Galvanically Isolated Power Supply for Conveyor Drive Safety
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Solution Overview
Problem
Existing transport conveyor drives, such as those for elevators and escalators, face challenges in ensuring safe stoppage of motors and activation of brakes during safety issues without relying on complex and maintenance-prone contactors or relays.
Innovation Solution
A transport conveyor drive design that incorporates a frequency converter with a motor controller and safety signal interface, utilizing galvanically isolated power supplies for STO circuits and brake controllers, referenced to a DC link bus bar, eliminating the need for contactors or relays by controlling power switches and brake coils through isolated power supplies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contactors or relays are used to ensure safe stoppage of motor and activation of brake, then safety is improved, but device complexity increases and maintenance requirements increase
Solution Approach 1:
The patent extracts and eliminates contactors and relays from the system by implementing a safety concept where the motor controller and brake controller directly control power switches and brake coils through isolated power supplies. This removal of intermediate components simplifies the device while maintaining safety through controlled power interruption to the inverter and brake activation circuits.
Solution Approach 2:
The patent replaces mechanical contactors and relays with electronic control mechanisms. The motor controller and brake controller use electronic power switches (IGBTs/MOSFETs) and isolated power supplies to achieve safe stoppage and brake activation, substituting mechanical switching with solid-state electronic control.
2Reliability
If contactors or relays are used for safe stoppage and brake activation, then safety is improved, but ease of manufacture deteriorates
Solution Approach 1:
The patent removes contactors and relays from the manufacturing process, reducing the number of components that need to be sourced, assembled, and tested. The simplified circuitry with direct electronic control reduces manufacturing complexity and improves ease of manufacture while maintaining safety through the isolated power supply architecture.
3Ease of manufacture
If traditional power supply configuration is used, then ease of manufacture is maintained, but circulating currents cause noise and interference
Solution Approach 1:
The patent introduces an isolated power supply as an intermediary between the control circuits and ground. This isolation barrier prevents circulating currents from forming between different ground potentials, eliminating noise and interference while maintaining ease of manufacture through a straightforward power supply implementation.
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 ensures safe and reliable operation by preventing control signal passage to power switches in case of safety issues, reducing circuit complexity, and avoiding circulating currents that cause noise, while maintaining high safety standards without the need for contactors or relays.
Implementation Method 1
A motor drive has a frequency converter, i.e. a rectifier and an inverter which are connected via a DC link, whereby the inverter comprises power switches for supplying electric power to the elevator motor
Implementation Method 2
The STO circuit is configured to transfer or cut the control pulses to the power switches dependent on the power received from the isolated power supply
Implementation Method 3
the secondary side is configured to be connected to a brake coil of the elevator
Data Source
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AI summary
The invention relates to a transport conveyor drive having a rectifier and an inverter which are connected via a DC link (57), whereby the inverter comprises power switches (55) for suppling electric power to an transport conveyor motor, comprising a motor controller (54) for controlling the power switches (55) of the inverter which is configured to produce control pulses in the control poles of the power switches (55), at least one safety signal interface (12), which is adapted to receive safety signals from a safety controller (14) of the transport conveyor, and a brake control circuit (26) having an output for supplying power to a brake coil (28) of an electromagnetic brake, wherein the motor controller (54) is referenced to a first bus bar in the DC link (57), at least one STO circuit (50, 52) is connected between the motor controller (54) and each of the power switches (55) of at least one half bridge of the inverter, the STO circuit (50, 52) being referenced to the first bus bar of the DC link (57) and is configured to transfer/cut the control pulses to the power switches (55), a galvanically isolated power supply (15, 42) for the STO circuit (50, 52) is connected between the safety signal interface (12) and the STO circuit (50, 52), such that an output terminal of the isolated power supply (15, 42) is referenced to the same bus bar of the DC link (57) as the motor controller (54), the isolated power supply (15, 42) being controlled via at least one safety signal received via the safety signal interface (12), and/or - the brake control circuit (26) comprising a transformer (32) with a primary and a secondary side, the transformer primary side being referenced to a/the first bus bar (DC-, -) of the DC link (57) and the secondary side being configured to be connected to a brake coil (28) of an transport conveyor brake, and an isolated power supply (15, 42) is connected between the safety interface (12) and the brake controller (24) to supply (15, 42) power to the brake controller (24), whereby an output terminal of the isolated power supply (15, 42) is referenced to the same bus bar of the DC link (57) as the brake controller (24).