Low Voltage APF Active Power Filter

APF stands for Active Power Filter.Also known as Active Harmonic Filter.What is filtering?To put it simply: tap water in rivers contains all kinds of pollutants, and we install a water purifier at home to filter out impurities. Similarly, the current in the power grid is just like river water. APF filters out interference (impurities) in electricity to ensure stable and high-quality power consumption.

An active power filter is a new type of electronic device for dynamic harmonic suppression and reactive power compensation. It is capable of compensating for harmonics with variable magnitude and frequency, as well as fluctuating reactive power.Active power filters feature high controllability and fast response. They can track and compensate for each order of harmonics and automatically generate variable reactive power on demand. Their performance is not affected by the power system, with no risk of harmonic amplification.

Functions of APF

It is a power electronic device that generates harmonic voltage or harmonic current to counteract the harmonic voltage or current in the power system.As a new-type power electronic device for dynamic harmonic suppression and reactive power compensation, it can compensate harmonics with variable magnitude and frequency, as well as fluctuating reactive power.

For a 50Hz power supply, the fundamental frequency is 50Hz. The 3rd harmonic frequency is 150Hz, the 5th harmonic is 250Hz, and the 7th harmonic is 350Hz, and so on.(The 3rd, 5th, 7th harmonics are equivalent to impurities in water, which will damage the power quality of the power grid.)

Low Voltage Active Power Filter

Classification of APF

By application environment: Indoor type, Outdoor type.
By wiring type: Three-phase three-wire system, Three-phase four-wire system.
By structural form: Wall-mounted type, Cabinet type, Rack-mounted type.
By cooling method: Natural cooling type, Forced air cooling type, Water cooling type.

Working Principle of APF

Counteract harm with countermeasures.The core principle of APF is to detect harmonics in real time and generate compensation current with equal magnitude and opposite phase to offset the impact of harmonics on the power grid.
An active power filter is a new special power harmonic control device developed with modern power electronic technology and digital signal processing technology based on high-speed DSP chips.It mainly consists of two core parts: the reference current calculation circuit and the compensation current generation circuit. The reference current calculation circuit monitors the line current in real time, converts analog current signals into digital signals, and transmits them to the high-speed Digital Signal Processor (DSP) for data processing. It separates harmonics from the fundamental wave and outputs driving pulses in the form of Pulse Width Modulation (PWM) signals to the compensation current generation circuit. This drives the IGBT power modules to generate compensation current that is equal in amplitude and opposite in polarity to the grid harmonic current. The generated compensation current is injected into the power grid to compensate or offset harmonic currents and actively eliminate power harmonics.
In addition, the active power filter is also equipped with the function of reactive power compensation.

Working Process

Detection: Sensors collect harmonic components in load current in real time.
Calculation: The controller (usually DSP, Digital Signal Processor) rapidly calculates the required compensation harmonic current.
Generation: The inverter outputs compensation current with equal amplitude and reverse phase to the original harmonics.
Injection: The compensation current is injected into the power grid to counteract original harmonics, restoring the grid current to a pure sine wave.The whole process is completed within milliseconds, realizing dynamic and adaptive filtering performance.