Frequency converter in the crane electronic control system application

Introduction
Lifting industry using PLC- inverter gradually in recent years to promote and popularize , especially in large lifting equipment , with PLC program control to replace the traditional relay - contactor control ; replaced with a variable speed motor winding series resistance rotor speed ; asynchronous motor with inverter motor or replace the motor winding , coupled with advanced fieldbus technology and HMI system to improve the control accuracy and stability of the equipment , reduce the failure rate , and the energy-saving effect is remarkable , easy repair and maintenance , improve production efficiency to become a good way .
Control scheme
A large heavy machinery manufacturing plants, bears all the bulky equipment assembly , positioning, docking and other tasks, the  overhead gantry crane  high performance requirements , the use of an overhead crane used QD250/50t siemens S7-400 PLC, ABB inverter , touch screen and other high-performance configuration, application of advanced Profibus fieldbus technology , with encoder feedback direct torque control, and advanced human-machine interface system.
Divided into the main bridge crane hook, deputy hook , carts , trolleys and other four parts. Due to the main  eot crane  hoisting mechanism in most typical applications , control is also the most complex , so the main hoisting example in this chapter detailing its control.
1, PLC
The whole system S7-400 PLC as the core of electronic control , the main power supply module , CPU, input and output modules and interface modules and other components. Acquisition by a limit switch input modules , thermistors, inverter and other equipment fault feedback signal state ; receiving master controller , buttons, switches send control commands concentrated in the CPU operation and program operation result output module and Profibus fieldbus send contactors and inverters perform device to the drive motor , hydraulic brake , cooling fan and other complete various production tasks.
2, Profibus fieldbus system serial communication
Profibus is an open serial communication standard that enables data exchange between various automation components . In this system with S7-400 as the main station to the agencies as a slave drive by DP interface module and RS485 shielded twisted rapid real-time data exchange .
Set the inverter communication parameters :
98.02 = fieldbus communication module activation
51.01 = Profibus-DP field bus type selection
51.02 l = 3 to set the main inverter station address
51.03 = 1500 selected communications transmission rate of 1.5Mbit / s
51.04 = PPO4 select data type 4 ( 6 process data as a standard block )
As a master PLC CPU reads from the slave state of various input information, namely primary l read from the drive status word and actual values, including the drive is ready , power- response operation, the torque verification OK, inverter failure , the actual motor speed and other information ; and write information to a variety of output from the station , about the control word and speed reference written inverter. Including communications test position, from fieldbus PLC system Drive on, the start signal from the host system , fault reset signal and the actual frequency reference and so on. The complex signal conversion , monitoring, feedback process all data transmission via Profibus chain , and CPU quick focus easily .
3 , advanced man-machine interface system
TP270 touch screen and PLC Profibus bus is also used for data transmission and exchange , real-time display and monitor the operational status of the agencies and the voltage, current, torque, speed and other operating parameters , and can use its own real time fault diagnosis system Symptom judge , recording failure of various parameters , so that operators and maintenance personnel can fully understand the state of the system in a timely manner , and may prompt fault information to inspection and maintenance , to achieve accurate and fast troubleshooting effect , the real achieve a human intelligence .
4, the frequency control system
1 ) Lifting conditions and requirements
Hoisting mechanism requires a larger speed ratio and mechanical characteristics of hardness to suit the precise weight lifting requirements ; require a large starting torque ,bridge gantry crane excellent dynamic torque response ability to adapt to sudden load change , ensure that the heavy secondary lifting capacity ; must solve regenerative braking energy feedback and processing, in order to shorten the deceleration stopping time ; slide the hook must solve the problem .
2 ) conversion function application
According to the hoisting mechanism characteristics and technical requirements , the drive uses with a tachometer feedback interface 800 series drives, with ACC 7.2 Special upgrade software , form a closed loop direct torque control, through the pre-excitation function and starting torque setting , the motor starts instantaneous torque up to 300 %, achieved an excellent starting characteristics . built-in brake chopper , external braking resistor , braking process so that the generation of energy through regenerative braking resistor to be released , to achieve the purpose of rapid braking . Using a mechanical brake control function, so that the motor torque and brake release closely with better improve the safety of the equipment , the ability to withstand the impact of frequent starting and reliability also increased significantly .