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What are DC-to-AC converters (Inverters)? its design, working & applications

In most electronic projects, the conversion of DC voltage to AC voltage is a common problem. DC-to-AC Converters or Inverters are electrical circuits that convert direct current (DC) input into alternating current (AC) output. They’re utilized in power electronic applications when the power input is a pure 12V, 24V, or 48V DC voltage that needs to be converted to an AC output at a specific frequency.

DC-to-AC Converters (Inverters)

In this blog, we discuss the basics of DC-to-AC Converters (Inverters), Its  design, working & applications

Inverters

These are used in numerous wide range of applications, including PV systems, battery storage systems, traction drives, variable speed drives, etc. Converting from DC to AC is more difficult since an oscillator is required to reverse the current direction at the desired frequency. For converting DC voltage to AC voltage, most inverters use resistors, capacitors, transistors, and other circuit elements.

Concept of Alternating current (AC) & Direct current (DC)

Alternating Current

In an alternating current, the current changes direction and flows forward and backward. An alternating current is a current whose direction changes on a regular basis (AC). It has a frequency that is not zero. AC generators, dynamos, and other devices produce it.

Simple AC Circuit

Direct Current

The current in the direct current does not fluctuate in magnitude or polarity. Direct current is when the current in a conductor always flows in the same direction. It has a frequency of zero. Cells, batteries, and DC generators, among other things, create it.

Simple DC Circuit

What is DC to AC Converter?

DC to AC converters is used to convert a DC power source to an AC power source. In this case, the DC power supply and positive voltage source are rather steady, however, AC oscillates around a 0V base stage, often in a sinusoidal or square mode.

DC to AC Converter

Converting a voltage source from a battery into an AC signal is a popular inverter technology used in electronics. They typically run at 12 volts and are found in applications such as automotive, lead-acid technology, and photovoltaic cells, among others.

A simple inverter circuit consists of a transformer coil arrangement and a switch. To swiftly oscillate back, a standard transformer can be linked to the DC signal’s input through a switch. An alternating current signal is an output throughout the secondary coils due to bi-directional current flow in the primary coil of the transformer.

Types of Inverters

There are 3 major types of inverters:

  • Sine Wave (sometimes referred to as a “true” or “pure” sine wave)
  • Modified Sine Wave (actually a modified square wave)
  • Square Wave
  • Sine Wave

A sine wave inverter, often known as a pure or true sine wave inverter, converts the waveform generated by hydroelectric power or a generator. A sine wave inverter has the primary advantage that all of the equipment on the market is designed for a sine wave. This ensures that the device will perform to its utmost potential.

A sine wave is required by several appliances, such as bread machines, light dimmers, and some battery chargers. Pure sine wave inverters are more complicated and therefore more expensive.

2. Modified Sine Wave

The waveform of a modified sine wave inverter is similar to that of a square wave, but with an extra step or two. Many types of equipment, including motors, household appliances, and other products, will perform well with modified sine wave inverters. Some loads are difficult to handle and necessitate the use of a pure sine wave converter.

3. Square Wave

The d.c. supply is switched between positive and negative to create a square wave. Square waves are the cheapest inverters, but there are only a few. A square wave inverter is capable of running simple tools using universal motors, but not much else.

Steps for DC-to-AC Conversion

The block diagram illustrates the key components of a DC-to-AC Converter or Inverter.

DC-to-AC Converters Inverter

1. Input Filter — To deliver a clean voltage to the inverter circuit, the input filter removes any ripple or frequency disturbances on the d.c. supply.

2. Inverter – this is the main power circuit. The d.c. is turned into a multilayer PWM waveform at this point.

3. Output Filter — the output filter filters out the PWM wave’s high-frequency components, resulting in a nearly sinusoidal output.

Inverters are complicated devices that can convert DC to AC for general power supply applications. Inverters allow us to take advantage of the simplicity of DC systems while still using equipment built for use in an AC environment.

Pulse Width Modulation

Pulse Width Modulation is the most widely utilized technique in inverters (PWM). PWM is a technique that uses a pulse to turn a DC voltage on and off. Each pulse’s width is adjusted so that the overall electrical result resembles that of a sine wave.

This is a conventional inverter’s PWM waveform. To generate the necessary output, a single DC voltage is turned on or off. To create an output waveform that more closely resembles a sine wave, additional input DC voltage levels are used.

Harmonics will be formed because the PWM waveforms are not sinusoidal. As a result, the more levels used, the more the output will resemble a sine wave and the harmonic content will be lower. Inverters use transformers, capacitors, and inductors to filter the PWM waveform and reduce harmonic content.

H-Bridge Circuit

The majority of the inverter is made up of simple H-Bridge configurations. The circuit uses Insulated Gate Bipolar Transistors to build a single-phase H-Bridge circuit (IGBT).

In the circuit above, the IGBT acts as a switch. They turn on when a signal is applied to them, and they switch off when the signal is removed. A positive DC supply is applied to the load by closing Q1 and Q4. A negative DC supply across the load will arise from Q2 and Q3. The control circuits are then employed to generate the needed gate signals, resulting in the desired PWM waveform.

Short circuits must be avoided at all costs. This is accomplished by simultaneously closing Q1 and Q2. It is vital to switch off one set of IGBT before turning on the next to avoid this. In order to reduce potential voltage build-up during the transition phase, diodes provide a necessary channel for inductive current. Smoothing is provided by the capacitor, which evens out any variations in the DC supply.

Limitations of DC-to-AC Converters (Inverters)

• The use of a transistor can reduce the circuit’s efficiency.

• The use of switching transistors might generate cross-over distortion in the o/p signal. Using biassing diodes, we can minimize this limit to some extent

Applications

  •  DC-to-AC Converters are used to charge the batteries in automobiles
  • They are also used to drive low-power AC motors and are used in solar power systems.
  • DC to AC converters can be used to send power to loads across dc transmission lines.

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