Crane Inverter Control for Overload Reduction
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Solution Overview
Problem
Existing cranes, particularly offshore cranes, face challenges in effectively managing overload conditions due to high system inertia in electric hoist cable drives, leading to cost-intensive design modifications to reduce inertia and protect against load peaks.
Innovation Solution
A control device is implemented to detect overloads by changing the operating state of the inverter, allowing the boom to be rocked about the luffing axis or the slewing gear to be rotated, thereby reducing the overload, and is controlled automatically to maintain power, torque, and speed limitations, utilizing sensors to monitor and adjust the hoist rope drive.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If electric motors with reduced mass inertia are used, then the system inertia is reduced, but the cost increases
Solution Approach 1:
The patent replaces mechanical inertia reduction measures with an electronic control system. The inverter controls the electric motor's torque and speed dynamically, allowing the system to respond to overload conditions without requiring physical changes to the motor's inertia characteristics. This substitution of mechanical solutions with electronic control resolves the contradiction by achieving the same protective function at lower cost.
Solution Approach 2:
The patent changes the operating parameters of the electric motor through the inverter, dynamically adjusting torque and speed in response to detected overload conditions. By monitoring phase currents and controlling motor output parameters, the system can reduce peak loads without requiring permanent mechanical modifications, thereby avoiding the costs associated with using motors of different inertia ratings.
2Reliability
If the winch torque is limited by separating the winch and hoist drive by a coupling, then the hoist rope can be withdrawn in overload, but the device complexity increases
Solution Approach 1:
The patent replaces the mechanical coupling-based torque limitation system with an electronic control system. The inverter electronically controls the motor torque based on real-time monitoring of phase currents, eliminating the need for mechanical couplings or clutches. This electronic approach achieves the same overload protection function while reducing mechanical complexity and improving reliability through fewer moving parts.
Solution Approach 2:
The control system automatically detects overload conditions through phase current monitoring and self-regulates the motor torque without requiring mechanical disconnect devices. The system serves itself by using the electrical parameters already present in the drive system to detect and respond to overload conditions, eliminating the need for separate mechanical protection devices.
3Force
If several smaller electric motors per winch are used, then the system inertia is reduced, but the device complexity increases
Solution Approach 1:
The patent replaces the mechanical solution of using multiple smaller motors with a single motor controlled by an inverter. The inverter enables the single motor to dynamically adjust its torque output, achieving the same inertia reduction benefits as multiple motors would provide, but with simpler mechanics and fewer components requiring installation and maintenance.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution effectively reduces load peaks, increases the permissible wave height for offshore operations, enhances the utilization of the crane's steel structure, and increases the maximum load capacity without increasing wave height, while maintaining power and torque constraints.
Implementation Method 1
A control device is implemented to detect overloads by changing the operating state of the inverter
Data Source
Figure 1
Figure 2~3
AI summary
The present invention relates to a crane with a boom that can be tilted about a rocker axis and/or with a slewing mechanism that can be rotated about a rotary axis, a hoist rope drive controlled by an inverter, and a rocker element that is designed and arranged such that the boom can be rocked about the rocker axis by means of the rocker element, wherein the crane has a control device that is designed to control the rocker element and/or the slewing mechanism in such a way that the boom is rocked about the rocker axis and/or the slewing mechanism is rotated about the rotary axis in order to reduce an overload acting on the crane and/or on the boom, wherein the control device is further designed to detect the overload by means of a change in an operating state of the inverter.