Development of Three-Phase On-Board Battery Charger for PHEV without High-Capacity Electrolytic Capacitor Ying-hao, Zhang Department of Electrical Engineering Graduate School, Myongji University Advisor Professor Byung-Moon Han
A new two-stage on-board battery charger which can operate in both three-phase mode and single-mode is proposed for plug-in hybrid electric vehicles (PHEVs). It consists of three identical chargers which connect to battery in parallel, and each of them has a cascaded structure of high frequency resonant converter with a constant switching frequency for electrical isolation, and buck-boost converter for charging control and harmonic regulation of input current under wide range line-input voltage. This structure uses small link capacitors so that high-capacity electrolytic capacitors can be removed in automotive applications. An LLC resonant converter is proposed in the first stage. The parallel buck-boost converters operating in discontinuous conduction mode are employed in the second stage, so that the voltage stress of components could be reduced and the simple controller can be used to control charging current. Digital control of converter is realized by applying DSP (Digital Signal Processor) that performs constant current through duty control of buck-boost converter. Duty ratio of LLC converter is unregulated. Proposed Converter stably operates in various load condition (within 10kW) and it is proven that the proposed converter achieves efficiency of higher than 93% and power factor of higher than 0.99 through experiment..