Power Rectifiers
For: Level-5
Nepal Electricity Authority
By: Er. Gopal Sapkota
Electrical Engineer
Nepal Electricity Authority
Rectifier/Converter
Rectifier
Rectifier is an electronic circuit that converts the alternating current
(AC) into direct current (DC) by allowing a current to flow through
the device in one direction only, using semiconducting devices.
Types:
Single Phase Rectifiers
Three Phase Rectifiers
Controlled Rectifiers
Uncontrolled Rectifiers
Half Wave Rectifiers
Full Wave Rectifiers
Bridge Rectifiers
Center-Tapped Rectifiers
Single Phase Half Wave Diode Rectifier
Single Phase Full Wave Rectifier
Centre Tapped and Bridge Rectifier
Sinlge Phase Controlled Rectifier for R-Load
1-Phase have wave rectifier for RL-Load
Converter Filters
C-Filter
L-Filter
The property of inductor is to oppose the change in current
flowing through it.When current through it tends to increase
or decrease,an emf “called self induced emf” is induced that
opposes the cause of curent variation
Inductor filter requires full wave rectifier as current flows
through the rectifier all the time
Inductor filter is better for large load current
The positive peak of filtered output Vout is always less than
that of the rectifier output since a part of rectifier output is
absorbed by the inductor.
Other Filters are:
L-C (Choke Input) Filters
Pi-Type and T-Type Filters
Question: Define Firing angle in Controlled Rectiifer Circuit
Definition: The firing angle is the angle at which the gate signal is
applied to the SCR to turn it on within each AC half cycle. It is
measured from the zero-crossing point of the AC voltage
waveform.
Control: The firing angle is a control parameter that regulates
when the SCR starts conducting within each half-cycle. By
adjusting the firing angle, we can control the portion of the AC
waveform during which the SCR conducts.
Range: The firing angle typically ranges from 0° to 180° in each
half-cycle of the AC waveform.
Purpose: It controls the output voltage and power delivered to the
load. A smaller firing angle means the SCR turns on earlier,
resulting in higher power delivery. In comparison, a larger firing
angle means the SCR turns on later, resulting in lower power
delivery.
Conduction Angle,β
Relationship with Firing Angle: The conduction angle
complements the firing angle and can be calculated as
β=180∘−α, where α is the firing angle.
Duration: The conduction angle represents the duration
the SCR conducts current in each half-cycle. The firing
angle directly influences it.
Types of 3-phase Rectifiers
Three phase half wave rectifiers
Three phase Mid-point 6 pulse rectifiers
Three phase bridge rectifiers
Three phase twelve pulse rectifier
Three phase half wave diode rectifier
Construction
Circuit diagram is shown below. It uses a three phase T/F with Delta-Star
configuration. Diodes D1,D2 and D3 are connected on each phase
individually.Their cathodes are connected together to a common load ‘R’.
This circuit is also called common cathode for a 3-phase half wave rectifier
Working:
Diode in each phase conduct
when phase voltage across it
is maximum.
when diode of any one phase
conducts,other phase diodes
are reverse biased
For a complete input
cycle,there are 3 output
pulses.
Va=Vmsin(ὡt)
Vb=VmSin(ὡt-120)
Vc=VmSin(ὡt-240)
Three Phase Bridge Rectifier
Construction/Working:
Circuit diagram is shown below.It consists of six diodes
All diodes are arranged in three legs,each with 2 diodes
Upper diodes; D1,D3 and D5 called positive group,they conduct when their
phase voltages are at maximum positive value.
Lower diodes; D2,D4 and D6 called negative group,they conduct when
their phase voltages are at miniumum negative value.
Any two diode,one from positive group and other from negative group
conduct together.
Line voltage appers at output terminal as both phase diodes operate at
any instant.
For each cycle of input voltage,there are six pulse in rectified voltage.
References:
1. Power Electronics, By: Muhammad H. Rashid
2. Industrial Power Electronics, By: Prathak.ganguly
3. Power Electronics,By: J.S.Chitode
4. Power Electronics,By: Dr. P.S.Bimbhra
Thank YOU
