Hee-Jong Jeon

Series-Connected Forward–Flyback Converter for High Step-Up Power Conversion

Recently, small-scale and highly-distributed photovoltaic power sources have been researched for the high generation efficiency even under severe partial shading conditions. However, power conditioning systems for the sources needs high step-up voltage gain due to the low output of the generating sources. This paper presents a newly-suggested high step-up topology employing a Series-connected Forward-FlyBack (SFFB) converter, which has a series-connected output for high boosting voltage-transfer gain. SFFB is a hybrid type of forward and flyback converter, sharing the transformer for increasing the utilization factor. By stacking the outputs of them, extremely high voltage gain can be obtained with small volume and high efficiency even with a galvanic isolation. The separated secondary windings in low turn-ratio reduce the voltage stress of the secondary rectifiers, contributing to achievement of high efficiency. The single-ended scheme is also beneficial to the cost competitiveness. In this paper, the operation principle and design guidelines of the proposed scheme are presented, along with the performance analysis and numerical simulation. Also, a 100 W SFFB DC/DC converter hardware prototype has been implemented for experimental verification of the proposed converter topology.

Dynamic Analysis and Controller Design for Standalone Operation of Photovoltaic Power Conditioners with Energy Storage

Energy storage devices are necessary to obtain stable utilization of renewable energy sources. When black-out occurs, distributed renewable power sources with energy storage devices can operate under standalone mode as uninterruptable power supply. This paper proposes a dynamic response analysis with small-signal modeling for the standalone operation of a photovoltaic power generation system that includes a bidirectional charger/discharger with a battery. Furthermore, it proposes a DC-link voltage controller design of the entire power conditioning system, using the storage current under standalone operation. The purpose of this controller is to guarantee the stable operation of the renewable source and the storage subsystem, with the power conversion of a very efficient bypass-type PCS. This paper presents the operating principle and design guidelines of the proposed scheme, along with performance analysis and simulation. Finally, a hardware prototype of 1-kW power conditioning system with an energy storage device is implemented, for experimental verification of the proposed converter system.

Controller design of power conditioning systems with energy storage device for renewable energy source under stand-alone operation

With depletion of fossil fuels and environmental contamination, it has become important to use renewable energy. For the stable utilization of the renewable energy sources, energy storage device must be employed. The renewable and distributed power sources with energy storages can operate under stand-alone mode such as uninterruptable power supply when black-out occurs. This paper proposed a dynamic response modeling for a renewable power generation systems including a bidirectional charger/discharger for battery, and also suggests the DC-link voltage controller design of the charger/discharger under stand-alone operation in order to analyze a method for guaranteeing the stable operation while fully utilizing the power from the energy storage device. In this paper, the operation principle and design guidelines of the proposed scheme are presented, along with the performance analysis and simulation using MATLAB and PSIM simulation. Finally, 1kW power conditioning system with energy storage device hardware prototype has been implemented for experimental verification of the proposed converter system.

Controller Design of a Novel Power Conditioning System with an Energy Storage Device for Renewable Energy Sources under Grid-Connected Operation

As a result of the depletion of fossil fuels and environmental contamination, it has become important to use renewable energy. For the stable utilization of renewable energy sources, energy storage devices must be used. In addition, renewable and distributed power sources with energy storage devices must operate stably under grid-connected mode. This paper proposed dynamic response modeling for renewable power generation systems including a charger/discharger with an energy storage device in order to derive a method to guarantee stable operation while fully utilizing the energy from the energy storage device. In this paper, the principle operation and design guidelines of the proposed scheme are presented, along with a performance analysis and simulation results using MATLAB and PSIM. Finally, a hardware prototype of a 1kW power conditioning system with an energy storage device has been implemented for experimental verification of the proposed converter system.

DC-Link ripple reduction of series-connected module integrated converter for Photovoltaic systems

Recently, Building Integrated Photovoltaic (BIPV) generation systems have been studied in renewable energy engineering field because the systems require small space installation and a reduced building — material cost in spite of the performance degradation from partial shading. In case of a MIC with series connected output, it is easy to obtain a high DC-Link voltage for grid-connected applications. However, DC-Link voltage ripple also increases as the number of modules increases. In this paper, as a manner of ripple reduction, interleaved control method is applied to the PV MIC modules. For the implementation of the phase synchronization, Zigbee (Xbee-pro) wireless communications transceiver and DSPs Series Communications Interface are utilized. A 80W hardware prototype two boost-type of MIC is built to verify the DC-Link voltage ripple reduction.

