A small scale Wind Energy Conversion System (WECS) has tremendous diversity of use and operating conditions, and consequently is evolving rapidly along with the large scale WECS for generation of electricity in either on grid or off grid applications. In recent years, the grid connected Small Wind Turbine (SWT) industry is primarily dominated by the Permanent Magnet Generators (PMGs) based topology. The Power Conditioning Systems (PCS) for grid connection of the PMG based topology requires a rectifier, boost converter and a grid-tie inverter. However, a small wind turbine may be based on Wound Rotor Induction Generators (WRIGs). The WRIG based topology can employ a rectifier, a chopper and an external resistor in the rotor side while the stator is directly connected to the grid. These two topologies have diverse losses that fluctuate with the wind speed. This paper presents a comparative study of a PMG and WRIG based topologies for SWT systems. The study employs numerical simulation to investigate the conversion losses for both topologies. It is demonstrated that a WRIG based topology offers less losses than a PMG based topology. The comparison is further enhanced by investigating the annual energy capture, annual energy loss and efficiency for the wind speed data and Weibull distribution of three different locations of Newfoundland, Canada. The study shows that a WRIG based topology is an optimum alternative in terms of performance characteristics within a slip variation of 15%.

This work presents a power electronics reliability comparison of the power conditioning system for both the Permanent Magnet Generator (PMG) and Wound Rotor Induction Generator (WRIG)-based small Wind Energy Conversion Systems (WECS). The power conditioning system for grid connection of the PMG-based system requires a rectifier, boost converter and a grid-tie inverter, while the WRIG-based system employs a rectifier, a switch and an external resistor in the rotor side with the stator directly connected to the grid. Reliability of the power conditioning system is analyzed for the worst case scenario of maximum conversion losses at a predetermined wind speed. The analysis reveals that the Mean Time Between Failures (MTBF) of the power conditioning system of a WRIG-based small wind turbine is much higher than the MTBF of the power conditioning system of a PMG-based small wind turbine. The investigation is extended to identify the least reliable component within the power conditioning system for both systems. It is shown that the inverter has the dominant effect on the system reliability for the PMG-based system, while the rectifier is the least reliable for the WRIG-based system. This research indicates that the WRIG-based small wind turbine with a simple power conditioning system is a much better option for small wind energy conversion system.

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Abstract-This paper presents the dynamics of a phosphoric acid fuel cell (PAFC) and its associated power electronics. The modeling of the power conditioning system for phosphoric acid fuel cell is discussed here. This model is based on empirical equations. The simulation is done using Matlab/Simulink and its Power System Blockset (PSB). This model mathematically calculates cell output voltages and their consequent losses. It also calculates the ac output from the system by simulating an inverter dc input from the fuel stacks. The V-I curves and dynamics can be observed. The effects of variation in outputs for different inputs can also be observed. This model is easy to understand and it requires less computational time.Index Terms-Distributed generation, dynamic modeling and simulation, phosphoric acid fuel cell, power conditioning system. I. INTRODUCTIONRecently alternative or renewable energy is becoming more popular because of increasing energy consumption. People are also becoming aware of environment impact and declining fossil fuels. Common alternate energy sources are fuel cells, wind turbines, micro-turbines, photovoltaic etc. These are also referred as distributed generation (DG). Fuel cells have drawn more attraction from different distributed generation since it has the potential capability of providing both heat and power [1].A fuel cell (FC) is an electrochemical device that converts the chemical energy of the fuel directly into electrical energy. Fuel cells have a low environmental impact and operate silently in practical situations with high efficiency and long lifetime. So they can represent a very good option as a DG [2].A power conditioning stage is essential to produce commercial ac power since the output of a fuel cell is dc electricity [3]. So fuel cell plants can produce this ac power. Generally there are three major subsystems in a fuel cell plant which are a reactant supply subsystem to convert natural gas to a hydrogen-rich gaseous fuel, a power section subsystem including a thermal management assembly to generate dc power and a power conditioning subsystem to convert the dc power generated in the power section subsystem to ac power [4]. Fig. 1 shows the process.According to the type of electrolyte used, the most Among them, PAFC has one of the most advanced technologies available commercially. It is possible to improve the performance of a fuel cell by changing the operating variables (e.g. pressure, temperature, gas composition, current density etc.). It is important to select an operating point (cell voltage and related current density) of a fuel cell till the system requirements are satisfied [6].This paper represents a model of the last two subsystems of Fig. 1. A dynamic modeling of phosphoric acid fuel cell (PAFC) system including dc to ac power conversion is proposed here. The model is based on empirical equations. This model includes fuel stacks to produce dc power and a dc to ac inverter to produce ac power. The model is validated by Sim Power Systems (SPS) block set of Matlab...