How Does DC to AC Inverter Circuit Works

DC to AC inverter’s function is to convert Direct Current (DC) voltage to Alternating Current (AC) voltage.  DC to AC inverter is commonly used for converting High Voltage DC (HVDC) transmission voltage back to AC, and for converting the DC output voltage of a photovoltaic (PV) solar panel to suitable AC voltage. The output AC voltage of the inverter can be a 60 Hz square wave or a pure sine wave. Of course, an inverter with pure sine wave output is more expensive than with a square wave output because of additional filters used.

How Does DC to AC Inverter Circuit Works 

A simple DC to AC inverter circuit is basically composed of 4 stages;

1. an astable circuit  that generates a 60 Hz square low voltage wave signal. A 555 timer IC can also be use.
2. The power amplifier
3. A filter
4. Transformer

Generally, a DC to AC inverter circuit schematic diagram looks like this;


For demonstration purposes, the 60 Hz generator astable circuit is represented as a signal generator.

Basically, the power amplifier circuit just amplifies the output 60 Hz signal of the signal generator to approximately 24 V (peak-to-peak) square wave voltage. If this is to be use to convert a DC voltage to AC like in PV system or in HVDC to AC conversion, the DC voltage input will be connected in the “DC 24V” terminals.

Note that the above circuit doesn’t have a filter yet to filter out the high frequency component of the square wave to come up with a pure sine wave signal. At load side, the voltage should like this;

 

In commercially available DC to AC inverters, a sophisticated filter is used to produce a pure sine wave output. These kind of filters is, basically, a high pass filter that completely remove all of the signal with frequencies more than 60 Hz. 

After filtering, the output voltage is transformed to a suitable voltage level using a transformer.
 




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