Input current ripple reduction and high efficiency for PEM fuel cell power conditioning system

© 2017 IEEE. To solve the issues of the open-loop control accuracy in a proton exchange membrane (PEM) fuel cell power conditioning system (PCS) with active clamp push-pull DC/DC converter for input current ripple reduction, a novel closed-loop digital-controlled method is proposed. The proposed PEM fuel cell PCS consists of a high-efficiency high-step-up current-fed resonant push-pull DC/DC converter and a half-bridge inverter. A fully digital-controlled strategy in the active-clamped circuit is employed to reduce the voltage spike and low frequency current ripple (LFCR) on the power switches for improving the lifespan of PEM fuel cell and raising the system reliability. By using the closed-loop current ripple reduction control, the LFCR is further reduced. A 300 W prototype is implemented and tested. Experimental results show that the minimum efficiency at full load is about 94.8% and the ripple current is less than 1.2% of the rated input current

Performance comparison of input current ripple reduction methods in UPS applications with hybrid PEM fuel cell/supercapacitor power sources

An uninterruptible power supply (UPS) system with different input current ripple reduction methods is proposed, and a comparison research has been conducted about these methods. The proposed UPS system consists of a 63-cell 300 W proton exchange membrane (PEM) fuel cell stack, two 16-cell supercapacitors (SCs) in series, a high-efficiency push-pull DC/DC converter and a half-bridge DC/AC inverter. Besides that the traditional push-pull DC/DC converter has inherent advantages of low input-current stress and high voltage conversion ratio, the SCs, LC filter, and an active clamp circuit are employed to reduce the input current ripples in the UPS system. First, the input current ripple generation and performance without an external component are analyzed and modeled in the PEM fuel cell. Then the input current ripple reduction methods mentioned above are proposed and operated in the designed UPS system. Finally, the experimental results show that the input current ripple can be further reduced by using different current ripple reduction approaches, and the active compensation method has better performance than the passive compensation method. The input current ripple is less than 5% of the rated input current. © 2014 Elsevier Inc. All rights reserved

A plug-and-play ripple mitigation approach for DC-links in hybrid systems

© 2016 IEEE.In this paper, a plug-and-play ripple mitigation technique is proposed. It requires only the sensing of the DC-link voltage and can operate fully independently to remove the low-frequency voltage ripple. The proposed technique is nonintrusive to the existing hardware and enables hot-swap operation without disrupting the normal functionality of the existing power system. It is user-friendly, modular and suitable for plug-and-play operation. The experimental results demonstrate the effectiveness of the ripple-mitigation capability of the proposed device. The DC-link voltage ripple in a 110 W miniature hybrid system comprising an AC/DC converter and two resistive loads is shown to be significantly reduced from 61 V to only 3.3 V. Moreover, it is shown that with the proposed device, the system reliability has been improved by alleviating the components' thermal stresses

New approaches to improve the performance of the PEM based fuel cell power systems

Fuel cells are expected to play an important role in future power generation. However, significant technical challenges remain and the commercial breakthrough of fuel cells is hindered by the high price of fuel cell components. As is well known, the fuel cells do not provide the robust source characteristics required to effectively follow the load during significant load steps and they have limited overload-handling capability. Further, the performance of the fuel cell is significantly degraded when the CO (Carbon Monoxide) is contained in the hydrogen fuel. In this thesis several new approaches to improve the performance of PEM based fuel cell power systems are discussed. In the first section an impedance model of the Proton Exchange Membrane Fuel Cell Stack (PEMFCS) is first proposed. This equivalent circuit model of the fuel cell stack is derived by a frequency response analysis (FRA) technique to evaluate the effects of the ripple current generated by the power-conditioning unit. Experimental results are presented to show the effects of the ripple currents. In the second section, a fuel cell powered UPS (Uninterruptible Power Supply) system is proposed. In this approach, two PEM Fuel Cell modules along with suitable DC/DC and DC/AC power electronic converter modules are employed. A Supercapacitor module is also employed to compensate for instantaneous power fluctuations including overload and to overcome the slow dynamics of the fuel processor such as reformers. A complete design example for a 1-kVA system is presented. In the third section, an advanced power converter topology is proposed to significantly improve the CO tolerance on PEM based fuel cell power systems. An additional two-stage dc-dc converter with a supercapacitor module is connected to the fuel cell to draw a low frequency (0.5Hz) pulsating current of the specific amplitude (20-30[A]) from the fuel cell stack. CO on the catalyst surface can be electro-oxidized by using this technique, and thereby the CO tolerance of the system can be significantly improved. Simulation and experimental results show the validity and feasibility of the proposed scheme

