Design And Construction Of A 200W Sine Wave Power Inverter System

1.0 INTRODUCTION

An inverter converts DC power to standard AC power. Inverters are used to operate electrical equipment from the power produced by a car or boat battery or renewable energy sources, like solar panels or wind turbines. DC power is what batteries store, while AC power is what most electrical appliances need to run so an inverter is necessary to convert the power into a usable form. For example, when a cell phone is plugged into a car cigarette lighter to recharge, it supplies DC power; this must be converted to the required AC power by a power inverter to charge the phone. There are different types of inverters with different sine wave, but in this work we are focusing on the pure sine wave type of inverter.

In pure sine-wave, the output voltage of a sine-wave inverter has a sine wave-form like the sine wave-form of the mains / utility voltage. In a sine wave, the voltage rises and falls smoothly with a smoothly changing phase angle and also changes its polarity instantly when it crosses 0 Volts.

Sine wave inverters are used to operate sensitive electronic devices that require high quality waveform with little harmonic distortion. In addition, they have high surge capacity which means they are able to exceed their rated wattage for a limited time. This enables power motors to start easily which can draw up to seven times their rated wattage during start up. Virtually any electronic device will operate with the output from a pure sine wave inverter.

Sine wave inverter has the following characteristics:

1. High efficiency
2. Low standby losses
3. High surge capacity
4. Low harmonic distortion

To get a sinusoidal alternating current from the output of our transformer, we have to apply a sinusoidal current to the input. For this we need an oscillator.  An amplifying transistor can be made to oscillate by feeding some of the amplified output back to its input as positive feedback. The positive feedback in an electronic circuit can be tuned using extra components to produce the frequency we require (generally either 50 or 60 cycles per second to mimic mains electricity).

1.2 OBJECTIVE OF THE STUDY

The output voltage of a sine-wave inverter has a sine wave-form like the sine wave-form of the mains / utility voltage. In a sine wave, the voltage rises and falls smoothly with a smoothly changing phase angle and also changes its polarity instantly when it crosses 0 Volts. The objective of this project is to design and construct a to design a device that will produce a sine wave-form of the mains / utility voltage which is rated  200W which can be powered from the source of 12V battery.

1.2 PURPOSE OF THIS WORK

The purpose of this work is to design an electrical device that converts direct current (DC) to alternating current (AC); the resulting AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits. The output of this work produces a sine wave-form of the mains / utility voltage which is rated 200W which can be powered from the source of 12V battery.

1.3 SIGNIFICANCE OF THE PROJECT

• Some electronic devices may pick up inverter noise while operating with modified sine waveform. Using fluorescent lighting can be problematic when using modified sine wave inverters. Most of the equipment on the market is designed for use with sine waves. Some appliances, such as microwaves, drills, clocks or speed motors will not produce full output if they don’t use sine wave current, moreover they may damage the equipment. Some loads, such as light dimmers will not work without sine wave at all. It’s safe to say any electronic device that requires sensitive calibration can only be used with pure sine wave inverters
• Pure Sine Wave output is the most compatible AC power from an inverter, and it is the best waveform for all AC electrical appliances.
• Pure Sine Wave output eliminates interference, noise, and overheating.
• Reduces audible and electrical noise in fans, fluorescent lights, electronics gear and magnetic circuit breakers.
• Prevents glitches and noise in monitoring equipment.
• It can be efficiently electronically protected from overload, over voltage, under voltage, and over temperature conditions.
• Inductive loads like microwave ovens and variable-speed motors operate properly, quieter and cooler. Some appliances will not produce full output if they do not use Pure Sine Wave power.
• Some appliances, such as variable speed drills and bread makers, will not work properly without Pure Sine Wave power.

1.4 LIMITATION OF THE PROJECT

• More expensive than Modified Sine Wave power inverters. Physically larger than their Modified Sine Wave counterparts.
• The built-in circuit becomes far more complex due to multiple conversions from AC (Alternating Current) to DC (Direct Current) and back to AC (Alternating Current). 3-DC, 4-D or All DC inverter ACs have even more conversions taking place as there are more components working on DC.
• Repair costs increase as components are more sophisticated and as a result, more expensive. They require more effort to build or repair.
• Response Time: The inverter 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 inverter shall be capable of operating at +10% to -15% of the nominal frequency, 50Hz.
• Rating: this device shall be rated at 200VA.
• Access Requirements: The inverter 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 display line voltages.
• Ventilation: The inverter isolation transformer shall be designed for convection cooling. Fan cooling is required for the MOSFET used.

