A Novel Dual Boost Rectifier for Power Factor

Improvement
S.S Darly, Dr. P. Vanaja Ranjan Bindu. K.V, &Dr. B. Justus Rabi,
Dept of EEE, Anna University, Chennai. Dept of EEE, RREC, Chennai

Abstract— This paper discuses the reduced high conduction also have power factor close to unity [4]. So far, a variety of
loss and improved efficiency of the input rectifier-bridge of a passive [5] and active PFC techniques have been proposed.
conventional boost PFC converter. By designing the necessary While the passive PFC techniques may be the best choice at
techniques and methodology, the overall Power Factor (PF) can low power, cost sensitive applications, the active PFC
be improved to the expectation. The cause of having low PF for a techniques are used in majority of the applications owing to
diode-capacitor type of rectifiers is related to non-linearity of the their superior performance. The objective of this work is to
input current. . Method of re-shaping the input current develop a circuit with all the necessary components and
waveform to be similar pattern as the sinusoidal input voltage is
control system that will incorporate into the design of any
done by the Boost converter and the related controls that act as a
Power Factor Correction (PFC) circuit. The results of the single-phase rectifier and hence, improves the power factor.
designed system were compared with the boost rectifier without The AC mains utility supply ideally is supposed to be cleaned
PFC control. Higher efficiency can be achieved by using the and free from high voltage spikes and current harmonics in
bridgeless boost topology. In this paper, digital simulation of order to ensure good quality and efficient power system
bridgeless PFC boost rectifiers, also called dual boost PFC harmonics to electronics equipment. Discontinuous input
rectifiers, is presented. Performance comparison between the current that exists on the AC mains caused by the non-linearity
conventional PFC boost rectifier and the bridgeless PFC boost of the rectification process could be shaped to follow the
rectifier is performed. sinusoidal form of the input voltage. The process of shaping
Index Terms-Dual boost PFC rectifier, power factor correction
the input current is done by the Boost converter, which is
(PFC), single phase rectifier, boost converter.
properly controlled by the related circuitry [6]. The control
circuits for this project used low-cost components, easily
Keywords-Dual boost PFC rectifier, power factor correction (PFC), available yet giving excellent performance and satisfactory
single phase rectifier, boost converter. results.
I. INTRODUCTION II. RECENT DEVELOPMENTS
I n the world today, dc power supplies are extensively used The development of the technologies, have emerged
inside most of electrical and electronic appliances such as in as additional drivers for new applications. One such
computers, monitors, televisions, audio sets and others . The application is commercial transport airplanes where single-
high power non linear loads (such as static power converter, phase PFC converters capable of meeting stringent airborne
arc furnace, adjustable speed drives etc) and low power loads power quality requirements for in-flight entertainment (IFE),
(such as fax machine, computer, etc) produce voltage avionics, communication, and other single-phase loads. The
fluctuations, harmonic currents and an imbalance in network proliferation of variable-speed motor drives in home
system which results into low power factor operation of the appliances has also generated a new need for high-power (up
power system [1]. There is a need of improved power factor to a few kilowatts), high-efficiency, and low-cost single-phase
and reduced harmonics content in input line currents as well as PFC converters [7]. There are different drivers for home
voltage regulation during power line over-voltage and under- appliance applications of PFC converters in recent years: New
voltage conditions. The uninterruptible power supplies (UPSs) functions, such as variable washing cycles in washing
have been extensively used for critical loads such as machines and different cooking modes in automatic rice
computers for controlling important processes, some medical cookers; Reduction of energy consumption in air conditioners
equipment, etc. The traditional UPS draws harmonic currents. and refrigerators through the use of variable-speed motor
The uncontrolled diode bridge rectifier with capacitive filter is drives.
used as the basic block in many power electronic converters. III. PRINCIPLE OF OPERATION RECTIFIER
Due to its non-linear nature, non-sinusoidal current is drawn WITH BOOST CONVERTER
from the utility and harmonics are injected into the utility
lines. The nature of rectifiers either it is conventional or switch
mode types, all of them contribute to low PF, high THD [2]
and low efficiency to the power system [3]. It is well known
that these harmonic currents cause several problems such as
voltage distortion, heating, noises, reducing the capacity of the
line to supply energy. Owing to this fact there’s a need for
power supplies that draw current with low harmonic content & Fig 1a: Rectifier with Boost Converter

978-1-61284-379-7/11$26.00 2011
c IEEE 122
 phase power supplies operates by rectifying the ac line voltage
and filtering with large electrolytic capacitors. This process
generates a distorted input current waveform with large
harmonic content [10]. Thus, the resulting power factor is very
poor (around 0.6). The reduction of input current harmonics
and high power factor operation are important requirements
for power supplies. In these applications, ac-dc converters
featuring almost unity power factor are required [11]& [12].

