Improved Instantaneous Flux and Current Control for Three-Phase Dual-Active Bridge DC-DC Converters

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Abstract
The three-phase dual-active bridge converter (DAB3) is a promising topology for high-power medium-frequency dc-dc conversion as it features inherent soft-switching capability and galvanic isolation. To enable a highly dynamic control of bidirectional power flow in the DAB3, the instantaneous flux and current control (IFCC) has recently been published. It supplements the state-of-the-art instantaneous current control (ICC) with a flux control feature to eliminate transient dc-bias flux linkage in the transformer core. The IFCC yields excellent results for transformers with negligible winding resistance, eliminating overshoots and oscillations in both transformer current and flux. When applied to less efficient transformer designs, however, residual oscillations in the dc currents are still observed. To guarantee oscillation-free dead-beat behavior for any values of winding resistance, this paper proposes an improved instantaneous flux and current control (IIFCC). The mathematical derivation is consistent with the basic idea of the improved instantaneous current control (IICC), which is shown to be a special case of the suggested generalized solution. To further reduce the computational load of the digital controller, an approximate closed-form solution based on Taylor’s theorem is provided for calculation at run-time with sufficient accuracy. Simulations and an experimental verification on a down-scaled hardware prototype confirm the effectiveness and superior performance of the proposed approach.