Power consumption and device size have been placed at the primary concerns for battery-operated portable applications. Switching converters gain popularity in powering portable devices due to their high efficiency, compact sizes and high current delivery capability. However portable devices usually operate at light loads most of the time and are only required to deliver high current in very short periods, while conventional buck converter suffers from low efficiency at light load due to the switching losses that do not scale with load current. In this research, a novel technique for buck converter is proposed to reduce the switching loss by reducing the effective voltage supply at light load. This buck converter, implemented in TSMC 0.18 micrometers CMOS technology, operates with a input voltage of 3.3V and generates an output voltage of 0.9V, delivers a load current from 1mA to 400mA, and achieves 54 percent ~ 91 percent power efficiency. It is designed to work with a constant switching frequency of 3MHz. Without sacrificing output frequency spectrum or output ripple, an efficiency improvement of up to 20 percent is obtained at light load.

The systems which contain coarsely quantized signals are commonly found in applications where the actuators and/or sensors can only output a finite number of levels. This thesis focuses on the problem of synthesizing a finite-level control force for a certain control task, first presenting a systematic design method based on the theory of sliding modes and then applying it to the designs of the class-D audio amplifier and synchronous buck converter. At the first part, a novel three-level modulation technique for a class-D audio amplifier is designed by the sliding mode control theory. The simulated and experimental results conform to the excellent performance of this three-level modulation scheme. In particular, the proposed modulation scheme improves the poor efficiency of a conventional two-level class-D audio amplifier when the audio input signal is small, also excludes the output LC filter. The experiment shows that the designed three-level class-D amplifier achieves a minimum total harmonic distortion plus noise of 0.039% and an efficiency of 85.18%. At the second part, the controller of a synchronous buck converter is designed. The proposed self-oscillating controller stabilizes the buck converter in sliding mode, without the need of a triangular wave generator like the conventional PWM method. A 12V/1.5V synchronous buck converter with proposed control is built in the laboratory. The experiment shows 0.66% of the static output ripple and 3% of the load regulation error in response to the 15A step change of the load current at a slew rate of 50A/£gs.

In this dissertation, new high frequency link power conversion systems for the fuel cell power conditioning are proposed to improve the performance and optimize the cost, size, and weight of the power conversion systems. The first study proposes a new soft switching technique for the phase-shift controlled bi-directional dc-dc converter. The described dc-dc converter employs a low profile high frequency transformer and two active full-bridge converters for bidirectional power flow capability. The proposed new soft switching technique guarantees soft switching over wide range from no load to full load without any additional circuit components. The load range for proposed soft switching technique is analyzed by mathematical approach with equivalent circuits and verified by experiments. The second study describes a boost converter cascaded high frequency link direct dc-ac converter suitable for fuel cell power sources. A new multi-loop control for a boost converter to reduce the low frequency input current harmonics drawn from the fuel cell is proposed, and a new PWM technique for the cycloconverter at the secondary to reject the low order harmonics in the output voltages is presented. The performance of the proposed scheme is verified by the various simulations and experiments, and their trade-offs are described in detail using mathematical evaluation approach. The third study proposes a current-fed high frequency link direct dc-ac converter suitable for residential fuel cell power systems. The high frequency full-bridge inverter at the primary generates sinusoidally PWM modulated current pulses with zero current switching (ZCS), and the cycloconverter at the secondary which consists of only two bidirectional switches and output filter capacitors produces sinusoidally modulated 60Hz split single phase output voltage waveforms with near zero current switching. The active harmonic filter connected to the input terminal compensates the low order input current harmonics drawn from the fuel cell without long-term energy storage devices such as batteries and super capacitors.

This thesis studies residential dc distribution system with primary focus on point-of-load (POL) converters. The growing number of inherently dc loads, increasing penetration of distributed energy resources (DERs) and advancements in power electronic converters are some of the reasons to reconsider the existing residential ac distribution system. A dc distribution system can achieve higher efficiency by eliminating the ac-dc rectifiers and power factor correction stages currently used in most domestic electronic appliances. In this thesis, 380V is identified as a suitable voltage level for the main dc bus. Safety issues are discussed and common domestic loads are characterized. Two common converter topologies – buck and flyback converters are suggested as POL converters for heating and LED lighting loads respectively. State-feedback control is designed and implemented for buck converter and current mode control of flyback converter is implemented. A 500W POL buck converter using state-feedback with integral control is designed and tested for heating load applications. Finally a small dc distribution system is simulated using the converter models. The response of the system is stable under load and line changes. / text

