Half-Bridge Variable Dead Time for Zero-Voltage Switching
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Solution Overview
Problem
Existing half-bridge converters experience thermal losses due to a dead band longer than required, which is necessary to prevent shoot-through events, leading to inefficiencies and increased thermal stresses on semiconductor devices.
Innovation Solution
A method for dynamically calculating a variable dead band based on real-time circuit models to ensure zero-voltage switching while minimizing switching and reverse conduction losses, using a processor to calculate equivalent capacitance, ZVS charge requirements, and updating dead bands for each commutation point.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed dead band is used to prevent shoot-through events, then reliability is improved, but thermal losses increase due to excessive dead band duration
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed dead band to a dynamically adjusted dead band. The controller calculates the minimum required dead band duration based on real-time parameters including equivalent capacitance, link voltage, and current, allowing the dead band to adapt to changing operating conditions. This resolves the contradiction by providing just enough dead band to prevent shoot-through while minimizing unnecessary duration that causes thermal losses.
Solution Approach 2:
The patent changes the parameter of dead band duration from a fixed value to a variable parameter calculated based on circuit conditions. By computing the minimum dead band time using the formula involving equivalent capacitance, link voltage, and current, the system optimizes the dead band parameter to prevent shoot-through events while reducing thermal losses associated with excessive dead band duration.
2Reliability
If a fixed dead band is used to ensure safe switching, then device protection is improved, but switching losses increase
Solution Approach 1:
The system dynamically adjusts the dead band duration based on real-time circuit conditions rather than using a fixed conservative value. By calculating the minimum required dead band based on equivalent capacitance, link voltage, and current, the system provides adequate device protection while minimizing the dead band duration to reduce switching losses.
Solution Approach 2:
Instead of using an excessive fixed dead band that guarantees protection but causes losses, the patent applies partial action by calculating and applying only the minimum necessary dead band duration. This partial approach provides sufficient protection against shoot-through while avoiding the excessive duration that would cause unnecessary switching losses.
3Reliability
If a longer dead band is used to ensure zero-voltage switching, then switching safety is improved, but reverse conduction losses increase
Solution Approach 1:
The patent changes the dead band parameter from fixed to variable, calculating the precise minimum duration needed to achieve zero-voltage switching based on real-time parameters. This prevents both shoot-through events and excessive reverse conduction losses by applying only the necessary dead band duration rather than a conservative fixed value.
Data Source
AI summary
An improved method for zero-voltage switching (ZVS) of a voltage-fed half-bridge using a variable dead band is provided. The duration of the dead band is determined dynamically and is precisely long enough to ensure the absence of shoot-through events while also minimizing or eliminating switching losses and reverse conduction losses. The method generally includes: (a) calculating the equivalent capacitance as seen by the current source charging the midpoint of the half-bridge; (b) calculating the ZVS charge requirement based on the link voltage and the equivalent capacitance; (c) calculating the charge delivered by the current source over time during a dead band vector, equating the result to the ZVS charge requirement, and solving for the ZVS time requirement at each commutation point over the switching cycle; and (d) updating the dead bands for each commutation of each half-bridge in the switched-mode power converter.