frequency conversion overhead traveling crane
Application of frequency conversion speed regulation in overhead traveling crane
First, brief description of the overhead crane
The bridge crane is currently widely used in industrial and mining enterprises in a lifting hoisting equipment. It is generally divided into three basic mechanisms: for lifting heavy lifting mechanism, for lateral movement mechanism for moving heavy objects (i.e. bridge crane car movement organization) and for the longitudinally moving heavy objects (i.e. bridge the crane traveling mechanism)
Where in the hoisting mechanism of the overhead traveling crane is to control the reversing of the three-phase asynchronous motor, and the reel is driven by the coupling and the reducer to raise or lower the wire rope. The bridge crane two mobile agencies, respectively, by controlling the three-phase asynchronous motor positive and negative, through the coupling and reducer drive wheel rotation.
Second, the bridge crane frequency control of the overview
Bridge crane frequency control principle: In the asynchronous motor of the number of pairs of p and slip s of a certain circumstances, only to change the power supply frequency of the asynchronous motor f, can achieve the speed of the asynchronous motor. However, when the power supply frequency f is less than the rated operating frequency of the motor changes, the terminal voltage U ≈ (where: E1-induced electromotive force, f-power supply frequency, w-series turns, k-winding coefficient, φ-motor Of the flux), only to maintain U / f constant, in order to ensure that the motor flux φ unchanged to ensure that the motor performance unchanged. And when the power supply frequency f is greater than the rated operating frequency of the motor, the motor speed exceeds the rated speed, if still maintain U / f constant, the terminal voltage U will exceed the rated motor voltage, which is not allowed, therefore, the rated speed , The power supply voltage should be kept constant and rated, only increase the frequency f of the power supply, the motor flux φ will be reduced, the output torque will also be decreased, while the output power is approximately constant.
Bridge crane frequency control mode is generally used U / f control, vector control and direct torque control. Hoisting mechanism of the crane which uses a closed-loop vector control or closed-loop direct torque control; and mobile institutions generally open-loop U / f control mode or open-loop vector control mode.
Bridge crane frequency control is generally divided into hoisting agencies variable frequency speed control and mobile agencies, mainly by the organization of the inverter motor, inverter, control devices and line protection switches and other components. However, in order to prevent the inverter interference to the outside world and their protection, and improve the accuracy of motor control, generally in the inverter around with AC / DC reactor, the brake unit and braking resistor, filter and transmission card pieces, etc. . Which, according to the use of different overhead crane mechanism, the hoisting mechanism used in the variable frequency motor are equipped with optical rotary encoder to improve speed accuracy and response speed. At the same time control devices using PLC and relay combined to replace the past, the use of AC contactor control, the control system reliability, flexible application, the line is simple, easy to use and low failure rate.