A Bidirectional Resonant Converter for Aerospace Applications
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In this thesis, an isolated resonant bidirectional converter is proposed for transportation applications such as mid-size electrified airplanes. The proposed converter is capable of transferring the nominal power in both directions, either from the high voltage side to the low voltage side (step-down mode), or from the low voltage side to the high voltage side (step-up mode). It is shown that the converter transfers full power over the entire range of terminal voltages with guaranteed zero voltage switching (ZVS) for all the voltage and power levels. The achievement of ZVS switching is obtained through the right combination of modulation scheme and low-cost passive auxiliary circuits added to the main converter. Two modulation schemes are developed to achieve the aforementioned merits. The first proposed modulation scheme decouples the switching frequency from other control variables and combines them in a straightforward manner to gain a single control variable and, at the same time, maintain soft switching without complex calculations or lookup tables. This provides the capability of using the well-established control approaches for this converter system. The second modulation scheme provides the same functionality under constant frequency operation. The inter-bridge phase-shift uniquely determines the duty-cycles for both of the bridges on either side such that soft switching operation is maintained in all the working conditions. Having the phase-shift as the only independent control variable reduces the problem from a multivariable to a single-variable control problem that allows the use of well-established control methods without compromising the functionality of the system. In addition to the modulation schemes two types of low cost, robust passive auxiliary circuits are introduced with different flexibilities and component counts to guarantee the zero voltage switching of the converter. No active components are used and no limitation is imposed on the converter switches. All the analytical predictions are experimentally verified and the functionality of the proposed system is validated.