Use of Harmonic Anti-Technologies in Frequency Converters
This article was written under the influence of a statement about the products of one frequency converter supplier: “the use of harmonic anti-technologies helped to achieve a THDI (Total Harmonic Distortion Indicator) value below 30%, without using additional filtering elements.”
Harmonics and Their Impact on Power Quality
It is known that all converters with a rectifier input circuit generate harmonics that differ from the fundamental, and their quantitative indicators depend on the loads. For frequency converters with a DC link, which are military uncontrolled rectifiers with a filter at the output, the THDI value varies in the range of 30-105% and changes depending on the load and properties of the power supply network.
The quality of electricity is improved through the use of a passive AC harmonic input filter within 5%.
Modern Solutions for Power Grid Cleansing
These issues are addressed by using active and hybrid filtering components based on semiconductor technologies. They include:
- Active type filtering elements;
- Reactive power compensators.
Active Filtering Components
Active filtering components of higher harmonics represent the latest group of devices that enhance the quality of electrical energy. An active filter can be connected in parallel or in series with respect to the nonlinear electricity consumer. It limits the ingress of harmonics into the power grid.
An active type filtering component is an element that transforms the voltage with choke elements on the AC side of the converter, compensating for higher harmonics of current by generating current harmonics in the power grid that are out of phase with the largest harmonics of the current consumed by the frequency converter.
Danfoss Devices
The quality of current is ensured by the converter of the company Danfoss. Such drive mechanisms perform constant adjustment to reduce harmonics considering the load and conditions in the power grid, without affecting the connected motor.
The VLT® Low Harmonic Drive device has a modular design similar to the standard Danfoss high-power drive mechanisms, offering the same capabilities: built-in components for filtering high-frequency interference and convenient software.
Need for Filters
Why are active filtering elements and harmonic anti-technologies needed? The production of filters is not done just for the sake of it. In Europe, for example, electricity can be disconnected if the total harmonic distortion coefficient of current exceeds the allowable value for a specific power grid. In the presence of large harmonic distortions caused by converting units, filters become essential to address this issue.
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