A New Family of Converter Using a Non-Dissipative Cell to Aid
the Commutation
JOÃO BATISTA VIEIRA JUNIOR., ADRIANO ALVES PEREIRA, LUIZ CARLOS DE
FREITAS, VALDEIR JOSÉ FARIAS, ELINERI CÁSSIA CÂNDIDO CICHY AND LUIZ
HENRIQUE SILVA COLADO BARRETO
Department of Electrical Engineering
Federal University of Uberlândia
Av. João Naves de Ávila 2121, Campus Santa Mônica
Uberlândia MG Zip Code 38400-902
BRAZIL
Abstract: This paper presents a new non dissipative commutation cell applied to several converters creating a
new converters family. The new cell can be applied to isolated converters too (i.e. Full- bridge and Forward).
The new cell provides the ZCS commutation at the auxiliary switch when it is turned on, and in the ZCS and
ZVS way when the auxiliary switch is turned off. The main switch is turned on and turned off in the ZVS way.
Soft switching characteristics is obtained with the resonance of the cell components.
The main characteristic of this new non dissipative commutation cell is to work without an auxiliary DC
source, because the energy required for the resonance is obtained of the resonant components of the cell.
Several converters have been implemented using the new cell. Some experimental results of these prototypes
are presented. Simulation results of some converters using the new cell, the operational principle and the
theoretical analysis are presented in this paper.
Key-Words: - Soft switching, non-dissipative, DC-DC converters, PWM, high frequency, family of converters.
1 Introduction
Power supply units integrates almost every all of the
modern electronic equipment or apparatus to
perform some work, professional or entertainment.
In the last years these equipment are becoming more
complex (i.e. computers and telecom equipment),
and these equipment price and size are getting
lower. How the static converter integrate these
equipment, they must follows this trend. So, over
past ten years a very high effort has been moved in
the sense of obtaining higher efficiency and higher
power density in the switching mode power supplies
(SMPS). A way of to reduce de size of the SMPS is
to increase the switching frequency. Thus, filter
elements and transformers of the converter are
reduced. However, this, besides providing noises of
eletromagnetical interference – EMI and radio
frequency – RF, produces losses and, consequently,
low efficiency in a converter operation with hard
commutation.
A way to minimize these effects of the frequency
increasing is the soft switching. The soft switching
can be implemented in two ways: Zero Current
Switching (ZCS) or Zero Voltage Switching (ZVS).
In MOSFETs the zero voltage switching (ZVS)
technique is generally used, because the turn on
losses are large due to the intrinsic capacitances.
Some kind of circuits to implement soft
switching techniques for SMPS have been proposed.
These circuits reduce the switching losses, making
possible high frequency operation of the SMPS. The
first circuit used was the snubber [1, 2, 3]. Soon
after the snubbers, risen the QRCs (Quasi Resonant
Converters) [4, 5, 6], changing the research trends to
this area. Resonant converters have attracted a high
attention due to their low switching losses and low
EMI. Despite the great interest the QRCs presented
some undesirable characteristics such as load
limitations and control difficulties due to variable
frequency operation. Pulse-width-modulated quasi
resonant converters (PWM-QRCs) had appeared to
improve the QRCs characteristics, they operate with
fixed switching frequency, therefore they do not
have the control problem like the QRCs [7], but they
present the others disadvantages of the QRCs. QRCs
and PWM-QRCs have load limitation and high
current or voltage ratings for semiconductor devices.
These problems were solved in [8, 9], but these
topologies require an auxiliary source, adding
diodes and a large capacitor.
The aim of this paper is to present a new family
of soft switched converters, working with ZVS in
the main switch at the turn on and turn off
commutations without an auxiliary source, but
presenting the same characteristics and results. The
auxiliary switch is commutated in the ZCS form. In
some circuits of ZVS the energy to the resonance is
provided by the auxiliary source, in this new family
the resonance energy is provides by the resonant
circuit itself, thus the cell is self commutated.
This new family of soft switching converters can
reaches high-frequency and high power operation.
These converters provide:
- Soft switching for an wide load range;
- Conduction losses are almost the same
as those observed in the hard PWM
converters;
- They do not require an auxiliary source.
