Saturable Inductor Soft Landing for IGBT Diode Recovery
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Solution Overview
Problem
In power electronics circuits, the rapid switching of Insulated Gate Bipolar Transistors (IGBTs) leads to high voltage and current spikes due to rapid diode current decrease, causing avalanche breakdown and electromagnetic interference, while reducing the rate of current change to prevent these issues increases energy losses.
Innovation Solution
A combination switch comprising a Punch Through type IGBT, an anti-parallel diode, and a saturable inductor, where the diode and inductor are coupled in series, with the saturable inductor designed to come out of saturation at a low current level, reducing the rate of diode current decrease and minimizing voltage and current spikes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the rate of increase in current through IGBT is high, then switching speed is improved, but voltage and current spikes occur causing avalanche breakdown
Solution Approach 1:
A saturable inductor is introduced as an intermediary component connected in series with the anti-parallel diode. This inductor acts as a mediator that automatically regulates diode current: when diode current decreases rapidly (high dI/dt), the inductor generates a back-EMF that opposes the current change, preventing excessive voltage spikes and avalanche breakdown, while allowing fast switching when diode current is increasing.
Solution Approach 2:
The saturable inductor's inductance parameter changes dynamically based on current level. At high current levels, the inductor is saturated and presents low impedance, allowing rapid current changes. As current decreases and exits saturation, the inductance increases, providing stronger opposition to further current decrease, thus preventing voltage spikes during the critical turn-off phase.
2Reliability
If the rate of diode current decrease is reduced, then voltage and current spikes are minimized, but energy losses increase
Solution Approach 1:
The saturable inductor provides dynamic current regulation rather than a fixed resistance or inductance. During the switching transition, the inductor's effective impedance changes with current magnitude, allowing rapid current changes when beneficial while automatically slowing down current decrease when voltage spike prevention is needed, thus optimizing both efficiency and reliability.
Solution Approach 2:
The saturable inductor is a passive component that automatically regulates diode current based on its own saturation characteristics without requiring external control circuits or active components. The inductor self-adjusts its impedance to prevent voltage spikes during diode reverse recovery, eliminating the need for additional energy-consuming control mechanisms.
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
The solution achieves a 'soft landing' of diode current to zero, reducing high voltage and current spikes, minimizing electromagnetic interference, and maintaining switching efficiency by allowing rapid current change during most of the switching process.
Implementation Method 1
a saturable inductor designed to come out of saturation at a low current level
Data Source
AI summary
A combination switch includes an Insulated Gate Bipolar Transistor (IGBT), an anti-parallel diode, and a saturable inductor. The diode and inductor are coupled in series between a collector and an emitter of the IGBT. The inductor is fashioned so that it will come out of saturation when a forward bias current flow through the diode falls below a saturation current level. When the diode current falls (for example, due to another combination switch of a phase leg turning on), the diode current initially falls at a high rate until the inductor current drops to the saturation current level. Thereafter, the diode current falls at a lower rate. The lower rate allows the diode current to have a soft landing to zero current, thereby eliminating or reducing voltage and/or current spikes that would otherwise occur. Multiple methods of implementing and manufacturing the saturable inductor are disclosed.