Mitigation of low-frequency current ripple in fuel-cell inverter systems through waveform control

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Integration of an Active Filter and a Single-Phase AC/DC Converter with Reduced Capacitance Requirement and Component Count

Existing methods of incorporating an active filter into an AC/DC converter for eliminating electrolytic capacitors usually require extra power switches. This inevitably leads to an increased system cost and degraded energy efficiency. In this paper, a concept of active-filter integration for single-phase AC/DC converters is reported. The resultant converters can provide simultaneous functions of power factor correction, DC voltage regulation, and active power decoupling for mitigating the low-frequency DC voltage ripple, without an electrolytic capacitor and extra power switch. To complement the operation, two closed-loop voltage-ripple-based reference generation methods are developed for controlling the energy storage components to achieve active power decoupling. Both simulation and experiment have confirmed the eligibility of the proposed concept and control methods in a 210-W rectification system comprising an H-bridge converter with a half-bridge active filter. Interestingly, the end converters (Type I and Type II) can be readily available using a conventional H-bridge converter with minor hardware modification. A stable DC output with merely 1.1% ripple is realized with two 50-μF film capacitors. For the same ripple performance, a 900-μF capacitor is required in conventional converters without an active filter. Moreover, it is found out that the active-filter integration concept might even improve the efficiency performance of the end converters as compared with the original AC/DC converter without integration

Suppression of Second-Order Harmonic Current for Droop-Controlled Distributed Energy Resource Converters in DC Microgrids

Droop-controlled distributed energy resource converters in dc microgrids usually show low output impedances. When coupled with ac systems, second-order harmonics typically appear on the dc-bus voltage, causing significant harmonic currents at the converters resource side. This paper shows how to reduce such undesired currents by means of notch filters and resonant regulators included in the converters control loops. The main characteristics of these techniques in terms of harmonic attenuation and stability are systematically investigated. In particular, it is shown that the voltage control-loop bandwidth is limited to be below twice the line frequency to avoid instability. Then, a modified notch filter and a modified resonant regulator are proposed, allowing to remove the constraint on the voltage loop bandwidth. The resulting methods (i.e., the notch filter, the resonant regulator, and their corresponding modified versions) are evaluated in terms of output impedance and stability. Experimental results from a dc microgrid prototype composed of three dc-dc converters and one dc-ac converter, all with a rated power of 5kW, are reported

Power conditioning system topology for grid integration of wind and fuell cell energy

This paper shows the topology of the hybrid grid-connected power system and the performances of the front-end three-phase power inverter. The renewable sources of the hybrid power system consist of a solid oxide fuel cell and a wind-turbine. This type of combination is the most efficient one. The proposed topology benefits of the one common DC-AC inverter which injects the generated power into the grid. The architecture diminishes the cost of the power conditioning system. Moreover, due to the power balance control of the entire power conditioning system the bulk dc link electrolytic capacitor is replaced with a small plastic film one. The final power conditioning system has the following advantages: independent control of the reactive power, minimize harmonic current distortion offering a nearly unity power factor operation (0,998) operation capability, dc link voltage regulation (up to 5% ripple in the dc-link voltage in any operated conditions), fast disturbance compensation capability, high reliability, and low cost. The experimental test has been performed and the performances of the grid power inverter are shown

Modeling and analysis of power processing systems: Feasibility investigation and formulation of a methodology

A review is given of future power processing systems planned for the next 20 years, and the state-of-the-art of power processing design modeling and analysis techniques used to optimize power processing systems. A methodology of modeling and analysis of power processing equipment and systems has been formulated to fulfill future tradeoff studies and optimization requirements. Computer techniques were applied to simulate power processor performance and to optimize the design of power processing equipment. A program plan to systematically develop and apply the tools for power processing systems modeling and analysis is presented so that meaningful results can be obtained each year to aid the power processing system engineer and power processing equipment circuit designers in their conceptual and detail design and analysis tasks