Understanding the Working Principle of Active Power Filters

Active power filters have emerged as a revolutionary power electronic device that effectively tackles the issues of harmonics and reactive power in electrical systems. By dynamically suppressing harmonics and compensating reactive power, these filters play a crucial role in maintaining the quality and efficiency of power supply.

What are Harmonics and Reactive Power?

Before delving into the working principle of active power filters, let’s briefly understand the concepts of harmonics and reactive power.

Harmonics: In an electrical system, harmonics are unwanted frequencies that are multiples of the fundamental frequency. These harmonics are typically generated by non-linear loads such as power electronics devices, variable speed drives, and rectifiers. Harmonics can result in voltage and current distortions, leading to power quality issues, increased losses, and equipment malfunction.

Reactive Power: Reactive power is the power that oscillates between the source and the load without performing any useful work. It is caused by inductive or capacitive loads in the system. Reactive power can lead to low power factor, voltage fluctuations, and increased system losses.

The Role of Active Power Filters

Active power filters are designed to mitigate the negative effects of harmonics and reactive power. They employ advanced control algorithms and power electronics technology to actively monitor and regulate the current flowing through them.

Here’s a breakdown of the working principle of active power filters:

1. Current Sensing and Measurement

The active power filter continuously senses and measures the current flowing through it. This is achieved using current sensors such as current transformers or Hall effect sensors. The sensors provide real-time information about the magnitude and phase of the current.

2. Harmonic Detection and Analysis

Based on the current measurements, the active power filter detects the presence of harmonics. It analyzes the harmonic content and identifies the specific frequencies and magnitudes of the harmonics.

3. Generation of Anti-Harmonic Current

Once the harmonics are detected, the active power filter generates an equal and opposite anti-harmonic current. This current is injected into the electrical system, effectively canceling out the original harmonics. The anti-harmonic current is generated by an inverter or a similar power electronic device.

4. Reactive Power Compensation

In addition to harmonic suppression, active power filters also compensate for reactive power. They continuously monitor the power factor of the system and inject or absorb reactive power as required. This helps in balancing the system’s reactive power and maintaining a high power factor.

Benefits of Active Power Filters

Active power filters offer several benefits in terms of power quality and system efficiency:

  • Harmonic Mitigation: By actively suppressing harmonics, active power filters ensure a clean and distortion-free power supply, reducing the risk of equipment malfunction and improving overall system performance.
  • Reactive Power Compensation: The ability to compensate for reactive power helps in maintaining a high power factor, reducing voltage fluctuations, and minimizing system losses.
  • Flexibility and Adaptability: Active power filters can be easily integrated into existing electrical systems and can be programmed to adapt to changing load conditions and harmonic profiles.
  • Cost Savings: By improving power quality and reducing system losses, active power filters can lead to significant cost savings in terms of energy consumption and equipment maintenance.


Active power filters are an essential tool in modern electrical systems for addressing the challenges of harmonics and reactive power. By actively suppressing harmonics and compensating reactive power, these filters ensure a clean and efficient power supply, improving the overall performance and reliability of the system. Incorporating active power filters can lead to significant benefits in terms of power quality, cost savings, and system longevity.

Kaich-Power is a national high-tech enterprise specializing in power quality optimization, research and development, production and sales of various types of power protection equipment. We provide a variety of power protection equipment. For details, please refer to our company’s website or product details. We are waiting for your inquiries or calls 24 hours a day. Email: kaichelectric@gmail.com  WhatsApp:15855175763

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