Hanju Cha

A Three-Phase Current-Fed DC/DC Converter With Active Clamp for Low-DC Renewable Energy Sources

This paper focuses on a new three-phase high power current-fed DC/DC converter with an active clamp. A three-phase DC/DC converter with high efficiency and voltage boosting capability is designed for use in the interface between a low-voltage fuel-cell source and a high-voltage DC bus for inverters. Zero-voltage switching in all active switches is achieved through using a common active clamp branch, and zero current switching in the rectifier diodes is achieved through discontinuous current conduction in the secondary side. Further, the converter is capable of increased power transfer due to its three-phase power configuration, and it reduces the RMS current per phase, thus reducing conduction losses. Moreover, a delta-delta connection on the three-phase transformer provides parallel current paths and reduces conduction losses in the transformer windings. An efficiency of above 93% is achieved through both improvements in the switching and through reducing conduction losses. A high voltage ratio is achieved by combining inherent voltage boost characteristics of the current-fed converter and the transformer turns ratio. The proposed converter and three-phase PWM strategy is analyzed, simulated, and implemented in hardware. Experimental results are obtained on a 500-W prototype unit, with all of the design verified and analyzed.

A three-phase AC/AC high-frequency link matrix converter for VSCF applications

In this paper, a new three-phase high-frequency link matrix converter is discussed and the topology of conventional matrix converter is modified with the addition of a transformer for a variable speed constant frequency (VSCF) application. The proposed approach accomplishes voltage transfer ratio more than unity, galvanic isolation between both voltage sources and higher power density by employing a high-frequency transformer into the intermediate stage of the dual bridge matrix converter. It has a bidirectional power flow capability, controllable displacement power factor and lower harmonic distortion at both variable speed source and fixed frequency utility. Further, asynchronous or synchronous PWM can be employed depending on the frequency modulation ratio in the primary side converter and it guarantees full input voltage utilization for DC-link and near symmetric square wave pulse trains applied to high frequency transformer regardless of varying input frequency. The proposed approach is a competitive solution for VSCF distributed generating application such as wind-turbine and micro-turbine application. Simulation results are shown to demonstrate the advantages of the proposed system. Experimental results on a 230V, 3kVA 400 Hz to 60 Hz VSCF system based on DSP controller are presented.

Comparative analysis of low-pass output filter for single-phase grid-connected Photovoltaic inverter

Nowadays, the LCL-filter type becomes an attractive grid interfacing for grid-connected Voltage Source Inverter (VSI). LCL-filter can render the current harmonics attenuation around the switching frequency by using smaller inductance than L-filter. Moreover, system using LCL-filter does not depend on the grid impedance and has a better output response while comparing with LC-filter. Firstly, an analysis and design procedure of output LCL-filter for single-phase grid-connected Photovoltaic (PV) inverter system is presented in this paper. Due to the theoretical analysis, a comparison between the designed LCL-filter with L-filter and LC-filter based single-phase grid-connected PV inverter system is carried out. The comparison results are given to validate the theoretical analysis and effectiveness of filters.

Design and control of Proportional-Resonant controller based Photovoltaic power conditioning system

This paper presents a current control technique for a single-phase grid-connected DC/AC inverter which is used in Photovoltaic power conditioning system (PV PCS). A Proportional - Resonant (PR) controller is used for replacing the conventional Proportional - Integral (PI) controller in this system. By comparison with the conventional PI control method, the PR control can introduce an infinite gain at the fundamental frequency and hence can achieve zero steady-state error. A theoretical analysis of the PR controller is presented and verified by experiment. Furthermore, a pseudo synchronous d-q transformation is employed in current control scheme and an all-pass filter based single-phase digital phase-locked loop (PLL) is introduced to detect the phase of grid voltage. Based on the theoretical analysis, the control strategy is implemented on a 32-bit fixed-point TMS320F2812 DSP and tested in a 3kW prototype PV PCS. Simulation and experimental verify the high performance of the implemented control scheme.

A Novel Three-Phase High Power Current-Fed DC/DC Converter with Active Clamp for Fuel Cells

In this paper, a new three-phase high power current-fed dc/dc converter with active clamp is proposed. A three phase DC-DC converter with zero voltage switching (ZVS) with high frequency transformer isolation is shown. A single common active clamp branch is used to limit transient voltage across the three-phase full bridge and to realize zero-voltage switching (ZVS) in all switches by using the energy stored in the transformer leakage inductance. The proposed approach has the following advantages : an increase (by a factor of three) of input current and output voltage chopping frequencies; lower rms current through the inverter switches with higher power transfer capability; reduction in size of reactive (filter) components; better transformer utilization. The proposed converter is suitable for higher power fuel cell dc sources with low voltage outputs. The paper details the analysis, simulation and hardware implementation of the proposed system. Finally experimental results obtained on a 500 W prototype demonstrates the feasibility of the proposed scheme.

