Francesco Sichirollo

Reducing storage capacitance in off-line LED power supplies by using integrated converters

In this paper a new technique to reduce the LED current ripple and storage capacitance in high power factor (PF) off-line LED power supplies is investigated. The proposed methodology is based on the use of integrated power converters (IPC) to implement the power supply. Thus, the first stage operates in discontinuous conduction mode (DCM) to provide high PF. The second stage can be operated in either continuous conduction mode (CCM) or DCM. A family of IPCs is proposed to be used as LED lamp power supplies. A generalized analysis is carried out in order to obtain the important design equations and conditions. Finally, an example of an IPC is given, along with some experimental results to demonstrate the effectiveness of the proposed technique.

Power converters for future LHC experiments

The paper describes power switching converters suitable for possible power supply distribution networks for the upgraded detectors at the High Luminosity LHC collider. The proposed topologies have been selected by considering their tolerance to the highly hostile environment where the converters will operate as well as their limited electromagnetic noise emission. The analysis focuses on the description of the power supplies for noble liquid calorimeters, such as the Atlas LAr calorimeters, though several outcomes of this research can be applied to other detectors of the future LHC experiments. Experimental results carried on demonstrators are provided.

A Straightforward Methodology to Modeling High Power Factor AC–DC Converters

In this paper, a straightforward methodology to modeling high power factor (HPF) ac-dc converters is presented. The proposed methodology is based on the averaging technique directly applied to the converter under modeling. An averaged large-signal equivalent circuit is thus generated, which is useful to perform extremely fast simulations. From the large-signal model, both a steady-state and a small-signal analysis can be carried out to completely model the converter, achieving any desired steady-state characteristic and small-signal transfer function. The presented methodology is very intuitive and allows designers to achieve a natural understanding of the converter behavior. The methodology is illustrated with a HPF buck-boost converter operating in discontinuous conduction mode. Simulation and experimental results are provided to validate the proposed methodology.

Study of the Asymmetrical Half-Bridge Flyback Converter as an Effective Line-Fed Solid-State Lamp Driver

This paper illustrates the design and an experimental test of a line-fed solid-state lamp driver based on the asymmetrical half-bridge flyback converter. Its favorable characteristics, in terms of soft-switching range and circuit complexity, allow the converter to operate at variable switching frequency in the range of 300-450 kHz, supplying 6 W to the load with good efficiency. The considered lamp is made up of five series-connected high-power light-emitting diodes (Cree XR-E) and is supplied with 350-mA closed-loop-regulated constant current. While presenting similar complexity and overall efficiency with respect to a conventional driver, due to an original feedforward control technique that allows shrinking the input filter capacitor, the proposed circuit allows a significant volume reduction and consequent power density improvement.

Minimum loss control of low-voltage residential microgrids

Cooperative control of distributed energy resources can improve dramatically the operation of residential microgrids, in terms of voltage stability, distribution efficiency and power quality, while allowing cost-effective management and sharing of energy resources among prosumers (electric customers which produce and consume energy). This paper describes an optimum control technique which provides the above features and can be implemented in low-voltage microgrids by making use of a distributed ICT infrastructure of limited complexity and narrowband communication capability.

A Novel Double Integrated Buck Offline Power Supply for Solid-State Lighting Applications

A single stage offline power supply for LED lighting applications, based on the integration of a buck PFC and a tapped buck DC/DC converter, is presented in this paper. Besides the high step-down capability and the output current regulation, the proposed topology effectively provides power factor correction, so as to comply with the harmonic injection and energy saving standards EN 61000-3-2 and Energy Star. The low BUS voltage level, resulting from the use of an input step-down PFC stage, actually allows the use of film technology capacitors, instead of short lifetime electrolytic capacitors, to filter the BUS voltage and reduce the LED current ripple component at twice the line frequency. Thanks to the high reliability, the simple structure, the good line side spectral performance and the low component count, the proposed topology effectively results to be very suitable for medium power solid state lighting applications, as in the case of LED down-lighting. The issues related to the operation of the presented solution and to its design optimization will be carefully discussed. A prototype of the proposed AC/DC converter has been built and tested. The main experimental results will be described.

Small-signal modeling of the interleaved boost with voltage multiplier

High step-up ratio DC-DC converters for low-voltage high-current energy sources are nowadays the focus of an intensive research activity, thanks to the increasing interest for renewable energy sources like those based on photovoltaic panels and fuel-cells. One class of these high gain converter topologies combines a boost input stage with a voltage multiplier cell, to step-up the output voltage beyond the boost capability. The aim of this paper is to derive the small-signal model of the Interleaved Boost with Voltage Multiplier (IBVM), whose operation was described in [18]-[19]. The classical state-space averaging approach has been employed together with considerations on waveform symmetry. A reduced order model is also derived showing that, with ideal lossless components, the control-to-output voltage dynamics is identical to that of a standard boost converter having twice the inductance. The derived model is validated by simulations and by experimental measurements taken on a 1kW rated converter prototype that boosts a 24V battery voltage to 400V.

Use of current controlled mutual inductor to limit recycling current in the AHB-Flyback converter

Owing to its low component count and easy scalability towards high frequency operation, the Asymmetrical Half Bridge (AHB) Flyback converter is considered one of the most attractive solutions in compact offline, low power and low cost LED driving applications. Such converter can be properly designed to operate with a significant input voltage ripple so as to minimize the input filter capacitance and to guarantee the compliance with the EN 61000-3-2 standard without any kind of power factor correction (PFC). However, despite its inherent simplicity, this converter suffers the high primary side recycling current due to the need of guaranteeing the zero voltage commutation of the half bridge switches in the whole line half period. This paper presents a solution to this problem based on the idea of modulating the mutual inductor magnetizing inductance to compensate for the DC-link voltage variation at twice the line frequency. The aim is to keep, through the use of a current controlled variable inductance, the magnetizing current peak to peak ripple constantly equal to the minimum necessary to guarantee Zero Voltage Switching (ZVS) operation. A prototype, to drive, from the European line voltage (230VRMS at 50Hz) a 10W LED lamp, has been built and tested in order to verify the effectiveness of the proposed technique and converter performance. Experimental results are provided.

A high efficiency and high power factor offline converter for solid state street lighting applications

A high power factor, high efficiency offline driver for LED lighting applications is presented in this paper. Among all the suitable candidate topologies, a multiple stage structure has been chosen, to guarantee the greatest possible flexibility, thanks to the use of optimized topologies both on line side and on load side. Galvanic isolation is provided by means of an intermediate DC transformer stage. A comparison between two different implementations of the latter has been performed in order to better understand advantages and disadvantages of the two proposed topologies and find out an optimal configuration. Despite the presence of multi-stage conversion, a high (>;90%) overall efficiency is achieved. Analytical and experimental results are provided.

Line fed solid state lamp driver based on the asymmetrical half bridge flyback converter

The paper illustrates the design and operation of a line fed, solid state lamp driver based on the asymmetrical half bridge (AHB) flyback converter. The favorable converters characteristics, in terms of soft-switching range and circuit complexity, allow it to operate at variable switching frequency in the range 300–450 kHz, supplying 6W to the load. The lamp is made up of 5 series connected high power LEDs (Cree XR-E) and is supplied with 350 mA closed loop regulated, constant current. While presenting similar complexity and overall efficiency with respect to a conventional driver, the proposed circuit allows a significant volume reduction and consequent power density improvement.