The aim of this thesis is to design a controllable DC-link output voltage for isolated slotless tubular linear generators (STLG), which is capable of directly harnessing wave and solar thermal energies. For supplying stable DC-link voltage to load, a suitable voltage regulation circuit is designed based on the integrate system performance assessment. Electrical and mechanical parameters in this refined STLG design are involved to analyze the operational behaviors through magnetic equivalent circuit analysis at different operating modes. From the theoretical modeling and experimental results, both the AC-side and DC-side properties of generator outputs can then be thoroughly investigated. Finally, based on the performance of controllable rectifier model, a three-phase PWM rectifier has been established, and then the regulated DC-link voltage can be implemented using a DSP-based controller combined with required peripheral circuits.

The purpose of this thesis is to design and implement a linear quadratic optimal controller for a twin-buck converter with zero-voltage-transition (ZVT). The controller calculates duty ratio every cycle based on voltage and current feedback, as well as estimates the time instances when the synchronous rectification power switch current is zero. These time instances are crucial for ZVT operation. Via frequency modulation, the controller is designed to automatically regulate the output voltage to a desired value under load and voltage source variation. Simulations indicate that the proposed control design works. The controller is implemented using a Field Programmable Gate Array (FPGA). The experimental results match the simulations, which further verifies the applicability of the proposed voltage regulation strategy.

A DC to AC inverter can be classified in different topologies; some of these topologies are three level and multilevel inverter. Both types have some advantages and disadvantages. Three level inverters can be applied for low power applications because it is cheaper and has less semiconductor losses at high switching frequencies with poor total harmonic distortion (THD). Multilevel inverters (MLI) can be applied for higher power applications with less THD. However, the MLI has more cost and conductive power losses in comparison with three level inverters. In order to overcome the limitations of three and multilevel topologies, this thesis presents a new controlling topology of multilevel DC/AC inverters. The proposed multilevel inverter topology is based on a current source inverter, which consists of a buck/boost, boost and flyback converters, and an H-bridge inverter. The output voltage of the inverter is shaped through the control of just one main semiconductor switch. This new topology offers almost step-less output voltage without the need for multi DC source or several capacitor banks as in the case of other multilevel inverter topologies. The efficiency of the proposed topology is higher than other inverter topologies for medium power applications (2-10 kW). The proposed topology also generates smaller Total Harmonic Distortion (THD) compared to other inverter topologies. The two main key aspects of the proposed circuit is to keep the switching losses as low as possible and this is achieved through the control of a single switch at relatively low frequency and also to generate an improved AC Voltage waveform without the need for any filtering devices. The output frequency and voltage of the proposed circuit can be easily controlled according to the load requirements. The proposed inverter topology is ideal for the connection of renewable energy; this is due to its flexibility in varying its output voltage without the need of fixed turns-ratio transformers used in existing DC/AC inverter topologies. The harmonic contents of the output of this proposed topology can be controlled without the need of any filter. The simulation and practical implementation of the proposed circuits are presented. The practical and simulation results show excellent correlation.

Faster charging and availability of charging infrastructure are the two main challenges facing an accelerated transition to sustainable electri ed transportation. Both challenges can be solved by developing modular charging systems that are future proof all while having low running and installation costs. As such, this thesis focuses on developing modular and e cient DC/DC charging solutions with a wide charging voltage range capability to meet the needs of existing and next generation plug-in electric vehicles. The thesis starts with describing its motivation and gives an overview on the impact of charging technologies on the electri fication movement. Then, specifi c objectives and research contributions are laid out to narrow the focus of the reader. A review on existing charging systems, standards, architecture and features is presented. Existing isolated and on-isolated power converter topologies for DC-chargers are analyzed and research gaps in power converters with a wide charging voltage range are highlighted. A new single stage DC/DC converter topology and operation scheme is proposed to extend the charging voltage range. Modeling and analysis of the proposed solution was used to select the transition point between different operating modes. Impedance tolerance and pulse distortion was modeled to analyze the passive current sharing error at light and full load operation. The combination of the proposed topology and unique operating scheme reduced the voltage and current stress per device allowing the use of lower kVA rated devices leading to higher cost savings compared to other solutions. An experimental setup has been developed which showed the excellent performance of the proposed topology. The design and optimization strategy for the proposed dual-secondary dual-active bridge (DAB) converter topology is presented. A converter loss model is developed to take in to account: magnetic, switching, and conduction loss. Then, the design process and quantization scheme to quantize charging pro les into discrete energy points is explained, which entails parametric optimization using a genetic algorithm (GA) to minimize energy loss across widely varying charging pro les based on actual charging data. Comprehensive experimental testing was carried out to validate the proposed design strategy and excellent performance was achieved over an extended operating range. After the review of power magnetics used in isolated chargers, high parasitic capacitance in planar transformers was identi ed as an obstacle in the way of development of chargers, especially in charging applications that demand high switching frequencies or extended low power operation. Therefore, a novel planar transformer structure was proposed with ultra-low winding capacitance. The proposed co-planar transformer was compared to three other planar types to highlight the differences and bene fits. Four different prototypes of planar transformers were built with the same target speci fications, to compare the proposed structure against previous solutions. Impedance testing of the planar prototypes was carried to measure the winding stray capacitance and frequency response. Experimental power testing using a DAB converter setup showed excellent results in reducing voltage overshoot, high frequency oscillations, and power losses. Finally, a 30-kW dual-secondary DAB charging module was designed, implemented, and tested. The purpose of this work is to bridge the engineering gap between a proof of concept and a higher Technology Readiness Level (TRL) mature charging module, focusing more on regulatory standards and control system development. Experimental validation of the liquid cooled module showed excellent performance characteristics. / Thesis / Doctor of Philosophy (PhD)

In the thesis, we apply the state average method to model the time-average linear dynamic equation, which is used to design a gain scheduled linear quadratic optimal controller. Because the standard modulation method of the twin-buck converter is PFM(Pulse-Frequency Modulation) and twin-buck converter owns the soft-switching characteristic, the voltage step-down ratio, that is, control force can not be lowered less than 0.5. For expanding the range of control force of converter, we modulate the converter by means of mixed modulation of PWM/PFM. With the former odulation method, we have to calculate the discharging time of synchronous switch taken by controller to achieve zero-voltage-transition (ZVT). In the last part of this thesis, we verify the practicability of the controller and modulation method through soft simulation coded by MATLAB and hardware implementation of FPGA driven by Verilog.

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