RC-IGBT Half-Bridge Commutation Using Pre-Desaturation Control

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Solution Overview

Problem

Existing control methods for reverse conducting (RC) IGBTs in half-bridge circuits face challenges in efficiently managing the transition from blocking to conducting states, particularly in reducing switching losses and ensuring robust commutation without the need for a lock time.

Innovation Solution

The method involves controlling the first switch in IGBT-mode and the second switch in DIODE-mode, where the second switch is desaturated before and during the first switch's transition from blocking to conducting state, utilizing a processing unit to manage the gate voltages and ensure desaturation lasts at least as long as the first switch's mode change.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Loss of energy

If the second switch is kept in saturation during the first switch's transition, then the first switch can change state, but switching losses increase and commutation reliability deteriorates

Engineering Contradiction:

Improveswitching lossesVSAvoidcommutation reliability

Core Design Contradiction:

Loss of energyVSReliability

Solution Approach 1:

The second switch is desaturated in advance before the first switch transitions from blocking to conducting state. This preliminary desaturation action ensures that when commutation occurs, the second switch is already in a low-loss state, reducing switching losses while maintaining commutation reliability through proper timing control.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The control method applies preliminary anti-action by desaturating the second switch before commutation to counteract the potential harmful effects of saturation during switching. This prevents excessive switching losses and voltage spikes that would occur if the second switch remained saturated during the first switch's state transition.

Inventive Principle:

Principle #9Preliminary anti-action

2Loss of energy

If desaturation of the second switch is extended beyond the first switch's mode change, then switching losses are reduced, but switching time increases

Engineering Contradiction:

Improveswitching lossesVSAvoidswitching time

Core Design Contradiction:

Loss of energyVSLoss of time

Solution Approach 1:

The desaturation of the second switch is extended slightly beyond the first switch's mode change as a controlled excessive action. This ensures complete desaturation and minimizes switching losses, while the extension is limited to avoid excessive switching time. The control unit monitors and manages the desaturation duration to optimize the trade-off between loss reduction and time consumption.

Inventive Principle:

Principle #16Partial or excessive action

Data Source

PatentUS9641168B2Controlling reverse conducting IGBT

Publication Date: 2017.05.02 INFINEON TECHNOLOGIES AG

AI summary

A method for controlling a first switch and a second switch is suggested, wherein each switch is an RC-IGBT and wherein both switches are arranged as a half-bridge circuit. The method includes: controlling the first switch in an IGBT-mode; controlling the second switch such that it becomes desaturated when being in a DIODE-mode; wherein controlling the second switch starts before and lasts at least as long as the first switch changes its IGBT-mode from blocking state to conducting state.