Discover harmonic filter circuit

harmonic filter

In electrical power systems, harmonics are voltage, otherwise current occurs at different fundamental frequencies. Often considered noise inside the power line. The harmonics within a power system can be categorized into two types as voltage harmonics and current harmonics. But it is absolutely necessary to eliminate harmonics within power systems with a harmonic filter, otherwise the power delivery needs to be redesigned to control non-linear loads.

Current harmonics can be induced by variable speed drives (VSDs) called non-linear load. Likewise, voltage harmonics generally occur due to the generation of distorted voltage through the effect of current harmonics using source impedance. This article is an overview of the definition of a harmonic filter, it works with applications.

What is a harmonic filter?

A device which is used to attenuate, and reduce harmonics to acceptable ranges in a power system, is known as a harmonic filter. This harmonic filter is used at strategic operating circuit points to eliminate or reduce harmonic and resonance distortion. In general, harmonic distortion can occur due to excessive currents in and out of devices.

Harmonic filter avoids massive amounts of harmonics from equipment damage, reduces operation and lowers operating costs. Therefore they are used in various industries such as HVAC, oil and gas, mining and waste water to avoid component damage or utility provider fines.

harmonic filter



The harmonic filter can be designed with a range of different electronic components such as resistors, capacitors and inductors to prevent unnecessary harmonic currents and transmit them to ground. These filters are primarily designed to block out certain frequency harmonics.

Working principle

The working principle of the harmonic filter is to reduce distortion by deflecting harmonic currents within the paths of least resistance. These filters are capacitive at the fundamental frequency, so they are used to generate the necessary reactive power through transformers and also for power factor correction.

Types of harmonic filters

In general, harmonic filters are categorized into different types based on the applied voltage, rated power, 1 phase or 3 phases and other various parameters that depend on the load. These are highly effective filters that protect expensive electrical equipment from excess power due to harmonics.

There are two types of harmonic filters as active and passive. The main difference between these two components is the components used during filter design. Active harmonic filter uses active components such as integrated circuits, BJTs, IGBTs and MOSFETs while passive harmonic filter uses various passive components such as resistors, capacitors and inductors.

Active Harmonic Filters

It is very easy to use active filters to switch harmonics of a power line without relying on the reactive power of the fundamental frequency. These filters use great technology anywhere the filter uses self-created harmonic components and pumps them into the power line to cancel out unnecessary harmonics.

Compared with active filters, passive harmonic filters eliminate harmonics very easily within the power line, but their design is very difficult. Therefore the designer must design these filters based on the reactive power requirements of the load. So in this case, designing the passive filter is not easy and causes poor filter power under given loading conditions.

Active Harmonic Filter

Active filters are available using different topologies to remove harmonics within the power line. The following steps must be considered while designing an active harmonic filter.

This filter uses different types of semiconductor switches that need power to function.

Voltage source inverter with different power switches

Reference sampling and power line control

The PWM system as the harmonics injects the PWM firing signal into the power system.

Negative Harmonic Filters

Negative harmonic filters are readily available and are the most widely used. These filters use typical passive components such as capacitors, resistors, etc. to create a tank circuit. This circuit is primarily designed to operate at a similar resonant frequency compared to non-essential harmonics.

negative harmonic filter

These filters prevent unnecessary harmonics from being supplied and change the harmonic current source to temperature and defend the final load or device. There are four types of passive harmonic filters in use such as the high-pass filter, the sequential filter, the c-type filter, and the band-pass filter.

Harmonic filter in capacitor bank

Power factor correction needs to be designed to compensate for the reactive power demand and to inject harmonic currents through the device into the power supply system. In general, power supply systems in industries include a capacitor bank and an arrangement of tuned filters. Collaboration Analysis