AC crane control modernizations

Perhaps no other technological development in the past 30 years has done more to revolutionize overhead crane design than the AC Variable Frequency Drive (VFD). Today’s Variable Frequency Controls and Flux Vector Motor Controls have become the industry standard for crane control. Recent improvements in drive technology, such as a new generation of Insulated Gate Bipolar Transistors (IGBTs), sensor-less vector control, powerful micro-processors with flash memory, and improved algorithms, have allowed the downsizing of the power platforms and the inclusion of many high-performance features.

AC Variable Frequency Drives provide greater reliability; enhance performance; improve production throughput; prolong equipment life; and reduce maintenance costs, parts, and personnel in a variety of ways:

• They reduce the characteristic high starting currents of AC induction motors, thus minimizing the shock effect on both the load and the equipment. Features, such as programmable acceleration and dynamic braking produce softer stops and starts, assure smooth transitions between speed steps, and greatly reduce brake wear and required maintenance.
• Crane specific firmware, drive support tools, and wired/wireless communication with various peripheral devices provide valuable monitoring, status, performance, and diagnostic information. Features, such as Reverse Plug Simulation, Stall Prevention, Inching Control, Micro-Positioning Control, and Static Stepless “Simulation”, are built-in and individually selectable, further enhancing the crane’s performance.

No two applications are the same. Variable Frequency Drives provide the crane or hoist user with a variety of operating modes and a wide range of options

• Most single-speed squirrel cage motors can be controlled by VFDs, includingconical-rotor motors used by many European hoist manufacturers. Multiple control modes (two, three, and five step or infinitely variable speed) allow for changing the operation to suit the needs of specific applications or the desires of individual operators. A wider range of selectable speed choices (up to 1500:1) are available to the user compared to the fixed speed ratios provided by typical two-speed motors (2:1, 3:1, or 4:1) or micro-drives (10:1).
• Safety is built into modern Variable Frequency Drives. They include features which reduce the possibility of lifting an over capacity load, minimize or eliminate dangerous load swing, prevent overheating of the motor, detect and minimize rapid increases in motor torque, and provide safeguards that limit unauthorized modification of drive parameters or programming unsafe parameters

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