Active Soft-Switching Cell for ZVS AC-DC Power Conversion
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Solution Overview
Problem
High switching frequency in AC-DC power converters leads to excessive turn-on and reverse-recovery losses in SiC MOSFETs, limiting efficiency and power density, despite advancements in wide-band-gap materials like silicon carbide (SiC) diodes.
Innovation Solution
The implementation of an active soft-switching cell with a series inductor and auxiliary switch, allowing zero-voltage switching (ZVS) in SiC MOSFETs, reduces reverse-recovery losses and turn-on losses by controlling the rate of current change in the body diode, thereby enhancing efficiency and power density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If switching frequency is increased to achieve high power density, then power density is improved, but switching losses increase and efficiency deteriorates
Solution Approach 1:
A resonant inductor is introduced as an intermediary component between the SiC MOSFET and the load. This inductor creates a resonant circuit that enables zero-voltage switching (ZVS) by controlling the current waveform to naturally zero-cross at the switching instant, thereby eliminating switching losses while maintaining high switching frequency operation for high power density
Solution Approach 2:
The patent changes the operating parameters of the SiC MOSFET by implementing zero-voltage switching through the resonant inductor. By controlling the switching to occur when the voltage across the MOSFET is zero, the switching losses are dramatically reduced, enabling efficient high-frequency operation that achieves both high power density and high efficiency
2Device complexity
If hard-switching mode is used in SiC MOSFETs, then device simplicity is maintained, but turn-on and reverse-recovery losses become excessive
Solution Approach 1:
The resonant inductor serves as a mediator that transforms the hard-switching operation into soft-switching operation. By introducing this single component, the patent achieves zero-voltage switching without requiring complex multi-switch topologies, thus maintaining relative circuit simplicity while dramatically reducing turn-on and reverse-recovery losses
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 significantly reduces switching losses, achieving high efficiency and high power density while enabling bidirectional power flow and minimizing electromagnetic interference (EMI) noise.
Implementation Method 1
allowing zero-voltage switching (ZVS) in SiC MOSFETs, reduces reverse-recovery losses and turn-on losses by controlling the rate of current change in the body diode
Data Source
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AI summary
A circuit technique substantially reduces the switching losses in an AC-DC power conversion system caused by turn-on characteristics of a main switch and the reverse- recovery characteristic of a rectifier. The losses are reduced by using an active soft-switching cell having a series inductor (LS), a series capacitor (CS), a main switch (S2), a rectifier switch (S1), and an auxiliary switch (SA). The reverse-recovery related losses are reduced by the series inductor (LS) connected between the main and rectifier switches (S1, S2) to control the rate of current change in the body diode of the rectifier switch (S1) during its turn-off. The main switch (S2), the rectifier switch (S1), and the auxiliary switch (SA) operate under zero-voltage switching (ZVS) conditions.