This document discusses power electronics and various types of rectifiers. It covers topics such as diode rectifiers, controlled rectifiers, rectifier performance parameters, single-phase and three-phase rectifiers, and applications of single-phase controlled rectifiers in battery chargers. Diode and thyristor-based rectifiers are classified as uncontrolled and controlled rectifiers. Key performance parameters discussed include form factor, efficiency, ripple factor, and transformer utilization factor. Circuit diagrams and voltage and current waveforms of half-wave, full-wave, and bridge rectifiers are presented.
4. Rectifiers
AC to DC Convertors
Uncontrolled Rectifiers
Rectifiers based upon Diodes, stop conducting due to natural Commutation
Controlled Rectifiers
Rectifiers based upon Thrystor, stop conducting due to natural/ forced Commutation
5. A rectifier convert AC supply into unidirectional DC supply.
Alternating Sinusoidal Waveform
𝑉𝑎𝑣𝑔 = 0.636 𝑉𝑝𝑘
𝑉𝑟𝑚𝑠 = 0.707 𝑉𝑝𝑘
Line voltages measured
from Wall socket:
220 VRMS = 311V Vp-p
AC to DC conversion
Rectifiers
8. Diode D1 conducts during the
positive half-wave of the voltage.
Diode D2 conducts in the
negative half.
The current always flows from
the common point of the diodes,
through the load and back to the
central tap of the transformer.
Single Phase Full Wave Rectifier
(with Resistive Load)
Rectifiers
9. Single Phase Full Wave Rectifier
(with Resistive Load)
Full Wave Center-tapped Rectifier
Rectifiers
The output voltage varies between the peak voltage Vm and zero
in each cycle.
This variation is called “ripple”, and the corresponding voltage
is called the peak-to-peak ripple voltage, Vp-p.
Ripple % = (Vp-p/Vavg) x 100
11. In the full-wave rectifier circuit, the transformer has a turns ratio of 1:2. The transformer primary
winding is connected across an AC source of 230V (rms), 50 Hz. The load resistor is 50Ω. For this circuit,
determine the DC output voltage, peak-to-peak ripple in the output voltage, and output ripple frequency.
Example:
Solution:
Ripple % = (Vp-p/Vavg) x 100
= (325.3/207) x 100 =157
12. Full Wave Bridge Rectifier
Performance :
Performance is same as two diode
rectifiers because only two diode
operate at any given time.
Rectifiers
13. Current Flow on the Negative Half CycleCurrent Flow on the positive Half Cycle
The Bridge Rectifie
Full Wave Rectification
Using Cantered tap Tr.
Half Wave Rectification
Rectifiers
1/∏
14. These parameters are needed to compare the performances
among the different rectifiers architectures.
Generic scheme of a rectifier
Vp: Input of the AC voltages feed into the
transformer
Vs: Secondary of the transformer feed into
rectifier/rectifiers.
VL: Voltage output of the rectifier supplied to
load.
Assume:
Ideal switches (diodes or
thyristors) with zero commutation
time
Zero on-resistance (i.e., when
conducting they present neither
voltage drop nor losses).
The load itself is an ideal
resistance.
Commutation is the process by which we can turn OFF a thyristor.
So the process of switching OFF a thyristor or SCR is known as
Commutation.
Performance parameters
Rectifiers
15. The DC voltage on the load is
the average over the period T
of the output voltage of the
rectifier:
Generic Rectifiers
Similarly, it is possible to
define the r.m.s. voltage on
the load:
The ratio of the two voltages is the Form
Factor (FF):
This parameter is quite important
since it is an index of the efficiency of
the rectification process.
1. Form Factor (FF):
r.m.s. voltage on the load
The DC voltage or Vavg
Assumed the load is purely resistive
Performance parameters
Vrms =
=VL
Rectifiers
16. By assuming the load to be purely
resistive:
The rectification ratio (η), also known
as rectification efficiency:
Where:
OR
OR
FOR ideal switches, with no losses: RD = 0
The Ripple Factor (RF) is another important
parameter used to describe the quality of the
rectification.
It represents the smoothness of the voltage
waveform at the output of the rectifier
3. Ripple Factor (RF)
2. Efficiency:
V = IR
η = Pdc / Pac
Pac =Irms
2 (rf +
RL)
Pdc = Idc
2 RL
Performance parameters
17. This parameter characterized the ratio between the average power and
transformer secondary ( source) volt-ampere rating ( VA) rating.
Transformer Utilization Factor (TUF):
Where (VA)rating= Vs.Is,
Vs= the secondary ( source) rms voltage,
Is=IRMS : the secondary rms current .
This characterized the ratio between average output power
and the appearance power energized the system (transformer,
rectifier, and load):
Performance parameters
Where: VAP and VAS are the
power ratings at the primary and
secondary of the transformer
18. The Crest factor:
This parameter defines the measure of the peak
input current (IS)peak as compared with its rms
value IS:
Is1 is the rms value of fundamental component of the
input current. Is rms value of input current.
