Abstract
The dual active bridge (DAB) converters are widely used in the energy storage equipment and the distributed power systems. However, the existence of switching nonlinearity and control delay can cause serious stability problem to the DAB converters. Thus, this paper, studies the stability of a digitally controlled DAB converter with an output voltage closed loop controller. Firstly, to accurately study the stability in a DAB converter, a discrete-time model established in a whole switching period is obtained. The model considers the output capacitor ESR, the digital control delay, and sample-and-hold process. By using this model, the stabilities of the DAB converter versus the proportional controller parameter and the output capacitor ESR are analyzed and the critical values are predicted accurately. Moreover, the stability boundary of the proportional controller parameter and the output capacitor ESR is also obtained. The result shows that the value of the output capacitor ESR can have a great effect on the stability region of the proportional controller parameter. Finally, the theoretical analyses are verified by the simulation and experimental results.
Highlights
Applications such as plug-in hybrid electric vehicles [1], renewable energy storage [2], uninterruptible power supply (UPS) systems [3], aerospace applications [4] and smart grids [5] usually need an energy storage device, which increase the popularity of the bidirectional DC-DC converters
As the dual active bridge (DAB) converter has many advantages, such as galvanic isolation, zero-voltage switching, high power density, high efficiency, and symmetric structure [6], it has been drawn more attention compared with other bidirectional DC-DC converters
The matrices Ai and vectors Bi in (1) are expressed in (2) and (3). It can be seen from the expressions that this paper considers the output capacitor ESR
Summary
Applications such as plug-in hybrid electric vehicles [1], renewable energy storage [2], uninterruptible power supply (UPS) systems [3], aerospace applications [4] and smart grids [5] usually need an energy storage device, which increase the popularity of the bidirectional DC-DC converters. The complex dynamics in the digitally controlled DAB converter, caused by switching nonlinearity and control delay [13], may deteriorate the working performance and bring stability problem. It has not been studied in the existing literature. Considering the small ripple requirement in averaged model [17], establishing a discrete-time model is more appropriate as the transformer current in a DAB converter is purely AC. In this paper, a full discrete-time model in a whole switching period is established This model considers all the ESRs in the circuit, including the output capacitor ESR.
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