Safe Torque Off Control Unit for Electrical Drive Power Modules
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Solution Overview
Problem
Existing electrical motor drive systems face high costs and implementation challenges in achieving redundancy for Safe Torque Off (STO) functionality, particularly in preventing common-cause faults and accounting for stored energy, which can lead to unexpected component failures in the inverter circuitry.
Innovation Solution
A method involving the generation of safety-approved signals in the control unit that initiate two distinct shut-down procedures for the power unit, with a controlled normal stop followed by a procedure ensuring a torque-free state, utilizing safety-approved communication channels and devices like FPGAs to prevent abrupt power module shutdown.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If abrupt shutdown is used to achieve STO function, then torque is removed from motor, but power module components are damaged
Solution Approach 1:
The control unit initiates a preliminary controlled shutdown sequence before executing the STO function. This preliminary action allows the power module to transition gradually, preventing abrupt changes that would damage components while still achieving the required torque removal for safety
2Reliability
If redundancy is implemented using two separate electro-mechanic components, then STO safety level is improved, but system cost and complexity increase
Solution Approach 1:
The control unit and power unit are integrated into a unified system where the control unit directly manages the power module's shutdown sequences. This merging eliminates the need for separate electro-mechanic redundancy components while maintaining STO safety through controlled electronic shutdown procedures
3Productivity
If stored energy is not accounted for in STO procedure, then shutdown is faster, but unexpected torque production occurs
Solution Approach 1:
The control unit monitors the power module's state during shutdown and adjusts the shutdown sequence based on feedback regarding stored energy levels. This feedback mechanism ensures that all energy sources are depleted before the STO function is considered complete, preventing unexpected torque production
Data Source
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AI summary
A method and an arrangement of producing a safe torque off procedure of an electrical drive comprising a control unit and one or more power units having controllable semiconductor switches, wherein the method comprises detecting a signal (STO1, STO2) in a control unit indicating a requirement to stop the drive. The method comprises generating on the basis of the detected signal at least one safety-approved signal (STO12; Enable; Stop) which when received in a power unit initiates shutting-down of the power unit; feeding the generated at least one safety-approved signal to one or more power units, initiating the shutting down of the one or more power units upon the receipt of the at least one safety-approved signal, the at least one safety-approved signal initiating at least two different shut-down procedures of the one or more power units and at different time instants.