Introduction

Kinetic energy from flywheels has been in use for a variety of stabilizers and UPS units in the past.

Stabilizers with a short ride-through period consisting of a motor flywheel and generator may provide an isolated power source with a short ride through, the ride through being in the order of 1 s. The system consists of three shafts motor, flywheel, and generator. It is not practicable economically to increase the ride-through time since the loss of the incoming supply and dependence on the flywheel inertia will result in a slowing down of the rotational mass and, thus, in the output frequency being out of tolerance.

Circuit Developments

A further use of the flywheel occurs with the original design of rotary UPS systems as illustrated in Fig. 8.1. Under normal operation the mains supply drives the dc motor via the rectifier. On loss of mains the system derives power from the battery. However, at the point of loss of mains the dc machine sees an immediate drop in dc voltage corresponding to approximately 15 percent. (Note this voltage drop will vary slightly depending on the type of battery employed and the autonomy period.)

Figure 8.1

The dc machine regulator is comparatively slow in response. Thus, the flywheel enables the system to tolerate the dynamic change, resulting in the ac machine output remaining in tolerance.

Over time developments have enabled us to reconsider the use of kinetic energy. Recent developments in circuitry and components have now made it feasible to consider...