| Abstract |
Conventionally, grid-connected isolated AC/DC conversion is realized through a two-stage approach,resulting in an increased number of (magnetic) components and thus a cost-inefficient solution.Therefore, this paper focusses on an extension of a recently proposed control strategy, i.e.bidirectional charge control, for a bidirectional, isolated, series-resonant DC/DC converter. Bidirectionalcharge control targets a predefined charge displacement between two consecutive zerocrossingsof the resonant current and calculates the required switching levels for the semiconductorswitches accordingly. These switching levels are defined as a function of the charge differenceacross the resonant capacitor, realizing dynamic, bidirectional operation of the series-resonant converterwhile guaranteeing zero-voltage switching of all switches. In order to maintain grid quality,grid-tied converters are verified for compliance regarding their harmonic current emissions and totalharmonic distortion (THD). Therefore, power-factor correction (PFC) is a requirement for each ofthese converters. To achieve power-factor correction, a phase-locked loop is implemented with anouter control loop to realize sinusoidal grid-current waveforms and, as a result, low harmonic currentemissions that do comply to the standards and a low THD. The discussed control algorithm and thelinearization are verified through simulation for a 3kW electric vehicle battery charger to connect tothe single-phase grid. Nonetheless, wide primary, grid voltage and wide secondary, electric vehiclebattery voltage ranges have been shown applicable with bidirectional charge control. Although thesimulations show very promising results, realization on a prototype is recommended to validate thetheoretical analysis and prove the robustness of the proposed control strategy. |
