الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
- Due to the highly various usage of the semiconductor devices industry concerning their great functions, however these devices are considered to be the main source in generating the harmonics in electric networks (electric pollutants).
’These harmonics cause the following harms:-
1- Generating excessive temperature in transformers coils causing increasing in iron and copper losses.
2- Generating excessive temperature and occurring of mechanical vibrations in loads which are connected to motors.
3- Damage in the used capacitors improving power factors circuits.
4- Failure in the firing of thyristors or transistors circuits.
5- Failure in the relays and protection circuits.
For all the previous hanns, it is necessary to present effective method to eliminate the harmonics.
1- First method
By using the passive harmonic filters, other than eliminating the harmonics, they improve the power factor also. It consists of coils, capacitors and resistors (passive elements). But this method has its disadvantages such as:-
1- Both ofhannonics and fundamental cunents pass through the passive filter.
2- As a result of increasing in hannonics cUlTent, the damage takes place in the passive filter.
3- Practically resonance not occurs in a certain frequency, but in a band contains it.
4- The bad effect of the source impedance to the operation of filter, and generally review the parameters of network and filter.
2- Second method
By designing of the active power filter which estimates the value of all harnlonics order by estimator technique which enhances the control technique in controlling the inverter to inject a signal equal but opposing in direction (Phase Shift 180°) to the hannonics cunent or voltage, consequently the harnlonics are eliminated.