ADVANCED CONVERTERS FOR FUEL CELL POWER SYSTEMS

ADVANCED CONVERTERS FOR FUEL CELL POWER SYSTEMS

Adriana FLORESCU, Dan Alexandru STOICHESCU, Alina OPREA

University POLITEHNICA of Bucharest

Faculty of Electronics, Telecommunications and Information Technology

Department of Applied Electronics and Information Engineering

Abstract - DC-DC converters for fuel cell power system are usualy bi-directional and have complicated circuits, needing many devices and switching configurations. This article presents the most advanced and new converter suitable for many applications (including FCHEVs applications), including both the DC/DC converter and DC/AC inverter. It proves that high efficiences, low costs and future developments in fuel cell power systems can and will be achieved with simple, ingenious, widespread converters.

Keywords - Fuel cell (FC), PWM inverter, boosted PWM inverter, Z-source inverter, hibrid electrical vehicle (HEV).

1. INTRODUCTION

Fig. 1. A comparison of electrical system efficiencies between a fuel cell system and other

conventional energy conversion systems

Fig.3. Basic fuel cell power systems

Fig.4. Block diagram of fuel cell power system for stationary applications

Fig.4 represents the block diagram of a fuel cell power system for stationary applications, such as household applications. The main disadvantage of fuel cells is that they produce a low DC output

voltage with a wide range variation (fig.2) so an indirect DC/DC converter is connected in order to increase it. Multiple-stage power conversions including isolation are needed. A three phase inverter is placed at DC-DC converter's output in order to supply different types of loads. Fig. 5 represents the block diagram of a fuel cell power system for mobile applications such as hybrid vehicular applications. Besides the DC/DC converter and the traction inverter, the secondary battery guarantees the load leveling, assuring braking energy recovery and good performances in the transient operations. It also supplies with energy the air compressor, the hydrogen circulation pump and the cooling pump for inverter/motor etc. Fig.6 represents the block diagram of a fuel cell power system for portable applications such as laptops, cell phones or PDAs. It is similar to the block diagram in fig.4 excepting the inverter that is missing, taking account of the DC load. Isolation may be or may be not needed.

Fig.7. Fuel cell power system with traditional PWM inverter supplied by a bidirectional DC/DC converter

Fig.8. Fuel cell power system with DC/DC boosted PWM inverter supplied by a bidirectional DC/DC converter: a) block diagram of DC/DC Boost converter; b) detail of DC/DC Boost converter

Fig.9. Fuel cell power system with Z-source inverter supplied by a bidirectional DC/DC converter

Fig. 10. Calculated efficiency of inverters

Fig. 11. Inverter efficiency calculated using Mitsubishi average loss simulation software

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