2 The New Non Dissipative Cell
Fig. 1 shows the new commutation cell. It is
composed for two switches (S1 – main switch and
Sa - an auxiliary switch), two diodes (D1 and D2),
two resonant capacitors (CR1 and CR2) and a
resonant inductor (LR). Resonant components are
designed in the resonant frequency, therefore they
have a small size and do not taken substantial space.
This new cell can be integrated on all of basic CCCC converters getting the New Self Commutated
Non Dissipative Family. This family is presented in
Fig. 2 to 8.
Fig. 1 – The New Non Dissipative Cell.
Fig. 2 – Buck Converter
Fig. 4 –
Converter
Fig. 3 – Boost
Converter
Fig. 6 – Sepic Converter
Fig. 7 – Zeta
Converter
Fig. 8 – Forward Converter
This cell can be used in the isolated topologies as
the two transistor forward converter. In this case
some assumptions become this converter simpler,
how the resonance period is 1800, the capacitor and
the parallel diode with the capacitor can be
eliminated, getting an evolution of the original cell.
In the last case the resonant inductor must be
coupled with the filter inductor. Fig.9 shows this
evolution.
Fig. 9 - The ZVS PWM two transistors forward
converter with soft commutation.
Another isolated topology that uses the cell is the
full-bridge converter. In this converter the evolution
of the cell is more evident. The number of
components are drastically reduced, will be required
only two resonant capacitors (can be the intrinsic
capacitor of the MOSFETs) and a resonant inductor
(can replaced for the transformer leakage
inductance). When this cell is used in the full-bridge
converter it does not require the auxiliary switch.
This auxiliary function is done for upper switches,
when they are turned off. In this case upper switches
use phase shift control and bottom switches use
PWM control, so all switches are commutated in the
ZVS form, upper switches due to the phase shift
control and bottom switches due to the new cell.
Fig.10 shows this evolution.
Buck-Boost Fig. 5 –Cuk Converter
Fig. 10 - The PWM Full-Bridge DC-DC
Converter using phase-shift control and the selfresonant principle.
3 Principle of Operation
Principle of operation of the new self commutated
non dissipative cell will be presented. To simplify
the analysis, are assumed the follow assumptions:
- All of components are ideal;
- The resonant frequency is very higher
than the switching frequency;
- The input and output voltage are free of
ripples
- The circuit is working in steady state.
This cell has seven operating stages in a
switching cycle, how the basic operating is the same
for whatever converter, the operating described
below, for the Buck converter, is the same for all of
basic converters, but of course the voltage on Cr1
must be modified for each topology. The initial
voltage on Cr1 is the same than one maximum
voltage on the switch in the hard converters. So, if
the analysis is about the Buck converter, the initial
voltage on Cr1 is Vdc, if the analysis is about the
Boost converter, the initial voltage on Cr1 is
Vdc+Vo.
First Stage [t0;t1] t1  LINEAR CHARGE OF Lr :
This stage begins when switch Sa is turned on.
Current in the resonant inductor increases linearly
from zero to ILi. When it happens, D3 turns off and
this stage finishes.
Second Stage [t1;t2] t2  FIRST RESONANT
STAGE :
In this stage happens the resonance between Lr
and Cr1 and Cr2. Voltage on Cr1 (VCr1) decreases
from Vdc to 0, and Cr2 is charged. When VCr1 = 0,
diode D1 is turned on. At this time interval, switch
S1 can be turned on under zero voltage, concluding
the stage.
Third Stage [t2;t3] t3  MAGNETIZATION OF L1:
In this stage Vcr1 remains 0, Lr and Cr2 are in
resonance. ILr current decreases to 0. At this same
time, Cr2 is discharging. Now, switch Sa can be
turned off in a ZCS way. This stage will be
concluded when ILr is equal to zero.
Fourth Stage [t3;t4] t4  LINEAR CHARGE OF
Cr2 :
This stage begins when ILr is zero. During this
stage the resonant capacitor Cr2 is discharged by ILi
in a linear way.
