IGBT Turn-off Overvoltage Limiting via Gate Drive Injection
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Solution Overview
Problem
IGBTs in power inverter circuits face inefficiencies due to overvoltage issues during turn-off, which are exacerbated by stray inductance, leading to increased switching losses and the need to slow down turn-off processes, thereby impacting overall inverter efficiency.
Innovation Solution
The solution involves modifying the gate driver reference connection to inject a sample of overvoltage across the IGBT, using a resistive divider and/or transformer to optimize the parasitic inductance, thereby slowing down the gate voltage slope and reducing overvoltage during turn-off, while maintaining efficient turn-on behavior.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If IGBT turn-off is accelerated to reduce switching losses, then switching efficiency is improved, but overvoltage due to stray inductance increases causing device damage
Solution Approach 1:
A resistive divider is introduced as an intermediary element connected across the emitter stray inductance. This divider network (comprising first and second resistors) mediates between the high-frequency switching transient and the gate driver, providing a controlled impedance path that limits the voltage spike while allowing the switching operation to proceed. The intermediary structure transforms the harmful overvoltage into a controlled voltage distribution across the resistor network.
Solution Approach 2:
The invention changes the electrical parameters of the gate drive circuit by introducing a resistive divider network that modifies the voltage distribution during switching transitions. By adjusting the resistance values of the divider network, the overvoltage parameter is controlled to remain within safe limits while maintaining acceptable switching performance. The parameter change approach allows optimization of the trade-off between switching speed and overvoltage magnitude.
2Reliability
If turn-off speed is reduced to limit overvoltage, then device protection is improved, but switching losses increase reducing inverter efficiency
Solution Approach 1:
The resistive divider acts as an intermediary that provides device protection without requiring slow turn-off. By placing the divider across the emitter inductance, it creates a controlled voltage reference for the gate driver that inherently limits overvoltage exposure to the IGBT while allowing the switching transient to proceed at normal speeds, thus maintaining efficiency while ensuring reliability.
Solution Approach 2:
The resistive divider network provides implicit feedback by creating a voltage reference that responds to the switching transient. The voltage distribution across the divider resistors reflects the instantaneous overvoltage condition, and this feedback mechanism automatically adjusts the gate drive voltage to limit overvoltage without requiring external control intervention, thereby protecting the device while maintaining switching performance.
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 approach effectively reduces overvoltage during IGBT turn-off, minimizing switching losses and enhancing the overall efficiency of power converter systems by optimizing the parasitic inductance and voltage distribution across the emitter and collector.
Implementation Method 1
the parasitic inductance of the emitter of the second IGBT being increased to allow the control to limit an overvoltage at turn off of the second IGBT
Data Source
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AI summary
A turn-off overvoltage limiting for IGBT is described herein. The injection of a sample of the overvoltage across the IGBT in the gate drive to slow down the slope of the gate voltage decrease only during the overvoltage above a predetermined value is described herein. Techniques to increase the parasitic inductance to allow the control to limit an overvoltage at turn off of the second IGBT are also described herein.