A Parameter Design Method and a Fixed-Frequency Control Strategy for the Three-Phase DAB-SRC Based on the Time Domain Analytical Model

This article focuses on the model and the control strategy of the three-phase dual active bridge series resonant converter (DAB-SRC). Different from the common modeling method with the fundamental harmonic approximation, a precise time domain analytical (TDA) model is built. The analytical solution of voltage gain with respect to the frequency and the phase shift (PS) angle is given. The soft-switching region is also represented by an analytical expression and plotted in a 3-D coordinate system, which intuitively shows the influence of the control and circuit parameters. Therefore, the soft-switching operation can be ensured from the design stage. Based on this, the circuit parameter design guideline and a simple fixed-frequency PS control strategy are proposed to ensure that the converter can realize the soft switching with a wide load range. In addition, a feedforward controller is proposed, which uses a simple inverse proportion function instead of the complex trigonometric function through a curve-fitting method. By this means, the input voltage detection can be removed. The theoretical analysis results are verified by a 1.35-kW bidirectional experimental prototype, which can keep the soft-switching operation covering 10%–100% nominal load.