Linearized large signal modeling, analysis, and control design of phase-controlled series-parallel resonant converters using state feedback

This paper proposes a linearized large signal state-space model for the fixed-frequency phase-controlled series-parallel resonant converter. The proposed model utilizes state feedback of the output filter inductor current to perform linearization. The model combines multiple-frequency and average state-space modeling techniques to generate an aggregate model with dc state variables that are relatively easier to control and slower than the fast resonant tank dynamics. The main objective of the linearized model is to provide a linear representation of the converter behavior under large signal variation which is suitable for faster simulation and large signal estimation/calculation of the converter state variables. The model also provides insight into converter dynamics as well as a simplified reduced order transfer function for PI closed-loop design. Experimental and simulation results from a detailed switched converter model are compared with the proposed state-space model output to verify its accuracy and robustness

A New Single-Phase Single-Stage AC-DC Stacked Flyback Converter With Active Clamp ZVS

Single-stage AC-DC converters integrate an AC-DC front-end converter with a DC-DC back-end converter. Compared with conventional two-stage AC-DC converters, single-stage AC-DC converters use less components and only one controller, which is used to regulate the output voltage. As a result, the cost, size and complexity of AC-DC converters can be reduced, but single-stage converters do not perform as well as two-stage converters, and most have drawbacks that are related to the fact that the DC bus voltage is not controlled an can become excessive. A new single-phase single-stage AC-DC converter that uses stacked flyback converters is proposed in this thesis. The proposed converter consists of two low power flyback converters stacked on top of each other and an active clamp that helps the main switches operate with ZVS. The stacked structure helps reduce the voltage stresses typical fund in many single-stage converters. In the thesis, the operation of the converter is explained, the steady-state characteristics of the converter are determined and its design is discussed. The feasibility of the new converter is confirmed with experimental results obtained from a 100VAC~220VAC worldwide input, 48V output, 100kHz switching frequency and 200 W output power prototype converter

Analysis And Design Optimization Of Resonant Dc-dc Converters

The development in power conversion technology is in constant demand of high power efficiency and high power density. The DC-DC power conversion is an indispensable stage for numerous power supplies and energy related applications. Particularly, in PV micro-inverters and front-end converter of power supplies, great challenges are imposed on the power performances of the DC-DC converter stage, which not only require high efficiency and density but also the capability to regulate a wide variation range of input voltage and load conditions. The resonant DC-DC converters are good candidates to meet these challenges with the advantages of achieving soft switching and low EMI. Among various resonant converter topologies, the LLC converter is very attractive for its wide gain range and providing ZVS for switches from full load to zero load condition. The operation of the LLC converter is complicated due to its multiple resonant stage mechanism. A literature review of different analysis methods are presented, and it shows that the study on the LLC is still incomplete. Therefore, an operation mode analysis method is proposed, which divides the operation into six major modes based on the occurrence of resonant stages. The resonant currents, voltages and the DC gain characteristics for each mode is investigated. To obtain a thorough view of the converter behavior, the boundaries of every mode are studied, and mode distribution regarding the gain, load and frequency is presented and discussed. As this operation mode model is a precise model, an experimental prototype is designed and built to demonstrate its accuracy in operation waveforms and gain prediction. iv Since most of the LLC modes have no closed-form solutions, simplification is necessary in order to utilize this mode model in practical design. Some prior approximation methods for converter’s gain characteristics are discussed. Instead of getting an entire gain-vs.-frequency curve, we focus on peak gains, which is an important design parameters indicating the LLC’s operating limit of input voltage and switching frequency. A numerical peak gain approximation method is developed, which provide a direct way to calculate the peak gain and its corresponding load and frequency condition. The approximated results are compared with experiments and simulations, and are proved to be accurate. In addition, as PO mode is the most favorable operation mode of the LLC, its operation region is investigated and an approximation approach is developed to determine its boundary. The design optimization of the LLC has always been a difficult problem as there are many parameters affecting the design and it lacks clear design guidance in selecting the optimal resonant tank parameters. Based on the operation mode model, three optimization methods are proposed according to the design scenarios. These methods focus on minimize the conduction loss of resonant tank while maintaining the required voltage gain level, and the approximations of peak gains and PO mode boundary can be applied here to facilitate the design. A design example is presented using one of the proposed optimization methods. As a comparison, the L-C component values are reselected and tested for the same design specifications. The experiments show that the optimal design has better efficiency performance. Finally, a generalized approach for resonant converter analysis is developed. It can be implemented by computer programs or numerical analysis tools to derive the operation waveforms and DC characteristics of resonant converter

