There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

http://ieeexplore.ieee.org/iel5/5610941/5624686/05624745.pdf

Power electronics

In this paper, the control strategy for a flexible microgrid is presented. The microgrid presented here consists of several line-interactive uninterruptible power supply (UPS) systems connected in parallel. The control technique is based on the droop method to avoid critical communications among UPS units. Thus, a flexible microgrid is obtained to operate in either grid-connected or islanded mode. A small-signal analysis is presented in order to analyze the system stability, which gives rules to design the main control parameters. Simulation and experimental results are presented, showing the feasibility of the proposed controller.

Control Strategy for Flexible Microgrid Based on Parallel Line-Interactive UPS Systems

It has become imperative for the power and energy engineers to look out for the renewable energy sources such as sun, wind, geothermal, ocean and biomass as sustainable, cost-effective and environment friendly alternatives for conventional energy sources. However, the non-availability of these renewable energy resources all the time throughout the year has led to research in the area of hybrid renewable energy systems. In the past few years, a lot of research has taken place in the design, optimization, operation and control of the renewable hybrid energy systems. It is indeed evident that this area is still emerging and vast in scope. The main aim of this paper is to review the research on the unit sizing, optimization, energy management and modeling of the hybrid renewable energy system components. Developments in research on modeling of hybrid energy resources (PV systems), backup energy systems (Fuel Cell, Battery, Ultra-capacitor, Diesel Generator), power conditioning units (MPPT converters, Buck/Boost converters, Battery chargers) and techniques for energy flow management have been discussed in detail. In this paper, an attempt has been made to present a comprehensive review of the research in this area in the past one decade.

Hybrid renewable energy systems for power generation in stand-alone applications: A review

In this paper, resonant tank design procedure and practical design considerations are presented for a high performance LLC multiresonant dc-dc converter in a two-stage smart battery charger for neighborhood electric vehicle applications. The multiresonant converter has been analyzed and its performance characteristics are presented. It eliminates both low- and high-frequency current ripple on the battery, thus maximizing battery life without penalizing the volume of the charger. Simulation and experimental results are presented for a prototype unit converting 390 V from the input dc link to an output voltage range of 48-72 V dc at 650 W. The prototype achieves a peak efficiency of 96%.

An LLC Resonant DC–DC Converter for Wide Output Voltage Range Battery Charging Applications

The high-frequency resonant converter has numerous well-known advantages over the traditional hard-switching converters. The most important advantage is that it offers a lower switching loss and a higher power density. Additionally, the soft-switching current waveform characterizes a lower electromagnetic interference (EMI). This study presents the circuit configuration with the least components to realize a highly efficient solar energy battery charger with a zero-voltage-switching resonant converter. The optimal values of the resonant components are determined by applying the characteristic curve and the electric functions derived from the circuit configuration. The experiment demonstrates the switching on and off of the main switches in a solar energy battery charger with a zero-voltage-switching resonant converter, wherein the switches are all operated using zero-voltage switching. The circuit efficiency in the overall charging process exceeds 80%.

A Novel High-Efficiency Battery Charger With a Buck Zero-Voltage-Switching Resonant Converter

This work presents a novel highly efficient and low-stress battery charger with a resonant switch converter - based on resonance and zero-voltage-transition soft-switching theory - that reduces defects associated with high voltage and high current stresses caused by the resonance of traditional resonant circuits. The novel battery charger meets the requirement that all circuit components must operate with zero-voltage switching. Experimental test results indicate that the proposed battery charger reduces the temperature of an active power switch, and switching losses are less than those obtained using a traditional pulsewidth-modulation converter as a battery charger.

High-Efficiency and Low-Stress ZVT–PWM DC-to-DC Converter for Battery Charger

White light emitting diode (LED) with high brightness has attracted a lot of attention from both industry and academia for its high efficiency, ease to drive, environmental friendliness, and long lifespan. They become possible applications to replace the incandescent bulbs and fluorescent lamps in residential, industrial and commercial lighting. The realization of this new lighting source requires both tight LED voltage regulation and high power factor as well. This paper proposed a single-stage flyback converter for the LED lighting applications and input power factor correction. A type-II compensator has been inserted in the voltage loop providing sufficient bandwidth and stable phase margin. The flyback converter is controlled with voltage mode pulse width modulation (PWM) and run in discontinuous conduction mode (DCM) so that the inductor current follows the rectified input voltage, resulting in high power factor. A prototype topology of closed-loop, single-stage flyback converter for LED driver circuit designed for an 18W LED lighting source is constructed and tested to verify the theoretical predictions. The measured performance of the LED lighting fixture can achieve a high power factor greater than 0.998 and a low total harmonic distortion less than 5.0%. Experimental results show the functionality of the overall system and prove it to be an effective solution for the new lighting applications.

Single-Stage Power-Factor-Correction Circuit with Flyback Converter to Drive LEDs for Lighting Applications

In this paper, the charge and discharge strategies were conducted for a future battery energy storage system (BESS) at the National Penghu University of Science and Technology, Makung, Taiwan. OpenDSS software was used to establish the power distribution system. A probabilistic neural network model was used to predict the daily load and photovoltaic (PV) generation curve for controlling the charge–discharge of the BESS. This study considered both the actual and predicted values of PV generation systems as well as the daily charge–discharge control of the BESS used to balance the peak and off-peak electricity consumption to shave peak loads under the two- and three-phase electricity-pricing methods. The average monthly electric bill and contract capacity were calculated, and the effects of different BESS capacities from the load curve were observed. The results were used to evaluate and determine the capacity required by the BESS. The prediction errors for the load and PV generation of the year were 6.22% and 7.14%, respectively. The electric bills and contract capacities of the actual and predicted values were compared, and the resulting difference was low; this implies that the proposed prediction method is practicable.

Sizing the battery energy storage system on a university campus with prediction of load and photovoltaic generation

This paper presents a novel application of half-bridge series-parallel resonant converter (HBSPRC) for dc source and secondary battery interface. The converter practically eliminates both low- and high-frequency current ripple on the battery, thus maximizing battery life without penalizing the volume of the charger circuit. Moreover, operation above resonance is preferred, because the power switches turn on at zero current and zero voltage; thus, the freewheeling diodes do not need to have very fast reverse-recovery characteristics. The proposed battery charger circuit has few components and low-energy conversion loss, which enhance the system's overall efficiency. Circuit operation modes are determined from the conduction profiles. Operating equations and an operating theory are also developed. Experimental results based on a 12-V 48-Ah battery charger are proposed to validate the analysis and to demonstrate the performance of the proposed approach. The maximum charging efficiency of the proposed topology during the overall charging period is 93.98%. Satisfactory performance is obtained from the measured results.

Yu-Lung Ke

Papers

A Novel High-Efficiency Battery Charger With a Buck Zero-Voltage-Switching Resonant Converter

High-Efficiency and Low-Stress ZVT–PWM DC-to-DC Converter for Battery Charger

Single-Stage Power-Factor-Correction Circuit with Flyback Converter to Drive LEDs for Lighting Applications

Sizing the battery energy storage system on a university campus with prediction of load and photovoltaic generation

Analysis and implementation of half-bridge series-parallel resonant converter for battery chargers