Advantages
High-Efficiency Operation Over Full Load Range:
Maintains ZVS (Zero-Voltage Switching) down to zero load, preventing efficiency degradation. Improves efficiency, especially at light loads where conventional control suffers from hard switching.
Realization of Silent Operation:
Avoids audible noise associated with burst mode by maintaining a fixed switching frequency, a key issue in conventional methods. Ideal for EV chargers and V2H systems.
System Miniaturization and Weight Reduction:
Reduced switching losses enable higher switching frequency design, which contributes to transformer miniaturization.
Background and Technology
| DAB converters, which are core to EV on-board chargers and Solid-State Transformers (SSTs), face a trade-off: ZVS fails at light loads, increasing switching losses, while the countermeasure, burst mode, causes audible noise. This technology is a control method that introduces a “power cancellation period” to intentionally send power in the reverse direction within a single switching cycle. During this period, all switches on the transmitting bridge are turned off, causing resonance between the inductor and the parasitic capacitance of the semiconductor switches, which reverses the inductor current polarity. This reversal generates temporary reverse power, canceling the forward power. This makes it possible to freely control the average transmitted power down to near zero, while continuously maintaining the necessary cur rent to achieve ZVS. Furthermore, to minimize unnecessary conduction losses during this cancellation period, the approach actively utilizes the “low-voltage-side bridge,” which requires less current to achieve ZVS, thereby suppressing the converter’s total losses. |
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Data
Demonstrated with a 3.3kW DAB converter (using 3.3kV SiC-MOSFETs on the high-voltage side).
Dramatic Loss Suppression Effect::
In the light-load region below 1.3kW, where conventional SPS control losses increase sharply, this technology suppresses the loss increase and maintains high efficiency.
Key to Loss Minimization:
Maximizes the use of the low-voltage-side device’s characteristic, which requires less current for ZVS (0.24A), to minimize unnecessary losses during the power cancellation period (compared to 0.75A for the high-voltage side).
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Expectations
This technology holds the potential to fundamentally enhance product performance in cutting-edge fields requiring both silent operation and light-load efficiency, such as EV on-board chargers (OBCs), V2G/V2H systems, Solid-State Transformers (SSTs), and data center power supplies.
The basic principle has been established, and we are now at the stage of aiming for product implementation. We are seeking flexible partnerships with companies interested in joint R&D for optimization, co-development of control ICs, or technology licensing.
Patents
Patent Pending
Researchers
Takanori Isobe (Associate Professor, University of Tsukuba)
Project ID:DD-05332