The differences between active power filter (APF) and active harmonic filter (AHF)
Jul 12, 2025| In the power system, the issue of power quality has become increasingly prominent, and harmonic pollution has become an important factor affecting the quality of power supply. Active power filters, as an effective means of controlling harmonics, are mainly divided into two types: active power filter APF and active harmonic filter AHF. Although these two technologies have similar goals, they differ significantly in their working principles, performance characteristics, and application scenarios.
I. Differences in Basic Concepts and Working Principles
The active power filter (APF) is an active filtering device that detects the harmonic components in the load current in real time, and then generates a compensation current with the same amplitude but opposite phase, thereby eliminating the harmonic components. Its core lies in the use of PWM converter technology and advanced control algorithms, which can dynamically adapt to changes in the load.
Although AHF belongs to the category of active filtering, its working principle focuses more on the targeted elimination of specific sub-harmonics. AHF typically employs a resonance control strategy and has a higher suppression efficiency for specific frequency harmonics. However, in terms of full-spectrum harmonic management, it is slightly inferior to the active power filter (APF).
II. Comparison of Performance Characteristics and Technical Parameters
From the perspective of performance indicators, active power filters (APFs) have a wider range of harmonic compensation capabilities. They can typically achieve full-spectrum compensation for 2 to 50 harmonic frequencies, with a response time generally within 100 μs, and a compensation efficiency of over 95%. This comprehensive performance makes them an ideal choice for complex harmonic environments.
In contrast, AHF performs better when dealing with specific sub-harmonics (such as 5th, 7th, 11th, etc., characteristic harmonics). Its compensation efficiency can be increased to 98%, and the device's own loss is lower. However, when it comes to non-characteristic harmonics or random harmonics, its adaptability is not as comprehensive as that of the **active power filter APF**.
III. System Structure and Cost Differences
The system structure of active power filter (APF) is relatively complex, including high-speed DSP processors, multi-level converter topologies and precise sensor networks. This results in a relatively high initial investment cost. However, considering its wide applicability to various harmonic scenarios, the life-cycle cost-effectiveness is remarkable.
The structure of AHF is more concise. It is mainly optimized for the preset harmonic frequencies and has a relatively simplified hardware configuration. The initial cost is approximately 20-30% lower than that of active power filter (APF). This cost advantage makes it particularly attractive in scenarios where the harmonic components are clear and stable.
The key to choosing between active power filter (APF) and active harmonic filter (AHF) lies in accurately assessing the harmonic characteristics of the site. For scenarios with complex and frequently changing harmonic components, the comprehensive performance advantages of active power filter (APF) are obvious; while for stable loads dominated by specific sub-harmonics, active harmonic filter (AHF) may offer better cost-effectiveness.