In this thesis, a capacitor semi-active hybrid energy storage system for electric vehicle is proposed. A DC-to-DC bi-directional converter is required to couple the supercapacitor to the system DC bus. Through literature reviews, it was decided that a dual-bridge resonant converter with HF transformer isolation is best suited for the hybrid energy storage application. First, a dual-bridge series resonant converter with capacitive output filter is proposed. Modified gating scheme is applied to the converter instead of the 50% duty cycle gating scheme. Comparing to the 50% duty cycle gating scheme where only four switches work in ZVS, The modified gating scheme allows all eight switches working in ZVS at design point with high load level, and seven switches working in ZVS under other conditions. Next, a dual-bridge LCL-type series resonant converter with capacitive output filter is proposed. Similarly, the modified gating scheme is applied to the converter. This converter shows further improvement in ZVS ability. Operating principles, design examples, simulation results and experimental results of the two newly proposed converters are also presented. In the last part of the thesis, a capacitor semi-active hybrid energy storage system is built to test if the proposed converters are compatible to the system. The dual-bridge LCL-type series resonant converter is placed in parallel to the supercapacitor. The simulation and experimental results of the hybrid energy storage system match closely to the theoretical waveforms. / Graduate

Advantages of electrochemical wastewater treatment over conventional wastewater treatment include its smaller footprint, modularity, and ability to meet increasingly stringent government regulations. A power supply that can be packaged with an electrochemical stack could make electrochemical wastewater treatment more cost-effective and scalable. For this application, the series and series-parallel resonant converters are suitable power converter candidates. With an output current specification of 100A, the series-parallel resonant converter (SPRC) is superior due to its simpler output stage. The thesis presents the design of a 500W SPRC for a wastewater treatment cell stack. A rudimentary cell model is derived experimentally. The closed loop analysis, controller design and simulation results are presented. The output voltage and current are estimated using sensed quantities extracted from the high voltage, low current primary side. Low voltage experimental results verify the operation of the power stage and voltage estimation circuitry in open loop pulsed operation.

Advantages of electrochemical wastewater treatment over conventional wastewater treatment include its smaller footprint, modularity, and ability to meet increasingly stringent government regulations. A power supply that can be packaged with an electrochemical stack could make electrochemical wastewater treatment more cost-effective and scalable. For this application, the series and series-parallel resonant converters are suitable power converter candidates. With an output current specification of 100A, the series-parallel resonant converter (SPRC) is superior due to its simpler output stage. The thesis presents the design of a 500W SPRC for a wastewater treatment cell stack. A rudimentary cell model is derived experimentally. The closed loop analysis, controller design and simulation results are presented. The output voltage and current are estimated using sensed quantities extracted from the high voltage, low current primary side. Low voltage experimental results verify the operation of the power stage and voltage estimation circuitry in open loop pulsed operation.

This work presents a new wireless Visible Light Communication lighting system targeted to future Smart Buildings. A digitally controlled LLC resonant dc-dc converter targeted to white LED luminaires is demonstrated. Visible Light Communication is implemented with minimal incremental cost, by operating the LLC converter in burst mode, without causing any visible disturbance. The converter operates with a regulated average LED current by adjusting the switching frequency, while the burst pulse timing is controlled to minimize the current disturbance and minimize the value of the output capacitor. Variable Pulse Position Modulation is used to modulate the data, while supporting a range of dimming settings. A digital demodulation scheme that supports variable frequency transmission is demonstrated. The 80 W, 400 V to 23 V converter experimental prototype has a peak efficiency of 93.8 %. The bit error rate of the complete system is fully characterized versus distance and angle.

This work presents a new wireless Visible Light Communication lighting system targeted to future Smart Buildings. A digitally controlled LLC resonant dc-dc converter targeted to white LED luminaires is demonstrated. Visible Light Communication is implemented with minimal incremental cost, by operating the LLC converter in burst mode, without causing any visible disturbance. The converter operates with a regulated average LED current by adjusting the switching frequency, while the burst pulse timing is controlled to minimize the current disturbance and minimize the value of the output capacitor. Variable Pulse Position Modulation is used to modulate the data, while supporting a range of dimming settings. A digital demodulation scheme that supports variable frequency transmission is demonstrated. The 80 W, 400 V to 23 V converter experimental prototype has a peak efficiency of 93.8 %. The bit error rate of the complete system is fully characterized versus distance and angle.

A low-cost power router (PR), capable of dynamic, independent control of active- and reactive-power flows on meshed grids is presented. The operating principle, detailed schematics, and various possible implementations of the proposed power router are discussed. Various operating modes are identified and a control algorithm has been proposed and verified through simulations. Small-signal and frequency-domain models of the power router from basic time-domain equations are developed. A three-tier protection system based on the fail-normal switch to avoid single point-of-failure is presented. The operation of proposed protection system in isolating the converter and the grid in the event of faults is verified through simulation. An analytical method to evaluate the stability of a system with multiple power routers is proposed. Necessary conditions for the PR-controller design to ensure stable operation of a system with multiple power routers is proposed. These necessary conditions are verified through simulation studies. Potential applications of proposed power router in distribution system and the associated challenges in implementation are presented. The functionality and advantages of the proposed power router are experimentally demonstrated at 13 kV, 1 MVA. The proposed power router can result in a low cost power routing solution that can reduce electric grid congestion and efficient implementation of RPS mandates.