A Dual Active Bridge Converter With an Extended High-Efficiency Range by DC Blocking Capacitor Voltage Control

Abstract

A Dual Active Bridge (DAB) converter can achieve a wide high-efficiency range when its input and output voltages are equal, assuming a 1:1 turns ratio for its isolation transformer. If its input or output voltage is doubled, efficiency of the DAB will drop significantly, because of the introduction of hard switching and high circulating power. Thus, a new modulation scheme has been proposed, whose main idea is to introduce a voltage offset across the dc blocking capacitor connected in series with the transformer. Operational principle of the proposed modulation has been introduced, before analyzing its soft-switching area and circulating power mathematically. The final modulation scheme is not difficult to implement, but can help the DAB achieve soft switching, low circulating power, and thereby high efficiency, even with its input or output voltage doubled. These features have been verified by experimental results obtained with a 1.2 kW prototype.

Zero Voltage Switching Criteria of Triple Active Bridge Converter

“…By substituting the harmonic form expression of the delta circuit currents in (16)- (18) and duty cycle in (10)- (14), into the port currents in (4)-(6), the closed-form solution of the port current i σ,1 (τ j ), i σ,2 (τ j ) and i σ,3 (τ j ) at the events of switching transitions τ j can be obtained, and they are summarized in Table I. The times of switching event τ j are defined in Table IV.…”

“…In the available literature, two approaches for the first step can be found: piecewise expression or harmonic form expression of transformer currents. A piece-wise expression is easy to understand [14]; however, implementing it in a digital controller is somewhat complicated, since the expression changes in each switching pattern. The implementation becomes even more involved with increasing number of switching patterns when the modulation changes from a single-phase shift to a dual-phase shift or further to a triple-phase shift.…”

Transformer Current Ringing in Dual Active Bridge Converters

“…Then not only the power loss is increased, but also EMI issues get worse. Various modulation strategies were, therefore, proposed to extend the soft-switching region [10] [11] [12].…”

Enhanced DAB for Efficiency Preservation Using Adjustable-Tap High-Frequency Transformer

“…Another solution is to utilize resonance to extend the soft-switching region by adding extra components, passive or active (not lossless), which add to the design size and complexity [10], [12], [13] and lead to electromagnetic interference issues as the increased gain is based on frequency modulation [14]. DC blocking capacitor together with a new modulation scheme is proposed in [15] and the method could successfully increase efficiency for voltage gains around 2 p.u. but deteriorates the performance under normal operating conditions.…”