable-frequency Drive), more suitable for industrial production sites with harsh environments than general products.

B. Standardization and modularization. The structure of the entire VFD (Variable-frequency Drive) is very compact. The main board and expansion board are connected through bus slots, and the components are close to each other for easy maintenance. Due to the improvement of integration, the device has high reliability.

C. It has good interference resistance, reliable operation, is not affected by component aging and temperature drift, and can maintain stable control accuracy for a long time.

D. It can adapt to a wide range of power supply voltage fluctuations and can automatically adapt to the grid frequency changes of 45-65HZ.

E. It has a strong self-diagnosis processing function, providing supplementary information about the cause of the fault, making troubleshooting simpler and maintenance convenient.

F. Flexible and changeable communication capabilities. It can communicate and network in various ways such as USS, PEER TO PEER, PROFIBUS-DP, CAN, SIMOLINK, etc.

G. 32-bit CPU full digital control, rich configuration functions.

H. It can be optimized for specific AC motors to achieve excellent control performance.

I. It can also provide rated torque at low speed.

3. Synchronization

In the papermaking process, it is particularly important to maintain synchronous operation between various transmission subsystems. This synchronization is not only required during steady-speed operation, but also during the dynamic process of acceleration and deceleration. To this end, we take the following two measures to achieve the purpose of synchronization.

3.1 Improve the dynamic response of the system

All VFDs (Variable-frequency Drives) use the feedback method of photoelectric encoders. Through vector operations, it can determine and control the current components of torque and flux, and obtain dynamic characteristics comparable to DC drives. This basically ensures the feasibility of synchronization.

3.2 Establishing a speed set value chain

Establish a device-to-device communication process between each VFD (Variable-frequency Drive). In this way, the speed set value can be quickly and accurately transmitted to the first VFD (Variable-frequency Drive) in digital form, eliminating the adverse effects of signal drift and interference caused by line loss and interference in analog signal transmission. The different mechanical changes between each division are controlled by different proportional factors inside the VFD (Variable-frequency Drive), thereby achieving constant proportional operation of the linear speed of each division in dynamic and steady states.

The VFD (Variable-frequency Drive) option board SCB2 has an electrically isolated RS485 port, which can realize device-to-device connection between multifunctional VFDs (Variable-frequency Drives) through X129. Here, we use a parallel connection method, with one VFD (Variable-frequency Drive) as the active device and the others as slave devices. In this way, the active device can transmit the system linear speed set value to the slave device, thereby increasing the reliability of the entire system. Through the transformation of the paper machine production line, the user believes that the use of Siemens 6SE70 variable frequency speed control system has significant advantages in improving product quality, output, reducing daily maintenance and energy saving, and can fully meet the needs of the production site.