Inverter Load Abnormality Detection Circuit
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Solution Overview
Problem
Existing load abnormality detecting circuits for inverters face challenges in accurately and quickly detecting load abnormalities, leading to potential breakage of switching elements due to surge voltages and erroneous operations caused by noise components, especially when using SiC-MOSFETs, which experience ringing during high-speed operations.
Innovation Solution
A load abnormality detecting circuit that utilizes a phase shift detection method between the gate voltage signal and output current, employing a waveform shaper to eliminate noise and a data flip-flop for accurate phase shift detection, sending an abnormal load signal to prevent power supply to the load and protect the MOSFETs, and incorporating a mask mechanism to avoid false detections during startup.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a phase shift detection method is used to detect load abnormalities, then the detection accuracy is improved, but the detection speed deteriorates due to waveform shaping and noise filtering processes
Solution Approach 1:
The patent applies preliminary action by pre-shaping the gate voltage signal waveform before comparison. The waveform shaper circuit pre-processes the gate voltage signal to eliminate noise components and standardize the waveform shape in advance, so that when abnormality detection is needed, the comparison can be performed quickly without extensive real-time processing. This resolves the contradiction by preparing the signal in advance, achieving both accuracy (through pre-filtering) and speed (by avoiding real-time processing delays).
2Reliability
If waveform shaping and noise filtering are applied to eliminate noise components, then the detection reliability is improved, but the circuit complexity increases
Solution Approach 1:
The patent introduces a waveform shaper circuit as an intermediary component between the gate voltage signal source and the phase shift detection mechanism. This intermediary device performs the noise filtering and waveform standardization function, isolating the core detection logic from complex signal conditioning tasks. By using this dedicated intermediary component, the patent achieves reliable noise-free detection while keeping the main detection circuit simple and manageable.
3Productivity
If the inverter operates at high frequency to improve productivity, then the processing efficiency is improved, but the ringing phenomenon in SiC-MOSFETs increases causing erroneous detections
Solution Approach 1:
The patent converts the harmful ringing phenomenon into a beneficial feature for detection. Instead of trying to eliminate the ringing completely, the waveform shaper circuit is designed to recognize and accommodate the ringing characteristics of SiC-MOSFETs during high-frequency operation. The circuit learns the normal ringing pattern and distinguishes it from actual abnormality signals, thereby enabling high-frequency operation while maintaining detection accuracy. This transforms the previously harmful ringing into a known, manageable characteristic.
Data Source
AI summary
A load abnormality detecting circuit for an inverter to detect abnormality of a load during an operation of the inverter which has a self-arc-extinguishing element as a switching element and a phase synchronizing loop controlling an output frequency to be a resonance frequency of the load, the load abnormality detecting circuit includes a phase shift detection part that detects a phase shift between a gate voltage signal controlling ON/OFF of the self-arc-extinguishing element and an output current of the inverter which is applied to the load, and that sends a first abnormal load signal based on the phase shift.