I. Introduction

The paper industry is one of my country's basic industries. There are a large number of domestic pulp and paper companies with a wide distribution. The old paper machine drive system mostly uses a DC motor to drive each drive roller shaft, which can achieve stepless speed regulation, but the existence of carbon brushes makes maintenance quite troublesome. With the development of AC frequency conversion control system and communication technology, AC frequency conversion transmission system is more and more widely used in new paper machines, with wide speed range, good speed performance, power saving and easy operation. The modern paper machine system adopts a system composed of upper computer, PLC, frequency converter and AC motor to complete the monitoring, operation and production management of the paper machine.

Two papermaking process

The paper machine mainly refers to a complete set of equipment linking the divisions of the pulp into the paper web. The basic components are divided into wire, pressing, pre-drying, post-pressing, post-drying, calender, reeling machine, etc. according to the order of paper formation. The process flow is as follows: the pulp output from the headbox is dehydrated and formed in the wire section, compressed in the press section to make the paper layer uniform, dried before drying, then enters the post press for sizing, and then enters the post dryer for drying treatment. Then the paper is smoothed with a calender, and finally a mother paper roll is formed by a paper reel. The process flow chart is as follows:

Three papermaking transmission control system composition and control characteristics

The papermaking process is a continuous production process, so continuous and orderly control of the production line becomes the key to the papermaking process. In recent years, a large number of inverters have entered the paper industry and have achieved good technical and market effects. The Renault RNB8 high-performance multi-transmission inverter has good vector control characteristics and rich control functions. The powerful programmable logic module allows Users can apply flexibly to meet the control requirements of complex processes. Take the transmission system of Shandong Tianhe Paper Co., Ltd. No. 10 as an example. The control part is mainly composed of Siemens PLC and Renault RNB8 series inverter. The on-site man-machine interface uses Siemens touch screen. The system has 38 transmission points.

The system network diagram is as follows:

3.1 System accuracy index

Under the influence of interference signals (such as load, supply voltage, temperature), the maximum deviation of the set value of the controllable variable reflects the stability of the drive control system. The following deviation refers to the maximum deviation of the controllable variable at the operating temperature, that is, the minimum level of accuracy.

Static speed control accuracy: 24 hours speed deviation ≤0.05% under rated speed

Speed difference between two adjacent transmission points in 24 hours≤0.05%

Dynamic speed control accuracy: short-term speed deviation when there is interference (such as load changes)

≤0.1%

Speed chain function:

The paper machine takes the screen drive roller as the speed reference, and other transmission points need to be coordinated and synchronized with it.

The whole machine has a full digital speed chain function. When the paper roll speed is increased, the speed and control parameters when the transmission system stops and restarts will maintain the state before stopping;

Load distribution function:

The load distribution of the wire section: the screen drive roller is the main drive, which runs in the speed control mode, and the vacuum roll and the first screen guide roll are auxiliary drives, and it runs in the torque control mode;

Vacuum press roll, vacuum press lower roll, and suction roll: The vacuum press roll is the main drive and runs in speed control mode, and the vacuum press lower roll and suction roll are driven by the torque control mode. The second pressure roller is the main drive and runs in the speed control mode. The second rubber roller is driven by the torque control mode, and the dryer guide roller drives the load distribution‘

The calender, sizing machine, and each dryer blanket roll do load distribution.

Branch operation function:

With start/stop, run/crawl, speed up/down, jog/tighten and other operation functions;

The dryer drive has a forward and reverse jog function, which is conducive to maintenance and cleaning of waste paper;

The calender and reel have soft tension control function.

Machine operation function:

The whole machine stops normally; the whole machine increases/decreases speed.

RNB8 is a new generation of all-round low-voltage AC drive products developed based on RENLE's high-end frequency conversion speed control product technology platform. It can meet the needs of any industrial process, automation system, user and enterprise, and provide users in various industries. And applications provide unprecedented compatibility and flexibility.

The RNB8 series multi-motor drive inverter is a multi-motor drive product with positioning multi-point drive applications, high-performance speed and torque control, convenient and flexible system integration. RNB8 products can be applied to various applications, such as: paper machine main drive production lines, textile printing and dyeing machines, chemical fiber plastics, printing and packaging and other complex systems with high performance requirements and multi-point transmission applications.

