Application of load distribution control of the ho

2022-08-15
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With the continuous improvement of production technology and equipment level, especially in the production process of using large equipment, using multiple motors to drive the same equipment has been widely used. At this time, the load distribution control of multiple motors is particularly important

in the slab caster imported from VAI (VAI) in the Third Steelmaking Plant of Jigang, in order to realize the control of up to 20 tension straightening motors, the load distribution control technology is adopted. In order to ensure that the tension straightening torque on the slab is a constant, a load distribution function is provided between each motor. According to the total tension correction current on all motors, the load distribution controller can calculate a corresponding corrected speed setting value (speed deviation) for the tension correction motor, add the corrected setting value to the actual setting value of the tension correction motor, and send their sum as the total speed setting value to the corresponding tension correction motor frequency converter, so that the load distribution of the motor can be realized through the vector control of the frequency converter. According to the total load of all tension straightening motors, Neo plastics' plastic packaging additive aims to convert the waste in the landfill into useful biogas. The load of each motor can be corrected by setting its own load factor on HMI, and the load factor can be -100 0..+ 100%, the torque generated by a negative load factor reacts on the pouring direction to prevent the slab from sliding. In this way, by using the load distribution technology, the tension straightening torque on the slab in the whole sector can be made a constant, which ensures that the tensile force on the slab surface remains unchanged, so as not to cause problems in the quality of the slab due to uneven tensile force during the tension straightening process; At the same time, by tracking the casting flow of the red billet, PLC automatically modifies the load factor to ensure that the relevant data under different cooling conditions show that the red billet bears different pressures to ensure the surface quality of the red billet; All these ensure the quality of the slab. In addition, after realizing the load distribution control of the tension straightening motor, it can ensure that each tension straightening motor will not produce overload, so as to ensure the reliable operation of the motor, improve the operating life of the motor, reduce the equipment failure rate, and achieve the purpose of improving production efficiency

2 realization of control function

according to the control schematic diagram in Figure 1, in order to realize the distribution of motor load torque, the main control process can be divided into three parts:

L realize the design of load controller program in PLC

l carry out data communication between PLC and frequency converter. PLC reads the actual torque from the frequency converter and uses it as the input signal of load controller; The frequency converter reads the speed setting value (speed setting value + deviation value output by the load torque controller) from the PLC as the given signal of the frequency converter

l vector control mode is used in the frequency converter to control the speed and torque of a single motor

therefore, in order to realize the load distribution control of multiple motors, the main control process is to set the above three processes. In the slab caster imported from VAI (VAI) in the Third Steelmaking Plant of Jigang, the PLC adopts Siemens S7-400 series PLC as the master station, the frequency converter adopts Siemens book type frequency converter (masterdrivers VC) as the DP slave station, and the Profibus bus bus is used for communication between the master station and the slave station; The frequency converter adopts the encoder to detect the speed feedback to form the deceleration effect of the speed spring tension testing machine: degree closed loop, realizing vector control. Next, the design of load controller using PLC and the Profibus communication between PLC and frequency converter are introduced, while the vector control of frequency converter is not introduced here because of its many applications

2.1 design of load controller

since the output of the load controller is controlled as the deviation of the speed setting value of the frequency converter, the load controller is realized by programming in PLC. Siemens PLC of S7-400 series is used in the control system of slab caster in the Third Steelmaking Plant of Jigang, and the program design of load controller is programmed by STEP7 of Siemens. According to the load distribution control schematic diagram in Figure 1, first compare the torque setting value fseti with the actual torque value frefi read out from the frequency converter, output a corrected speed setting value after being controlled by a PID regulator, add it to the speed setting value as a deviation value of the motor speed setting value, and input it to the frequency converter as the total speed setting value (vtseti), and participate in the speed regulation process of the motor, Thus, the load distribution control and speed control of the tension straightening motor are realized. The program flow chart of PID adjustment of torque in PLC is shown in Figure 2

2.2 communication between PLC and frequency converter

in order to control the load distribution of the tension leveler motor, the load controller in PLC should read the actual torque of each motor from the frequency converter at any time. At the same time, the total speed setting value should be written into the frequency converter for load control and vector control of the tension leveler. Therefore, the correct realization of information communication between PLC and frequency converter is the key link of the whole load distribution control

in the slab caster imported from VAI (VAI) in the Third Steelmaking Plant of Jigang, the PLC adopts Siemens S7-400 series PLC, and the frequency converter adopts Siemens book type frequency converter (masterdrivers VC), which uses PROFIBUS bus for communication. PROFIBUS is a fieldbus standard conforming to European standard EN 50170. It mainly adopts layer 1-2 of OSI communication protocol layer. PROFIBUS between the master station and the master station works according to the token transfer process, that is, in a logic ring, the master station becomes a token that determines the time window and keeps it. Within this time window, the master station with the token can communicate with other master stations. At the same time, it uses a lower master-slave process to communicate with the slave station. PROFIBUS-DP bus mode is adopted here, which allows rapid data exchange between PLC and transmission device (such as frequency converter). Access to the transmission device is always carried out in the master-slave mode. The transmission device is always a slave station, and each slave station itself has a clear address. The message structure of PROFIBUS periodic transmission is shown in Figure 3:

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