Filtering systems

Filtration – improvement of rectifying systems output parameters
L and C reactance elements are used in rectifying systems in order to improve their properties. These elements fulfill two basic functions: they reduce the pulsation and store the energy when the value of rectified alternating voltage is high, in order to return that energy when the voltage is decreasing. These elements can be connected in two ways:

  • capacitive – in parallel to the load,  
  • inductive – in series to the load.  

Such solutions are applied mainly in rectifying systems which are characterized by disadvantageous suppression factor.

a) b)
Single-phase rectifying systems with resistance-capacitive load. Diagrams and runs of voltage and current: a) half-wave rectifier; b) full-wave rectifier 
Description: Odbiornik - Receiver

Comparing to the systems with resistance load the rectifying systems with resistance-capacitive load are characterized by better efficiency and lower pulsation. These systems achieve the best properties at high values of load resistance (RO). Therefore they are applied within the range of relatively small powers, mainly in 1-phase systems, rarely in 3-phase systems. 

Full-wave rectifier with resistance-inductive load.

 

The systems with resistance-inductive are usually of full-wave type, because it is hard to obtain a continuous current flow through the load in the 1-phase half-wave systems .
The constant component of the output voltage does not depend on the inductance.
Along with the inductance increase the pulsation factor decreases, so the share of variable components in the output voltage decreases :
 

When ωL/R0 relation increases then the output voltage run is approaching the ideal. The filtration properties of the rectifier with resistance-inductive load are improving also along with the load increase (IOS increases, RO decreases). Therefore such systems are applied for high load currents, mainly in 3-phase or 6-phase versions.

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