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Title: Study of electrolytic capacitor-less designs for light-emitting-diode (LED) lighting applications
Authors: Wu, Hao
Degree: Ph.D.
Issue Date: 2018
Abstract: In recent years, light emitting diodes (LEDs) have made good progress in general lighting applications, gradually replacing traditional incandescent, fluorescent and halogen lamps. Their main advantages are high luminous efficiency, long life span and being environmental friendly. However, many offline LED drivers are designed with electrolytic capacitors, leading to a short life span and limited range of operation temperature. Thus, electrolytic capacitor-less designs are expected for LED lighting applications, along with high power factor, constant output current and high power efficiency. This thesis is devoted to the study and design of effective LED driving solutions with no necessity of electrolytic capacitors. The main contributions of this thesis are summarized as follows: A single-output electrolytic capacitor-less LED driver is proposed, where a high efficiency is achieved by using a minimal power processing (MPP) configuration. Near perfect power factor correction (PFC) is achieved by a simple dual-output discontinuous-conduction-mode (DCM) pulse-width-modulation (PWM) front-end converter. One output of the front-end converter is connected to the LED load using a control switch. The other output is connected directly to a dc storage capacitor cascaded with a downstream DCM PWM converter driving the same LED load to achieve constant output current (COC) driving. The power flow is controlled to achieve the required MPP which can also reduce the storage capacitance by balancing only the ac input ripple power and the dc output power without power recycling. Thus, the design requires no electrolytic capacitor, hence extending the system life span. Furthermore, based on a single dual-winding coupled inductor, a single-inductor multiple-output (SIMO) LED driver with PFC function is proposed without the requirement of electrolytic capacitors, where a small storage capacitance is used to actively decouple the ac and dc input powers. Compared with previous works, the proposed PFC SIMO LED driver has some additional benefits, including a smaller line filter, multiple output currents without double line frequency ripple and a faster output regulation. With appropriate control strategy, an independent output regulation can be achieved for each output channel. Meanwhile, to improve the converter efficiency, the energy flow of the converter is optimized with an inductor current programming technique. Finally, an attempt is made to establish a DC power distribution for LED lighting. A family of bidirectional single-phase AC-DC three-phase-leg sinusoidal pulse-width-modulation (SPWM) converters with an AC storage capacitor for use in a nanogrid system is designed with a general control structure and a modulation for minimizing the AC storage capacitance. The general control structure is built based on a decoupled system with a power factor correction converter cascaded with an active AC power load at the DC bus. The decoupled system is developed based on a transformation in terms of differential-mode and common-mode voltages. The modulation introduces an extra zero-sequence voltage injection derived from the three-phase-leg SPWM voltages without introducing higher order harmonic distortions. A significant reduction of the AC storage capacitance and an improvement of converter efficiency are achieved.
Subjects: Hong Kong Polytechnic University -- Dissertations
Light emitting diodes -- Power supply
Pages: xxvii, 127 pages : color illustrations
Appears in Collections:Thesis

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