Digital Isolator STO Circuit for PWM Blocking in Motor Inverters
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Solution Overview
Problem
Existing elevator systems face challenges in achieving safe torque off (STO) operation, particularly in ensuring compliance with SIL 3 safety standards, due to complex monitoring and testing requirements of pulse width modulation (PWM) signal blocking methods.
Innovation Solution
The implementation of a digital isolator between a digital signal processor and an inverter in the elevator system, which selectively blocks PWM signals to prevent motor rotation, simplifying monitoring and testing for STO compliance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional PWM signal blocking methods are used for STO operation, then motor rotation can be prevented, but monitoring and testing complexity increases significantly
Solution Approach 1:
The patent introduces a digital isolator as an intermediary component between the control system and inverter. This isolator simplifies the STO implementation by providing a clear binary state (isolated/not isolated) that is easy to monitor and test, replacing complex PWM signal blocking mechanisms with a single digital isolation action that can be verified through straightforward diagnostic procedures.
2Reliability
If complex monitoring and testing methods are implemented for PWM signal blocking, then STO compliance can be achieved, but system complexity and cost increase
Solution Approach 1:
The patent extracts the monitoring and testing complexity from the STO implementation by using a digital isolator that provides inherent, easily verifiable isolation states. The isolator's clear binary output simplifies compliance verification, eliminating the need for complex monitoring circuits and testing procedures that would otherwise be required to ensure PWM signal blocking effectiveness.
Data Source
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AI summary
A control system for safe torque off (STO) operation is provided, including a motor, a digital signal processor (DSP) which outputs three-phase low side pulse width modulation (PWM) signals and three-phase high side PWM signals, an inverter receptive of the three-phase low side PWM signals and the three-phase high side PWM signals, the inverter being configured to combine the three-phase low side PWM signals and the three-phase high side PWM signals into a three-phase highvoltage output to control the motor, and a digital isolator electrically interposed between the DSP and the inverter and configured to selectively block at least a portion of the three-phase high side PWM signals from being received by the inverter.