1.5 PROBLEM OF THE PROJECT

Battery Under/Over-Charge: Every battery has its charge/discharge cycle. A permanently under-charged or over-charged battery cannot maintain its rated lifespan. Many of the modern day intelligent Inverters have over-discharge cut-off sensor that ensures that the batteries are not unduly over-charged or discharged. However, some of the cheap Inverters in the market are not equipped with this intelligent device, which causes the batteries to boil when over-charged or cause suffation to set up when the batteries are over-discharged and are not constantly kept at full charge. For batteries to serve their stated lifespan successfully without premature failure, they must be maintained at full or near full charge at all times.

Another thing to consider is that, batteries must not be over-discharged. In-fact, batteries are not expected to be discharged below 0.5 per cell, i.e. for a 12V battery, minimum voltage to discharge the battery must be around 10.8V. Once it is below this, most intelligent Inverters will begin to beep to alert that the battery is low and after sometimes shut itself down completely to prevent damaging the battery. At this point, it must be fully re-charged before use, even if the machine fails to shut itself down.

Over-Load: Basically, most domestic or industrial Inverters are designed for light loads- such as lighting, electronics appliances, and fan. Heavy high wattage equipment, like refrigerators, heating appliances, ovens, Air conditioners and pumping machine are not practically suitable for Inverters. While many of these appliances draw very heavy current from the battery causing it to run down quickly, they can also be too heavy for the capacity of the Inverter, causing it to shutdown under over-load condition or even burn the machine. When calculating the loads to be connected to the Inverter, the total demand load must not exceed the rating of the Inverter. Consideration must also be made to the difference between the Wattage rating of the appliances normally written on the name plate and the KVA rating of the Inverter. Since there is a difference between (Kilowatt (KW) Volt Ampere (VA) and Kilovolt Ampere (KVA), and most of the appliances are rated in KW while most Inverters are either rated in VA or KVA, some mathematical conversion has to be done to arrive at the actual capacity of the machine.

Wiring Circuit and Cable Sizing: While it is true that any road side technician can buy any Inverter sold in the market place and connect it, as long as it is seen to be working, care must be taken to the theoretical calculations involved in cable sizing for a particular installation and how the machine is connected to the load and the supply source. Wrong cable size is a potential fire disaster, loose termination and wrong wiring is another accident waiting to happen. Most fire incidents in homes and industries are caused by loose termination or wrong cable sizing.

Capacitor wear: The first reason for inverter failure is electro-mechanical wear on capacitors. Inverters rely on capacitors to provide a smooth power output at varying levels of current; however electrolytic capacitors have a limited lifespan and age faster than dry components. This in itself can be a cause of inverter failure.

Overuse: Using inverters beyond their operating limit, either by choice or due to oversight or lack of knowledge, can contribute to inverter bridge failure. Using any component at a rating higher than its operating limit will decrease its lifespan and lead to failure, so avoiding this issue simply comes down to checking that all inverters are being run correctly.

Ultrasonic vibrations: The final problem on the list is one that contributes to the mechanical stress placed on an inverter. Ultrasonic vibrations originating in the cores of inductive components cause friction, adding to the unwanted heat generated by the device and further damaging components in the inverter.

1.6 APPLICATION OF THE PROJECT

This study exposes me the applications and uses of a pure sine wave inverter which are as follows:

DC power source utilization

Inverter designed to provide 220 VAC from the 12 VDC source provided in an automobile. The unit shown provides more than 20 amperes of alternating current, or enough to power more than 200W load.

An inverter converts the DC electricity from sources such as batteries, solar panels, or fuel cells to AC electricity. The electricity can be at any required voltage; in particular it can operate AC equipment designed for mains operation, or rectified to produce DC at any desired voltage.

Uninterruptible power supplies

An uninterruptible power supply (UPS) uses batteries and an inverter to supply AC power when main power is not available. When main power is restored, a rectifier supplies DC power to recharge the batteries.

Induction heating

Pure Sine wave Inverters convert low frequency main AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power.

HVDC power transmission

With HVDC power transmission, AC power is rectified and high voltage DC power is transmitted to another location. At the receiving location, an inverter in a static inverter plant converts the power back to AC. The inverter must be synchronized with grid frequency and phase and minimize harmonic generation.

Variable-frequency drives

A variable-frequency drive controls the operating speed of an AC motor by controlling the frequency and voltage of the power supplied to the motor. An inverter provides the controlled power. In most cases, the variable-frequency drive includes a rectifier so that DC power for the inverter can be provided from main AC power. Since an inverter is the key component, variable-frequency drives are sometimes called inverter drives or just inverters.

