Cascode Power Conversion Device Switching Loss Reduction
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Solution Overview
Problem
The existing power conversion devices experience increased switching loss and heat generation due to reverse recovery current, leading to larger device sizes and cooling requirements.
Innovation Solution
A power conversion device is designed with bridge-connected arms comprising series-connected normally-on and normally-off switching elements, along with high-speed diodes and cascode-connecting diodes, to minimize reverse recovery current and switching loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If diodes are incorporated between source and drain regions of normally-off semiconductor elements, then return current can flow through the diode, but reverse recovery current causes increased switching loss and heat generation
Solution Approach 1:
The patent introduces an auxiliary switching element connected in parallel with the diode to act as an intermediary. This auxiliary element can divert the return current away from the diode during normal operation, preventing the diode from entering reverse recovery state and eliminating the associated switching losses while still allowing return current flow when needed
2Loss of energy
If reverse recovery current is reduced, then switching loss decreases, but device complexity increases due to additional switching elements
Solution Approach 1:
The auxiliary switching element is designed to serve multiple functions: it diverts return current to prevent diode reverse recovery, provides an additional current path for fault protection, and can operate in conjunction with the normally-off semiconductor element. This multi-functionality justifies the added complexity by delivering multiple benefits from a single component addition
3Temperature
If large cooling heat sinks are used to handle heat generation, then thermal management is improved, but device size increases
Solution Approach 1:
The patent applies preliminary action by reducing the switching loss at its source through the auxiliary switching element configuration. By preventing the diode from experiencing reverse recovery current, the heat generation is minimized before it occurs, thereby reducing the cooling requirements and allowing for a more compact device design without compromising thermal management
Data Source
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AI summary
Disclosed is a power conversion device which achieves reductions in switching loss due to a reverse recovery current and heat generation loss. Specifically disclosed is a power conversion device provided with a cascode element (21) configured by electrically connecting a normally-on switching element (4) and a normally-off switching element (5) in series and connecting a gate terminal of the normally-on switching element (4) and a source terminal of the normally-off switching element (5) via a cascode connection diode (7), and a high-speed diode (6) electrically connected in parallel with the cascode element (21) and having a cathode region connected to a positive electrode terminal and an anode region connected to a negative electrode terminal.