CONSTRUCTION OF A 2.5KW UNINTERRUPTIBLE POWER SUPPLY (UPS) SYSTEM

1.0 Introduction

It is pertinent to say that “Power” be it mechanical, solar and other sources more especially electrical is the bedrock of human existence on earth. Man through the generation of power can appreciate the fullness of the environment.

It is quite inconveniencing that constant power interruption and blackout is a very big problem in our country “Nigeria”. The constant power outages we are experiencing maybe as a result of poor power distribution, maintenance culture, personnel and low quality equipment.

To this effect, many premises dealing with highly sensitive equipment and the likes requires a reliable standby or backup power supply to guide against the epileptic power supply; hence, “The Uninterruptible Power Supply (UPS) system”

1.1 Definition

The Uninterruptible power supply (UPS) system is an electrical/electronic device that continues to supply electricity to the load for a certain period of time during a utility failure or when the line voltage varies outside the normal limits. Its typical application is in computer as a backup power. Lager modules can be used to power even an entire home.

Uninterruptible power supply (UPS) systems have been on the market for approximately 20years. These devices were originally developed to provide protection against the loss of data in a computer systems and computer driven machines because of sudden power failure and to effect an orderly shutdown in the event of power interruptions also enable users to save data that otherwise would be lost.

1.2 Advancement

Advancement in technology have improved and expanded the functions of UPS systems. Smaller more powerful devices are being sold to meet the requirements of changing markets. The increase in the number of data centers, telecommunication functions and the rise in networking have changed the demands of power management.

To reduce the risk of loosing data in the computer systems, break in telecommunication networks and burning of sophisticated electronic equipments to power failure of disturbances in power generation, many companies protects her equipments with Uninterruptible Power Supply(UPS) systems.

1.3 Mains Supply

A UPS takes its power from two or more sources simultaneously. It is usually powered directly from AC mains, while at the same time charging a storage battery. Should there be a dropout or failure of the mains, the battery instantly takes over so that the load never experiences an interruption.

Such a scheme can supply power as long as the battery charge suffices; for example, in a computer installation, giving the operator sufficient time to effect an orderly shutdown without loss of data or process. Other scheme of UPS may use an internal combustion engine or turbine to continuously supply power to a system in parallel with power coming from AC mains.

The engine-driven generators would normally be idling, but could come to full power in a matter of few seconds in order to keep vital equipments running without interruption. Such a scheme might found in hospitals or telephone central offices.

Perhaps, power from a wall socket is neither clean nor uninterruptible. Many abnormalities such as blackouts, brownouts or sags, spike, surges and noise from large machines can occur. Under the best conditions, power interruptions can be quite inconveniencing.

At their worst, they can cause loss of data in computer systems, damage to sophisticated electronic equipment and even loss of human life. Because of there inconveniences, it is necessary to have an Uninterruptible Power Supply (UPS) system which acts as a buffer and provides clean, reliable power to those vulnerable electronic equipment.

1.4 Generic Standard

The generic standard for UPS systems is IEC 62040 – 3, which defines limits on the amplitude and duration of deviation of the output voltage acceptable for switching power supply system (SMPS) load.

1.5 Principle Of Operation

During normal supply of the utility power, the output load is fed directly from the AC main's source while supplying the charger that would charge the battery simultaneously.

When the utility power source fail, the battery become a source of power to the inverter which eventually converts the 12V DC-to-220V AC or so in order to carry the connected load.

From the block diagram above, the AC mains is connected directly to the Automatic Bypass switch (electromechanical switch or relay) which closes in one way and opens in the other to bypass the inverter and supply the load directly or opens in one way and closes in the other to bypass the AC mains to supply the load from the inverter.

The battery charger is charging the battery simultaneously while the inverter at this point is redundant.

Should there be a mains failure, the transfer switch closes then the battery energizes the inverter which in turn inverts or converts the 12V DC-to-220V AC or so that will now supply the connected load.

From the Block diagram of figure3.6 in chapter three, the mains supply is connected directly to the Bypass switch (electromechanical switch or relay) then to the load.

From the main also comes the connection of the battery charger section which includes:

• A step-down transformer
• A bridge rectifier and
• A filter circuit.

– From the mains, a step-down transformer that steps 220V AC to 15V AC is connected (a portion of the charge voltage which would be charging must be a bit higher than that which is to be charged).

– From the step-down transformer, a bridge rectifier is connected which will in turn do that actual conversion from 15V AC to 12V DC.

– A filter circuit which is made up of inductors and capacitors is connected from the rectification circuit (bridge rectifier). The filter circuit removes or filter out ripples (i.e. it removes some portion of the AC that the bridge rectifier could not remove during or after rectification) in order to have clean dc output to the battery.

– From the charging section which ends at the filter circuit comes the connection of the battery perhaps 12V DC to be charged.

– A transfer switch which transfers power from the battery to the inverter section is connected

– From the transfer switch, the inverter unit which is made up of :

• The Oscillator circuit
• The Transistor circuit and
• The Step-up Transformer is connected.

– The oscillator (Astable Multivibrator) which generates pulses (square wave output) to ensure that the transistors switches exactly when they are meant to switch is connected followed by the high speed switch (FET) transistor.

– The transistor (FET) here serves as power switches and functions as current amplifier in addition to rectification when a battery is connected.

– From the transistor (high speed switch FET), a step-up transformer is connected which converts the 12V DC t0 220V AC or so.

– All the sub-unit as mentioned here are connected to the automatic bypass switch (electromechanical switch or relay) that filly link the output load.

1.6 Classification

Research on this project has classified UPS systems into three main classes; namely:

1. Standby or offline UPS
2. On-line UPS and
3. Line Interactive UPS

It also examines the status of rotary flywheel UPS technology, typically used to protect very large installations with high capacity requirements.

A standby or flywheel UPS technology typically used to protect very large installations with high capacity requirements.

A standby or offline UPS are connected via an electrical relay. When the voltage goes above or below a certain level, the relay opens and the voltage is recreated using the energy stored in the battery.

An On-line UPS are connected in series and constantly regulates voltage. Online UPS always delivers all or at least a portion of output power through its inverter even under normal line condition and therefore provides true uninterruptible power. While

The line interactive UPS are a hybrid technology, connected in parallel. This UPS under normal conditions smooth out and to some degree regulate the input AC voltages by a filter and a tap changing transformer.

In addition, the basic concept of a UPS system is to store energy during normal operation through battery charging system otherwise known as “charger” and releases energy through DC to AC conversion known as “Inverter” during a power failure. UPS is typically used to protect computers, data centers, telecommunication equipments and sophisticated electronic equipment where an unexpected power disruption could cause injuries, serious business disruption and/ or data loss.

1.7 Roles Of Ups

In all, the primary role of a UPS is to provide short-time power when the input power source fails.

A UPS does three main things for you. They are as follows:

1. It filters the power your machine sees, smoothing out spikes and voltage fluctuations that can stress or even damage your electronics.
2. It provides a certain amount of dwell time in the event your power goes out entirely. This can often get you through brownouts and short blackouts.
3. When the UPS is about to run out of power, it can arrange a graceful shutdown of your computer system so that no unpleasant things happen to your disk file systems. Because ensuring a clean shutdown is still a valuable contribution to any system administrator's peace of mind.

This material contains electrical diagrams, circuits, illustrations and more (Very detailed)