Basics of Inverters: Classification and Applications

We frequently encounter situations in electrical applications where one type of electrical energy must be converted into another. For example, alternating current can be converted to direct current and vice versa. To accomplish the goal of conversion, various converters are used.

A power inverter, as opposed to a rectifier, is a type of converter that converts direct current (DC) to alternating current (AC) of desired voltage and frequency using control signals and electronic switches.

Types of Inverters

Inverters are classified according to their input, output, power rating, and application.

Input Base Classification

  • Current-Fed Inverters Basics. Inverters with a constant input current are known as current-fed inverters. Their current is not affected by the load to which they are connected. Their voltage, on the other hand, varies depending on the load. A current link (inductor) is installed between the dc source and the power inverter in this configuration.
  • Variable Dc-Link Inverters. Variable dc-link inverters have variable input voltages that can be controlled by adjusting the values of the inductor and capacitor used in the DC link. Between the DC source and the inverter, a DC current link and a DC voltage link are provided in this type. The output voltage can be adjusted as needed.

Output Base Classification

  • Square Wave Inverter. The square wave inverter converts direct current (DC) input to alternating current (AC). While conversion is unquestionably simple, square waves contain high harmonic content, making them unsuitable for use in AC motors and transformers where high harmonic signals are present. It did, however, serve as a portal to new and improved emerging technologies.
  • Quasi Square Wave Inverter Basics. The square wave inverter was modified to produce quasi square waves. The output of a modified square wave, or quasi square inverter, is similar to the output of a square wave inverter, except that the output briefly goes to zero volts before switching positive or negative. It is simple, inexpensive, and works with the majority of electronic devices.
  • Sine Wave Inverter. A sine wave inverter, as the name implies, produces a nearly perfect sine wave output (less than 3% total harmonic distortion), making it compatible with utility-supplied grid power and all AC electronic devices. This is the type of inverter used in grid-tied systems.

This application necessitates a more complex design and costs more per unit power.

Sine Wave Inverters Output - Inverter Basics

Sine Wave Inverters Output

  • Multilevel Inverter. A multilevel inverter creates a desired voltage waveform. Because of the lower power ratings of the power devices used and the lower cost, it is suitable for inversion.

Inverter Basics: Resonant Inverters

To minimize switching losses, the output voltage or current is passed through zero in this class of inverters. When the output voltage is set to zero, this is referred to as zero voltage switching, and when the output current is set to zero, this is referred to as zero current switching.

The required circuitry can be in series or parallel, with series resonant inverters and parallel resonant inverters being the most common.

Boost Inverter Basics

The output voltage of this type of inverter is greater than the input DC voltage.

A DC-DC boost converter is installed between the DC source and the inverter, amplifying the DC voltage level before feeding it to the inverter.

Application Base Classification

Here are the different types of inverters and their applications:

Inverter Basics: Grid Tie Inverter

A sine wave inverter that is used to inject electricity into the power distribution system.

These inverters are timed to the grid’s frequency and voltage level. They typically have one or more maximum power point tracking features to extract the most power, as well as more sophisticated safety features.

A synchronous inverter is connected to a grid and allows for routing to or from the grid based on demand.

Stand Alone Inverters

A stand-alone inverter is frequently used to convert direct current generated by renewable energy distributed generation sources such as solar panels or small wind turbines to power homes and small industries, typically in remote locations without access to the main utility grid.

For maximum power point tracking and anti-islanding protection, solar inverter have special features designed for use with photovoltaic arrays.

Solar Micro Converter

A solar micro-inverter, as opposed to conventional solar inverter  devices that are connected to multiple solar panels, converts direct current (DC) from a single solar panel into alternating current (AC).

Air Conditioner Inverter Basics

An air conditioner inverter modulates the frequency of alternating current to control the speed of the air conditioner motor based on temperature control that is continuously adjusted.

Inverter Basics: Power Rating Base Classification

The power rating of an inverter is one of the most important specifications to consider when choosing an inverter. It is a measure of the maximum power that the inverter can output. 

Single Phase Inverter Basics

A single phase inverter is used in applications with low and medium power demands, as well as in single phase circuits. Single-phase inverters are notable for their low cost and ease of design.

Types of Inverters: Single Phase inverter

Single Phase inverter

Inverter Basics: Three Phase Inverter 

Three-phase inverters are recommended for high-power three-phase inversion applications. However, inversion in these types of inverters is more complicated than in single phase inverters.

Inverter Basics: Three Phase inverter

Three Phase inverter

Applications of Inverters

Inverters are widely used in industries and household appliances, and they have become indispensable in our daily lives. Some of the applications for inverters have already been mentioned in the application base classification.

Here are a few more major uses for inverters:

An Uninterruptible Power Supply (UPS) converts low frequency AC power to higher frequency for use in induction heating by utilizing batteries, a converter, and an inverter. To accomplish this, alternating current (AC) power is first rectified to provide direct current (DC). The ac inverter then converts the direct current power to high frequency alternating current power.

Inverter application in AC to DC Converters

Inverter application in AC to DC Converters

AC power is rectified and high voltage DC power is transmitted to the desired location when using HVDC power transmission. An  ac inverter converts the power back to alternating current at the destination location.

Inverter Basics: Application of Inverters in HVDC Systems

Inverter Fundamentals: Inverter Applications in HVDC Systems

A variable-frequency drive (VFD) is an essential component of industries in which the speed of motors is controlled to drive control valves at variable speeds by changing the frequency and voltage of the power supplied to the motor. To control the speed of the motor and thus the compressor, an inverter air conditioner employs a variable-frequency drive.

Application of Inverters in Variable Frequency Drives - Inverter basics

Use of Inverters in Variable Frequency Drives

Combination of rectifier and inverter makes a transformer with the advantage of variable frequency output along with variable level voltage over conventional transformer which only allows an AC voltage to be stepped up or down to a desired voltage at the same frequency.