Analytical Formulation of Copper Loss of Litz Wire with Multiple Levels of Twisting Using Measurable Parameters

Litz wire has been widely utilized in power transformers and inductors as a wire with low copper loss at high-frequency operation. The Litz wire is commonly made of many thin isolated strands twisted in multiple levels. Due to its complicated structure, the copper loss prediction of the Litz wire has been difficult, hindering the design optimization of the Litz wire structure. To overcome this difficulty, preceding studies have investigated the analytical copper loss models of the constituting elements of the Litz wire, i.e., the strands and the bundles of strands. The purpose of this article is to propose an analytical copper loss model of the Litz wire by utilizing these preceding knowledge. The proposed model is formulated only with parameters that can be measured by basic testing instruments. Besides, the proposed model considers the bundle structure of the Litz wire, which affects the local ac current distribution, and the twisting pitch, which causes the inclination of the Litz wire strands. The proposed model was tested by comparing the analytical prediction and experimental measurements of the ac resistance of commercially available Litz wires. As a result, the predicted ac resistance showed good agreement with the measured ac resistance, suggesting the appropriateness of the proposed model. © 1972-2012 IEEE

Multi-objective optimization of power electronic converters

L'abstract è presente nell'allegato / the abstract is in the attachmen

Design Approaches to Enhance Power Density in Power Converters for Traction Applications

This dissertation presents a design strategy to increase the power density for automotive Power Conversion Units (PCUs) consisting of DC-DC and DC-AC stages. The strategy significantly improves the volumetric power density, as evident by a proposed PCU constructed and tested having 55.6 kW/L, representing an 11.2 % improvement on the Department of Energy’s 2025 goal of 50 kW/L for the same power electronics architecture. The dissertation begins with a custom magnetic design procedure, based on optimization of a predetermined C-core geometrical relationship and custom Litz wire. It accounts for electrical and thermal tradeoffs to produce a magnetic structure to best accomplish volume and thermal constraints. This work is coupled with a control strategy for the DC-DC converter whereby a variable-frequency Discontinuous Conduction Mode (DCM) control is used to further reduce the required values of the passive components, to provide an increase in power density and a large improvement of low-power-level efficiency, experimentally demonstrated at full power through an 80 kW Interleaved Boost Converter. Integration of this enhanced DC-DC stage to the DC-AC stage requires a DC-Link capacitor, which hinders achieving power density targets. Increasing the switching frequency is an established method of reducing the size of passives. However, it is the RMS current sizing requirements that diminishes any gains achieved by raising the switching frequency. A synchronous carrier phase shift-based control algorithm, that aligns the output current of the boost stage with the input current of an inverter, is proposed to reduce the RMS current in the DC-Link capacitor by up to 25% and an average 20% smaller capacitor volume. Lastly, a new electrothermal platform based on paralleled discrete devices is presented for a 50 kW traction inverter. Embedded capacitors within the vacant volume of the hybrid material thermal management structure enables higher power density (155 kW/L) and significantly reduces cost

Design Approaches to Enhance Power Density in Power Converters for Traction Applications

This dissertation presents a design strategy to increase the power density for automotive Power Conversion Units (PCUs) consisting of DC-DC and DC-AC stages. The strategy significantly improves the volumetric power density, as evident by a proposed PCU constructed and tested having 55.6 kW/L, representing an 11.2 % improvement on the Department of Energy’s 2025 goal of 50 kW/L for the same power electronics architecture. The dissertation begins with a custom magnetic design procedure, based on optimization of a predetermined C-core geometrical relationship and custom Litz wire. It accounts for electrical and thermal tradeoffs to produce a magnetic structure to best accomplish volume and thermal constraints. This work is coupled with a control strategy for the DC-DC converter whereby a variable-frequency Discontinuous Conduction Mode (DCM) control is used to further reduce the required values of the passive components, to provide an increase in power density and a large improvement of low-power-level efficiency, experimentally demonstrated at full power through an 80 kW Interleaved Boost Converter. Integration of this enhanced DC-DC stage to the DC-AC stage requires a DC-Link capacitor, which hinders achieving power density targets. Increasing the switching frequency is an established method of reducing the size of passives. However, it is the RMS current sizing requirements that diminishes any gains achieved by raising the switching frequency. A synchronous carrier phase shift-based control algorithm, that aligns the output current of the boost stage with the input current of an inverter, is proposed to reduce the RMS current in the DC-Link capacitor by up to 25% and an average 20% smaller capacitor volume. Lastly, a new electrothermal platform based on paralleled discrete devices is presented for a 50 kW traction inverter. Embedded capacitors within the vacant volume of the hybrid material thermal management structure enables higher power density (155 kW/L) and significantly reduces cost

Transformador de alta frequência para aplicação a transformadores de estado sólido

