With the increased usage of electrical equipment for various applications, the demand for quality power apart from continuous power availability has increased and hence requires the development of appropriate power conditioning system. A major factor during development of these systems is the requirement that they remain environment-friendly. This cannot be realized using the conventional systems as they use batteries and/or engine generators. Among various viable technologies, fuel cells have emerged as one of the most promising sources for both portable and stationary applications. In this thesis, a new battery less UPS system configuration powered by fuel cell is discussed. The proposed topology utilizes a standard offline UPS module and the battery is replaced by a supercapacitor. The system operation is such that the supercapacitor bank is sized to support startup and load transients and steady state power is supplied by the fuel cell. Further, the fuel cell runs continuously to supply 10% power in steady state. In case of power outage, it is shown that the startup time for fuel cell is reduced and the supercapacitor bank supplies power till the fuel cell ramps up from supplying 10% load to 100% load. A detailed design example is presented for a 200W/350VA 1- phase UPS system to meet the requirements of a critical load. The equivalent circuit and hence the terminal behavior of the fuel cell and the supercapacitor are considered in the analysis and design of the system for a stable operation over a wide range. The steady state and transient state analysis were used for stability verification. Hence, from the tests such as step load changes and response time measurements, the non-linear model of supercapacitor was verified. Temperature rise and fuel consumption data were measured and the advantages of having a hybrid source (supercapacitor in parallel with fuel cell) over just a standalone fuel cell source were shown. Finally, the transfer times for the proposed UPS system and the battery based UPS system were measured and were found to be satisfactory. Overall, the proposed system was found to satisfy the required performance specifications.

Electrochemical capacitors (ECs) have drawn much attention owing to their fast charging/discharging rate, and long lifetime up to millions of cycles. Applications of EC range from large scale transportation to miniaturized electronics. The research reported herein explores the development of an economical process for the synthesis of high performance electrode material for high power ECs. A two stage synthesis process which consists of electroplating of molybdenum oxide followed by thermal nitridation was developed. X-ray diffraction and X-ray photoelectron spectroscopy revealed the material to be Mo oxide with nitrogen substitution, Moz(O,N). In a three electrode system, the Moz(O,N) electrodes showed capacitance as high as 16 mF/cm2. Symmetric EC cells achieved state of the art time constant of 100 ms. Ultrahigh power ECs were demonstrated for the first time using Moδ(O,N) electrodes and SiWA-H3PO4-PVA electrolyte, achieving with 10 ms time constant one of the lowest time constants reported for EC.

Electrochemical capacitors (ECs) have drawn much attention owing to their fast charging/discharging rate, and long lifetime up to millions of cycles. Applications of EC range from large scale transportation to miniaturized electronics. The research reported herein explores the development of an economical process for the synthesis of high performance electrode material for high power ECs. A two stage synthesis process which consists of electroplating of molybdenum oxide followed by thermal nitridation was developed. X-ray diffraction and X-ray photoelectron spectroscopy revealed the material to be Mo oxide with nitrogen substitution, Moz(O,N). In a three electrode system, the Moz(O,N) electrodes showed capacitance as high as 16 mF/cm2. Symmetric EC cells achieved state of the art time constant of 100 ms. Ultrahigh power ECs were demonstrated for the first time using Moδ(O,N) electrodes and SiWA-H3PO4-PVA electrolyte, achieving with 10 ms time constant one of the lowest time constants reported for EC.

No description available.

In recent years, Distributed Generators (DGs) and energy storage devices have gained more popularity due to growing energy and environmental concerns. Interconnection of DGs and storage devices in an electricity grid impacts its performance under steady state and transient conditions. This research aims at analyzing the impacts of distributed generators and energy storage devices on the transient stability of the grid. Battery and ultra-capacitor technologies have been taken as the two types of storage devices and their electrical characteristics have been modeled using Simulink. Impact of these devices has been analyzed by connecting them to the system by means of suitable power electronic converters. The developed methodology has been evaluated using small test systems in MATLAB/Simulink. Transient stability of the test systems has been assessed for different types and locations of faults as well as for different penetration levels of the DGs, with and without the energy storage devices. Impact on the system transient stability has been analyzed based on transient response of the generator rotor speed deviation, rotor angle and terminal voltage of the DGs. Finally, economic analyses have been carried out for different options of DGs, based on wind, diesel and biomass, along with the energy storage devices. Results indicate that the presence of DGs and storage devices enhances the transient stability of the system in most of the cases.

This thesis explores a rigorous approach to model the behaviour of an electrochemical cell. A simple planar electrochemical cell consisting of stainless steel electrodes separated by a sulfuric acid electrolyte layer is modeled from first principles. The model is a dynamic model and is valid under constant temperature conditions. The dynamic model is based on the Poisson-Nernst-Planck electrodiffusion theory and physical attributes such as the impact of nonlinear polarization, the stoichiometric reactions of the electrolyte and changes to the transport coefficients are investigated in stages. The system of partial differential equations has been solved using a finite element software package. The simulation results are compared with experimental results and discrepancies are discussed. The results suggest that the existing theory is not adequate in explaining the physics in the immediate vicinity of the electrode/electrolyte interface even though the general experimental and simulation results are in qualitative agreement with each other.

