Riccardo Pittini

SiC JFET cascode loss dependency on the MOSFET output capacitance and performance comparison with Trench IGBTs

In power electronics there is a general trend to increase converters efficiencies and power densities; for this reason new power semiconductors based on materials such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are becoming more popular. This is especially valid for renewable energies applications where the generated energy has a higher cost than with conventional energy sources. This paper proposes an experimental analysis of the switching performance of a high voltage SiC JFET connected in cascade connection with a low voltage MOSFET. The analysis focuses on the influence of the MOSFET output capacitance on the switching performance of the SiC Cascode connection in terms of switching energy loss, dV/dt and dI/dt stresses. The Cascode connection switching performances are compared with the switching performance latest Trench IGBTs. The analysis is based on a set of several laboratory measurements and data post-processing in order to properly characterize the devices and quantify whether the SiC JFET Cascode connection can provide good performances with a simple MOSFET gate driver.

Isolated full bridge boost DC-DC converter designed for bidirectional operation of fuel cells/electrolyzer cells in grid-tie applications

Energy production from renewable energy sources is continuously varying, for this reason energy storage is becoming more and more important as the percentage of green energy increases. Newly developed fuel cells can operate in reverse mode as electrolyzer cells; therefore, they are becoming an attractive technology for energy storage grid-tie applications. In this application dc-dc converter optimization is very challenging due to the large voltage range that the converter is expected to operate. Moreover, the fuel-electrolyzer cell side of the converter is characterized by low voltage and high current. Dc-dc converter efficiency plays a fundamental role in the overall system efficiency since processed energy is always flowing through the converter; for this reason, loss analysis and optimization are a key component of the converter design. The paper presents an isolated full bridge boost dc-dc converter (IFBBC) designed for this new application focusing on losses analysis. The system topology is briefly discussed and the major concerns related to the system, cells stacks and converter operating points are analyzed. The dc-dc converter losses are modeled and presented in detail; the analysis is validated on adc-dc converter prototype rated at 6 kW 30-80 V 0-80 A on the low voltage side and 700-800 V on the high voltage side (for a grid-tie application). The prototype is based on fully planar magnetic, Si MOSFETs, Si IGBTs and SiC diodes; efficiencies up to ~96.5% and ~97.8% were demonstrated depending on the converter operating point.

Analysis of planar E+I and ER+I transformers for low-voltage high-current DC/DC converters with focus on winding losses and leakage inductance

In this paper an analysis of two planar transformers designed for high-current switching applications is presented. Typical converter application is represented by fuel and electrolyser cell converters. The transformer designs are based on E+I and ER+I planar cores while the analysis focuses on winding resistance and leakage inductances which represent the main concerns related to low-voltage high-current applications. The PCB winding design has a one to one turn ratio with no interleaving between primary and secondary windings. The main goal was to determine if ER planar core could provide a significant advantage in terms of winding losses compared to planar E cores. Results from finite element analysis highlight that low frequency winding resistance is lower for the ER core since it is dominated by the lower mean turn length however, as the AC-resistance becomes dominating the winding eddy current losses increases more in the ER core than in the E core design. Calculated and simulated leakage inductances for the analyzed cores do not show relevant differences. A laboratory prototype based on E64 planar core is used as reference. Laboratory measurements highlight that FEM analysis provides more realistic results when computing the winding AC-resistance.

Comparative Evaluation of Three-Phase Isolated Matrix-Type PFC Rectifier Concepts for High Efficiency 380VDC Supplies of Future Telco and Data Centers

Due to the high energy consumption in data and telco centers, the use of 380V or 400V DC facility-level distribution has been proposed as an alternative to the conventional AC distribution for a more efficient power delivery structure. The DC voltage is powered from the three-phase mains by a PFC rectifier and in many cases a mains transformer is used to provide galvanic isolation. In order to achieve a high efficiency in the DC voltage generation and to implement the required isolation, a single-stage concept, such as a matrix-type rectifier that enables PFC functionality and galvanic isolation in a single conversion, can be beneficial. In addition, due to the fact that with the matrix-type rectifier the galvanic isolation is performed with a high-frequency transformer, this results in a more compact rectifier system compared to conventional systems where the mains-frequency isolation transformer is located at the input of the PFC rectifier. In this paper, an overview of isolated matrix-type PFC rectifier topologies is given and a new converter circuit is proposed, analyzed and comparatively evaluated against another promising PFC rectifier concept, the phase-modular IMY-rectifier.