A development of Diagnosis Monitoring System for UPS DC Link Capacitors using Zigbee Wireless Communication

Electrolytic power capacitors have been widely used in power conversion system such as inverter or UPS because of characteristics of large capacitance, high-voltage and low-cost. The electrolytic capacitor, which is most of the time affected by the aging effect, plays a very important role for the power-electronics system quality and reliability. Therefore it is important to diagnosis monitoring the condition of an electrolytic capacitor in real-time to predict the failure. In this paper, the on-line remote diagnosis monitoring system for UPS DC link electrolytic capacitors using low-cost single-chip zigbee communication modules is developed. To estimate the health status of the capacitor, the equivalent series resistor(ESR) of the component has to be determined. The capacitor ESR is estimated by using RMS computation using BPF modeling of DC link ripple voltage/current. Zigbee-based hardware experimental results show that the proposed remote capacitor diagnosis monitoring system can be applied to UPS successfully.

Controller design of grid-connected power conditioning system with energy storage device

The open voltage and short current characteristic of renewable energy source are changed according to environmental factors. For such reasons, Maximum Power Point (MPP) of renewable energy continually changes. Because of this characteristic, power conditioning system must be controlled to track the MPP. The stable control loop is supposed to be designed at MPP of renewable energy. Therefore, the small signal modeling must be done before the compensator design of the feedback control loop. In this paper, a bidirectional converter for charging/ discharging to energy storage is considered. For the controller design, the interaction of dynamic response between boost converter and charger/discharger in parallel should be investigated. According to the small-signal analysis, closed loop controller design was done. Also, verified the model using MATLAB and PSIM simulation. Finally, 1kW hardware prototype of power conditioning system with energy storage device has been implemented for experimental verification of the proposed converter system.

Bidirectional Power Conversion of Isolated Switched-Capacitor Topology for Photovoltaic Differential Power Processors

Differential power processing (DPP) systems are among the most effective architectures for photovoltaic (PV) power systems because they are highly efficient as a result of their distributed local maximum power point tracking ability, which allows the fractional processing of the total generated power. However, DPP systems require a high-efficiency, high step-up/down bidirectional converter with broad operating ranges and galvanic isolation. This study proposes a single, magnetic, high-efficiency, high step-up/down bidirectional DC–DC converter. The proposed converter is composed of a bidirectional flyback and a bidirectional isolated switched-capacitor cell, which are competitively cheap. The output terminals of the flyback converter and switched-capacitor cell are connected in series to obtain the voltage step-up. In the reverse power flow, the converter reciprocally operates with high efficiency across a broad operating range because it uses hard switching instead of soft switching. The proposed topology achieves a genuine on–off interleaved energy transfer at the transformer core and windings, thus providing an excellent utilization ratio. The dynamic characteristics of the converter are analyzed for the controller design. Finally, a 240 W hardware prototype is constructed to demonstrate the operation of the bidirectional converter under a current feedback control loop. To improve the efficiency of a PV system, the maximum power point tracking method is applied to the proposed converter.

Bidirectional Charging/Discharging Digital Control System for Eco-friendly Capacitor Energy Storage Device Implemented by TMS320F28335 chip

Recently, as the demand of the environmental-friendly energy storage system such as an electric double-layer condenser increases, that of the bidirectional charger/discharger for the systems also increases. However, when charging/discharging mode-change occurs, the charger/discharger employing a bi-directional DC-DC converter with a commercialized analog controller has a complex circuit scheme, and a poor transient response. On the other hand, if a single digital controller is used for the bi-directional mode, the system performances can be improved by application of an advanced power-processing algorithm. In the paper, an environmental-friendly power storage systems including an Electric Double Layer Capacitor(EDLC) banks were developed with a bi-directional buck-boost converter and a digital signal processor (TMS320F28335). A simulation test-bed was realized and tested by MATLAB Simulink, and the hardware experiment was performed which shows that the dynamic response was improved such as the simulation results.

A study on the performance improvement of DVR system using EDLC

In this paper a novel detection technique for voltage sag and phase of an input voltage is proposed to improve the performance of DVR system. With the proposed voltage sag detection method the detection time for the voltage sag is reduced and the performance is improved of DVR system. In addition to the conventional phase detection algorithm of an input voltage, simple logic circuit is adopted to detect the input voltage direction. The erroneous information around the zero-crossing points can be successfully removed by the proposed technique and the effectiveness of the proposed technique is verified by the experiments. EDLC, environment-friendly, and the high efficiency charging/discharging technique are adopted as an energy storage device. Experimental results are presented to verify the effectiveness.