Working Principle of Active Harmonic Filter

The PWM INVERTER technology is the basic building block of an Active Harmonic Filter. Active filters are new generation harmonic filters which use modern technologies and devices to provide revolutionary filtering solution.

Essentially, they are wide spectrum harmonic current sources capable of generating a large range of harmonic currents and use very high speed switching devices like IGBTs ensuring response time of a few milliseconds. They produce counter harmonic currents in phase opposition to that produced by non linear loads, and these generated currents are injected into the system in real time ensuring effective cancellation of all harmonics present in the network.

In addition to canceling the harmonic current, active filter are capable of improving the power factor by providing both capacitive and inductive reactive power in a step less manner. Presently, active filters are the most technologically advanced solutions available for harmonic filtering.

The Active filter uses a CPU for detecting the order and magnitude of the harmonics present in the network and generates a harmonic current spectrum in phase opposition to the measured spectrum. The control system of the Active Harmonic Filter is designed to operate in real time.

The block diagram of the Active Filter is as given below.

The Active filter is IGBT based harmonics generator. The active harmonic filter is connected in parallel to the load to be compensated. The harmonics present in the system is measured by the CPU  of active filter unit. The CPU controls the IGBT unit of the active filter. The CPU commands to the IGBT control unit to generate the harmonics spectrum in just phase opposition to the measured harmonic spectrum in a real time basis to nullify the load harmonics. The active filter provides very fast response to compensate the harmonic current.

The active filter can generate harmonics order from 2 to 50th. The cost of the active filter is much more than the passive filter but the complete eradication of the harmonics is possible using active filter.The active harmonic filter is also known as active harmonic conditioner.