This thesis deals with the design and realization of a DC/DC converter, which allows power conversion from 10-52 V input voltage to 10-52 V output voltage at a maximum output current of 3 A. The converter can communicate with the superior system via the CAN. In the first chapter I deal with the available integrated circuits of DC/DC converters, from which I choose one for my application. In the second chapter, I propose a block scheme of the converter, which includes the requirements from the assignment as well as my additional ones. In the third chapter I deal with the design of an electronic circuit and with the calculation of control loops. In the fourth chapter I propose firmware for the STM32 MCU, which controls the device and communicates with the superior system. In the last chapter the DC/DC converter is tested.

DC-DC converters can be separated into two main groups: switching converters and linear regulators. Linear regulators such as Low Dropout Regulators (LDOs) are straightforward to implement and have a very stable output with low voltage ripple. However, the efficiency of an LDO can fluctuate greatly, as the power dissipation is a function of the device’s input and output. On the other hand, a switching regulator uses a switch to regulate energy levels. These types of regulators are more versatile when a larger change of voltage is needed, as efficiency is relatively stable across larger steps of voltages. However, switching regulators tend to have a larger output voltage ripple, which can be an issue for sensitive systems. An approach to utilize both in cascaded configuration while providing a negative output voltage will be presented in this paper. The proposed two-stage conversion system consists of a switching pre-regulator that can track the negative output voltage of the second stage (LDO) such that the difference between input and output voltages is always kept small under varying output voltage while maintaining the high overall conversion efficiency. Computer simulation and hardware results demonstrate that the proposed system can track the negative output voltage well. Additionally, the results show that the proposed system can provide and maintain good overall efficiency, load regulation, and output voltage ripple across a wide range of outputs.

Electric vehicles (EVs) offer significant advantages over conventional internal combustion engine vehicles, including zero emissions and convenient overnight charging. However, there are still several challenges that need to be addressed. These challenges include limited driving ranges, slow refueling options while on-the-go, concerns related to the supply of lithium for batteries, and emissions associated with certain sources of electricity generation, such as coal. Adding on-board solar generation and/or fuel cell range extenders to EVs can help to mitigate some of these challenges, but also adds the need for optimal power electronic converters to manage the power flow of these multiple on-board energy sources, which is the focus of this thesis. This thesis first performs a comprehensive review of EV onboard chargers (OBCs) including charger system requirements by different standards and codes and different DC/DC power converters in the current infrastructures. Various power levels are compared and evaluated based on their component ratings, efficiency, cost, and power density. Secondly, there has been recent interest in harnessing solar power within electric vehicles, leading to the emergence of solar-charged electric vehicles (SEVs), which can offer extended driving ranges and less need for grid charging. These vehicles also offer a new opportunity for distributed generation when their traction batteries are fully charged, and the plugged-in vehicle is still generating solar energy. However, this also presents a unique power electronic dilemma. The OBC must exhibit high efficiency in two scenarios: firstly, during normal charging from the grid at power levels around 6.6 kW, and secondly, during vehicle-to-grid operation at significantly lower solar power levels, typically below 800 W. Unfortunately, conventional OBC designs tend to have low efficiency when operating at light loads. To tackle this challenge, this thesis proposes a novel bidirectional LLC-based converter, for use within the OBC, that achieves higher vehicle-to-grid efficiency at light loads than a traditional dual bridge converter. Detailed PLECS simulation results and experimental results are presented to verify the circuit. Thirdly, the presence of manufacturing variations can introduce parameter mismatches, resulting in voltage imbalances across capacitors in the proposed converter, or in other resonant converters with multiple transformer windings and two series-connected capacitors with a center connection. Such voltage imbalances pose significant concerns regarding safety and reliability. However, the existing capacitor balancing strategies developed for other converter topologies are not directly applicable to these new resonant multi-winding topologies. To address this issue, this thesis presents a novel method for achieving capacitor voltage balancing in a resonant multi-winding converter. The proposed method employs a straightforward approach to determine the appropriate balancing switching states. Time domain analysis is conducted to quantify the number of control cycles required, and an adaptive control strategy is introduced to enhance the balancing performance. The effectiveness of the proposed method and the beneficial effects on the converter's efficiency and bus capacitor sizes are validated through experimental investigations involving multiple bus capacitor sizes. Finally, though SEVs offer advantages over non-solar EVs, some challenges remain such as lithium supply concerns for large batteries, slow recharging, and driving range that is still limited compared to conventional vehicles. Fuel cell range-extended vehicles (FCREVs) can add a small fuel cell and hydrogen tank to allow quick refueling for long trips, and still use a reduced-size plug-in battery for the majority of short trips. This allows the driver to use efficient and convenient overnight charging for most daily commutes, and refuel with hydrogen on long-distance driving days if hydrogen stations are available. The smaller battery means that lithium requirements are reduced. Further, by adding on-board solar generation to a FCREV (S-FCREV), range can be further extended and grid charging requirements can be reduced. However, using conventional separate converters for a S-FCREV would be complex and costly, having a high number of semiconductor devices. To overcome this, the thesis proposes a practical multi-port converter that fulfills S-FCREV requirements with reduced components. A novel triple PWM and triple phase shift (TPTPS) control is proposed. Simulation and experimental results validate the proposed topology's operation and efficiency, offering a promising solution for integrating power electronics in S-FCREV applications. / Thesis / Doctor of Philosophy (PhD) / In the pursuit of sustainable transportation, recent scholarly investigations have placed significant emphasis on the advancement of electric vehicles (EVs) with a particular focus on solar-charged EVs and fuel cell range-extended vehicles (FCREVs) in order to help mitigate some of the drawbacks of battery EVs such as limited driving range, long refueling times, and charging impacts on the grid. Power electronic converters play a crucial role in managing the transfer of power between multiple energy sources, such as on-board solar panels, fuel cells, batteries, and connection to the grid. The objective of this thesis is to propose novel topologies and control for power electronic converters in solar-charged EVs and solar-charged FCREVs. Firstly, a novel bidirectional DC/DC topology is proposed for solar-charged EVs that allows a high-efficiency transfer of excess solar energy to the grid when the EV battery is full. Additionally, a novel control methodology for balancing the DC bus capacitors is introduced, aiming to reduce capacitor size and mitigate circulating unbalanced currents. Lastly, this thesis presents the pioneering practical implementation of a multi-port converter for a solar-charged FCREV, along with its adaptable control approach, enabling efficient power flow management among the grid, on-board battery, solar panels, and fuel cell.

