Application Of Plc And Frequency Converter In Speed Control System Of Portal Crane

With the rapid development of modern electronics industry, programmable controller PLC and frequency converter are widely used in various industrial fields, and their performance indicators are further improved. It is fully applicable to workplace motor traditional door in railway transportation industry. The control system of the crane adopts various contactors, relays, resistors and other components. The system failure rate caused by electrical equipment is high, which causes the improvement of mechanical failure and the reduction of the service life of the gantry crane. The application of the system can effectively solve the problem. These problems motor

1 Main features of the system
1) Significantly improve the structural stress state.
Due to the soft start and soft stop ratio function of the inverter, the crane starts smoothly and has a small impact on the mechanical and steel structures. After actual testing, the results also prove that the application of the variable frequency speed control system can greatly improve the steel structure. Performance inverter

2) Wide speed range and good performance The inverter
system adopts the magnetic flux vector controlled lifting inverter CIMR-G5A produced by Japan YASKAWA Co., Ltd., which has strong environmental adaptability and power supply voltage. AC380V± 15%, working environment temperature -10 °C ~ + 50 °C Inverter inverter modular design, high integration and high reliability. The system realizes closed-loop control, has strong speed limit, anti-stall and torque control capability, and has excellent servo response characteristics, and has strong adaptability to rapid load fluctuations. The system is equipped with a lifting speed and a 5-speed working speed for each car. The operator can modify the speed value of each gear according to the operation requirements, and can also select the operating potentiometer to achieve stepless speed regulation.

3) Simple structure, high reliability and easy maintenance.
The frequency conversion speed control system adopts an independent control cabinet. The system design is reasonable, the appearance structure is very simple, and the maintenance is convenient. In particular, the hoisting system can realize the functions of the original two sets of lifting control devices with one set of devices, which not only reduces the weight of the trolley, but also improves the stress state of the steel structure, increases the maintenance space of the trolley, and facilitates daily maintenance and maintain. The system also has functions such as overcurrent protection, overvoltage protection, undervoltage protection, short circuit protection, and grounding protection to ensure the accuracy and reliability of control and protection actions. At the same time, the system can also increase the self-diagnosis function, using the human-machine system and the system, through the communication with the PLC to achieve real-time fault display and processing countermeasures, easy to find faults and maintenance.

4) Improve work efficiency and reduce mechanical wear.
The crane hoisting system can automatically switch between the four speeds of the empty hook, the hook and the main hook according to the load, which reduces the auxiliary time of the speed switching alternately, reduces the labor intensity of the driver, and improves the operation of the device. The efficiency is about 30%. At the same time, the soft start and soft stop ratio of the inverter not only reduce the impact of the steel structure, but also reduce the wear of the brake wheel and the brake pad.

5) Improved security. The hoisting mechanism realizes closed-loop vector control and has the function of zero-speed torque, that is, the inverter can automatically output a sufficiently large torque (more than 150) in the event of a mechanical failure of the hoist mechanism brake. %) Does not cause the load to slip, which increases the security of the system.

6) Overload alarm.
• At 90% of the rated load, an intermittent alarm sounds to indicate the weight of the heavy object but works normally;
• 105% of the rated load, a continuous alarm sounds, automatically after 2s Cut off the inverter output, display the weight of the weight and stop the work;
• When the 120% of the rated load, a continuous alarm sounds, immediately cut off the inverter output, showing the weight of the weight and stop working.

7) The energy saving effect is remarkable.
The inverter selected by the system has an automatic energy-saving operation mode, which can greatly improve the power factor and work efficiency of the system, so the power saving rate can reach about 20%.

2 system block diagram (see Figure 1)

3Control mode and selection of lifting motor

1) The hoisting system adopts vector control, one inverter controls one hoisting variable frequency motor, and the automatic switching of its speed is completed by frequency conversion special weight measuring instrument and programmable controller, and the large and small car system control adopts V /F control, each inverter controls multiple motors. All limit protection contacts are used as input points for the PLC and are protected by program processing.

2) The selection of the hoisting motor should be considered to have a wide speed range. The variable frequency motor is used instead of the ordinary wire-wound motor. Under the closed-loop control condition of the variable frequency motor, 350Hz is constant torque speed regulation, and 50100 Hz is constant power speed regulation. The insulation grade of the motor is F grade, and the insulation structure has the adaptability to the inverter output high carrier frequency voltage. The motor adopts a unique cooling structure and uses a separate cooling fan to force air cooling, ensuring that the motor does not overheat when operating at low speed and constant torque, and can withstand overload of 200% of rated torque. % static load test with rated weight.

3) Select PLC with high reliability, simple programming, convenient use and perfect function to replace the original relay and contactor control mode, and combine with the inverter to realize “Mechatronics”.

Because of the interference factors of the inverter, the parameters of the PLC should be considered for interference. Therefore, the wiring and wiring should be protected against interference. The output line should be shielded by steel pipes. All control lines are used. Shield the line, and pay attention to the grounding problem. At the same time, Yaskawa should adopt software anti-interference measures in the process of programming.