What is harmonic and how to manage it?
Harmonics denote electrical quantities that possess frequencies which are integer multiples of the fundamental wave present in the current. This concept typically involves the Fourier series decomposition of periodic, non-sinusoidal electrical quantities. In this context, any electrical quantity with a frequency exceeding that of the fundamental wave, derived from the current, is classified as a harmonic. The harmonic order is determined by the ratio of the harmonic frequency to the fundamental frequency, mathematically represented as n=fn/f1.
The visual representation of harmonic waveforms is illustrated in Figure 1, depicting the distinct patterns associated with each harmonic component. Complementing this, Figure 2 presents a harmonic decomposition diagram, showcasing how these individual harmonic frequencies combine and are analyzed from the overall complex signal, thereby elucidating their contribution to the total electrical waveform.
Fig. 1 Harmonic oscillogram | Fig. 2 Harmonic Decomposition Diagram |
Where Harmonics Come From?
In today's world, many devices we use every day can create something called "harmonic" currents when they use electricity. Think of these harmonics like extra music notes that our electrical system wasn't expecting.
Devices That Cause Harmonics:
- Switch Mode Power Supplies (SMPS) found in computers, phone chargers, and TVs.
- Energy-saving light bulbs** with electronic ballasts that help them glow.
- Speed controllers for fans, pumps, and air conditioners.
- Uninterruptible Power Supplies (UPS)** that keep computers running during power cuts.
- Big machines with transformers and motors, like factory equipment and elevators.
- Even common household items** like TVs and kitchen appliances.
Also, various gadgets that turn AC power (what comes from the wall) into DC power (what most electronics need) can add harmonics. This includes things like battery chargers and adjustable voltage devices.
In industry, advanced tools like **frequency converters** have become super useful for controlling motor speeds, making factories more efficient. But, just like a side-effect, these converters create a lot of those extra harmonics. They make the electricity flow in a wavy, uneven way instead of a smooth, clean pattern.
These harmonics can cause the voltage in the grid, which is like the electricity's 'main road', to have dips and bumps. It's a bit like driving on a bumpy road—it might slow things down and make the ride less comfortable.
As technology advances, managing these harmonics becomes even more crucial to keep our power supply clean and reliable, just like maintaining a smooth highway for electricity to travel on.
Addressing harmonic distortions in electrical systems is crucial for maintaining power quality, ensuring equipment longevity, and preventing disruptions. Two primary approaches to mitigating harmonics are passive filtering and active filtering, each with its own advantages and applications.
Passive Harmonic Filters: Passive filters are essentially a combination of inductors (coils), capacitors, and sometimes resistors, designed to attenuate specific harmonic frequencies. They operate based on the principle of resonant circuits, targeting and absorbing harmonic currents before they can circulate back into the power grid. Passive filters are relatively simple, robust, and require minimal maintenance.
They are particularly effective at reducing low-order harmonics (e.g., 3rd, 5th, 7th) and are often cost-effective for applications where the harmonic spectrum is predictable and stable. However, their fixed tuning makes them less adaptable to changing harmonic loads, and they can potentially resonate with system impedances, causing overvoltage or amplifying other harmonic orders if not carefully designed.
Active Harmonic Filters (AHF): In contrast, active filters employ power electronics to actively monitor and inject compensating currents into the system to cancel out harmonic currents. AHFs consist of power converters, control algorithms, and a DC link capacitor. By constantly analyzing the network’s harmonic content, they generate precise counter-signals that negate the impact of harmonics in real-time.
This adaptability enables AHFs to handle a wide range of harmonic frequencies, making them highly effective in complex and variable load environments. They can dynamically adjust their compensation strategy as the harmonic profile changes, ensuring optimal performance even with unpredictable loads. While AHFs offer superior harmonic mitigation flexibility and accuracy, they come with a higher initial cost and require more sophisticated control systems compared to passive filters.
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