Electric vehicle drives

Adjustable speed motor control inverters are currently used to power the traction motors in some electric and diesel-electric rail vehicles as well as some battery electric vehicles and hybrid electric highway vehicles. In vehicles with regenerative braking, the inverter also takes power from the motor (now acting as a generator) and stores it in the batteries.

Air conditioning

An inverter air conditioner uses a variable-frequency drive to control the speed of the motor and thus the compressor.

Electroshock weapons

Electroshock weapons and tasters have a DC/AC inverter to generate several tens of thousands of V AC out of a small 9 V DC battery. First the 9VDC is converted to 400–2000V AC with a compact high frequency transformer, which is then rectified and temporarily stored in a high voltage capacitor until a pre-set threshold voltage is reached. When the threshold (set by way of an air gap or TRIAC) is reached, the capacitor dumps its entire load into a pulse transformer which then steps it up to its final output voltage of 20–60 kV. A variant of the principle is also used in electronic flash and bug zappers, though they rely on a capacitor-based voltage multiplier to achieve their high voltage.

1.7 INVERTER RATINGS
The ratings that you should look at when buying an inverter (depending on the type) are:

1. Continuous Rating: This is the amount of power you could expect to use continuously without the inverter overheating and shutting down.
2. Half Hour Rating: This is handy as the continuous rating may be too low to run a high energy consumption power tool or appliance, however if the appliance was only to be used occasionally then the half hour rating may well suffice.
3. Surge Rating: A high surge is required to start some appliances and once running they may need considerably less power to keep functioning. The inverter must be able to hold its surge rating for at least 5 seconds. TVs and refrigerators are examples of items that require only relatively low power once running, but require a high surge to start.
4. IP rating – defines the ability of the inverter seals to prevent water and dust ingress. Although some inverter manufacturers claim high IP ratings suitable for outdoor installation, the quality and location of the seals and ventilation will greatly affect the ability of the inverter to outlast the many years solar installations are expected to work.
5. Peak efficiency– represents the highest efficiency that the inverter can achieve.

1.8 IMPORTANT CONSIDERATION FOR INVERTERS

Before going into construction of an inverter, students must know the following:

OUTPUT FREQUENCY

The AC output frequency of a power inverter device is usually the same as standard power line frequency, 50 or 60 hertz

If the output of the device or circuit is to be further conditioned (for example stepped up) then the frequency may be much higher for good transformer efficiency.

OUTPUT VOLTAGE

The AC output voltage of a power inverter is often regulated to be the same as the grid line voltage, typically 220 VAC, even when there are changes in the load that the inverter is driving. This allows the inverter to power numerous devices designed for standard line power.

Some inverters also allow selectable or continuously variable output voltages.

OUTPUT POWER

A power inverter will often have an overall power rating expressed in watts or kilowatts. This describes the power that will be available to the device the inverter is driving and, indirectly, the power that will be needed from the DC source. Smaller popular consumer and commercial devices designed to mimic line power typically range from 150 to 3000 watts.

Not all inverter applications are solely or primarily concerned with power delivery; in some cases the frequency and or waveform properties are used by the follow-on circuit or device.

BATTERIES

The runtime of an inverter is dependent on the battery power and the amount of power being drawn from the inverter at a given time. As the amount of equipment using the inverter increases, the runtime will decrease. In order to prolong the runtime of an inverter, additional batteries can be added to the inverter.

When attempting to add more batteries to an inverter, there are two basic options for installation: Series Configuration and Parallel Configuration.

Series configuration

If the goal is to increase the overall voltage of the inverter, one can daisy chain batteries in a Series Configuration. In a Series Configuration, if a single battery dies, the other batteries will not be able to power the load.

Parallel configuration

If the goal is to increase capacity and prolong the runtime of the inverter, batteries can be connected in parallel. This increases the overall Ampere-hour(Ah) rating of the battery set.

If a single battery is discharged though, the other batteries will then discharge through it. This can lead to rapid discharge of the entire pack, or even an over-current and possible fire. To avoid this, large paralleled batteries may be connected via diodes or intelligent monitoring with automatic switching to isolate an under-voltage battery from the others.

1.9 DIFFERENCE BETWEEN CONVENTIONAL GENERATOR AND INVERTER

1.10 PROJECT WORK ORGANISATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this works is on the introduction to pure sine wave power inverter. In this chapter, the background, significance, objective limitation and problem of pure sine wave power inverter were discussed.

Chapter two is on literature review of pure sine wave power inverter. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.

Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references.