FUEL CELL AND ELECTRICAL POWER ENGINEERING

Power Transfer Analysis in a Utility-Interconnected Fuel Cell Distributed Generator

Chapter 1: Introduction

Background of the study

Distributed generation (DG) generally refers to smallscale (typically 1 kW-50 MW) electric power generators that produce electricity at a site close to the customers tied to an electric distribution system. The power generator can be a fuel cell, a microturbine, or any kind of renewable energy source (wind, photovoltaic). Many studies indicate that DG will play a significant role in future power system structure. A study by the Electric Power Research Institute (EPRI) indicates that in 2010, 25% of new generation will be distributed. Among DG systems, much attention IS focused on environmentally- friendly fuel cells, microturbines, photovoltaic and wind generators. (Agbossou, 2011: 633 - 640)

Problem Statement

A stand-alone Renewable Energy System (RES) based on hydrogen production was tested successfully at the Hydrogen Research Institute (HRI). The system consists of a 10 kW wind turbine generator (WTG) and a 1 kW solar photovoltaic (PV) array as primary energy sources. The system is designed such that the excess energy with respect to load demand is stored as electrolytic hydrogen produced via an electrolyzer. (El-Sharkh, et al, 2010: 2022-2228)The stored hydrogen can then be used by a fuel cell system to produce electricity. This grid-connected fuel cell DG can be used to reduce peak power demand in distribution networks. By providing a portion of the energy on site, DG systems can reduce a branch current, which in turn leads to reduced losses and increased voltage throughout the feeder grid. Such a system can also be used to provide ancillary services in a deregulated electricity market.

To achieve this goal, the power transfer between fuel cell DG and distribution network must be analyzed and well understood. The difference in line characteristics can provided some power transfer problem: while for transmission lines, the reactance Xline is usually large compared to the resistance Rline that can be neglected. For distribution networks on the other hand, the reactance and resistance are of comparable magnitude. This fact must be taken into account when analyzing power transfer in DG systems interconnected to distribution networks.

Purpose of the paper

This proposed paper will present an analysis of the active and reactive power transfers when a fuel cell DG is connected to a utility distribution network. The DG power transfer capability is estimated according to distribution lines characteristics, inverter's topology, and regulation via output voltage amplitude, phase angle and current. Matlab/Simulink simulation models are provided to support the theoretical analyses. The relationship between output voltage phase angle and hydrogen flow is presented.

Significance of the study

Fuel cells are electrochemical devices that convert the chemical energy directly into electrical energy (Fig. 1). In a typical fuel cell, a gaseous fuel (e.g. hydrogen) is fed continuously to the anode compartment and an oxidant(e.g. oxygen from the air) is fed continuously to the cathode compartment; the electrochemical reactions take place at the electrodes to produce an electric current. Although having components and characteristics similar to those of a typical battery, ...