Why are active harmonic filters used to purify the power supply?

In modern industrial and commercial power systems, non-linear loads such as frequency converters, LED lighting, servo drives, and UPS are becoming increasingly common. These devices enhance efficiency and control accuracy while generating a large amount of harmonic current. Harmonic pollution is like "toxins" in the power grid, causing voltage distortion, overheating of equipment, malfunctions, and even permanent damage.

So, why are active harmonic filters (APFs) specifically used for purifying power supplies? What are the underlying principles and advantages of this approach?

I. The Hazards of Harmonics: Why Is "Purification" Necessary?

To understand the role of APF, one must first comprehend the hazards of harmonics. Harmonics are high-frequency components that are integer multiples of the fundamental frequency (50/60 Hz). Their presence can lead to:

1. Increased energy consumption and heat generation: This leads to overheating of transformers, cables, and motors, accelerates insulation aging, and significantly increases energy loss.

2. Causing equipment malfunctions: Disrupting the normal operation or causing incorrect actions of precision electronic devices (such as PLCs, medical instruments); leading to overcurrent resonance and burnout of capacitors.

3. Threat to system security: Causes the neutral line current to be excessively high, even exceeding the phase current, thereby increasing the risk of fire; leads to distortion of the voltage waveform, affecting the power quality of the entire power grid.

II. Why choose active filters for purification?

1. The filtering effect is outstanding and the dynamic response is rapid.

The APF can simultaneously filter out various harmonics ranging from 2nd to 51st order, or even higher. The filtering rate is usually above 97%.

The response speed is extremely fast (usually within 100 μs), and it can perfectly compensate for the harmonics generated by rapidly changing loads (such as press machines, welding machines), achieving real-time tracking and cancellation.

2. Highly adaptive, without causing resonance

The passive filter may form a parallel resonance with the grid impedance, thereby amplifying a certain harmonic and causing an accident. However, the APF is a controlled current source, and its characteristics will not resonate with the grid, making it extremely safe.

It can automatically track the changes in grid harmonics and adaptively compensate for them. There is no need to worry about failure due to load variations or changes in the grid structure.

3. Multi-functional, versatile in use

In addition to suppressing harmonics, APF usually also has the functions of compensating reactive power (improving power factor) and balancing three-phase loads. A single device can solve multiple electrical energy quality problems and has extremely high cost-effectiveness.