Control Panel Operation
Variable Frequency Drive Description & Operation
VFD based Control Panels are slowly replacing all the contactor based panels in traditional industrial
Cranes due to huge number Benefits inherent with Variable Frequency Drives.A VFD is basically a power
electronics conversion system.A three phase Power Supply on the order of 415Vac at 50Hz is input to the
Variable Frequency Drive.
First, The VFD rectifiers this 3 phase AC power into DC with the help of 6 Diodes or 6 SCRs
This DC power is filtered and Stored in large bulky capacitor banks.
The output stage of the VFD then inverts this DC power into AC with the help of heavy duty semiconductor switching devices such as IGBTs or Mosfet.
VFD is Programmed according to the Hoisting,Cross Travel or Long Travel Motion
A very advanced user programmable real time microprocessor controls all the three operations mentioned above.This helps in programming the VFD according to the user requirement.
Many Parameters of the VFD Panel can be Programmed such as:
1st Speed, 2nd Speed of each motion can be set according to the Crane Pendant push button or Radio Remote Controls can then be used as Logic Inputs.
Brake Logic Control
Used to control an electromagnetic brake by the drive, for horizontal and vertical hoisting applications. Maintain motor torque in the upwards direction during brake opening and closing
Positioning by Limit Switch Sensors
The Crane can be Slowed Down or Stopped after taking the output of the limit Switch as its logical input.Stopping Distance can be configured according to the user requirement.
Precise Position of the crane in any direction such as Hoisting,Cross Travel & Long travel is directly controlled by the VFD with the help of digital encoder.
Dynamic Braking parameters
Dynamic Braking Resistors can be used along with the VFD to dissipate the regenerative energy of the motor while braking.
To fine tune the control process of the VFD , the Proportional ,Integrative and Derivate parameters can be fine tuned to reach the VFD speed set point.
Motor Control Algorithm
Many motor control algorithms such as V/F , FOC ,Variable Torque are available to choose from the list. V/F insures that output voltage is proportional to the frequency.
For optimizing movement of the crane, correct motor parameters can be set within the Drive.Parameters such as motor power,Motor Current, Motor Max Frequency, etc.
Auto Fan Control
If the VFD heats up, the Internal Fans can be automatically started to cool off the Drive.
In-Built Circuit Protection
Anand systems VFD based control panel have many upstream and downstream protection devices such as Fuses, Circuit Breaker &Single Phase Preventers.
Circuit breaker will protect the control panel from Short circuit . Miniature Circuits Breakers are used in place of fuses because of its advantages over fuses. A MCB will trip incase its overcurrent rating is crossed and then It can be reset without any hand-operated restoration. MCB is used as an option to the fuse switch in most of the circuits. An MCB cab be reused several times while a fuse needs to be thrown away after it disconnects the circuit.Debugging of the control panel becomes easy when a circuit breaker is used.
Many fuses are used throughout the control panel upstream of the VFD .When an overcurrent or short circuit occurs , Incase of the MCB not tripping, the fuse will melt and protect the crane from damage.
Single Phase Preventer
During the condition of an opening of one of the three phases applied to the motor, the Motor starts drawing more than 2 times the current to generate the same amount of torque. This harms the motor , the wiring, the drive and the connectors. Hence, Anand systems uses Single Phase preventer which opens the circuit in a fault condition.