Primary parallel secondary series flyback converter (PPSSFC) with multiple transformers for very high step-up ratio in capacitive load charging applications

Flyback converters are widely used in several applications, however, with this topology it is very challenging to achieve high voltage operation especially with very high step-up ratio (>500) within limited space. This paper presents a new flyback-based topology which utilizes primary parallel and secondary series transformer connection in order to achieve very high step-up ratio (up to 650) as well as high voltage operation (~2 kV) in a small volume. The topology is presented and analyzed. The advantages and disadvantages of the proposed topology are discussed. A prototype used to verify the proposed topology has been implemented. Finally, experimental results are used to validate the performance of the proposed topology.

High current planar transformer for very high efficiency isolated boost dc-dc converters

This paper presents a design and optimization of a high current planar transformer for very high efficiency dc-dc isolated boost converters. The analysis considers different winding arrangements, including very high copper thickness windings. The analysis is focused on the winding ac-resistance and transformer leakage inductance. Design and optimization procedures are validated based on an experimental prototype of a 6 kW dc-dc isolated full bridge boost converter developed on fully planar magnetics. The prototype is rated at 30-80 V 0-80 A on the low voltage side and 700-800 V on the high voltage side with a peak efficiency of 97.8% at 80 V 3.5 kW. Results highlights that thick copper windings can provide good performance at low switching frequencies due to the high transformer filling factor. PCB windings can also provide very high efficiency if stacked in parallel utilizing the transformer winding window in an optimal way.

An interface board for developing control loops in power electronics based on microcontrollers and DSPs Cores -Arduino /ChipKit /dsPIC /DSP /TI Piccolo

In this paper a new control-interface card for developing simple control loops and generating test signals for power electronic converters is presented. The control board can operate with two computational cores (Texas Instruments and Microchip) allowing using the preferred DSP architecture and development environment. Moreover, the interface board can operate with open hardware Arduino-like boards such as the ChipKit Uno32. The paper also describes how to enhance the performance of a ChipKit Uno32 with a dsPIC obtaining a more suitable solution for power electronics. The basic blocks and interfaces of the boards are presented in detail as well as the board main specifications. The board operation has been tested with three core platforms: TI Piccolo controlSTICK, a Microchip dsPIC and a ChipKit Uno32 (Arduino-like platform). The board was used for generating test signals for characterizing 1200 V Si and SiC power semiconductors. A 6 kW dc-dc converter prototype is presented; the converter is based on the developed interface board.

High current planar magnetics for high efficiency bidirectional dc-dc converters for fuel cell applications

Efficiency is one of the main concerns during the design phase of switch mode power supply. Planar magnetics based on PCB windings have the potential to reduce the magnetic manufacturing cost however, one of their main drawbacks comes from their low filling factor and high stray capacitance. This paper presents an analysis of different planar windings configurations focusing on dc and ac resistances in order to achieve highly efficiency in dc-dc converters. The analysis considers different copper thicknesses form 70 μm up to 1500 μm (extreme copper PCB) taking into account manufacturing complexity and challenges. The analysis is focused on a high current inductor for a dc-dc converter for fuel cell applications and it is based on FEM simulations. Analysis and results are verified on a 6 kW dc-dc isolated full bridge boost converter prototype based on fully planar magnetics achieving a peak efficiency of 97.8%.

Analysis of DC/DC converter efficiency for energy storage system based on bidirectional fuel cells

Renewable energy sources are fluctuating depending on the availability of the energy source. For this reason, energy storage is becoming more important and bidirectional fuel cells represent an attractive technology. Fuel cells require high-current low-voltage dc-dc or dc-ac converters as power interface to the grid. In power electronics, the converter efficiency is characterized at fixed operating voltage for various output power. This type of characterization is not suitable for fuel cells, since as the power from the fuel cell increases, the cell voltage decreases. This paper analyses how the fuel cell I-V characteristics influences the power electronics converter efficiency and their consequence on the overall system. A load-dependent efficiency curve is presented based on experimental results from a 6 kW dc-dc converter prototype including the most suitable control strategy which maximizes the dc-dc conversion efficiency.

Analysis and comparison based on component stress factor of dual active bridge and isolated full bridge boost converters for bidirectional fuel cells systems

This paper presents an analysis and comparison of isolated topologies for bidirectional fuel cell systems. The analyzed topologies are the dual active bridge (DAB) and the isolated full bridge boost converter (IFBBC). The analysis is performed based on the component stress factor (CSF). Results highlight that the DAB has lower CSF than the IFBBC for narrow converter operating points. On the other hand the IFBBC presents a more homogeneous CSF over the entire converter operating range. Finally, experimental results obtained from a 30-80 V 80 A 6 kW 40 kHz IFBBC are presented. The converter achieves efficiencies up to 98.2% and 97.45% depending on the converter power flow.