Design And Construction Of A 500W Uninterruptible Power Supply (UPS)

1.0 INTRODUCTION

In this modern society, electricity has great control over the most daily activities for instance in domestic and industrial utilization of electric power for operations. Electricity can be generated from public supply to consumers in different ways including the use of water, wind or steam energy to drive the turbine as well as more recently the use of gas. Generators, solar energy and nuclear energy are also source of electricity.

In Nigeria and some other parts of the world today, the electricity power supply to consumers (at homes and industries) is not maintained at a stipulated voltage say 240 volts.  But the electronic gadgets and some other power operated machines, that we use in our homes, offices and industries requires power with constant and interruptible  for their efficiency, and to avoid damage by the voltage. In Nigeria, there is inconsistence supply of electricity by the power supplying company to the consumers.  The use of additional electric power source such as electric power generators and most recently the use of semiconductor power devices such as the Bipolar Transistor, Thyristors and particularly MOSFET to generate electric power in conjunction with a DC battery in few kilowatts. An Inverter offers a better additional power source to Generators as well as UPS considering its long duration, cost effectiveness and maintainability.

Uninterruptible Voltage supply is an electronic control circuit or device that is capable of providing a constant output voltage even when there is variation in load or input voltage as low as 160 volt can be boost up to 240 volt by stabilizer at output stage without any voltage fluctuation with a backup battery which provide additional power to the device during mains power outage.

It is designed to meet up with the AC voltage safety, stability and accuracy demand in industries and in homes. Uninterruptible power supply is useful in devices such as computer Power supplies, alternators and central power station generator plants, voltage regulators control the output of the plant. In an electric power distribution system, voltage regulators may be installed at a substation or along distribution lines so that all customers receive steady voltage independent of how much power is drawn from the line.

An uninterruptible power supply is designed to automatically maintain a constant AC voltage level. An AC Voltage supply may be a simple “feed-forward” design or may include negative feedback control loops. It makes use an electromechanical mechanism, and other electronic components. Depending on the design, it may be used to regulate one or more AC voltages.

This project is designed to stabilize an AC input voltage of 160-250V to give an AC output voltage of 240V at 50Hz automatically. The automatic feature can be achieved by the electronics devices used such voltage comparator IC, electro-magnetic device (relay), auto- transformer and other electronics devices

1.1 PURPOSE OF THIS PROJECT

The purpose of this project is to design and construct an uninterruptible power supply. This device stabilizes an AC input voltage of 160-260V to give an AC output voltage of 240V with a backup power source which provide additional power to the device during mains power outage automatically at 50Hz using a 12v battery. The automatic feature can be achieved by the electronics devices used such voltage comparator IC, electro-magnetic device (relay), auto- transformer and other electronics devices.

1.2 OBJECTIVE OF THE PROJECT

The objective of this work is to construct a device whose function is to maintain constant and uninterruptible power to electrical appliances, and power line conditioning to the equipment load of 500w under a wide variety of conditions, even when the utility input voltage, frequency or system load vary widely and also indicate when the battery of the system gets low. An uninterruptible power stabilizer consists of an all copper, multiple tapped, contain independently controlled inverse parallel electronic switches for each of the 7 taps per phase to provide tight voltage regulation, rechargeable battery and an inverter. The phase current shall be monitored for zero current recognition to initiate any required tap change. Linear devices shall be used for line synchronization to prevent phase shift errors normally associated with zero current crossing acquisition.

1.3 SIGNIFICANCE OF THE PROJECT

The uninterruptible power supply is a voltage regulator planned to mechanically sustain a constant voltage level and supply an uninterruptible power to devices. It can also use electromechanical components. It can be used majorly to regulate one or more DC or AC depending on the design. Therefore, the functions of this equipment are very wide and can be used majorly for various purposes. Electronic voltage regulators can be used majorly for various purposes. It has various functions like it can be used mainly for stabilizing the DC voltages that can be used by the processor and its main parts. In central power station generator plants and automobile alternators, voltage regulators control the output of the plant. In this distribution system, it may be installed at along distribution lines so that all clients recognize steady voltage self-regulating of how much power is drawn from the line. There are many functions of operating the AC depending upon the design. It is very good option to maintain the constant voltage level. Automatic voltage regulator is a superb invention of science, which is an electric device designed to authorize a constant voltage in a settable level. It is very helpful to maintain the preferred voltage for the generators within particular limits. The main working of it depends upon the laws of electromechanical physics. It consists of numerous vigorous and unreceptive electrical parts like thermostats, adopters and diodes. Apart from this, there are many reliable Automotive Suppliers in India that produce many kinds of equipments like generator, regulator and other major parts. They are well known for various kinds of functions and various specifications. They not only produce higher quality products, but also they will provide some additional benefits with the parts of these equipments. Auto Voltage Regulator Generator is the most important part for great amplifier to work. Its types are many, but they are highly in functionality and better performance. They are well equipped with self functioning controls and starts up functions which make them very easy and useful to handle easily and completely. They have different sizes, shapes and colors. There are also automatic regulators which are so small that they can be easily places on a small printed circuit board. They are very easy and portable to handle. They may cover a higher volume of small house sometimes. Therefore, there is a wide variety in the uninterruptible power supply sand each has its own specifications.

