How Power Electronics Generate Harmonics in Electrical Systems

Modern electrical systems rely heavily on power electronic devices such as chargers, LED drivers, computers, UPS systems, and variable frequency drives. These devices improve efficiency and enable advanced control of electrical equipment. However, they also introduce a major power quality issue known as harmonics.

In this blog, we will understand how power electronics generate harmonics and why these distortions occur in electrical systems.

What Are Power Electronic Devices?

Power electronic devices are equipment that convert and control electrical power using semiconductor switches.

Unlike traditional electrical loads such as motors or heaters, power electronic devices use components like:

• diodes

• thyristors

• transistors

• IGBTs

• MOSFETs

These semiconductor devices switch electrical current rapidly on and off, allowing efficient power conversion and control.

Common power electronic equipment includes:

• mobile chargers

• laptop adapters

• LED drivers

• UPS systems

• rectifiers

• variable frequency drives (VFDs)

While these devices are extremely useful, their switching operation introduces non-linear current flow, which generates harmonics.

Why Power Electronics Produce Harmonics

Traditional electrical loads draw current smoothly from the power supply. This produces a clean sinusoidal current waveform.

Power electronic devices behave differently.

They draw current in short pulses instead of smooth waves. This pulsed current creates distortion in the electrical waveform, leading to harmonic currents.

The more power electronic devices connected to a system, the higher the harmonic distortion in the electrical network.

Common Power Electronic Devices That Generate Harmonics

Let us look at some of the most common sources of harmonics in modern electrical installations.

Chargers and SMPS Power Supplies

Most electronic devices today use Switched Mode Power Supplies (SMPS).

Examples include:

• mobile chargers

• laptop adapters

• computer power supplies

• televisions

SMPS units convert AC power to DC using rectifier circuits and high-frequency switching devices.

This switching process causes non-linear current draw, which generates harmonics in the electrical system.

In buildings with many electronic devices, SMPS loads can significantly increase harmonic distortion.

LED Lighting and LED Drivers

LED lighting systems are widely used today because of their high energy efficiency.

However, LED lamps use electronic drivers to convert AC supply to the required DC current.

These drivers often use switching circuits, which produce harmonic currents.

Large commercial buildings with thousands of LED lights can therefore experience significant harmonic levels.

Variable Frequency Drives (VFDs)

Variable Frequency Drives are commonly used in industries to control the speed of motors.

Applications include:

• pumps

• compressors

• HVAC systems

• conveyor systems

VFDs convert AC supply to DC and then back to variable frequency AC.

This conversion process involves rectifiers and inverters, which generate strong harmonic currents, especially the 5th and 7th harmonics.

UPS Systems

Uninterruptible Power Supply (UPS) systems are widely used in:

• data centers

• hospitals

• IT facilities

• office buildings

UPS systems use rectifiers, batteries, and inverters to provide backup power.

These power conversion stages introduce harmonic distortion into the electrical system.

Impact of Power Electronics Harmonics

When harmonics generated by power electronic devices increase beyond acceptable levels, they can cause several problems such as:

• overheating of transformers

• increased cable losses

• capacitor bank failures

• nuisance tripping of circuit breakers

• neutral conductor overheating

This is why harmonic analysis is becoming an important part of modern electrical system design.

Wrapping Up

Power electronic devices have become an essential part of modern electrical systems. However, their switching operation introduces non-linear currents, which generate harmonics in the electrical network.

Equipment such as SMPS power supplies, LED drivers, variable frequency drives, and UPS systems are among the most common sources of harmonics today.

Understanding how power electronics generate harmonics is the first step toward identifying power quality problems and designing effective mitigation solutions.

In the next blog, we will explore how harmonics affect electrical equipment, industries, and electricity consumers.