F. Gennaro

Soft-Switching Converter With HF Transformer for Grid-Connected Photovoltaic Systems

In this paper, the design, realization, and performance evaluation of a single-phase 3-kW dc/ac power converter, using an active-bridge dc/dc converter and a full-bridge dc/ac, are introduced, presenting a novel solution on the industrial scenario for the considered application. Control algorithms, including the maximum power point tracking, paralleling to the grid, and converter switching signals, are digitally implemented on a standard microcontroller.

Thermal instability of low voltage power-MOSFETs

This paper analyzes an anomalous failure mechanism detected on last generation low voltage power metal oxide semiconductor (MOS) devices at low drain current. Such a behavior, apparently due to a kind of second breakdown phenomenon, has been scarcely considered in literature, as well as in manufacturer data sheets, although extensive experimental tests show that it is a common feature of modern low voltage metal oxide semiconductor held effect transistor (MOSFET) devices. The paper starts by analyzing some failures, systematically observed on low voltage power MOSFET devices, inside the theoretical forward biased safe operating area. Such failures are then related to an unexpected thermal instability of the considered devices. Experimental tests have shown that in the considered devices the temperature coefficient is positive for a very wide drain current range, also including the maximum value. Such a feature causes hot spot phenomena in the devices, as confirmed by microscope inspection of the failed devices. Finally, it is theoretically demonstrated that the thermal instability is a side effect of the progressive die size and process scaling down. As a result, latest power MOSFETs, albeit more efficient and compact, are less robust than older devices at low drain currents, thus requiring specific circuit design techniques.

Single chip integration for motor drive converters with power factor capability

In this paper, an innovative converter topology is presented that allows to improve the performance of electronically commutated motor drives, aimed to equip home appliances. The proposed topology is based on a modified C-dump converter configuration, where the energy recovery stage acts as an active power factor controller (PFC) for offline operation. This is made possible by introducing a new technique to manage the free-wheeling energy that is recovered back to the dc bus by a suitable high frequency (HF) transformer. The proposed approach allows to omit the PFC stage that is included in motor drives devoted to home appliance applications in order to comply with power quality requirements. Moreover, the proposed converter topology features only low side or high side configuration switches, allowing to simplify the design of the drive and easily integrate the power semiconductors in a single chip exploiting smart power technologies. Simulations and experimental results confirm the validity of the proposed approach.

A Novel Converter System for Fuel Cell Distributed Energy Generation

To interface the fuel cells (FCs) to grid/loads a DC/AC energy conversion system is required with the capability to act as an energy buffer for matching generator-load dynamics. A new power converter design is proposed based on cascade connection of a DC/DC and a DC/AC converter. The DC/DC converter has to control the FC current ripple and regulate the power flow from the FC. It is characterized by only two main switches of low side type, operated with an interleaved control technique which requires the use of two boost inductance chokes. Such a control strategy provides input current ripple cancellation, which is mandatory in fuel cell systems. A regenerative active clamp circuit is also used in order to prevent high peak voltages on the two main switches, maintaining a high efficiency. The proposed DC/DC converter is tested on a laboratory prototype and represents a new cost effective topology, able to operate under a wide range of input voltages and load conditions with high efficiency

A digitally controlled double stage soft-switching converter for grid-connected photovoltaic applications

A photovoltaic generator exhibits nonlinear voltage-current characteristics and its maximum power point varies with solar radiation and temperature. In order to suitably connect the photovoltaic generator with the grid, single or multi-stage inverters are used addressing many specifications as high efficiency and large input voltage range. In the paper, the design, realization and performance evaluation of a single-phase 3 kW DC/AC power converter, using an active bridge DC/DC converter and a full bridge DC/AC is introduced, presenting a novel solution on the industrial scenario for the considered application. The control algorithms, including the maximum power point tracking, paralleling to the grid, and converter switching signals are digitally implemented on a standard microcontroller.

A comparative study of different buck topologies for high efficiency low voltage applications

In this paper, a comparison is performed between six different configurations of buck power converters for low voltage applications. The considered converters operate under hard and soft switching conditions and are equipped with conventional and synchronous output rectification. The comparison is based on overall efficiency, power device stresses, electromagnetic emissions and power converter sizes. Guidelines are finally given to help designers of high frequency low power SMPS in selecting the best topology according to the specific design.

A Multi-stage Converter for Domestic Generation Systems Based on Fuel Cells

A new cost effective system for distributed power generation systems based on a fuel cell is proposed, designed and tested by means of a lab prototype. A review of different solutions to connect an energy buffer stage to the power source is firstly considered according to cost reduction criteria and efficiency maximization. Then, the 3kW generation system is sized according to a typical domestic daily load profile, while the energy storage elements are chosen in order to both compensate the fuel cell slow dynamic response and to supply the daily peak load energy demand. Finally, a suitable control technique able to cope with fuel cell and energy buffer dynamics, is implemented and the performance of the proposed system are evaluated by simulation and experimental results

Common mode current elimination in multi-drive industrial systems

The paper deals with the common mode current issue in a multi-drive system. Common mode currents are caused by step variations of the common mode voltage, strictly related to the sequence of the inverter states during the voltage pulsewidth modulation. An inexpensive technique that allows to compensate the common mode voltage variation in multi-drive systems composed of two or more inverters is proposed, in order to eliminate the common mode currents. The common mode current paths and generation mechanisms are reviewed and the influence of the inverter state sequence on the common mode voltage and currents is pointed out. Based on such considerations, a new digital PWM modulation strategy is introduced to compensate the common mode voltage variations generated in a two PWM inverter system.

A Simple Unity Power Factor Motor Drive for Home Appliances

This paper describes a low-power Switched Reluctance motor drive for home appliances featuring close to unity power factor and low cost. The proposed drive includes a compact Power Factor Controller input stage based on a quasiresonant boost topology. The converter structure is suitable for integration and allows one to develop an inexpensive chip implementing all the main functions required by such a drive. Experimental results on a prototype are presented to evaluate the efficiency of the proposed drive.This paper describes a low-power Switched Reluctance motor drive for home appliances featuring close to unity power factor and low cost. The proposed drive includes a compact Power Factor Controller input stage based on a quasiresonant boost topology. The converter structure is suitable for integration and allows one to develop an inexpensive chip implementing all the main functions required by such a drive. Experimental results on a prototype are presented to evaluate the efficiency of the proposed drive.

Active Common Mode Current Reduction in Multiinverter Systems

The paper deals with the common mode current issue in a multidrive system. Common mode currents are caused by steep variations of the common mode voltage, strictly related to the sequence of the inverter states during the voltage pulsewidth modulation. An inexpensive technique that allows compensation of the common mode voltage variation in multidrive systems composed of two or more inverters is proposed in order to eliminate the common mode currents. The common mode current paths and generation mechanisms are reviewed and the influence of the inverter state sequence on the common mode voltage and currents is pointed out. Based on such considerations, a new digital PWM modulation strategy is introduced to compensate the common mode voltage variations generated in a two PWM inverter system.The paper deals with the common mode current issue in a multidrive system. Common mode currents are caused by steep variations of the common mode voltage, strictly related to the sequence of the inverter states during the voltage pulsewidth modulation. An inexpensive technique that allows compensation of the common mode voltage variation in multidrive systems composed of two or more inverters is proposed in order to eliminate the common mode currents. The common mode current paths and generation mechanisms are reviewed and the influence of the inverter state sequence on the common mode voltage and currents is pointed out. Based on such considerations, a new digital PWM modulation strategy is introduced to compensate the common mode voltage variations generated in a two PWM inverter system.