Study On Low-Power Digital AC-DC Converter

ABSTRACT:The switch-mode power supply (SMPS), emerged in1970s, has already been the mainstream and applied in most power converter designs today. Nowadays, although most SMPSs are still designed with analog controllers, the digital SMPS has always been a research hotspot.In this thesis, an ARM MCU powered, fuzzy controller based digital SMPS charger has been designed. With the digital control, the charger device could have a wide range voltage output and an enhanced charging control algorithm. It could charge batteries with different nominal voltages, solving the existing problem that one battery charger can only charge batteries of one nominal voltage.In this thesis, the facts and developments of the digital SMPS and electric bicycle chargers are introduced firstly. Then, the common SMPS topologies and control methods, as well as VRLA batteries and their charging methods are analyzed.As designed for36V and48V VRLA batteries, the specifications and general scheme of the digital SMPS charger are determined, and the design of software and hardware are introduced in this thesis. The hardware consists of an analog controlled Boost PFC Circuit and a digital controlled Flyback converter. As for the controller unit, the MCU controller circuit, the sensoring circuits, and the MOSFET driver circuits are also designed. Based on the analysis of the analog control and the digital PID control method, a fuzzy controller with asymmetric fuzzifier is designed. Then the controller is verified with a computer simulation implemented with MATLAB and a Saber circuit model. The performance is evaluated with a PID controlled comparison.The software design includes the enhanced charging control program, the fuzzy controller program and other system software. The enhanced multi-stage charging control program automatically switches between two groups of voltage threshold in order to charge both36V and48V VRLA batteries effectively and safely.Finally, experiments and their results are describe in this thesis. The device performance is thus tested and verified.