The technique usually employed to correct power

factor of single-phase power supplies consists of a front-end
full-bridge diode rectifier followed by a boost converter, as
Fig 1b: Waveforms of related voltages and current shown in fig 4. This approach is good for a low to medium
power range [13]. As the power level increases, the diode
Figure 1a and 1b above show the basic configuration bridge begins to become an important part of the application
of a rectifier that uses Boost converter technique as PFC with and it is necessary for the designer to deal with the problem of
its respective voltages and currents [8]. For an ordinary how to dissipate the heat in limited surface area. The
rectifier without PFC, the input current I would be highly non- dissipated power is important from an efficiency point of
linear especially when the capacitor C1 is having large value. view.
By operating the Boost converter in Continuous-Conduction
Mode (CCM, the input current would be Sinusoidal.

IV. DESIGN CONCEPT OF THE RECTIFIER WITH PFC

The mains AC input voltage is rectified and supplied
to the Boost converter, which mainly consists of an inductor, a
power MOSFET, a power diode and a bulk capacitor. The
Error Amp 2 with predetermined reference voltage senses the
DC output voltage across the bulk capacitor. The error voltage
Ve2 from the amplifier then is fed to the multiplier and
multiplied with the template sinusoidal input voltage to get the
reference current, IL (reference). The error Ve1 that is the
output of Error Amp 1, as the difference of IL (actual) and IL
(reference) provides the correct timing logic for the switching
driver circuit to turn on and off the MOSFET in the Boost Fig 4: Conventional PFC Boost Rectifier
converter. Hence, this method ensures continuous conduction
of current flow for the full cycle of the input voltage.
VI.BASIC BRIDGELESS PFC BOOST RECTIFIER
Input Output The circuit shown from a functional point of view is
Rectifier Boost Converter similar to the common boost converter.

ILac
Vact Driver
ILref
Err Amp Vout
Multiplier
Vref
Error Amp 2
Fig 3: PFC control strategy block diagram

V. REVIEW OF CONVENTIONAL PFC BOOST

RECTIFIERS Fig: 5 Bridgeless PFC Boost rectifier

The conventional boost topology is the most efficient In the traditional topology current flows through two
for PFC applications. It uses a dedicated diode bridge to of the bridge diodes in series. In the bridgeless PFC
rectify the AC input voltage to DC, which is then followed by configuration [14], current flows through only one diode with
the boost section [9]. The conventional input stage for single the Power MOS providing the return path. The operation can

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2011 1st International Conference on Electrical Energy Systems 123

be analyzed in two stages: operation as the boost converter and difference between the bridgeless PFC and conventional PFC
the operation for return path for the AC input signal. is bridgeless PFC inductor current only goes through two
semiconductor devices, but inductor current goes through
When the AC input voltage goes positive, fig 5(a) the three semiconductor devices for the conventional PFC circuit.
gate of S1 is driven high and current flows from the input The bridgeless PFC uses one MOSFET body diode to replace
through the inductor, storing energy. When S1 turns off, the two slow diodes of the conventional PFC [16]. Since both
energy in the inductor is released as current flows through D1, the circuits operates as a boost DC/DC converter; the
through the load and returns through the body diode of S2. switching loss should be the same. Thus the efficiency
improvement relies on the conduction loss difference between
the two slow diodes and the body diode of the MOSFET [17].
Besides, comparing with the conventional PFC, the bridgeless
PFC not only reduces conduction loss, but also reduces the
total components count.

