Basics Of Inverter

As discussed in one of our previous blogs, the importance of electricity in our lives. There are two types of current flow in our circuit: Direct current (DC) and Alternating Current (AC).

The Direct current (DC) system is the one in which current does not change its direction while flowing from the electrical source (cells, batteries) to the load (resistor, inductor, or capacitor). The current remains fixed to a constant value. For example, as a kid, you might have played a simple electric game, in which you used to connect a cell to a small bulb or a motor. This system works on DC in which the current flows from the positive terminal of the cell to the negative terminal.

But in an alternating current (AC) system, the current reverses its direction periodically. Sine waves, square waves, triangular waves are some examples of alternating current.

Why do we need Inverter?

Most of the appliances we use at homework on alternating current (sine wave). But, the current obtained from the solar PV array is DC in nature. To make it useful for us, we convert this into AC with the help of inverters. 

We must have noted that some years ago (10-12 years), when the power supply was cut, and the home appliances started working on the inverter, a humming sound was heard from the fan. This is because the fan was supplied with the square wave instead of the sine wave. This led to the creation of mechanical vibration and made the fan noisy. Modern inverters use some advancing techniques to produce the wave which very close to the sine wave, thus eliminating the sound and heat produced to a minimum, thereby increasing the efficiency. But, as the square wave inverters are very basic and easy to understand, so in this blog, we will look at, how to design a square wave inverter.

Bridge connection of an inverter

This is the basic circuit that we will use to invert our DC electricity.

S1, S2, S3, and S4 are four switches and the load (bulb or motor) is connected between points A and B. To obtain an inverted square wave, we need to operate these switches in a particular fashion. Let us understand how it works.

Situation 1

When S1 and S4 switches are closed and S2 and S3 are open, point A is connected to the positive side of the battery while point B gets connected to the negative side of the battery. So, the potential difference between A and B becomes VA-VB=Vdc.

Situation 2

When S2 and S3 switches are closed and S1 and S4 are open, point B is connected to the positive side of the battery while the point A gets connected to the negative side of the battery. So, the potential difference between A and B becomes VB-VA=Vdc, i.e. VA-VB=-Vdc.

Now, as the frequency of supply in India is 50 Hz, which means that 1 full cycle is completed in 1/50 (0.02) seconds, so for the first 0.01 seconds switches S1 and S4 will remain closed (with S2 and S3 open). In the remaining 0.01 seconds switches S2 and S3 will remain closed (with S1 and S4 open). The full cycle will come out to be as shown in the figure below:

Now, we need to do this switching every 0.01 seconds, which means, in 1 second we need to turn it on and off 100 times. This task is impossible with the help of mechanical switches. So, special semiconductor switches are used for this purpose, which are designed to switch 1000 times every second. Thus, the combination of switches switching at the right time gives us our desired result.

The inverter explained above is a very simple model and in modern times, the design and circuit of inverters are prepared to provide a wave very close to the sine wave.

The ratings of the inverter differ based on the power requirement. So, while installing the solar PV plant, one should take care of the rating of not only the inverter but all the components that are to be used like wires, batteries, etc.

SolarOcta takes care of all the above factors and makes sure that the solar PV plant gives the maximum output, even after many years of usage of the plant. We understand that a person shifting towards the sun for the electricity is paying a price initially. So, we want the output from the plant to be satisfactory to the customer. To meet these requirements, we use inverters from various brands according to their rating and capacity. These brands include Delta, Luminous, Havells, Growatt, Sungow, Goodwe, Soils, Polycab, etc.

The requirements of a customer are carefully studied and the optimized combination of equipment is provided without compromising with the quality.


Pursuing Bachelors of Electrical engineering from DTU, Delhi. Interested in applications of the renewable energy sector. Writing blogs to express my views on Clean Technologies and Sustainability Development. I believe that the renewable sector is one of the fast-growing areas in the world and it will be the majority energy-producing source in the coming future.

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