Threephase Rectifiers Rectifiers SEE 4433 Half wave Singlephase

Three-phase Rectifiers

Rectifiers (SEE 4433) Half wave Single-phase Uncontrolled (diode) Controlled (SCR) Full wave Single-phase Uncontrolled (diode) Controlled (SCR) Three-phase Uncontrolled (diode) Controlled (SCR)

Uncontrolled (diode) Three-phase Rectifiers • At any one time, only ONE of the upper diodes can conduct • The most forward biased diode will conduct – this will depend on the instantaneous phase voltage since the upper diodes have a common cathode • At any one time, only ONE of the lower diodes can conduct • The most forward biased diode will conduct – this will depend on the instantaneous phase voltage since the lower diodes have a common anode

Uncontrolled (diode) Three-phase Rectifiers • At any one time, only ONE of the upper diodes can conduct • The most forward biased diode will conduct – this will depend on the instantaneous phase voltage since the upper diodes have a common cathode • At any one time, only ONE of the lower diodes can conduct • The most forward biased diode will conduct – this will depend on the instantaneous phase voltage since the lower diodes have a common anode

Uncontrolled (diode) Three-phase Rectifiers • The load voltage, vo, is the difference between the phase voltage (line-line voltage) For example, when D 1 and D 6 conduct, using KVL -van +v. O +vbn = 0 ==> v. O = van – vbn = vab

Uncontrolled (diode) Three-phase Rectifiers • The load voltage, vo, is the difference between the phase voltage (line-line voltage) When D 1 and D 2 conduct, using KVL -van +v. O +vcn = 0 ==> v. O = van – vcn = vac

Uncontrolled (diode) Three-phase Rectifiers

Uncontrolled (diode) Three-phase Rectifiers

Controlled (SCR) Three-phase Rectifiers • The transition of output voltage to the maximum instantaneous line-line voltage can be delayed • The reference of delay angle is when the SCR should conduct if it is a diode

Controlled (SCR) Three-phase Rectifiers

Controlled (SCR) Three-phase Rectifiers Delay angle beyond 90 o is possible if the load is active (e. g. DC motor). The power is transferred from the load to the source.