Luiz C. G. Freitas

Front-End Converter With Integrated PFC and DC–DC Functions for a Fuel Cell UPS With DSP-Based Control

This paper presents the development of a boost converter with integrated power factor correction (PFC) and dc-dc functions for a proton exchange membrane fuel cell (PEMFC) uninterruptable power supply (UPS). Through the use of a passive resonant soft-commutation cell, which besides providing improvements in efficiency and reduced electromagnetic interference, produces a naturally controlled supercapacitor charger circuit. Supercapacitors are employed in order to provide a proper startup of the PEMFC and to improve its dynamic response. The control strategy is implemented using a digital signal processor and is based on the average current control method for sinusoidal input current imposition ensuring, therefore, a high input power factor and low harmonic distortion of current. The main features of the proposed solution are the use of a PEMFC as an energy storage system, which replace the battery banks commonly used in UPS systems, eliminating the common drawbacks related to working life and maintenance issues, and the use of a front-end converter with integrated PFC and dc-dc functions eliminating the necessity of using an additional and dedicated dc-dc converter for the PEMFC. During power failure or even in conditions of severe voltage sags on the ac mains, the PEMFC is activated assuring the continuous power supply to the electronic load connected to the dc link. In this paper, the authors present the full study description including experimental results that corroborate with the theory herein presented.

Modeling and control of a single-stage current source inverter with amplified sinusoidal output voltage

Alternative energy sources has been attracting great interest in the area of static converter development. This fact is related to issues like sustainability and the world environment, which is contributing to viability of this type of energy source. The main challenge is to develop systems that transform this DC energy in AC. Within this subject, this paper focuses the establishment of a new control strategy applied to a step-down/step-up single-stage inverter with imposed waveforms of input inductor current and output voltage. The proposed control strategy provides high voltage gain without using high frequency transformer, which contributes to weigh and size reduction of the proposed DC-AC converter structure. Theoretical analysis are presented and corroborated by experimental results of a 180W laboratory prototype fed by a fuel cell.

PEM fuel cell dynamic model for electronic circuit simulator

This paper presents a PEM fuel cell dynamic modeling, to be employed with electronic circuit simulator software - PSIM. Simulations of the proposed model for the fuel-cell, supplying a step-up DC-DC converter are presented. Comparisons with existing models are also made. Practical results are presented in this paper for a Ballard 1.2kW Nexa Power Module for theoretical-experimental comparisons.

Proposal for preprogrammed control applied to a current-sensorless PFC boost converter

The development of front-end converters for power factor correction and DC link voltage control of power electronics converters such as, UPS, Inverters, and Switched Power Supplies, has been attracting great interest from the scientific community that works toward the achievements of cost reduction, high efficiency, and reliability. In this context, this paper proposes a microprocessed control technique for sinusoidal input line current imposition in front-end ac-dc converters. This gave rise to an innovative sensorless boost converter, named in this work as PFC-Boost-CSL. The proposed method is based on experimental acquisition of gate-drive signal sequences for different load conditions. These signals correspond to a complete cycle of the AC input voltage and are recorded in the microcontroller memory in order to be reproduced when used in a boost converter without current sensor. In the operation of PFC-Boost-CSL, a suitable switching sequence is sent to drive the power switch in order to minimize output voltage error and maintain a sinusoidal input current. Aiming to prove the proposed control concept, a 600W PFC-Boost-CSL prototype was built and analyzed in laboratory and the main experimental results are presented herein.

Current-sensorless PFC Boost converter with preprogrammed control strategy

The development of front-end converters for power factor correction and DC link voltage control of power electronics converters such as, UPS, Inverters, and Switched Power Supplies, has been attracting great interest from the scientific community that works toward the achievements of cost reduction, high efficiency, and reliability. In this context, this paper proposes an innovative microprocessed control technique for sinusoidal input line current imposition in front-end sensorless Boost converters, named in this work as PFC-BOOST-CSL. The proposed method is based on experimental acquisition of gate-drive signal sequences for different load conditions. These signals correspond to a complete cycle of the AC input voltage and are recorded in the microcontroller memory in order to be reproduced when used in a Boost converter without current sensor. In the operation of PFC-BOOST-CSL, a suitable switching sequence is sent to drive the power switch in order to minimize output voltage error and maintain a sinusoidal input current. Aiming to prove the proposed digital control concept, a 600W PFC-BOOST-CSL prototype was built and analyzed in laboratory and the main experimental results are presented herein.

