Research On Multiphase/Multi-modular Boost DC-DC Converters With Stable Control Schemes

In this thesis, the multiphase/multi-modular boost DC-DC converters with stablecontrol schemes is presented. The multiphase boost DC-DC converters are design for highvoltage and high power applications. This can be achieved by the adjustment of voltagedoubler rectifiers on the secondary side of high frequency transformers. To achieve high outputvoltage, voltage doubler rectifiers are introduced whereas for high output power parallel dioderectifiers are considered. This research mainly focuses on boost DC-DC converters and boosthalf bridge (BHB) DC-DC converters along with their control schemes. In order to analyze thebehavior of multiphase boost DC-DC converter a stable control strategy is developed. Thestable control strategy for three phase boost DC-DC converter would be considered forsimulation but can be extend to N-number of phases. The stable control strategy consists ofonly three voltage loops which will be enough to have an appropriate and an efficient operationof three phase boost DC-DC converter. Thus the equal power balance sharing can be obtainedbetween input and output. Moreover, the stability of control strategy will be verified bysimulating the multiphase boost DC-DC converter for the same and mismatch turn ratios ofhigh frequency transformers. Similarly, for the analysis of multiphase boost-half-bridge (BHB)DC-DC converter a control scheme will be developed based on FPGA for high powerapplications. FPGA will be used to generate the control signals for the proposed multiphaseBHB DC-DC converter. In order to check the effectiveness and stable operation of the controlstrategy, the proposed multiphase converter will be configured for the same and/or mismatchturn ratios of high frequency transformers. The three inductor currents will have the sameaverage value so that the power balance sharing can be achieved no matter the turn ratios of high frequency transformers are same or mismatch. Furthermore, the working modes ofmultiphase DC-DC converters will be analyzed. The working mode of multiphase converterswill be described and drawn in detail. Finally, the working modes for each multiphase DC-DCconverter will be verified by simulation and experimental results.The multi-modular boost DC-DC converter can be connected into four possible formsdue to their series/parallel configuration at input and output side. This research will explore aconfiguration for boost half bridge DC-DC converters, connected in series at the input andparallel (ISOP) at the output, such that the converters share the input current and load voltageequally. The same converters connected in input-series and output series (ISOS) will share theequal voltage at the input and output side. Similarly, input-parallel output-parallel (IPOP)configuration describes the correlation between input current sharing (ICS) and output currentsharing (OCS) of the basic modules of the (IPOP) converter. Dynamic control strategies havebeen developed to achieve the above said objectives for the four basic forms of multi-modularconfiguration. In order to verify the effectiveness and stability of control scheme, the multi-modular boost half bridge (BHB) DC-DC converter in each form has been simulated for thedifferent load conditions such as for fixed load, half load and continuously varying load. Theresults are found to be satisfactory at each load condition and validate the proposed converterstructures. The system proposed here is comprising of two modules but can be extended tothree or more.In the last part of the thesis a general discussion is reported and the main findings of theresearch are highlighted with future recommendations.