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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

Galvanic isolation between the grid and energy storage unit is typically required for bidirectional power distribution systems. Due to the recent advancement in wide-bandgap semiconductor devices, it has become feasible to achieve the galvanic isolation using bidirectional isolated DC/DC converters instead of line-frequency transformers. A survey of the latest generation SiC MOSFET is performed. The devices were compared against each other based on their key parameters. It was determined that under the given specifications, the most suitable devices are X3M0016120K 1.2 kV 16 mohm and C3M0010090K 900 V 10 mohm SiC MOSFETs from Wolfspeed. Two of the most commonly utilized bidirectional isolated DC/DC converter topologies, dual active bridge and CLLC resonant converter are introduced. The operating principle of these converter topologies are explained. A comparative analysis between the two converter topologies, focusing on total device loss, has been performed. It was found that the CLLC converter has lower total device loss compared to the dual active bridge converter under the given specifications. Loss analysis for the isolation transformer in the CLLC resonant converter was also performed at different switching frequencies. It was determined that the total converter loss was lowest at a switching frequency of 250 kHz A prototype for the CLLC resonant converter switching at 250 kHz was then designed and built. Bidirectional power delivery for the converter was verified for power levels up to 25 kW. The converter waveforms and efficiency data were captured at different power levels. Under forward mode operation, a peak efficiency of 98.3% at 15 kW was recorded, along with a full load efficiency value of 98.1% at 25 kW. Under reverse mode operation, a peak efficiency of 98.8% was measured at 17.8 kW. The full load efficiency at 25 kW under reverse mode operation is 98.5%. / Master of Science

Fuel cells typically produce low-voltage high-current output because their individual cell voltage is low, and it is nontrivial to balance for a high-voltage stack. In addition, the output voltage of fuel cells varies depending on load conditions. Due to the variable low voltage output, the energy produced by fuel cells typically requires power conditioning systems to transform the unregulated source energy into more useful energy format. When evaluating power conditioning systems, efficiency and reliability are critical. The power conditioning systems should be efficient in order to prevent excess waste of energy. Since loss is dissipated as heat, efficiency directly affects system reliability as well. High temperatures negatively affect system reliability. Components are much more likely to fail at high temperatures. In order to obtain excellent efficiency and system reliability, low-voltage high-current power conditioning systems should be carefully designed. Low-voltage high-current systems require carefully designed PCB layouts and bus bars. The bus bar and PCB trace lengths should be minimized. Therefore, each needs to be designed with the other in mind. Excessive PCB and bus bar lengths can introduce parasitic inductances and resistances which are detrimental to system performance. In addition, thermal management is critical. High power systems must have sufficient cooling in order to maintain reliable operation. Many sources of loss exist for converters. For low-voltage high-current systems, conduction loss and switching loss may be significant. Other potential non-trivial sources of loss include magnetic losses, copper losses, contact and termination losses, skin effect losses, snubber losses, capacitor equivalent series resistance (ESR) losses, and body diode related losses. Many of the losses can be avoided by carefully designing the system. Therefore, in order to optimize efficiency, the designer should be aware of which components contribute significant amounts of loss. Loss analysis may be performed in order to determine the various sources of loss. The system efficiency can be improved by optimizing components that contribute the most loss. This thesis surveys some potential topologies suitable for low-voltage high-current systems. One low-voltage high-current system in particular is analyzed in detail. The system is called the V6, which consists of six phase legs, and is arranged as a three full-bridge phase-shift modulated converter to step-up voltage for distributed generation applications. The V6 converter has current handling requirements of up to 120A. Basic operation and performance is analyzed for the V6 converter. The loss within the V6 converter is modeled and efficiency is estimated. Calculations are compared with experimental results. Efficiency improvement through parasitic loss reduction is proposed by analyzing the losses of the V6 converter. Substantial power savings are confirmed with prototypes and experimental results. Loss analysis is utilized in order to obtain high efficiency with the V6 converter. Considerations for greater current levels of up to 400A are also discussed. The greater current handling requirements create additional system issues. When considering such high current levels, parallel devices or modules are required. Power stage design, layout, and bus bar issues due to the high current nature of the system are discussed. / Master of Science

This work deals with theory of switched power sources. There is description of the ways for connection and their practice purposes. In the next parts there are defined requirements on input supply circuit for these sources, especially for the form of output current. There are mentioned the basic connecting methods of PFC circuits and these methods modify the output current to meet the requirements of specification ČSN EN 61000- 3- 2. In the next parts there are shown simulations of PFC circuits made by Pspice application. Further is the basic description of sources construction for the sources which were used for testing and measuring. The final part deals with evaluation of the measuring on the chosen computer’s source. It compares between the manufacturer’s solutions and PFC circuit made by ourselves.