High Efficiency Power Converters for Vehicular Applications

The use of power electronics in the electrical propulsion systems leads to the optimal and efficient utilization of the traction motors and the energy sources (batteries and/or fuel cells) through the recourse to suitable power converters and their proper control. Power electronics is also used for implementing the multiple conversions of the energy delivered by the sources to feed the various loads, most of them requiring different waveforms of voltage (ac or dc) and/or different levels of voltage. This work focuses on the solutions aimed at improving the efficiency of power converters for vehicular applications, which is of great importance because of the limited amount of energy that can be stored in the electric vehicles. The study takes into consideration both the traction applications and the battery charging applications whether it is done by conductive means or by wireless power transfer (WPT) systems. The improvement in traction drive efficiency results in an increment of the drivetrain efficiency of the vehicle, leading to an extension in the driving range, while the employment of efficient power converters is required to charge batteries with increasingly large capacity. The losses of power devices are even more significant when they operate at high frequencies to compact the size of the filter elements and/or the transformers. The losses of power devices can be minimized by making the commutation soft or by replacing the conventional devices with the new generation devices based on wide bandgap (WBG) semiconductor materials. In this work, the properties of the WBG semiconductor materials are illustrated and the operation of the devices based on these materials are analyzed to grasp better their characteristics and performance. The losses of individual devices (i.e. diode, IGBT, MOSFET) as well as the operation of power converters for various applications are examined in detail. To evaluate the performance of the SiC devices in electric vehicle applications, an AC traction drive for the propulsion of a typical compact C-class electric car has been considered. Two versions of the inverter have been investigated, one built up with conventional Si IGBTs and the other one with SiC MOSFETs, and the losses in the semiconductor devices of the two versions have been found along the standard New European Driving Cycle (NEDC). By comparing the results, it is emerged that the usage of the SiC MOSFETs reduces the losses in the traction inverter of about 5%, yielding an equal increase in the car range. To complete the study, calculation of the efficiency has been extended to the whole traction drive, including the traction motor and the gear. Afterwards, a power factor correction (PFC) circuit, which is commonly used to mitigate the distortion in line current, has been studied. The study is started by considering the basic and the interleaved PFC configurations and by defining their circuit parameters. After selecting the interleaved configuration, the magnitude of voltages and currents in the PFC rectifier has been determined and the values obtained have been verified by a power circuit simulation software. The digital signal processing (DSP) has been also studied as it is used for the control operation of the PFC. At last, a prototype of PFC rectifier with interleaved configuration is designed. The design process and the specification of the components are described in brief. A prototype of synchronous rectifier (SR) is designed for the output stage of a WPT system. With respect to conventional rectifiers, in SRs the diodes are replaced by MOSFETs with their antiparallel diodes. MOSFETs are bidirectional devices that conduct with a low voltage drop. During the dead time, the diodes in antiparallel to the MOSFETs are conducting. At the end of dead-time, signals are applied at the MOSFET gates that make conducting all along the remaining period, thus reducing the conduction losses. The dead-time length is optimized by using fast switching devices based on SiC semiconductor materials. The prototype is designed and tested at the line frequency. The experimental results obtained from the prototype corroborate both the analytical results and the simulation results. As SR exhibits is working with high efficiency at the line frequency, it is expected that at the higher operating frequencies of the WPT systems, the performance of SR will be even better. A DC-DC isolated power converters used to setup the battery charger through wire system are studied. Two topologies of DC-DC converters, i.e. Dual Active Bridge (DAB) and Single Active Bridge (SAB) converters, are considered. For both the topologies operation are described at steady state. For SAB converter, two possible modes of operation are examined: discontinuous current conduction (DCM) and continuous current conduction (CCM). Soft-switching operation of both SAB and DAB converters, obtained by the insertion of auxiliary capacitors, is analyzed. Moreover, the soft-switching operating zone for the two converters are found as a function of the their output voltages and currents. Finally, the comparative analysis of soft-switching operation of SAB versus DAB converter is presented. The thesis work has been carried out at the Laboratory of “Electric Systems for Automation and Automotive” headed by Prof. Giuseppe Buja. The laboratory belongs to the Department of Industrial Engineering of the University of Padova, Italy

ESSE 2017. Proceedings of the International Conference on Environmental Science and Sustainable Energy

Environmental science is an interdisciplinary academic field that integrates physical-, biological-, and information sciences to study and solve environmental problems. ESSE - The International Conference on Environmental Science and Sustainable Energy provides a platform for experts, professionals, and researchers to share updated information and stimulate the communication with each other. In 2017 it was held in Suzhou, China June 23-25, 2017