Inverter Basics: Classification and Applications

What is an Inverter?

In electrical applications, we often come across where one form of electrical energy needs to be converted into another form. e.g., alternating current into direct current or vice versa. Different converters are used to achieve the purpose of conversion. Unlike rectifiers which convert AC into DC; Inverter is a type of converter that changes direct current (DC) to alternating current (AC) of desired voltage and frequency with the help of control signals and electronic switches. Here in this post, we are going to discuss inverter basics, classification and application of power inverters.

Types of Inverters

Inverters are classified into different types based on input, output, application and power rating.

Input Base Classification

Voltage Fed Inverter Basics

These are constant input voltage inverters. Current varies according to load demand but voltage remains independent of the connected load i.e., constant. In this type, a voltage link in the form of capacitor is provided in between the dc source and the inverter. Voltage fed inverter carry the characteristics of buck-converter as the output rms voltage is always lower than the input DC voltage.

 Current-fed inverters basics

Current-fed inverters are those which have constant input current. Their current is independent of the connected load. However, their voltage does vary according to the load applied. In this type, a current link (inductor) is provided in between the dc source and the inverter.

Variable DC-link inverters

Variable dc-link inverters are those whose input voltage is controllable by adjusting the values of inductor and capacitor used for DC link. In this type, DC current link and DC voltage link both are provided in between the DC source and the inverter. The output voltage can be adjusted accordingly.

Output Base Classification

Square Wave inverter

The square wave inverter converts DC input into square wave AC output. Undeniably, conversion is easy but square wave contains high harmonic contents making it unsuitable for use in AC motors and transformers where high harmonic signals are strongly. However, it became a gateway to new and better emerging technologies.

Quasi Square Wave inverter basics

Quasi square wave came as modification of square wave inverter. The output of a modified square wave, quasi square inverter, is similar to a square wave output except that the output goes to zero volts for a time before switching positive or negative. It is simple and low cost and is compatible with most electronic devices.

Sine Wave Inverter

As name suggests, A sine wave inverter produces a nearly perfect sine wave output (less than 3% total harmonic distortion) enabling it compatible with utility-supplied grid power and with all AC electronic devices. This is the type used in grid-tie inverters. This application demands Its design to be more complex and it costs more per unit power.

Multilevel Inverter

A multilevel inverter synthesizes a desired voltage waveform. Less power ratings of power devices used and cost makes it suitable for inversion purposes.

Inverter Basics: Resonant Inverters

This is the class of inverters in which output voltage or current is passed though zero to minimize switching losses. If the output voltage is passed through zero, it is called zero voltage switching and if the output current is passed through, it is called zero current switching. The required circuitry can be in series or parallel further dividing up into series resonant inverters and parallel resonant inverters.

Boost Inverter Basics

As obvious from the name, this type of inverter is developed in which the output voltage is greater than the input DC voltage. Boost inverter has a DC-DC boost converter in between DC source and the inverter, which first amplifies the DC voltage level and then feeds it to the inverter.

Application Base Classification

Inverter Basics: Grid Tie Inverter

A type of sine wave inverter designed to inject electricity into the electric power distribution system. Such inverters are synchronized with the frequency and voltage level of the grid. They usually contain one or more maximum power point tracking features to extract the maximum amount of power, and also include more sophisticated safety features. A synchronous inverter connects to a grid and allows routing to or from the grid depending on need.

Stand Alone Inverters

A stand-alone inverter is often used to translate direct current produced by renewable energy distributed generations sources like solar panels or small wind turbines to power the houses and small industries, mostly in remote locations lacking main utility grid.  Solar inverters have special features adapted for use with photovoltaic arrays for maximum power point tracking and anti-islanding protection.

Solar Micro Converter

A solar micro-inverter, differentiated from conventional solar inverter devices which are connected to multiple solar panels, transforms DC from a single solar panel into an AC.

Air Conditioner Inverter Basics

An air conditioner inverter modulates the frequency of the alternating current to control the speed of the air conditioner motor according to continuous adjustment of temperature control.

Inverter Basics: Power Rating Base Classification

Single Phase Inverter Basics

Single phase inverter is used in low and medium power demand applications or in single phase circuits. Low cost and ease of design are distinct features of single-phase inverter.

Inverter Basics: Three Phase Inverter 

In need of high-power three-phase inversion applications, three-phase inverters are preferred. However, inversion in these types of inverters is more intricate than that of in single phase inverters.

Applications of Inverters

Inverters are widely used in industries and home appliances and have become essential for our daily life. Some of the applications have been mentioned above in application base classification of inverters. Here are some other major applications of inverters:

An Uninterruptible Power Supply (UPS) uses batteries, converter and an inverter to convert low frequency AC power to higher frequency for use in induction heating. To do this, AC power is first rectified to provide DC power. The inverter then changes the DC power to high frequency AC power.

With HVDC power transmission, AC power is rectified and high voltage DC power is
transmitted to desired location. At the destination location, an inverter converts the power back to AC.

A variable-frequency drive (VFD) is vital part of industries where speed of motors is controlled by to drive the control valves at variable speed by changing frequency and voltage of the power supplied to the motor. An inverter air conditioner uses a variable-frequency drive to control the speed of the motor and thus the compressor.

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.

Conclusion

I hope you’ve liked this article on the basics of power inverters, their types and applications. You may also like our detailed article on the working and construction of a power system and Load flow analysis in ETAP software.

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