Multilevel Converter Switching Device Failure Detection Circuit
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Solution Overview
Problem
Multilevel converters face challenges in detecting switching device failures, particularly during short-circuit conditions, as existing methods like desaturation circuits only detect failures when the device is turned ON and do not provide signals when the gate drive signal is turned OFF, leading to potential chain reactions and destruction of the converter.
Innovation Solution
A switching device failure detection circuit with logic modules and a voltage calculation module that compares actual and expected voltage states across switching devices, using comparators and a failure detection algorithm to identify mismatches and detect failures even when the gate drive signal is OFF, preventing secondary damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a desaturation circuit is used to detect switching device failure, then failure detection is provided when the switching device is turned ON, but no failure signal is provided when the gate drive signal is turned OFF
Solution Approach 1:
The voltage detection circuit is designed to monitor switching device voltage across all operating states (both ON and OFF states), making the detection system universal rather than state-specific. The circuit uses voltage dividers and comparators that remain functional regardless of the switching device state, enabling comprehensive failure detection coverage.
Solution Approach 2:
The detection system dynamically adapts to different switching states by continuously monitoring voltage levels and comparing them against expected ranges. The circuit responds differently to voltage patterns characteristic of ON-state failures versus OFF-state failures, providing state-appropriate detection without requiring separate detection circuits for each state.
2Reliability
If comprehensive failure detection is implemented for both ON and OFF states, then all possible short-circuit failure conditions are detected, but system complexity increases
Solution Approach 1:
A single voltage detection circuit performs multiple functions by detecting failures in both ON and OFF states, eliminating the need for separate detection circuits for each state. The same hardware infrastructure (voltage dividers, comparators, microcontroller) handles all detection scenarios, reducing overall system complexity while maintaining comprehensive coverage.
Solution Approach 2:
The voltage detection circuit uses the existing voltage present across the switching device in different states as its detection signal source, without requiring additional sensors or complex measurement infrastructure. The circuit self-adapts to the voltage conditions present in each state, simplifying the detection architecture.
Data Source
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AI summary
A multilevel converter includes a plurality of phase legs (40) each having at least two inner switching devices (44, 46), at least two outer switching devices (42, 48), at least two clamping diodes (50, 52), a split DC link (53) and a switching device failure detection circuit (70). The switching device failure detection circuit includes a logic module (72, 74, 76, 78) for each of the switching devices, a voltage calculation module (80) and a failure detection algorithm (82). The logic module generates a blocking state logic signal (Vc1, Vc2, Vc3, Vc4) by comparing a switching device voltage (Vsw1, Vsw2, Vsw3, Vsw4) and a threshold reference voltage (Vth) and the voltage calculation module determines an expected voltage blocking state (Vs1, Vs2, Vs3, Vs4) for each of the switching devices based on the gate drive signals (G1, G2, G3, G4) of the switching devices and an output current direction (Io). The failure detection algorithm detects a failure condition in any of the switching devices based on the blocking state logic signals and the expected voltage blocking states of the switching devices.