Real Time Active Harmonic Filter (AHF)

Harmonics and Power Quality :

The term Power Quality relates to the amplitude, frequency and distortion of the electrical supply. Whilst the utility provides a supply which has the amplitude and the frequency within controlled limits, it is the consumer and his equipment that distorts both the voltage and current waveforms. Prior to the proliferation of modern power electronics, most loads were linear drawing a sinusoidal current following the supply voltage. However, nowadays the most common loads are non-linear, utilizing power that is not sinusoidal. Non- linear equipment use converters to transform AC power to DC power. The type of converter, the semiconductor and load characteristics dictate the current drawn by the source. Since the current drawn is not sinusoidal, harmonics are generated. Harmonic Distortion caused by non-linear loads on the supply network results in currents in the system that are of a higher magnitude than expected and contain harmonic frequency components. The economic effects of these harmonics are shorter equipment life, reduced energy efficiency, and a susceptibility to nuisance tripping.

Effects of Harmonics :

- Overheating of transformers, cables and motors
- Nuisance tripping of circuit breakers
- Over—stressing of PF correction capacitors
- Reduced current carrying capacity of cables due to skin effect
- Neutral burnout
- Insulation Breakdown
- Zero crossing noise
- Voltage distortion
- Excitation of network resonance
- Increased carbon footprints
- Improper operation of microprocessor based equipments
- Non – Compliance with utility regulations

The Solution: AIM Active Harmonic Filter

The most efficient solution for active filtering of harmonics. smooth reactive power compensation and load balancing.
By actively monitoring the non-linear current demanded by the load, the AIM Active Harmonic Filter (AHF) electronically generates an adaptive current waveform which matches the shape of the non—linear portion of the load current. By injecting this matching current into the bus in real time, the AHF stops the destructive current at the point of connection.

By this mode of cancellation. the AIM AHF provides the industry‘s best attenuation of harmonic currents. The AHFs IGBT Converter Bridge reacts at micro-second speed to changes in the non-linear load current, allowing cancellation even as the high frequency harmonic components change.
The AHF is not affected by changes in the impedance in the system, nor will it react with other devices.The AHF will also not adversely affect the resonant points in the system. The AHF has no series components allowing an easy-to- install connection. If greater capacity is required. the AHF has built—in circuitry to allow for simple paralleling. Paralleled systems are available for single point field connections.

Unique Features

Adaptive Injection Mode(AIM) Harmonic Filter

The AHPs electronic bridge draws leading reactive current from the power line, stores it in a DC capacitor bus and delivers it back to the line as harmonic current, meeting the load’s demand for non—linear current at the point of connection. The source delivers fundamental current.

Industry’s Best Harmonic Cancellation Device

Unlike a tuned filter. the AHF continuously measures the load’s changing non-linear current and injects the required waveform to supply the loads harmonic current demand from the 2nd to the 51st harmonic.

Easy To Apply

The AHF is a non—resonating, non—tuned device. It can be installed anywhere on the distribution system. A simple measurement to determine the magnitude of harmonic current is all that is needed. For new installations the equipment manufacturer or your AHF supplier can provide the required data.

IGBT Bridge

The AHF’s Class-D Switching Mode Current Source Amplifier uses Insulated Gate Bipolar Transistors. These are high frequency switched power electronic devices that allow high resolution and micro-second response to match the loads non-linear current waveform. The AHF is connected parallel to the bus through a soft start circuit. When energized the AHF draws leading reactive current and the converter uses this to charge the internal DC Bus. The current transformers on two of the phases measure the load current. An electronic “notch filter” rejects the fundamental frequency component and passes the “distortion current components” (harmonic as well as non-harmonic, transient and sub-harmonic components). Electronically controlled linear attenuators reduce the harmonic current signals to limit the AHF’s harmonic current output to the unit’s rated BMS value.