Fifth Stage [t4, t5] t5  PWM STAGE
When VCr2 voltage is equal to zero turning on
diode D2, this stage begins. During this stage energy
is transferred from the input to the output (Li). This
stage finishes when switch S1 is turned off in a ZVS
way.
Sixth Stage [t5, t6] t6  LINEAR CHARGE OF CR1
In this stage, the branch composed by Vdc, Cr1,
D2 and Li is in conduction. This stage begins when
switch S1 is turned off and it finishes with the
conduction of diode D3. With switch S1 turned off,
diode D2 turns on and the resonant capacitor Cr1 is
charged from 0 to Vdc, concluding this stage. This
way, switch S1 turning off is under zero voltage
(ZVS), since the initial voltage VCr1 of that stage is
0.
Seventh Stage [t6;t7] t7  LINEAR DISCHARGE
OF Li:
This stage begins when voltage in resonant
capacitor Cr1 reaches Vdc and it finishes with the Sa
turning on.
Figs. 11 to 17 show the seven stages of the Buck
converter.
Fig. 11 – First Stage
Fig. 12 – Second Stage
Fig. 13 – Third Stage
Fig. 14 – Fourth Stage
Fig. 15 – Fifth Stage
Fig. 16 – Sixth Stage
Fig. 17 – Seventh Stage
Fig. 18 shows the theoretical waveforms of one
switching cycle. All converters of the proposed
family approximately have the same waveforms, of
course considering the relative voltage and current
to each converter.
Fig. 18 – Theoretical Waveforms of the New
Converters Family.
4 Analysis Results
The output voltage Vo, can be obtained by the
analytical study of the operating stages and with the
following assumptions: all components and switches
are ideal, the output is an ideal current source (Io) or
an ideal voltage source (Vo) depending on the
converter, the input voltage (Vdc) are ripple free.
The static gain of the Buck Converter can be
obtained from equations 1 to 20 and is defined by
equation (21). The static gain for another converter
can be obtained from table 2.
4.1 – Mathematical Analysis of the Converter
where:
D = Duty Cycle;
FS = Switching Frequency;
fo = Resonance Frequency;
g = static gain.
Table 3 – Static Gain
Converter
Static Gain
Buck
g
Boost
1
In this section, the analytical expressions describing
the operation of the proposed buck converter are
presented. The equations for another converter are
the same of the buck converter.
Table 1 – Definitions
1
(2)
(1) K  Cr 2  3
Ts 
Cr1
Fs
1
1
1


C Cr1 Cr 2
o 
2 
2 
4 
(3)  
1
(5)  
1
Lr C
1
(7)
Lr Cr 2
(9)
Lr ILi
Cr 2 (Vdc  Vo)
Z 02 
3 
Lr ILi
(4)
C (Vdc  Vo)
1
(6)
Buck-Boost
Lr Cr1
Lr
(8)
Cr 2
Lr ILi
Vo
F 
 1  K 1  
 g  D  S arccos   
 
Vdc
2fo 
2
 K  K
(10)
Cuk
Cr 2  VCr (t 3)
Lr ILi
(11)
Zeta
(12)
Sepic
Cr1(Vdc  Vo)
Y   22  2 2

2C  K
2C  K
 K2 
 2K 2
Cr 2
Cr 2

VCr (t3 )  Z 02 ILi  (Vdc  Vo) 2C  Cr12   2 1  Y 2 
(13)
(Vdc  Vo)
K
Y
2
Table 2 – Time Interval of Each Stage
First Stage[t0,t1]

(14)
t 1 
o
Second Stage[t1,t2]
C  Cr1
arccos
C
t 2 
o
(15)
Third Stage[t2,t3]
K
arccos
Y
t 3 
(21)
1 g
g
1 g
g
1 g
g
1 g
g
1 g
From equation (21), can be observed that the
static gain depends on the duty cycle, resonant
frequency (0), and normalized output current ().
Figs. 19 to 21 show the static gain for Buck-Boost
converter, Buck converter and Boost converter. As
it can be seen, except for light loads, the voltage
conversion ratio is very close to the conventional
PWM with a dependence on duty cycle.