Proposal of a hybrid rectifier structure with HPF and low THD suitable for front-end trolleybuses systems supplied by AC distribution networks

This paper presents the development and the experimental analysis of a new single-phase hybrid rectifier structure with high power factor (PF) and low harmonic distortion of current (THDI), suitable for application in traction systems of electrical vehicles pulled by electrical motors (trolleybus), which are powered by urban distribution network. This front-end rectifier structure is capable of providing significant improvements in trolleybuses systems and in the urban distribution network costs, and efficiency.

True zero current turn-on and turn-off converter family: Analysis, simulation and experimental results

This paper presents a new non dissipative commutation cell applied to a buck converter. The commutation cell is composed by one main switch and two auxiliary switches operating with zero current turn on and off. This new soft-commutation cell presents the following advantages: soft-commutation for a wide load ratio, better current distribution among semiconductors, besides, the main switch must be rated at nominal load current. Therefore, a new true zero turn on and off converter family capable of operating in high frequency could be achieved, providing high power density and efficiency.

Design of an Internal Model Control strategy for single-phase grid-connected PWM inverters and its performance analysis with a non-linear local load and weak grid

This paper presents the design of a controller based on Internal Model Control (IMC) applied to a grid-connected single-phase PWM inverter. The mathematical modeling of the inverter and the LCL output filter, used to project the 1-DOF IMC controller, is presented and the decoupling of grid voltage by a Feedforward strategy is analyzed. A Proportional - Resonant Controller (P+Res) was used for the control of the same plant in the running of experimental results, thus moving towards the discussion of differences regarding IMC and P+Res performances, which arrived at the evaluation of the proposed control strategy. The results are presented for typical conditions, for weak-grid and for non-linear local load, in order to verify the behavior of the controller against such situations.

Simulated Annealing ‑ MPPT in Partially Shaded PV Systems

This paper is about simulated annealing (SA) algorithm used to tracking the maximum power point (MPP) applied to photovoltaic array. The present method adjusted the SA algorithm to variables analysed on photovoltaic systems (PV). Therefore, the power is the objective function and it depends on duty cycle, which is the independent variable. Initially, the SA algorithm is at random. However, the convergence methods lead the system to a global optimal point. Hence, the SA would avoid the ineffective exploration on the local optimal solutions like MPPT classic algorithms, mostly when the photovoltaic array is under partial shading conditions. The simulations have been done by PSIM software and the code could have been implemented in a digital signal controller (DSC).

A novel single-phase HPF hybrid rectifier suitable for front-end trolleybus systems

This paper proposal presents the development and the experimental analysis of a new single-phase hybrid rectifier structure with high power factor (PF) and low harmonic distortion of current (THDI), suitable for application in traction systems of electrical vehicles pulled by electrical motors (trolleybus), which are powered by urban distribution network. This front-end rectifier structure is capable of providing significant improvements in trolleybuses systems and in the urban distribution network costs, and efficiency. The proposed structure is composed by an ordinary single-phase diode rectifier with parallel connection of a switched converter. It is outlined that the switched converter is capable of composing the input line current waveform assuring high power factor (HPF) and low THDI, as well as ordinary front-end converter. However, the power rating of the switched converter is about 34% of the total output power, assuring robustness and reliability. Therefore, the proposed structure was named single-phase HPF hybrid rectifier. A prototype rated at 15 kW was developed and analyzed in laboratory. It was found that the input line current harmonic spectrum is in accordance with the harmonic limits imposed by IEC61000-3-4. The principle of operation, the mathematical analysis, the PWM control strategy, and experimental results of a 15 kW prototype are also presented in this paper.