Can the active harmonic filter completely eliminate odd harmonics ranging from 2 to 50?

In theory, it is possible. However, in practical application, "complete elimination" is a relative concept. The final effect depends on the performance of the filter, its capacity design, installation location, and the complexity of the power grid environment. Active harmonic filters are one of the most advanced and effective devices for modern grid harmonic control, but their capacity is not unlimited.

I. The Working Principle and Technical Advantages of APF

To understand its filtering capability, one must first grasp its working principle. The core of the APF is an inverter based on power electronics technology (IGBT). It detects the load current in real time (using algorithms such as instantaneous reactive power theory or Fourier transform), quickly calculates the harmonic current components within it, and then immediately generates a compensation current of the same magnitude but opposite direction as these harmonic currents, and injects it into the power grid.

II. Why is it difficult to achieve an absolute "complete elimination"?

Although the APF has strong capabilities, in engineering practice, the pursuit of 100% absolute filtering is neither realistic nor economical. The limitations mainly come from the following aspects:

1. Capacity Limitation (The Most Critical Factor)

APF is an active device, and its compensation capacity is determined by its rated current (such as 50A, 100A, 300A). If the total harmonic current generated by the load exceeds the rated output capacity of the APF, the APF will enter a saturation current-limiting state and will be unable to provide sufficient compensation current, resulting in some harmonics being unable to be filtered out.

2. Performance Limitations

Switching frequency: The IGBT switching frequency of the APF determines the highest harmonic order that it can precisely compensate for. The higher the switching frequency, the more harmonics it can compensate for, and the more expensive it becomes. For the 50th harmonic (2500 Hz), the mainstream APF switching frequency is sufficient to cover it, but for higher-order harmonics, it will become less effective.

3. Installation and its impact on system impedance

Installation location: The ideal installation point for an APF is as close as possible to the input end of the harmonic source load. If the installation point is too far from the load, the system's line impedance will weaken the compensation effect of the APF, especially for high-frequency harmonics.