Watkins-Johnson Derivative Topology And Its Application

Inverter is one of significant research subjects in the field of renewable energy application,and also a research hotspot in the field of transportation such as automobile and train power supplies.Off-grid inverter occupies the core part of grid-connected inverter and photovoltaic power generation system.At the present stage,almost all applications that realizing voltage inversion adopt the full-bridge topology regardless of power level and voltage level.Inherent shortcomings of full-bridge mainly include large quantities of power switches;floating switches inconvenient to drive;addition of dead-time that simultaneously turn off all leg switches in case of shoot-through;snubber circuits and active clamp circuits suppressing the inrush current induced by parasitic inductances and releasing the voltage stress of power switches.Therefore,study and improvement of voltage inversion topology possess indispensable theoretical and practical significance.This dissertation improves the Watkins-Johnson(WJ)topology which originated in the 1970s and has received minimal attention since then,and solves the problems exist in the full-bridge based inverter in a topological manner,pushes the WJ topology into DC/AC voltage inversion field,changes the present situation that the WJ topology only used in DC/DC converter,and adds a new candidate in the voltage inversion family.The original WJ topology has been improved in this work to have merits include:fewer switches are needed;ground switches ease of driving;alternatively turn-on dispense with dead-time;input end energy recovery functionality.This dissertation involves improvement approach of WJ topology,and applications in the inverter field of the improved WJ topology.The principal research achievements are summarized as follows.First of all,improving and optimizing original WJ topology by means of inductor coupling and switch low-side-izing.Analysis includes steady-state analysis and small signal analysis,the former gives the input-to-output steady-state transfer function as well as the relationship between the inductor average current and the load current,the latter adopts the state-space averaging approach to attain the small-signal model and its canonical form which providing a theoretical basis to the derivation of small-signal transfer function and port impedances.In addition,the deviation generated by nonideal parameters are discussed.Secondly,applying the improved WJ topology to the HF-link inversion stage of isolated inverter,realizing voltage inversion followed by the high-voltage DC bus.Discussions about control strategies are also conducted,the duty cycle function for open-loop control is derived,and the closed-loop model together with loop compensator for feedback control is designed.Middlebrook's extra element theorem is used for designing the input filter,and magnetic theories are applied to coupled inductor design.Shortcomings such as high voltage stress renders the improved WJ topology suitable for inverter applications of low voltage level and low power level.Moreover,the transfer function to topology(TF2T)theoretical system is proposed,and terminologies including basic topology set,expanded topology set,derivative topology set,topology operator,derivative operator are defined.This approach inverts the conventional analysis method of switching-mode power supply.By invoking TF2T approach,arbitrary constructed steady-state transfer function can be converted to practical topology theoretically.Finally,traversing all possible two-element series derived topologies according to TF2T approach,L3 topology is derived and nominated,which belongs to single-stage non-isolated step-up inversion topology.Different from the traditional step-up stage plus inversion stage two-stage structure,in which the DC-link high-capacity capacitor maintains the high-voltage bus stable,the intermediate capacitor in L3 topology behaves as a pulse link capacitor,relaying high-frequency dynamic voltage.The efficiency is improved and the circuit complexity is reduced.In order to output a pure sinusoidal waveform,the open-loop and closed-loop control strategies are studied.Theoretically,L3 topology has ability to produce any amplitude higher than the input,nonetheless nonideal parameters restrain its step-up ability and distort the output waveform,therefore the L3 inverter is suitable for low step-up ratio and low power applications.Experimental prototype circuits have been constructed corrsponding to HF-link inversion stage and L3 inverter respectively,for acquiring waveform,for analyzing data,and for verifying the effectiveness of approaches proposed in this dissertation.At last,summarizing the entire work and providing advises for further research.To sum up,in this dissertation,there are 113 figures,3 tables,233 formulae,and 139 references.