With the escalating number of vehicles on the road, great concerns are drawn to the large amount of fossil fuels they use and the detrimental environmental impacts from their emissions. A lot of research and development have been conducted to explore the alternative energy sources. The fuel cell has been widely considered as one of the most promising solutions in automobile applications due to its high energy density, zero emissions and sustainable fuels it employs. However, the cost and low power density of the fuel cell are the major obstacles for its commercialization. This thesis designs a novel converter topology and proposes the control method applied in the Fuel Cell Hybrid Vehicles (FCHVs) to minimize the fuel cell's cost and optimize the system's efficiency. Unlike the previous work, the converters presented in the thesis greatly reduce the costs of hardware and energy losses during switching. They need only three Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs) to smoothly accomplish the energy management in the cold start, acceleration, steady state and braking modes. In the converter design, a boost converter connects the fuel cell to the DC bus because the fuel cell's voltage is usually lower than the rating voltage of the motor. In this way, the fuel cell's size can be reduced. So is the cost. With the same reason, the bidirectional converter connected to the ultracapacitor works at the buck pattern when the power is delivered from the DC bus to the ultracapacitor, and the boost converter is selected when the ultracapacitor provides the peaking power to the load. Therefore, the two switches of the bi-directional converter don't work complementarily but in different modes according to the power flow's direction. Due to the converters' simple structure, the switches' duty cycles are mathematically analyzed and the forward control method is described. The fuel cell is designed to work in its most efficient range producing the average power, while the ultracapacitor provides the peaking power and recaptures the braking power. The simulation results are presented to verify the feasibility of the converter design and control algorithm.

High mobility has been a standard in the modern world for decades. This has resulted in high energy consumption, diminishing fossil energy reserves and rising levels of greenhouse gases. By recovering the energy lost in deceleration of vehicles the total energy consumption can be decreased and exhaust emissions reduced. This can be done with a kinetic energy recovery system (KERS) that converts kinetic energy to electric energy during deceleration, which then can be used for acceleration. KERS requires an electrical storage device with high power density, due to the high power levels generated at heavy braking. Batteries does not generally meet these requirements, especially in the cost-effective point of view, but different types of capacitors can be used to obtain a cheap and effective system. To get such an energy storage device small, lightweight and inexpensive while the technology is sustainable requires avoidance of rare metals and hazardous materials. In this master thesis energy and power levels for KERS has been modelled, based on standardized measurements techniques and small paper-based supercapacitors have been built and tested in order to model size, weight and price for a full-scale energy storage device to a KERS-application. The models showed that energy consumption in urban traffic could be reduced with 18% and with an electrode material for the energy storage device with a capacitance of about 1500 F/m2 a reasonable size and weight is obtained. To reach these values of capacitance in paper-based supercapacitors further testing is required on area and layer dependence and for different electrodes.

This thesis explores a rigorous approach to model the behaviour of an electrochemical cell. A simple planar electrochemical cell consisting of stainless steel electrodes separated by a sulfuric acid electrolyte layer is modeled from first principles. The model is a dynamic model and is valid under constant temperature conditions. The dynamic model is based on the Poisson-Nernst-Planck electrodiffusion theory and physical attributes such as the impact of nonlinear polarization, the stoichiometric reactions of the electrolyte and changes to the transport coefficients are investigated in stages. The system of partial differential equations has been solved using a finite element software package. The simulation results are compared with experimental results and discrepancies are discussed. The results suggest that the existing theory is not adequate in explaining the physics in the immediate vicinity of the electrode/electrolyte interface even though the general experimental and simulation results are in qualitative agreement with each other.

As the world's energy use continues to grow, the development of clean distributed generation becomes increasingly important. Fuel cells are an environmentally friendly renewable energy source that can be used in a wide range of applications and are ideal for distributed power applications. In this study, the power conversion element of a dual single-phase, 10 kW stand-alone fuel cell system is analyzed. The modular converter consists of a DC-DC front-end cascaded with a half-bridge inverter. The entire system is accurately modeled, to help determine any interactions that may arise. Control strategies based on simplicity, performance, and cost are evaluated. A simple voltage loop, with careful consideration to avoid transformer saturation, is employed for the phase-shifted DC-DC converter. Several experimental transfer functions were measured to confirm the modeling assumptions and verify the control design of the DC-DC converter. Two control options for the inverter are explored in detail, and experimental results confirm that the modulation index must be controlled to regulate the output voltage during various load conditions. The final system is implemented without the use of current sensors, thus keeping the inverter cost down. Experimental results using a power supply are given for resistive, inductive, and nonlinear loads and the performance is acceptable. Fuel cell test results, including transient response, are also displayed and analyzed. / Master of Science