1.4 THE SCOPE OF THE PROJECT

The design and construction of an uninterruptible power supply is the project we are construction.  I am working on this machine because we have some idea on how this machine can be constructed and also on how it works.  We are also doing this because we want to learn more about it.

As we have mentioned earlier, this device is a protective device that protects our electrical and electronic appliances out of current and voltage fluctuation and unexpected power interruption. This is how it works.  When this system is plugged into the socket or supply, it will receive a minimum voltage of 120vac and filter the current and voltage thereby brings out suitable voltage output to be used by the devices in it, then when there an unexpected power outage from the utility mains the system will automatically switch over to the inverter source thereby providing additional power to the appliances in use.

So, I am building or constructing this device to reduce risk and damages the fluctuation of current / voltage caused by power fluctuations and unexpected power interruption and the device is rated 500W.

1.6 LIMITATION OF THE PROJECT

The system design shall be capable of operating at an input frequency range of -15% to +10% of nominal, without clearing protective devices or causing component failure within the uninterruptible power supply. During mains power outage the system shall be working with inverter source section, but when generator or utility power is restored, the uninterruptible power supply shall automatically restart. Upon turn on or restart, the output of the uninterruptible power supply shall not exceed the specified output regulation limits.

Response Time: The uninterruptible power supply shall respond to any line voltage variation in 1/2 cycle while operating linear or non-linear loads, with a load power factor of 0.60 of unity. Peak detection of the voltage sine wave shall not be permitted to avoid inaccurate tap switching due to input voltage distortion.

Operating Frequency: The uninterruptible power stabilizer shall be capable of operating at +10% to -15% of the nominal frequency, 50Hz.

Rating: this device is rated at 500VA.

Access Requirements: The uninterruptible power supply shall have removable panels on the front, rear and sides as required for ease of maintenance and/or repair.

Metering: An input meter is provided to reading line voltages

Ventilation: The uninterruptible power supply isolation transformer shall be designed for convection cooling. A fan cooling is required for the solid state electronic switching devices.

1.7 BENEFIT OF THE PROJECT

An uninterruptible power supply  provides an alternate source energy that can be provided power when the primary power source is temporarily disabled the switchover time must be small enough to not cause a disruption in the operation of the loads it protects against multitier of power disturbances and power outage offers protection against.

• Equipment not operating properly.
• Computer and equipment damage.
• Data loss
• Time and expense to recover back to where you were, if even possible.

1.8 APPLICATION OF THE PROJECT

There are lots of applications or uses of UPS in our daily life.

1. UPS For Computer: The main use of UPS is give power backup to the computers. It protects the computer’s from being mislaid if the power goes out.
2. Home appliances: A UPS is used for home appliances such as TV & LCDs to provide regulated voltage. It defend the sensitive electronics from variations in the voltage supplied to them.
3. To giving backup supply to cordless phones and Fish Aquarium Pump, UPS are the best power supply.
4. Outdoor use: When a UPS system is placed outdoors, it should have some specific features that guarantee that it can tolerate weather with a ‘minimal to none’ effect on performance. Factors such as temperature, humidity, rain, and snow among others should be considered by the manufacturer when designing an outdoor UPS Operating temperature ranges for outdoor UPS systems could be around −40 °C to +55 °C.

Outdoor UPS systems can be pole, ground (pedestal), or host mounted. Outdoor environment could mean extreme cold, in which case the outdoor UPS system should include a battery heater mat, or extreme heat, in which case the outdoor UPS system should include a fan system or an air conditioning system.

5. Multiple redundancy: Many computer servers offer the option of redundant power supplies, so that in the event of one power supply failing, one or more other power supplies are able to power the load. This is a critical point – each power supply must be able to power the entire server by itself. Redundancy is further enhanced by plugging each power supply into a different circuit (i.e. to a different circuit breaker). Redundant protection can be extended further yet by connecting each power supply to its own UPS. This provides double protection from both a power supply failure and a UPS failure, so that continued operation is assured. This configuration is also referred to as 2N redundancy. If the budget does not allow for two identical UPS units then it is common practice to plug one power supply into mains power and the other into the UPS.
6. Internal systems: UPS systems can be designed to be placed inside a computer chassis. There are two types of internal UPS. The first type is a miniaturized regular UPS that is made small enough to fit into a 5.25-inch CD-ROM slot bay of a regular computer chassis. The other type are re-engineered switching power supplies that utilize dual power sources of AC and/or DC as power inputs and have an AC/DC built-hiswitching management control units.
7. DEFINITION

Inverter Unit:This unit converts a DC voltage into an AC voltage with the help of a oscillator.