A new three-phase interleaved isolated boost converter with active clamp for fuel cells

In this paper, a new three-phase high power dc/dc converter with an active clamp is proposed. The converter is capable of increased power transfer due to its three-phase power configuration, and it reduces the rms current per phase, thus reducing conduction losses. Further, interleaved operation of three-phase boost converter reduces overall ripple current, which is imposed into fuel cells and realizes smaller sized filter components, increasing effective operating frequency and leading to higher power density. Each output current of three-phase boost converter is combined by the three-phase transformer and flows in the continuous conduction mode by the proposed three-phase PWM strategy. An efficiency of above 96% is mainly achieved by reducing conduction losses and switching losses are reduced by the action of active clamp branches, as well. The proposed converter and three-phase PWM strategy are analyzed, simulated and implemented in hardware. Experimental results are obtained on a 500 W prototype unit, with all of the design verified and analyzed.

A Three-Phase Interleaved DC–DC Converter With Active Clamp for Fuel Cells

In this paper, a three-phase interleaved dc-dc converter with an active clamp and three-phase pulsewidth modulation (PWM) method are proposed. The proposed converter has a three-phase interleaved boost converter, which consists of three input inductors, three active clamp switches, three-phase high frequency transformer, and diode rectifiers. Interleaved operation of a three-phase boost converter reduces overall ripple current, which is imposed into fuel cells and realizes smaller sized filter components, increasing effective operating frequency, and leading to higher power density. Each output current of the three-phase boost converter is combined by the three-phase transformer and flows in the continuous conduction mode, which leads to a reduction of rms current through switches and transformer windings. A peak efficiency of above 95% is achieved by a reduction in the conduction losses resulted by continuous current conduction and switching losses reduced by the action of active clamp branches, as well. The proposed converter and three-phase PWM strategy are analyzed, simulated, and implemented in hardware. Experimental results are presented to verify the feasibility of the proposed converter.

Battery ripple current reduction in a three-phase interleaved dc-dc converter for 5kW battery charger

This paper proposes a battery ripple current reduction method and design of three-phase interleaved dc-dc converter for 5kW battery charger, which is applied for stabilizing a wind-power generating system. The charger consists of three-phase interleaved dc-dc converter, which is the interface of batteries and DC link, and a grid connected inverter. Lead-acid battery is modeled in the first order R-C model by MATLAB/Simulink and battery parameters are measured by the pulsed current and constant current discharge test. The battery is connected to the three-phase interleaved dc-dc converter in order for reduction of ripple current to 8% from 32.5%, increase of battery lifetime and reduction of total size of inductors. The ripple current is further reduced to 2% from 8% by connecting a filter capacitor and design rule of filter capacitor is analyzed. The controller for charging and discharging mode is designed and the proposed reduction methods of battery ripple currents are verified in a 5kW charger.

DC Micro-Grid Operational Analysis with a Detailed Simulation Model for Distributed Generation

This paper describes operational analysis results of the DC micro-grid using detailed model of distributed generation. Detailed model of wind power generation, photo-voltaic generation, fuel cells generation was implemented with the user-defined model of PSCAD/EMTDC software that is coded with C-language. The operation analysis was carried out using PSCAD/EMTDC software, in which the power circuit is implemented by built-in model and the controller is modeled by user-defined model that is also coded with C-language. Various simulation results confirm that the DC micro-grid can operate without any problem in both the grid-tied mode and the islanded mode. The operational analysis result confirms that the DC micro-grid make it feasible to provide power to the load stably. And it can be utilized to develop an actual system design and building.

A New Bi-directional Three-phase Interleaved Isolated Converter with Active Clamp

In this paper, a new bidirectional three-phase dc-dc converter and three-phase PWM strategies have been proposed for battery application. The proposed converter acts as an three-phase isolated buck converter when battery is charged from dc link (buck mode) and an three-phase isolated boost converter when battery discharges energy (boost mode). In the buck mode, three-phase hybridge rectifier is employed to improve efficiency and an interleaved operation of three-phase buck converter reduces overall charging current ripple, which is imposed into battery. The interleaved operation increases effective operating frequency and thus, leads to a realization of smaller sized filter components. In addition, the proposed three-phase PWM strategy transfers energy through three-phase paths with zero voltage switching (ZVS) capability. In the boost mode, an interleaved operation of three-phase boost converter induces the same properties as in the three-phase buck converter. In addition, three-phase active clamp branch mitigates not only switching losses by zero voltage switching but also electromagnetic noises caused by hard-switched voltage spikes. These characteristics of the proposed converter reduce operating losses significantly and result in the whole converter efficiency above 95%. The proposed converter and three-phase PWM strategies are analyzed, simulated and implemented in hardware. Experimental results are obtained on a 500W prototype unit, with all of the design verified and analyzed.