INVERTER

What is the function of Inverter?

There are two types of electrical energy; AC power and DC power. In our regular life, generally we use AC power for our household equipment and in office also we need AC power. But we cannot store electrical energy in the form of AC. We can store only DC power. For that, we use a battery. The batteries are run on very low voltage. The battery cannot be used to run household appliances. Power generated from a diesel generator or power supplied by the utility is AC power and most of all appliances are also designed to run on AC power.

Now you think what is the function of the inverter in office or home. The inverter is used to supply back up power when utility fails to supply power or during maintenance. The inverter takes DC power from the battery and converts it into AC power. This is the main function of an inverter.

Types of inverter:

(A) According to the output characteristic (shape of AC wave they produce), inverters are classified into three types.

                1) The square wave inverter

                2) The modified sine wave inverter or quasi-sine wave inverter

                3) The pure sine wave inverter

        The output waveform of this inverter is a square wave. This type of inverter is not used because the shape of the output waveform is not suitable for most running appliances. Construction of square wave inverter is easy and cheap in cost. but square wave inverters are obsolete from the market because of fewer applications.

        In this type of inverter, the output waveform is not a pure sine wave and not a square wave. The shape of the output power is similar to the staircase. This shape is useful for appliances like television, radio etc. but not useful for sensitive devices like a battery charger, variable speed motor and heaters. In this waveform some amount of noise is present. It is cheap compared to pure sine wave inverter. So, it depends on the application, if you require inverter for selected household application only then go for this inverter otherwise go for pure sine wave inverter.

        This is the best inverter for all type of applications and efficient for all nature of the load. Generally, if cost is not considerable than always use pure sine wave inverter. The shape of output power is a pure sine wave. This shape is the same as utility power. Filters are used to getting a pure sine wave. The pure sine wave inverters are the costliest inverter compared to all another inverter.

(B) The output of the inverter is AC power and there are two types of AC power; single phase and three phase. According to output power inverter can classify into two types;

                1) single phase inverter

                2) three phase inverter

        This is depending on the utility connection. For a small load, single phase connection is provided and for large load three phase connection is provided. Generally, for domestic load single phase connection is used and for industrial load three phase connection is used.

(C) According to a source of input;

                1) current source inverter (CSI)

                2) voltage source inverter (VSI)

        In CSI, the input is a current source. This type of inverters is widely used in the medium voltage industrial application, where high-quality current waveform are compulsory. But CSIs are not popular.

        In VSI, the input is a voltage source. This type of inverter is widely used in all applications because it is more efficient and have higher reliability and faster dynamic response. VSI is capable of running motors without de-rating.

Applications:

1) An uninterrupted power supply (UPS) supplies AC power with the help of inverter and battery combination.

2) Speed control of electric motor: An inverter is designed to produce a variable output voltage and by controlling the output voltage of the inverter, we can control the speed of an electric motor.

3) In the compressor of refrigerator and air-conditioner: In the simple inverter, single speed compressor switches on and off periodically. But in inverter compressor, VFD (variable frequency drive) is used to control the speed of compressor motor and according to this control of cooling is done.

4) Solar: Output of solar PV panels is DC. So, we have to convert it to AC for that inverters are used.

5) HVDC transmission line: For bulk power transmission, HVDC transmission line has more advantages than HVAC transmission line. In this transmission network, power is generated in AC and convert in DC with the help of rectifier and transmit this DC power for long distance. At receiving end power is converted into AC with the help inverter.

Simulation of simple three-phase inverter:

https://articleelectrical.blogspot.com/2018/11/simulation-of-three-phase-inverter.html