Hybrid Freewheeling Diode Module for Power Switching Oscillation Damping
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Solution Overview
Problem
The use of Schottky-diodes as freewheeling diodes in power switching modules for IGBTs leads to strong oscillations during switching, which can be mitigated by reducing switching speed, but this increases switching losses, necessitating a solution that reduces oscillations without increasing losses.
Innovation Solution
A power switching module incorporating a freewheeling unit with a pn-diode and a Schottky-diode, where the pn-diode is integrated in a first semiconductor material with a smaller band-gap and the Schottky-diode in a second semiconductor material with a larger band-gap, connected in parallel, with the pn-diode having a reverse peak current between 0.5 to 1.8 times that of the Schottky-diode's capacitive current peak, and a current ratio between the two diodes ranging from 0.05 to 0.25, to damp oscillations effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If Schottky-diodes are used as freewheeling diodes to enable faster switching, then switching losses are reduced, but strong oscillations occur during switching
Solution Approach 1:
The patent combines a pn-diode and a Schottky-diode in parallel to form a hybrid freewheeling unit. The pn-diode provides soft recovery characteristics that dampen oscillations, while the Schottky-diode maintains fast switching and low conduction losses. This merging of two different diode types resolves the contradiction by allowing both oscillation suppression and efficient current handling simultaneously.
Solution Approach 2:
The patent optimizes specific parameters including the reverse peak current ratio (0.5 to 1.8 times the Schottky-diode's capacitive current peak) and the area ratio between pn-diode and Schottky-diode (0.08 to 0.3). These parameter adjustments ensure the pn-diode provides sufficient damping current while the Schottky-diode maintains its fast switching capability, resolving the oscillation-losses contradiction.
2Object-generated harmful factors
If switching speed is reduced to minimize oscillations, then oscillations are dampened, but switching losses increase
Solution Approach 1:
By merging the pn-diode's oscillation-damping capability with the Schottky-diode's fast switching capability in a parallel configuration, the system achieves both low oscillations and low switching losses simultaneously, eliminating the need to trade one for the other through switching speed adjustment.
Solution Approach 2:
The pn-diode acts as an intermediary element that provides a controlled current path during switching transitions. Its reverse peak current serves as a mediator to dampen oscillations without significantly increasing total switching losses, as it operates in parallel with the low-loss Schottky-diode path.
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 configuration significantly reduces oscillations during switching without significantly increasing switching losses, by allowing the pn-diode to provide a tail current that damps oscillations while maintaining efficient current handling.
Implementation Method 1
a reverse peak current which is from about 0.5 to about 1.8 of a capacitive current peak of the Schottky-diode
Data Source
AI summary
A power switching module includes a three-terminal power semiconductor device designed for a rated current and a freewheeling unit. The freewheeling unit includes a pn-diode integrated in a first semiconductor material having a first band-gap, and a Schottky-diode integrated in a second semiconductor material having a second band-gap that is larger than the first band-gap. The Schottky-diode is electrically connected in parallel to the pn-diode.