Active dynamic filtering

Active dynamic filtering, ADF, is a three-phase power electronics-based power flow control technology that can effectively be used to isolate and remove electrical behaviours that cause excess losses and disruptions in the electrical network.

Example on behaviours as described in [ [http://comsys.se/solutions/power-quality power-quality] comsys solutions] that cause losses and disruptions are harmonics, reactive power, phase unbalance, flicker and resonance. All these behaviours exists naturally in most electrical networks due to the use of modern equipment and machinery. The increasing use of electronic loads such as rectifiers, motor adjustable speed drives and fluorescent lighting adds frequency components (harmonics) which are not natural to the electrical network designed to operate balanced loads at a single frequency and will cause losses and affect the capacity of the power supply. Surveys of power quality issues indicates that costs from losses due to these behaviours are increasing. According to Leonardo Energy Pan-European Power Quality Survey in 2007 it amounted annually to EUR 150bn [ [http://www.leonardo-energy.org/drupal/files/PQ%20Survey%20%20webinar%2025-09-2007.pdf?download] Leonardo Energy, Pan-European Power Quality Survey 2007] only in Europe.

Electrical behaviours has traditionally been addressed using fixed passive filtering techniques controlling the frequency content or circulating reactive (magnetization) currents. These filtering and power factor correction devices was equipped with simple mechanical and later electro-mechanical control to stepwise filter and compensate for the undesired behaviours.

With the development of power electronics and semiconductors that could switch high currents at high voltage, new approaches was made possible.

Thyristors started to replace elecro-mechanical switching devices in compensation systems in the 1980s. This improved the performance and the possibility of following the dynamics of modern electrical loads. Thyristor driven compensation methods are referred to as "static" and implies the use of circuits switched without moving parts. Static VAR compensators compensate dynamic loads under automatic control but are limited in that they still connect and disconnect passive filter elements and can only achieve a limited operational dynamic performance.

The generation of power transistors based on IGBT or MOSFET technologies developed during the 1980s and 1990s made it possible to design digital switches that could operate as amplifiers rather than as switches. This made it possible to use signal processing of high power high electrical current the same way signal processing is performed in audio circuits using either analog or digital amplifers. High power amplifier configurations all use switching amplifer designs that emanates from class-D switching amplifier topology.

Active power compensation and filtering methods such as ADF that utilize transistor based digital amplification techiques are commonly referred to as active power conditioners.

Active power conditioners such as the ADF has the ability to continuously follow the dynamics of the power flow to and from electrical loads and fully compensate for undesired electrical behaviours with little or no delay. Power conditioners can be placed both in serie and parallel with the load or generator that requires compensation. Parallel connection is the most common configuration and the operating principle shown in [ [http://comsys.se/explore/technology Explore technology] ADF Operating Principle ] .

Active power conditioners can improve electrical efficiency, network stability and power quality for most applications within power generation and consumption. The adoption of this new generation of power quality solutions started in the late 1990s and is now becoming more widespread driven by increasing electricity price, rising demand on supply availability, efficiency regulations and environmental issues.

Applications with high degree of harmonics, network unbalance and voltage variations benefit from new technologies as active power conditioners e.g. windfarms, electric arc furnaces (EAF), data centers and welding systems.

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