Fuel Cell Plant Concept with Dynamic Characteristics of a Rotating Generator

Fuel cell plants will be powering future electrical systems. Fuel cells normally generate direct current (DC) which must be converted into alternating current (AC) for transmission efficiency and for broader use by numerous loads of different characteristics. An AC load consists of real power and reactive power. The real power is generated by fuel cells. However, the reactive power must be created by other means. It is possible to create reactive power with DC/AC inverters where the inverter feeds AC to inductors and capacitors. Usually inverters have very little overload capability (1-2X for about a second). On the other hand, if a synchronous condenser is installed on the AC bus, then the AC system needs to draw only the real power through the inverter. The reactive power is supplied by the synchronous condenser. The synchronous condenser could be designed to provide several times its nominal rating during transient or short period of time. Need for such overload is created when motors are started or when lines containing transformers are energized. A synchronous condenser could be the source of leading or lagging reactive power to meet needs of AC loads. A synchronous condenser is a rotating synchronous machine that has inertia and could store energy in its rotating mass. This inertia could be used to store or withdraw energy while fuel cells are reacting to rapid load changes. A fuel cell system together with synchronous condensers could be made to behave as an AC rotating generator with inertia and to supply real and reactive power. This paper discusses an arrangement of such a system