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Application of Rockwell PLC and frequency converter in the automatic control of converter tilting at Jiuquan Iron and steel company

Jiuquan Iron and steel company has three 120t top and bottom combined blowing converters for 2million steelmaking. Converter 1 has been put into operation in April 2005, and converter 2 # and converter 3 # have been put into operation in early 2006. The tilting and oxygen lance systems of the three converters adopt the Allen Bradley Logix platform control system of Rockwell Automation Company NetLinx network architecture ControlNet and 1336 force AC converter based on field oriented vector control technology realize the automatic control of converter tilting and oxygen lance system. Its self diagnosis and protection functions are reliable, which reduces the downtime of equipment failure and greatly improves the production efficiency

1 analysis of converter tilting load characteristics

in the converter system, four tilting motors are used for the tilting part of the furnace body, which are rigidly connected through the reducer, and the full suspension fixing mode and torque rod torque absorption mode are adopted, as shown in Figure 1

according to the process requirements, the tilting angle of the converter is positive and negative 360 °. When the axis of converter mouth and bottom direction is perpendicular to the ground plane, it is in the zero position state. Therefore, the tilting load torque of the furnace is a function of angle mfz=f( θ), It belongs to negative potential energy load. In addition, according to the process design description, the converter is designed according to the positive torque, that is, the lower part of the furnace trunnion is higher than the upper part, and the lower part is heavier than the upper part. Thus, when the electric control system of the converter fails or the holding brake force is not enough, the positive torque of the furnace body can be used to ensure that the furnace mouth is upward, so as not to cause accidents such as steel pouring. However, when the bottom of the maintenance furnace is removed and there is too much steel slag sticking to the furnace mouth, the upper part of the furnace body may be heavier than the lower part. Because the center of gravity of liquid steel changes with the change of converter inclination, negative torque may appear during furnace maintenance and slag or steel tapping. When the furnace body is in the positive torque state, the motor is in the electric operation state. When the furnace body is in the negative torque state, the motor is in the feedback braking state. The mechanical characteristics and load characteristics of the motor are shown in Figure 2

rated torque/current: 1750n · m/230a

encoder for speed feedback: ia-1024

2 system function

2.1 control function

each frequency converter of converter tilting frequency conversion system is controlled in two ways:

(1) single machine commissioning and maintenance of frequency converter are completed on human-machine interface operation panel (HMI)

(2) the linkage operation of the equipment is realized through the PLC system (operation location: in the central control room or next to the machine during normal production, and in the cabinet door of the frequency converter cabinet during online commissioning)

in any case, the uniqueness of the control mode can be guaranteed, and the switching of the control mode is realized through the change-over switch and button on the cabinet door, which is convenient and reliable

four tilting converters of converter work in the mode of 1 master and 3 slave during normal operation; When one of them fails, the remaining three devices work in the mode of 1 master and 2 slave after conversion and adjustment; Further, when two of them fail, the remaining two devices work in the mode of 1 master and 1 slave after conversion and adjustment

2.2 system configuration and function realization

according to the process requirements and control functions of the tilting mechanism, each converter tilting frequency conversion system is configured with a relatively independent PLC (PLC 12 for 1# converter), which realizes the communication between the converter and PLC through the control bus control net network interface (as shown in Figure 3), and realizes the communication with the converter main PLC (plc11 for 1 converter) system (as shown in Figure 4). The main hardware configuration of the system is as follows:

tilting frequency converter: 1336t-b250-aa-gt3en-l4, 4 sets (including braking components); ControlNet optical fiber module: 1786-rpfs, 4 pieces; Control system: one 1756-l55m22 logix5555 controller

in the converter drive frequency conversion control system, four frequency converters are connected through optical fiber to form a master-slave application working group. During operation, one of them is set in the main drive working mode, and the other three work in the secondary drive mode. The secondary drive frequency converter works in torque mode. The speed of the main frequency converter is given by the PLC system through the i/o port of the frequency converter, The master frequency converter sends operation information to the slave through drive to drive L. as the sealing machine is the last process in the packaging production line, ink communication, including the speed, torque and switching state of the host, the speed/torque tracking and accurate torque distribution with the master transmission are automatically realized by the parameter setting of the master and slave device, and the speed synchronization and torque distribution in multi motor transmission are realized

when the system operates normally, P electroplating process: metal material electroplating pretreatment process LC system communicates normally with converter tilting frequency converter through CNB bus to realize control and data acquisition. When a fault is caused by some reason, such as a slave frequency converter or motor fault, the fault frequency converter automatically stops working, and the other three frequency converters continue to work, and the control load of the main frequency converter is evenly distributed among the three frequency converters; When the main frequency converter or motor fails, the main frequency converter stops working and sends a fault signal. At this time, another frequency converter can be set as the main drive to form a new master/slave working group. Different results will appear when selecting packaging materials. Continue to work according to the master/slave mode, and the new main frequency converter is responsible for speed control and load distribution

in addition, the tilting of the converter needs to be strictly monitored to prevent the "car sliding" fault. In the converter drive frequency conversion control system, the PLC control program is used to make the holding brake loosen when the torque is established at a certain output torque after the system starts, and hold tightly when the torque drops to a certain output torque after the system stops, which greatly improves the reliability of the system application

in order to monitor the tilting position of the converter, an encoder is installed on the main shaft of the equipment, and the signal is transmitted to the PLC system through the fieldbus. The signal is calculated, converted and displayed on the screen through the PLC

3 parameter setting and link of 1336 force inverter

3.1 parameter setting of 1336 force inverter

because there are many functional parameters of the inverter, it is not necessary to set and debug each parameter in practical application. Most of them can adopt default values, and some parameters can be generated after doing autotune, such as PID parameters of speed regulator and slip regulator, q-axis and d-axis voltage at rated speed and rated current The rated, maximum and minimum slip frequency of the motor, etc. do not need to be set manually. Some parameters should be set according to the load characteristics and functions of the motor. The main parameters are motor nameplate parameters, limit parameters (including speed and current), calibration parameters, link parameters and communication ports. In addition, after replacing the motor of the same model, the original parameters can continue to be used without changing. However, after the feedback type is changed, due to the great impact on the whole system, we need to do autotune again. According to the process parameters and relevant characteristics of the tilting motor, table 1 lists the settings of some parameters of 1 tilting frequency converter

3.2 parameter link of frequency converter

through the link of parameters around the development of new energy vehicles, PLC can control the start and stop signal of frequency converter, receive the feedback signal of frequency converter and transmit the signal between frequency converter and frequency converter. Table 2 takes 1 tilting frequency converter as an example to illustrate the corresponding relationship between parameter link and PLC

4 Conclusion

since the 2million steel-making 1# converter of Jiuquan Iron and Steel Co. was put into operation in April 2005, the tilting frequency converter system has met the process requirements, operated stably and reliably, and achieved good results. (end)

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