THE DESIGN AND CONSTRUCTION OF A 5KVA PURE SINE WAVE UNINTERRUPTIBLE POWER SUPPLY(UPS) AT 220V, 50HZ USING PIC16F877 WITH A 24V/200AH BATTERY
Electricity is the principal force that powers modern society. It lights buildings and streets, runs computers and telephones, drives trains and subways and operates all variety of motors and machines (“Powering a Generation”, 2014).
It is important to recognize that electricity is not mined or harvested, it must be manufactured. Since it is not easily stored in quantity, it must be manufactured at the time of demand. Electricity is a form of energy, but not an energy source. Different generating plants harness different energy sources to make electrical power. Some of these sources are thermal plants, kinetic plants, geothermal power and solar photovoltaics (“Generating Electricity”, n.d.).
Since, the demand for electricity in this area of the world is alarming, there is the need for the production or generation of constant electricity, due to the epileptic condition of electricity in the country. This gives rise to the design and construction of a 5KVA pure sine waveUninterruptible Power Supply(UPS). UPS is an acronym which stands for Uninterruptible Power Supply. Sudden interruption of power sometimes throws the nation as a whole into darkness for hours. The effect is that, the nation as a whole experiences a great harvoc that also affects social economic life of the nation.Due to all these problems caused by the sudden interruption of power supply, it became a great concern to engineers and technicians to find solution to the problem since they are the world problem solver who convert dreams to reality. Hence, the need for an Hybrid Uninterruptible Power Supply (HUPS). As the name implies, a UPS maintains continuous supply of electricity to our system when there is power failure. It also ensures that there is no damage to the electronic equipment or home appliances when there is power surge. All functions performed by UPS earn it to be defined as a device that serves as an alternative source of power when there is power failure. It is majorly used as a backup for computer systems and some household appliances. The uninterruptible power supply finds its use in hospitals, schools, offices and also in various houses (“Uses of UPS”, 2011).
The hybrid Uninterruptible Power Supply (UPS) has more than one means of charging the battery. Apart from charging the battery through mains, it is also incorporated with solar panel (photovoltaic cell) hence the name hybrid. The solar panel (PVC) is able to charge the battery with the help of charge controller which regulates voltages from the solar panel to the require voltage needed to charge a 24V dc battery.
The UPS are of two types, the rotary and static type. The rotary UPS uses an alternating current motor (AC motor), and alternating current generator (AC generator), these two are coupled together for the power needed by the AC load. The AC motor aids the continuous driving of the AC generators so as to give continuous power supply when its need arises. The static type UPS has no moving parts, it is highly efficient and provides continuous power supply at the time primary AC power fails.
UPS is classified as ON-LINE and OFF-LINE according to their voltage and frequencyfluctuations. The ON-LINE UPS is constantly ON. It is required where there is a wide range variation in voltage and frequency that are needed to be stabilized.
The OFF-LINE UPS takes its supply from the mains and is passed through a stabilizer at the same time it is charging the battery. It is also refers to as standby UPS. Off-line UPS is used as back-up in areas where fluctuation of voltage and frequency is less (“Classification of UPS”, 2012).
Sunlight, a natural form of energy generates DC current to power solar panel by both infrared and ultraviolet ray in the electromagnetic field spectral as it radiates on to the solar panel.
However, UPS deals with its use with respect to how it is being trapped to generate DC current for human use, the solar energy could be trapped into a panel already designed to attract electron being ionized from their ground orbit and then flow into the UPS that convert it into AC current by inversion. The energy generated in this form is being stored in batteries in form of charges so that it can be used at a later time (“Photovoltaic Cell”, 2016).
Solar power is the conversion of sunlight into DC current. Sunlight can be converted directly into usable energy using photovoltaic cell (PVC) or indirectly with Concentrated Solar Panels (CSP) which normally focuses the suns energy. A solar cell or photovoltaic cell (PVC) is a device that converts sunlight into DC current using the photo electric effect (“Solar Energy”, 1999).
Solar cell produces direct current (DC) power which fluctuates with the intensity of the radiated light. This usually requires conservation to certain desired voltage or alternating current (AC) which requires the use of INVERTER for inversion (“Photovoltaic Cell”, 2016).
