Basic Inverter Operation

The basic circuits include an oscillator, control circuit, drive circuit for the power devices, switching devices, and a transformer.

The conversion of dc to alternating voltage is achieved by converting energy stored in the dc source such as the battery, or from a rectifier output, into an alternating voltage. This is done using switching devices which are continuously turned on and off, and then stepping up using the transformer. Although there are some configurations which do not use a transformer, these are not widely used.
The DC input voltage is switched on and off by the power devices such as MOSFETs or power transistors and the pulses fed to the primary side of the transformer.
The varying voltage in the primary induces an alternating voltage at secondary winding. The transformer also works as an amplifier where it increases the output voltage at a ratio determined by the turn’s ratio. In most cases the output voltage is raised from the standard 12 volts supplied by the batteries to either 120 Volts or 240 volts AC.

Inverter output waveforms

The inverters are classified according to their output waveforms with the three common types being the square wave, the pure sine wave and the modified sine wave.
The square wave is simple and cheaper, however, it has a low power quality compared to the other two.
The modified square wave provides a better power quality (THD~ 45%) and is suitable for most electronic equipment.
These have rectangular pulses that have dead spots between the positive half cycle and the negative half cycle (THD about 24%).

Modified sine waveform

The true sine wave inverter has the best waveform with the lowest THD of about 3%.
However, It is the most expensive and used in applications such as medical equipment, stereos, laser printers and other applications requiring sinusoidal waveforms. These are also used in the grid ties inverters and grid connected equipment

Applications

Inverters are used for a variety of applications that range from small car adapters to household or office applications, and large grid systems.
Uninterruptible power supplies
As standalone inverters
In solar power systems
As a building block of a switched mode power supply

Grid connected systems

A grid connected renewable energy system converts DC electricity from a power source, such as solar panels, to AC mains power and feeds it into the grid.
It usually consists of the energy source, an inverter and a meter. If there is a mains grid power failure, a grid connected renewable energy system disconnects from the grid and energy from solar panels is not available.
Battery banks connected to the grid, with an appropriate inverter, may work as an uninterruptable power supply to make energy available during a power outage for all or some of the electrical loads in a home or business.

A solar panel is a collection of solar cells.

The solar panel converts the solar energy into electrical energy. The solar panel uses Ohmic material for interconnections as well as the external terminals. So the electrons created in the n-type material passes through the electrode to the wire connected to the battery. Through the battery, the electrons reach the p-type material. Here the electrons combine with the holes. When the solar panel is connected to the battery, it behaves like other battery, and both the systems are in series just like two batteries connected serially. The solar panel has totally consisted of four process steps overload, under charge, low battery and deep discharge condition.