· Book-type modular design for saving cabinet space, suitable for compact installation of multiple units side by side, with high cabinet space utilization.

· Energy-saving and high-efficiency common DC bus connection, automatic distribution of electric power consumption and braking power generation energy, saving braking energy consumption, and high power utilization.

· Centralized power supply with low grid pollution reduces the harmonic pollution and EMI interference from the input side of the inverter to the grid.

· The communication technology adopts PROFIBUS-DP communication to realize the long-distance high-speed communication between the inverter and the inverter, and the inverter and the upper computer controller system.

· Excellent performance of multi-machine synchronous control. Multi-machine synchronous control has excellent performance of fast response, high precision and strong stability, and can realize the dynamic synchronous operation of multiple motors with load.

· Excellent performance of multi-machine synchronous control. Multi-machine synchronous control has excellent performance of fast response, high precision and strong stability, and can realize the dynamic synchronous operation of multiple motors with load.

4.1 Common DC bus electrical wiring diagram

Electrical diagram of public DC bus system

4.2 Vector control

This mode is a control mode established on the basis of the motor dynamic model and vector decoupling control principle. In theory, it is represented by an external speed loop and two internal current loops. This mode does not require speed feedback and can achieve medium speed regulation accuracy, with a speed regulation range of 1:50.

4.3 RNB8 master/slave control function realization

The master/slave control is applied to the occasion that multiple motors drive a device at the same time, and the load between the transmissions can be evenly distributed. This is the ideal application for motors coupled with each other through gears, chains, and conveyor belts.
The external control signal usually only needs to be connected to the main drive. The master can control up to 8 slaves through the CAN communication connection. The external control system can read the feedback information from the slave through the master.

Master/slave control connection diagram:

According to the coupling mode of the motor, it is divided into rigid connection and flexible connection:

• Rigid connection is realized by fixed connection of gears or chains. The speed of the master/slave motor needs to be strictly synchronized. The control focuses on achieving an even distribution of load torque, which can achieve high dynamic response characteristics. Usually the master is speed control, and the slave is torque control.

• The flexible connection is realized through the connection of equipment such as conveyor belts, and a slight speed difference between the master and slave motors is allowed, so high dynamic response characteristics cannot be achieved. Usually the master is speed control, and the slave is speed control or torque control.

Master/slave communication

RNB8 drive master/slave communication is based on CAN bus communication protocol. The master sends control words, speed setting, torque setting, etc. to the slave. The control unit integrates a CAN bus communication interface.

Examples of master/slave control parameters

In this example, both the master and slave are speed controlled, the torque of the slave is limited, and the master is given by external network communication.

Host settings:

• Set to speed vector control, parameter n0.08 control mode=4 sensorless vector.

• Set external network communication, see parameter group nF communication parameter group for details.

• Set CAN bus address, defined as host, parameter nF20 CAN bus address =1.

Slave settings:

• Set to speed vector control, parameter n0.08 control mode=4 sensorless vector.

• Set CAN bus address, defined as slave, parameter nF.20 CAN bus address=2～9.

• Select master/slave control mode, parameter CAN bus online mode=3 limit follow.

• Activate the load sharing function, the parameter nA.00 load sharing enable=1 is valid.

• Select the current reference source of the slave, parameter nA.04 current reference source=2CAN bus.

• Adjust the slave setting and set the parameter nF.24 Slave setting correction coefficient.

Note:

• The master/slave address is unique and cannot be repeated. When the CAN bus address is set to 1, it is defined as the master, and addresses 2 to 9 are the slaves. See parameter nF.20 CAN bus address for details.

• Select the master/slave control mode according to the master/slave connection characteristics, see parameter nF.23 CAN bus online mode for details.

• Master/slave connection failure or alarm information, and slave failure information are displayed on the master drive, and the user can Deal with the fault promptly according to the fault information.

4.4 Compatibility

The RNB8 multi-transmission inverter is compatible with the communication of a variety of frequency conversion products, such as: ACS550/600/800, Siemens 6RA70/6SE70/MM440, etc. For details, please contact RENLE.