Uninterruptible Power Supply (UPS) 250 Caterpillar

General Information

Usage:

Introduction

The system is a three-phase 480 Volt 60 Hz uninterruptible power supply (UPS). The system uses a flywheel to store energy mechanically in the form of a rotating mass. During normal operation, the flywheel will be rotating at a constant speed. The typical speed of the flywheel is 7700 RPM. The power from a utility will be delivered by the system to an external load. When power from the utility is interrupted, the system will convert the mechanical energy that is stored in the flywheel to electrical energy. This energy will be used by the external load. When the power from the utility is available again, the system will transfer the load back to the power from the utility.

Block Diagram of the System

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Illustration 1	g00654987
Functional Block Diagram

Illustration 1 shows a simplified block diagram of the system. The nodes that are shown in illustration 1 are in the following list: Input, Inverter and Output

The nodes determine the state of the system. The input node and the output node are externally available. These nodes are used in order to attach the system to a power source and to the load. The inverter node is used internally by the system.

The DC Bus is also identified in illustration 1. The DC Bus is used as a power source for the field coil currents. The mode of the system determines if the bus is used as a power source for the flywheel or as a power source for the utility inverters.

The main functional blocks are shown in illustration 1. A description of each function is in the following list:

Input Contactor (K1) - A mechanical contactor that is used to control the flow of electricity into the system

Output Contactor (K2) - A mechanical contactor that is used to control the flow of electricity from the system

Bypass Contactor (K3) - A mechanical contactor that is used to bypass the system

Static Switch - The switch is a semiconductor device (thyristors). The Static Switch is used to isolate the system from the utility grid when an outage occurs.

Utility Inverter - The Utility Inverter is a semiconductor device that is used to rectify the AC voltage on the inverter node into a DC voltage. When the power from the utility is lost, the utility inverter will invert the voltage from the DC Bus to 480 volt, 60 Hz AC voltage for the load.

Flywheel Inverter - The Flywheel Inverter is a semiconductor device that is used to invert the DC Bus voltage into AC signals. When the power from the utility is not available, the flywheel inverter will rectify AC signals from the flywheel into the DC Bus voltage.

Field Coil Driver - The Field Coil Driver is a semiconductor device that is used to drive current through the field coils. The field coils are used to generate magnetic forces that act upon the flywheel. These forces are controlled in order to provide a lifting force on the flywheel. The force prolongs the life of the bearing.