An inverter is used to produce an uninterrupted 220V AC supply to the device connected as the output load. The inverter gives constant AC voltage at its output when the AC mains power supply is not available (“How an Inverter Works”, 2008).
Multiple solar cells are connected inside modules. These modules are then arranged together to form arrays, which are wired to an inverter which produces power of a desired voltage according to the specification of the inverter, for AC frequency/phase use (“Solar Energy”, 2017).
A UPS system ensures continuous power supply to the load. It is achieved by using solid state circuitry which employs a battery and solar energy as the alternative energy source. Typically, the basic system consists of rectifier circuit, inverter circuit and static switch and the PV. Under normal operation, power to the load is fed through the circuit. Unavailability of the public mains supply for any reason, then the load is fed from the battery/inverter, as shown in fig. 1.1 (“Uninterrupted Power Supply”, 2017).
The uninterruptible Power Supply provides clean and reliable power to vulnerable electrical equipment. The basic concept of the UPS is to discharge energy during normal operation.
The UPS system has the technology for inverting the DC source from the battery to AC sine wave to supply the load. Inverter system has advanced over the years. The earlier circuit resulted in square wave output clearly requiring a large filter and a poor dynamic performance with development in circuitry and availability of switching devices, step wave systems were developed with an increase in system dynamic performance, with development in circuitry, sine wave has been achieved, with an increased in system dynamic performance (“Uninterrupted Power Supply”,2017).
To provide uninterrupted power supply to domestic appliances and lightings where there is public mains supply failure and also generates a stable source of power supply.
The objectives are:
⦁ To avoid noise in the surrounding which is produced by gasoline engines such as diesel and petro generators.
⦁ To save cost of fueling and maintenance of gasoline engine generators.
⦁ To reduce damage of electronic appliances as a result of unstable power supply.
⦁ To ensure that, there is continuous power supply.
⦁ To generate 220V AC output from a 24V DC source.
The UPS was designed for loads not exceeding 5KVA, pure sine wave at 220V, 50Hz using PIC16F877 with a 24V/200AH battery.
UPS systems are the best when it comes to back-up since they can come up very fast and they generate little or no noise unlike generator. Even in an area with constant power supply, power outage due to natural cause and faults are usually unannounced. It is therefore very important having a reliable back-up power installed.
⦁ It cannot support a load that consumes power that exceeds the rated voltage.
⦁ The wave form of the output voltage is DC, there is need for the construction of an inverter.
⦁ Getting the actual time that will come ON and OFF to be able to maximize the battery usage.
SUMMARY, CONCLUSION AND RECOMMENDATION
The design and construction of the 5KVA pure sine wave hybrid Uninterrupted Power Supply was made up of four stages; the photovoltaic cell, charge controller unit, battery unit and the inverting unit. The inverting unit comprises the power supply unit stage, the oscillating stage, power MOSFET stage and transformer stage. The charge controller regulates the voltage needed to charge the battery, so as to give a DC voltage of 24V, this is fed to the oscillator which the oscillator stage generates an output of 5V pure sine wave at 50Hz and then fed to the two banks of MOSFET with frequency of 50Hz each, the voltage is then amplified by the MOSFETs to 24V AC at 50Hz which serves as input to the transformer and steps it up to 220V AC.
Pure sine wave of 5KVA, 220V, 50Hz suitable for all AC loads was achieved. With various loads not exceeding 5KVA tested, the output voltage did not exceed 220volts and the actual duration for the 24V/200AH battery used is 20hours. Efficiency of 75% was achieved and cost of the UPS is #125,235.00
For effective and efficient utilization of electricity in the country at large, the following recommendation will be useful.
1. Government could subsidize the cost of importation of Renewable Energy Technologies (RET) most especially the Deep Cycle Battery and Solar PV to bring down the high cost in Nigeria.
2. Private individual and organization should be encouraged by appropriate authorities to invest on uninterruptible power supply in the country.
3. Consequently, the wide difference bodies (universities, polytechnics and other research institutes) and manufacturing industries must be bridged.
4. The department should create more avenues i.e. workshop for practical work to upgrade the students ability to design practical projects..