Input Power Factor:
φ : angle between the fundamental components of
voltage and current. It’s called displacement angle
Displacement factor
19. Half-wave rectifier
From physics point of view:
The ideal power converter is the one that supplies the best direct current to the load
Should have very low ripple factor
Should very high stability,
Simplest structure. Only one diode is
placed at the secondary of the
transformer.
the rectification process occurs
only during half-periods.
Load current iL(t) always circulates in
the secondary winding in the same
direction.
Single phase Half Wave Rectifier with Resistive Load
20. Using equation from last slide:
Waveforms of the single-phase, single-way, half-wave rectifier
And, similarly,
The rectification process occurs only during the half-periods.
Vavg = = 0.318 Vs
0.5 VsVrms =
21. Determine:
1- the average and
rms voltage and
current
2- the efficiency,
TUF,
3- FF, RF, and the
peak reverse
voltage across the
diode (PIV).
4- the CF, and the
input PF.
Single phase rectifier has a purely resistive load of 10Ω, energized by voltage source of 220V
throughout two windings transformer with ratio 2:1.
Example:
Cont..
22.
23. 1. Low ( poor) transform utilization 28.6%, which means that the transformer must be 1/0.286=3.49 times
larger that when it is used to deliver power from a pure ac voltage.
2. Low ( poor) rectification efficiency = 40.5%
3. Presence of current dc component in the secondary current causing additional losses ( winding and core
heating).
4. High ripples 121% greater than that when the source is pure dc
5. High ripple factor, which means that a filter with large capacitance is required for smoothing the output
voltage, therefore this yield high capacitor starting current problem.
Therefore this rectifier configuration is rarely used due to the weakness in quality of it's power and
signal parameters.
Comments:
Analyzing these rectifier parameters one can easily conclude the followings:
24. Single Phase rectifier with Resistance
and Inductance Combined Load
Low frequency High frequency
Short Circuit Open Circuit
25. The phase difference is = 90 degrees., with voltage leads the current. This leads to a
positive phase for inductive circuits since current lags the voltage in
Voltage and Current relationship in
an Inductor
27. AC circuit with a load consisting of
both inductance and resistance
If it was only R load
I =E/R = 120v/60 Ω
I = 2 Amp
28. Single phase diode rectifiers (p = 1)
With RL Load
Voltage
Voltage
Current
Current
R+L+D0 load
R+L load
-Ve due to L
I due to Diode
29. Waveforms of the single-phase, full-wave rectifier
Rectifiers
Performance Half wave Full Wave
FF 1.571 1.11
η 0.405 0.81
RF 1.21 0.483
30. Find the performance of the Full wave rectifier shown below that is designed to be
used at home to drive 200 Ω resistive load.(use ideal diodes)
Example:
Form Factor
Efficiency
Ripple Factor
Other important parameters
5:1
35. Performance parameters for some
multi-phase topologies
Topologies:
The study of geometrical properties and spatial relations unaffected by
the continuous change of shape or size of figures
Increasing the number of phases in a multi-phase, single-way rectifier, the
result of the rectification is improved
36. For an uncontrolled three-phase bridge rectifier, six diodes are used, and the circuit
again has a pulse number of six. For this reason, it is also commonly referred to as a
six-pulse bridge.
Six-pulse diode bridge rectifier
41. dc
Single phase controlled
rectifier with resistive load
Voltages across SCR
Voltages across LOAD
Current through the LOAD
cos 0 = 1
Source Voltages
42. Rectifiers
Single Phase Half
Controlled Rectifiers
• During the positive half cycle of the input,
T1 and D2 are forward biased.
• When T1 is fired, then the load current
flows through T1 and D2 to ground.
• Now the voltage passes through negative
going zero crossing of the input voltage, D4
comes into conduction by commutating D2
and then the load voltage becomes zero
Positive half cycle of the
input
43. Rectifiers
• During the negative
half cycle, T3 and D4
are forward biased.
Negative half cycle
Single Phase Half Controlled
Rectifiers
• When T3 is triggered
load current start
flowing through T3
and D4 to lower
potential.
45. Rectifiers
Single Phase Fully Controlled Rectifier
Complete control on negative and
positive half cycle of the input
46. • During the positive half cycle of the
input signal T1 and T2 are forward
biased and when these are triggered or
fired these are starts conducting so that
load current flow through them.
Working of fully controlled full wave rectifier
• During the negative half cycle of the input AC, T3 and T4 are in the forward
blocking state and when a gate pulse is applied to them, they will turn ON and
load current starts flowing through them
• At the same time, across T1 and T2 a negative voltage causes to the commutation of
these thyristors immediately.
50. In the previous example the operation is performed in four quadrantes:
I- half cycle 0 < α < ∏
II- half cycle ∏< α <2∏
III- half cycle 2∏< α <3∏
IV- Half cycle 3∏< α < 4∏
All quadrant operation of single-
phase controlled rectifiers
