Pwm control of dual active bridge: Comprehensive analysis and experimental verification

The dual-active-bridge (DAB) topology is ideally suited for high-power dc–dc conversion, especially when bidirectional power transfer is required. However, it has the drawback of high circulating currents and hard switching at light loads, if wide variation in input and output is expected. To address these issues, this paper presents a comprehensive analysis and experimental results with pulsewidth-modulation (PWM) control of the DAB. The PWM control is in addition to phase-shift modulation between the two H-bridges. The analysis addresses PWM of one bridge at a time and of both bridges simultaneously. In the latter, five distinct modes arise based on the choice of PWM and load condition. The possibilities are analyzed for optimizing power density and efficiency for low-load operation. Finally, a composite scheme combining single and dual PWM is proposed that extends the soft-switching range down to zero-load condition, reduces rms and peak currents, and results in significant size reduction of the transformer. Experimental results are presented with a 10-kW prototype.

I. Introduction

The dual-active-bridge (DAB) topology [1] is ideally suited for high-power galvanically isolated dc–dc conversion. It has advantages of high power density, zero-voltage switching (ZVS), bidirectional power transfer capability, a modular and symmetric structure, and simple control requirements. It can also be used for multiport operation [2], [3], a feature that is useful in interfacing several dc sources and loads using a single converter. Details of DAB operation and comparison with other topologies can be found in [1] and [4]–[6]. Although several other bidirectional isolated dc–dc converter topologies [7]– [11] have been proposed in literature, the simple symmetric structure and simple control mechanism of the DAB are unique attributes. Small-signal modeling for the DAB with phase-shift modulation has been presented in [12]. The DAB converter has also been proposed as a building block for modular high-power converters [13], [14].