High Frequency Low Cost DC-AC Inverter Design with Fuel Cell
Source for Home Applications
ABSTRACT:
This paper presents a new design of highfrequency Dc/Ac inverter for home applications using fuel cellsor photovoltaic array sources. A battery bank parallel to the DClink is provided to take care of the slow dynamic response of thesource. The design is based on a push-pull dc/dc converterfollowed by a full-bridge PWM inverter topology. The nominalpower rating is 10kW. Actual design parameters, procedure andexperimental results of a 1.5kW prototype are provided. Theobjective of this paper is to explore the possibility of makingrenewable sources of energy utility interactive by means of lowcost power electronic interface.Keywords: FEC2001, fuel cell, inverter, filter, DSP, push pull,harmonics, PWM.
I. INTRODUCTION
Generation of electricity from non-conventional energysources is fast emerging as an important area of research in thenew millennium. Conservation of energy or the effectiveutilization of energy is the most critical issue in the field ofpower management today. The most commonly used alternatesources of energy are fuel cells, micro turbines andphotovoltaic cells [1]. In this paper, a 10kW design for a highdensitypower inverter is presented for conversion of energyfrom DC fuel cells to AC power to be used mainly fordomestic utility applications. The need for such products hasrisen due the thrust being provided by the deregulation ofpower industry, environmental concerns and demand forclean, reliable and quality power. Besides the domestic sectorother sectors stand to benefit from this proposed research likethe aerospace, automotive and industry. The power electronicinterface between the non-conventional energy source and theapplication load holds the center stage for the success of thisresearch. As per Future Energy Challenge 2001 competitionguidelines [2], a low power inverter has been redesigned,tested and prototyped, to deliver a 1.5kW load. Experimentalresults are also provided
.II. DESIGN RATIONALE
The configuration is achieved using a high frequency dcdcpush-pull converter at the input side followed by a fullbridgePWM inverter and a low-pass filter at the output side.Due to the simplified power stage and the application ofDSP-based sinusoidal pulse width modulation technique,output voltage Total Harmonic Distortion (THD) is reducedand a relatively smaller overall inverter size is achieved. Theproposed practical circuit operates from a 48V DC fuel cellinput and outputs a regulated 120V AC, 60Hz sinusoidalvoltage having 3-wire configuration [5]. The output isconfigured like a conventional household ac supply: a split railwith center ground. Each rail is 120 V rms to ground, whilethe rail-to-rail potential is 240 VAC. The reason is to allow theunit to be used directly in domestic applications with nospecial circuit configurations. The major focus area of thedesign was proper filter circuit so that the output of theinverter is absolutely clean and suitable for domesticappliances. The inverter design will be rugged andmaintenance free. Hence, customized packaging techniquesare used to meet the domestic ambience. The block diagramand circuit schematic for the proposed inverterimplementation is shown in Figs. 1(a) and (b) respectively.To reduce the size of the system transformer, the first stagewill consist of a high frequency push-pull dc-dc converter.The second stage consists of two half-bridge invertersarranged in a full-bridge configuration. The control techniqueused in the second stage is sinusoidal PWM. The third stagerepresents the low pass filter with passive components, due tothe relatively high attenuation of the low harmoniccomponents for the output voltage waveform. The input stageconsists of power devices Q1 and Q2, transformer T1, inductorL1, L2 and dc bus capacitors C1 and C2. The dc push-pullconverter boosts the bus voltage to 240VDC for the inverter toproduce 110VAC. The output inverter stage consists of powerdevices S1 - S4, output inductors L3, L4 and capacitors C3 andC4. Using the well-known sinusoidal PWM technique, thiscircuit generates a sine wave output voltage


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