Interleaved Buck/Boost Converters for Fuel Cell and Li-ion Battery Hybrid Energy System

Abstract

Proton exchange membrane (PEM) fuel cells (FCs) are widely used in electrical vehicle systems Since the PEM FCs can not provide very high levels of instant current to the load lithium batteries and supercapacitors are usually used in combination with the FCs to provide higher instant power to the load In addition the lithium battery and supercapacitor can also supply extra energy to the load when the PEM FCs can not provide enough In this dissertation two types of buck/boost DC - DC converters with interleaved control techniques are proposed for the PEM FC lithium battery and supercapacitor hybrid energy system The ripple current on the input and output can be reduced by using interleaved control compared with the traditional single converter topology Thus the overall performance of the interleaved control can be improved with a smaller-sized capacitor The proposed novel non-inverting buck/boost converter is used to transfer the PEM FC energy to the DC-bus and also provide energy to the load The common ground issue can be solved by the proposed non-inverting buck/boost converter In addition the output power can be increased with the interleaved control technique The counts of power switches and diodes can also be decreased by the integrated converter The operating principles and steady-state analysis of the proposed non-inverting buck/boost converter are discussed in detail Finally a laboratory prototype is implemented to verify the performance of the proposed converter; the FC output voltage is 24~45 V and the output is 28 V/800 W Synchronous rectifiers are also adopted to improve the system efficiency This dissertation also proposes a three-ports interleaved buck/boost DC - DC converter which transfers energy from the FC to the lithium battery and from the lithium battery to the DC-bus voltage by using an integrated coupled inductor A digital signal processor (dsPIC30F4011) is also adopted to control the power flow When the FC can not provide sufficient energy to the load the lithium battery energy and supercapacitor will supply extra to the load When the FC supplies sufficient energy the digital signal processor (DSP) can also control the proposed three-ports converter to charge the battery appropriately The operating principles and steady-state analysis of the proposed three ports non-inverting buck/boost converter are discussed in detail A laboratory prototype is implemented with an FC output voltage of 24~45 V and battery output of 24 V/ 10Ah The DSP is used to control the proposed two converters to manage the energy among the FC lithium battery and load A laboratory prototype is implemented to verify the effectiveness of the proposed converters

Date of Award	2014 Sept 5
Original language	English
Supervisor	Tsorng-Juu Liang (Supervisor)