Introduction to Inverters

Current is defined as the flow of electrons. It is denoted by I and the SI unit of current is Ampere. There are mainly two types of currents: Alternating Current (AC) and Direct Current (DC). In general AC is used to travel over long distances and users require DC.

So, there are many devices that are used to convert incoming Alternating current to Direct Current. Examples include SMPS, Power Adapters, Chargers etc. But we also need devices that convert Direct Current to Alternating Current.

An inverter is a device that is used to convert Direct current to Alternating Current. However the output is not a sine wave. It can be square wave, quasi square wave or PWM. But in most scenarios the value of DC power is low. But we require high Alternating Currents. This can be achieved in two ways:

• First we need to step up the DC power. Then we can make use of inverter to convert DC to AC.
• Secondly, we convert low powered DC to low powered AC. Then we increase the power of Alternating current by stepping it up.

Types of Current in general :

• Direct Current: In this type of current, electrons flow in constant direction. In other words we can say that it is unidirectional in nature.
• Alternating Current : In this type of current, electrons change the direction periodically. It can be compared to sinusoidal wave. The main advantage of using AC current over DC current is that it helps to supply current to long distances without involving much cables.

Inverters can also be used to change voltage levels.

There are mainly five components of an inverter. They are as follows:

Microcontroller

A microcontroller is also known as Digital Signal Processor. This is the core of the inverter that is responsible for managing the switching of electric conversion. It also regulates the voltage so that the frequency remains stable. Microcontroller also detects faults or issues if present. This processor also ensures that maximum output and minimum energy loss.

Bipolar Junction Transistors

A transistor is a semiconductor device whose task is to amplify the signals. These are used to basically switch quickly from one type to another type. Here two kinds of transistors PNP or NPN are used.

Filter

This is used to filter the frequencies based on the requirements. It will allow to pass high frequencies if high frequencies are required and vice versa. It also smooths waves so as to produce perfect AC output.

MOSFETs

MOSFETs or Metal-Oxide-Semiconductor-Field-Effect-Transistor are responsible for high switching. They are used for switching between high frequencies so that the inverter can correctly chop off the Direct currents and convert them to AC.

Heat Sink and Cooling System

Since in inverter there is switching between high frequencies and converting low powered DC to high powered AC, a large amount of heat is dissipated. So to avoid over heating appropriate heat sinks are required. Also cooling systems are required so as to maintain the temperature of the inverter.

There are basically three types of inverters based on the output. They are as follows:

1. Sine wave

In this type of inverter, the output produced is a sine wave. Since AC current adheres to sinusoidal waveform, this is the most commonly used inverter. It is useful in all expensive electronic devices. Since sine waves reduce distortion, the circuitry is complex. The main advantage is it produces clean output.

2. Modified Sine Wave

Modified Sine waves is a combination of sine wave and square wave. It uses series of steps to approximate the sine wave. This inverter is most commonly used in household applications. The circuitry is less complex as compared to sine wave. However the drawback is it does produce noise and distortion.

3. Square Wave

Square wave produces basic AC output. The curve ranges between positive and negative values. It has a straight forward circuitry. However the output does not comply with the sine wave. Hence it is susceptible to harmonic noises and distortion. These inverters are cheap and have short lifespan because they tend to get heated easily.

4. Grid Tied Inverters

Grid Tied Inverter is a type of inverter that converts DC to AC which can be in turn injected in the electrical grids. They are useful in solar panels, turbines etc. In this solar energy is fed into the panels and accordingly the power is generated.

5. Three Phase Inverters

These types of inverters are used in industrial as well as commercial areas. They convert the DC power to AC power. This AC power is useful in motors, pumps etc. It is to be noted that three phase AC power is generated by these inverters.

The task of the inverter is to convert DC to AC. It takes up the incoming DC current, uses oscillators to increase the frequency of the signal. Here oscillators are basically the transistors( MOSFETs and BJTs). After this the improved DC is passed to transformer. The transformer steps up the signal and improves the waveform so as to produce AC output. Meanwhile filters filter out the frequencies so that the appropriate output is generated.

An inverter should have some characteristics that will have good efficiency as well as long lifespan. Some characteristics an inverter should have are as follows:

1. The output is a crucial component for inverters. Sine waves produce clean output while square waves produce basic AC output.
2. Proper cooling mechanisms should be used so as to cool the inverters.
3. An inverter should have high efficiency above 90%. It also should be efficient under any circumstances.
4. The inverter should produce accurate AC voltage. In general 120 V or 240 V should be generated by any inverter.
5. It should produce output that will have least harmonic distortion.

There are various applications of inverter. Some of them are as follows:

• Inverters provide power supply when the grid power is not available.
• It provides backup during adverse weather conditions.
• It is widely used in vehicles, boats etc.
• They are used in telecommunications where DC power is extracted from solar panels and is converted to AC power

Some advantages of inverter are as follows:

Advantages

• Since inverter converts DC to AC it is useful during power outages.
• It is combined with renewable resources so that appropriate output is generated.
• It is useful in remote areas as small quantity of DC is converted to high frequency AC .

Some disadvantages of inverter are as follows:

Disadvantages

• Inverters are usually bulky because of the large inbuilt circuitry. It is also expensive.
• Maintaining an inverter is costly since it requires proper ventilation and cooling.

Some precautions should be taken while using an inverter. Some of them are as follows:

• Store the inverter in a cool dry place.
• Ensure proper ventilation so that the inverter works at room temperature.
• Use fuse or circuit breaker on DC part so as to avoid overloading
• Regular Maintenance is must. Check the wirings or any other electrical part so as to avoid damages.
• When inverter is not in use, disconnect it so as to avoid any potential damage.

Inverter is an important device because it provides power source when there are power cuts. It can turn on electrical appliances and can be an alternative backup.

What Conversion Efficiency an Inverter should have?

Conversion Efficiency is defined as the efficiency exhibited by an inverter when it converts DC to AC. The typical conversion efficiency an inverter should have is 90% or above.

Why Total Harmonic Distortion should be low in inverter?

THD or Total harmonic Distortion is defined as the distortion produced in the output wave. It is also considered as a check to measure the purity of the wave. Generally inverters should have 3% or below value of THD.

What is Grid Tie Inverter?

Grid Tie Inverter is a type of inverter that converts DC to AC which can be in turn injected in the electrical grids. They are useful in solar panels, turbines etc.