Multilevel Converter Protection via Control Logic
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Solution Overview
Problem
Multilevel converters, particularly those used in high-power industrial applications, face significant electrical and thermal stress during short-circuit conditions, leading to switching device failure and a potential chain reaction, with existing protection methods involving additional costly hardware.
Innovation Solution
A protection scheme that utilizes control logic to manage switching devices in phase legs connected to the same DC bus, detecting failures of inner switching devices or clamping diodes and adjusting gate signals to prevent overcharging of capacitors, thereby preventing further device failures without requiring additional hardware.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If additional hardware protection circuits (snubber or crowbar) are employed, then the converter bridge is protected from chain reaction failures, but the system cost and complexity increase
Solution Approach 1:
The existing switching devices in the multilevel converter are made to protect themselves by implementing control logic that detects failure conditions and automatically adjusts gate signals to prevent chain reaction failures, eliminating the need for separate protection hardware
Solution Approach 2:
The patent replaces the mechanical/electrical protection hardware (snubber circuits, crowbar circuits) with a control logic system that uses software-based detection and response to achieve the same protection function
2Productivity
If switching devices operate under high electrical stress during short-circuit conditions, then the converter maintains operational capability, but thermal breakdown and device failure risk increase
Solution Approach 1:
The control logic continuously monitors the operational state of switching devices and provides feedback to detect failure conditions, enabling real-time adjustment of gate signals to prevent thermal breakdown and device failure during short-circuit conditions
Solution Approach 2:
The control logic takes preliminary action by detecting failure conditions before they propagate to other devices, and proactively adjusts gate signals to prevent chain reaction failures before they occur
Data Source
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AI summary
A three level neutral point clamped (NPC) converter (78) includes a plurality of phase legs each having at least two inner switching devices (50, 52, 150, 152, 250, 252), at least two outer switching devices (48, 54, 148, 154, 248, 254), at least two clamping diodes, (56, 58, 156, 158, 256, 258) and a protection circuit (80). An inner component failure sensing circuit (102) is employed in the protection circuit (80) to detect a failure condition in any of the inner switching devices (50) or clamping diodes. The protection circuit (80) further includes a gating signal generation circuit (106) configured to generate a turn ON signal for a respective outer switching device (48) that is adjacent to the failed inner switching device (50) or the clamping diode.