Dissertação para obtenção do grau de Mestre em Engenharia Eletrotécnica Ramo: Automação e Eletrónica IndustrialA presente dissertação de mestrado tem como objetivo o estudo teórico do transformador de alta frequência incorporado nos transformadores de estado sólido (Solid State Transformer) e parte do sistema de controlo inerente ao transformador de estado sólido. O foco da presente dissertação consiste no estudo do transformador de alta frequência, mais concretamente no desenvolvimento de um conjunto de etapas que permitam o dimensionamento otimizado deste a partir das características nominais pretendidas para o conversor e a respetiva obtenção do modelo equivalente. Abordando algumas das topologias e materiais disponíveis no mercado, para os núcleos magnéticos, enrolamentos e condutores e a respetiva análise das vantagens e desvantagens de cada um. Bem como a análise do impacto sobre estes, devida a operação em alta frequência e respetivas soluções que permitem reduzir este impacto, com as enumeras vantagens que a utilização destes têm relativamente aos transformadores tradicionais de 50/60Hz. Em complemento é efetuado o estudo, de uma forma mais simplificada, de parte do esquema de potência do transformador de estado sólido, nomeadamente os conversores de potência, que se encontram imediatamente antes e depois do transformador de alta frequência, respetivamente. Tal como o estudo de uma técnica de controlo que permita o correto funcionamento deste. Abordando igualmente os semicondutores de potência disponíveis no mercado, técnicas de comando dos semicondutores de potência e controlo do conversor por forma a permitir bidirecionalidade de potência. Por último, elaboração de um modelo para simulação numérica e respetiva implementação prática em laboratório, por forma a validar o esquema equivalente obtido para o transformador de alta frequência e a validação da técnica de controlo desenvolvido.This master's thesis aims to theoretically study high-frequency transformers incorporated in solid state transformers and the part of the control system inherent in solid state transformers (SST). This dissertation focuses on developing a set of steps to design an optimized high-frequency transformer from the nominal characteristics desired for the converter and the respective obtaining of the equivalent model. It will address some of the topologies and materials available on the market for magnetic cores, windings, and conductors and the respective analysis of the advantages and disadvantages of each of them. It will also analyze the impact of a high-frequency transformer operation and the solutions that allow this impact to be reduced without forgetting the numerous advantages of their use over traditional 50/60 Hz transformers. In addition, it is conducted a more simplified study of a part of the power scheme of the Solid State transformer, namely the power converters - which are immediately before and after the high-frequency transformer, respectively. As well as the study of a control technique that allows its correct operation. It also addresses the power semiconductors device available on the market, control techniques for them, and the control of the converter to allow power bidirectionality. Ultimately, a model for numeric simulation and its laboratory implementation will take place to validate the equivalent scheme obtained for the high-frequency transformer and validate the developed control technique.N/

Electromagnetic Model-Based Measurement, Sensing, and Detection for Wireless Power Transfer

Advances in measurement, sensing, and detection are the basis of technological development, which drives or hampers innovation, technology adoption, confidence in the value services, and security. As electric vehicles (EVs) become one of the dominant means of transportation in the next few decades with wireless power transfer for charging, the accuracy and fairness of energy metering and charging safety become prominent. This dissertation aims to develop smart electromagnetic measurement and detection systems integrated for wireless charging. A small number of sensors sample the electromagnetic field to reconstruct the information needed for power measurement for fair metering and foreign object detection for safe wireless charging. This electromagnetic model-based measurement, sensing, and detection provide accurate solutions for receiver coil misalignment and power level variations. First, Faraday coil transfer-power measurement (FC-TPM) is presented for fair metering and transactions of wireless charging in electric vehicles. The transfer-power is defined from the Poynting vector, which is the directed power density. The winding losses in the transmitter and receiver coils are derived and decomposed based on heat dissipation to show how the measurement of transfer-power demarcates the losses and imposes the costs for power losses to each coil based on physical power dissipation, resulting in fair metering. FC-TPM employs non-contact, open-circuited sense coils to calculate the transfer-power. The information obtained from the sense coils (e.g., sense coil voltages) is combined uniquely for the power reconstruction, which is accurate despite receiver coil misalignment without explicitly measuring the misalignment. The coupling coefficient variations to the misalignment are approximated by quadratic functions, explaining why a linear combination of multiple sense coil voltages results in accurate power reconstruction across the variation. Furthermore, this method is accurate over other types of variations (e.g., operating frequencies, different types of wires) since polynomials can generally approximate variations. FC-TPM was demonstrated in hardware accurately within 0.1% errors despite a receiver coil misalignment of up to 10 cm using a 1kW wireless power transfer system. Second, Electromagnetic Model-Based Foreign Object Detection (EM-FOD) is presented for safe wireless power transfer, where foreign objects neighboring wireless power transfer systems are fire hazards. The same electromagnetic physics model, constructed by the transmitter, receiver, and sense coils, is the normal model and can be used to detect the hazardous objects by excluding them from the original normal model. A target information (e.g., the transmitter coil current) reconstruction by the normal model becomes inaccurate when there is a foreign object. The detection metric is a sequent error in the information reconstruction compared to the true information obtained by an independent measurement simultaneously. The detection metric is invariant to receiver coil misalignment and power level, allowing less risky pre-startup low-power detection. Hardware demonstrations show that a 2 cm diameter U.S. nickel coin can be detected using only 9 W regardless of a receiver coil misalignment of up to 10 cm. This dissertation is concluded by presenting a calibration-transfer strategy to consider the practical deployment of the wireless charging models for FC-TPM to energy service stations. Open-circuited sense coils are chosen as transfer standards that convey accurate data obtained from the certified standard in standards laboratories to the transmitter and sense coils in energy service stations.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169905/1/sungyul_1.pd

Research on Switched-Mode Power Supply for Efficient Use of Renewable Energy

長崎大学学位論文 学位記番号:博(工)乙第4号 学位授与年月日:平成31年2月20日Nagasaki University (長崎大学)論文博