VII. BRIDGELESS PFC BOOST RECTIFIER WITH TWO

DC/DC BOOST CIRCUITS

To reduce the common-mode noise of the bridgeless

PFC boost rectifier the topology of the bridgeless PFC boost
rectifier needs to be modified to always provide a low-
frequency (LF) path between the ac source and the positive or
Fig. 5(a) Positive Half cycle of Basic bridgeless PFC boost negative terminal of the output [18-19]. In Fig. 6, in addition
rectifier to diodes D3 and D4, which are slow recovery diodes, a
second inductor is also added, resulting in two dc/dc boost
During the-off time, the current through the inductor circuits, one for each half-line cycle. During a positive half-
L (i.e., during this time the inductor discharges its energy) line cycle, the first dc/dc boost circuit, LB1 -D1 –S2 is active
flows in to the boost diode D1 and close the circuit through the through diode D4 , which connects the ac source to the output
load. ground. During a negative half-line cycle, the second dc/dc
boost circuit, LB2 -D2-S1 , is active through diode D3, which
connects the ac source to the output ground.
It should be noted that switches S1 and S2, in both
bridgeless PFC boost rectifiers can be driven with the same
PWM signal, which significantly simplifies the
implementation of the control circuit. The drawback of the
bridgeless PFC boost rectifier in is that it requires an
additional gate-drive transformer. The drawback of the
bridgeless PFC boost rectifier in Fig.6 is that it requires two
inductors. However, it should also be noted that two inductors
compared to a single inductor have better thermal
performance.
Fig 5(b): Negative Half cycle of Basic bridgeless PFC boost
rectifier

During the negative half cycle circuit operation is

mirrored as shown in fig 5(b) S2 turns on, current flows
through the inductor, storing energy. When S2 turns off,
energy is released as current flows through D2, through the
load and back to the mains through the body diode of S1back
to the input mains. Note that the two Power MOSFETs are
driven synchronously. It doesn't matter whether the sections
are performing as an active boost or as a path for the current to
return. In either case there is benefit of lower power
Fig 6: Bridgeless PFC rectifier with two DC/DC Boost
dissipation when current flows through the Power MOSFETs
Circuits
during the return phase.
Thus, in each half line cycle, one of the MOSFET
operates as active switch and the other one operates as a diode,
both the MOSFETs can be driven by the same signal [15]. The

124 2011 1st International Conference on Electrical Energy Systems

VII (a) SIMULATION RESULTS

The computer simulation of proposed converter is

done using Matlab/Simulink and the results are presented.
Bridgeless PFC rectifier with two DC/DC Boost Circuits is
shown in Fig.7 (a). The controlled switch implemented is the
power MOSFET with its inherently slow body diode.
Simulated line voltage and line current waveforms of
bridgeless PFC boost rectifier operating at 85-Vrms line
voltage and 264-Vrms are shown in figure 7(b) and 7(d)
respectively. It can be seen that from the waveforms current
and voltage are out of phase. DC output voltage for different
input voltage (rms) shown in Figs 7(c) and 7(e) respectively.

Fig 7(c): Measured dc output voltage waveforms of bridgeless

PFC boost rectifier operating at 85-Vrms line voltages. Vout =
384Vdc

Fig 7(a): Bridgeless PFC rectifier with two DC/DC Boost

Circuits

Fig 7(d) : Measured line voltage and line current waveforms of

bridgeless PFC boost rectifier operating at 264-Vrms line
voltage.
Fig 7(b) : Measured line voltage and line current waveforms of
bridgeless PFC boost rectifier operating at 85-Vrms line
voltage

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 Fig 9(a): Power wave forms

Experimental results of the prototype is presented

input voltage and output voltage waveforms of bridgeless PFC
Fig 7(e): Measured dc output voltage waveforms of bridgeless boost rectifier are shown in figure 9(d) and 7(e) respectively.
PFC boost rectifier operating at 264-Vrms line voltages. It can be seen that the power factor is improved shown in Figs
Vout=1200 Vdc 9(b) and 9(c) respectively.

VII (b) EXPERIMENTAL RESULTS

The proposed rectifier prototype was built to verify
the operation; the critical relationships of voltage boost and
simulation results are presented. Experimental results are
verified and demonstrated promising the features and the
Controller waveform at power factor correction. It should be
noted that the power factor is improved up to the expected
level and working for a frequency of 50Hz successfully. Fig. 8
shows the experimental setup.

Fig 9(b): Power factor without PFC

Fig. 8 Photo of Experimental Set up

Fig 9(C): Power factor with PFC

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