Automatic Control Unit: This provides all the required control needed to meet up the objectives of the whole system.

Battery Unit:This is a secondary cell unit capable of storing enough DC voltage of which is later converted to AC voltage.

 Active redundancy: Parallel UPS configuration in which several UPS units with equal outputs are parallel connected and share the load. In the event one UPS unit fails, the other units pick up its share without any interruption in the supply of power to the load.

Alternate power source: Backup source used in the event of a mains failure. The connection time and the duration of the source depend on the type of source used.

Back-up time: Time during which the UPS can supply the rated load with nominal-quality power while utility power is down. This time depends on the battery and the efficiency of the UPS. Typical backup ranges from five minutes to several hours.

Battery circuit breaker: DC circuit breaker that protects the battery of a UPS.

Charger: Device associated with the rectifier and used to supply the battery with the electrical power (DC current) required to recharge and/or float charge the battery.

Circuit breaker (battery): DC circuit breaker that protects the battery of a UPS.

Inverter: UPS subassembly that recomposes a sine-wave output (regulated and without breaks) using the DC current supplied by the rectifier-charger or the battery. The primary elements of the inverter are the DC/AC converter, a regulation system and an output filter.

Inverter (off-line or stand-by): UPS configuration in which the inverter is parallel-mounted to the load supply line and backs up the utility. This configuration offers a substantial cost reduction but is applicable only to low outputs, under 3 kVA, because it results in an interruption lasting up to 10 ms during transfer and does not filter inrush currents.

Inverter (on-line): UPS configuration in which the inverter is in series mounted between the utility and the load. All power drawn by the load passes via the inverter. This is the only configuration used for high outputs.

On-line inverter: UPS configuration in which the inverter is in series mounted between the utility and the load. All power drawn by the load passes via the inverter. This is the only configuration used for high outputs.

Output (rated): Apparent power Pn that the UPS can deliver under given load conditions (power factor = 0.8).

Power factor: between the active power(true power) P supplied to a load and the apparent power S supplied to said load by an AC power supply.

Power source (alternate): Backup source used in the event of a mains failure. The connection time and the duration of the source depend on the type of source used.

PWM (Pulse Width Modulation): Inverter high-frequency chopping technique using a means of regulation enabling rapid modification of pulse widths over a single period, thus making it possible to maintain the inverter output within tolerances even for non-linear loads.

Rated output: Apparent power Pn that the UPS can deliver under given load conditions (power factor = 0.8).

Rectifier/charger: UPS component that draws on the mains the power required to supply the inverter and to float charge or recharge the battery. The alternating input current is rectified and then distributed to the inverter and the battery.

Redundancy (active): Parallel UPS configuration in which several UPS units with equal outputs are parallel connected and share the load. In the event one UPS unit fails, the other units pick up its share without any interruption in the supply of power to the load.

Redundancy (standby): UPS configuration in which one or several UPS units operate on stand-by, with no load or only a partial load, and can immediately back up a faulty UPS unit by no-break transfer of the load, carried out by a static switch.

Reliability: Probability that a device will accomplish a required function under given conditions over a given period of time. Rms value of AC current with harmonics The rms value Yrms of a non-sinusoidal alternating current may be determined on the basis of the individual harmonic currents: where Y is the rms value of the fundamental.

UPS (Uninterruptible Power supply): An electrical device providing an interface between the mains power supply and sensitive loads (computer systems, instrumentation, etc.). The UPS supplies sinusoidal AC power free of disturbances and within strict amplitude and frequency tolerances. It is generally made up of a rectifier/charger and an inverter together with a battery for backup power in the event of a mains failure.

Voltage: DC voltage applied to the battery to maintain its charge level. This voltage depends on the type of battery, the number of cells and the manufacturers recommendations.

Voltage Harmonics: All alternating current which is not absolutely sinusoidal is made up of a fundamental and a certain number of current harmonics which are the cause of its deformation (distortion) when compared to the theoretical sine-wave. For each current harmonic of order n and an rms value In, there is a voltage harmonic with an rms value Un. If Zsn is the voltage source output impedance for the harmonic of the nth order, then: Un = Zsn x In