Static Gain
(16)
2
Fourth Stage[t3,t4]
1
t 4 
2 3
(17)
Fifth Stage[t4,t5]
t 5  DTs  t 4  t 3
(18)
Sixth Stage[t5,t6]
1
t 6 
1   4
(19)
Seventh Stage[t6,t7]
t 7  DTs  t 6  t 5  t 4  t 3  t 2  t1
4.2 – Static Gain
(20)
Fig. 19 – Static gain to the Buck-Boost Converter
using the new auxiliary commutation cell.
Fig. 22 – Commutation Detail on the Main Switch to
Cuk Converter.
Fig. 20 – Static gain to the Buck Converter using
the new auxiliary commutation cell.
Fig. 23 – Commutation Detail on the Auxiliary
Switch to the Cuk Converter.
Fig. 21 – Static gain to the Boost Converter using
the new auxiliary commutation cell.
5 Simulation Results
The proposed converters were studied by simulation
to verify the theoretical analysis. All converters
presented in Figs. 2 to 8 and two isolated topology
presented in this paper were simulated, but some
results will be presented only. In this way, the Figs.
22 and 23 present the simulation results for Cuk
converter and Figs. 24 and 25 show those for Sepic
converter. Simulation results have been obtained
with the following parameters set:
Cr1 = 1nF (Cuk)
Cr2 = 10nF (Cuk)
Cr1 = 2nF (Sepic)
Cr2 = 8nF (Sepic)
Li = Lo = 700uH
Fs = 100kHz
Lr = 3uH
Input Voltage = 300V
Duty Cycle = 0.2
Rload = 20 (Cuk)
Rload = 10 (Sepic)
to – t2 – delay time Output Voltage
between SA gate and Cuk = -85.5V
S1 gate
Sepic = 95V
0,7s (Cuk)
0.7s (Sepic)
Fig. 24 – Commutation Detail on the Main Switch to
Sepic Converter.
Fig. 25 – Commutation Detail on the Auxiliary
Switch to Sepic Converter.
6 Experimental Results
Proposed converters with the new commutation cell
have been implemented at laboratory. First results
were obtained for Full-Bridge converter with the
following parameter set, with the purpose of proving
your accuracy and efficiency. Vdc=130V;
Vo=66.5V; Io=2.75A; FS=100kHz; CR1=CR2=2.2F;
LR=15H.
Fig. 26 – Detail of the commutation in the S1 and S2
switches of the Full-Bridge Converter.
Fig. 30 – Detail of the commutation in the Sa switch
of the Full-Bridge Converter.
Experimental results to another converters are
almost the same of these converters presented.
7 Conclusions
Fig. 27 – Detail of the commutation in the S3 and S4
switches of the Full-Bridge Converter.
Fig. 28 shows the efficiency curve for the
proposed converter. It is treated in a comparative
way between the circuit operating in soft switching
and the circuit operating in hard switching (without
the resonant elements). The operation with the
resonant elements elevates the efficiency of the
converter.
Fig. 28 – Efficiency of the Full-Bridge Converter
with Hard Switching and Soft Switching.
The second experimental results were obtained
for Boost converter with the following parameter
set:
Vdc=180V;
Vo=200V;
Output_Power(Po)=600W, FS=100kHz; CR=10F,
CR2=27F; LR=2.5H, Boost_Inductor(Li)=500H
Fig. 29 – Detail of the commutation in the S1 switch
of the Boost Converter.
In this paper, a new and simple alternative was
introduced to obtain the soft commutation
characteristic. The cell does not use an auxiliary
source to get the soft commutation in main switches.
Experimental results show that the auxiliary
switches are turned on in the ZCS way and they are
turned off is in the ZCS and ZVS ways. Main
switches are turned on and turned off in the ZVS
way. ZVS on main switches is obtained without an
auxiliary source, this reduces the amount of
necessary components.
Switching frequency is constant, and the static
gain is almost the PWM one for bigger s, this fact
turns the control technique easier.
The new cell was associated in several
converters. These converters have been simulated
and implemented, final results, of the commutations,
were almost the same for all of converters, of course
taking shelter the had values of voltage and current
for each converter.
As the converters, associated with this new cell,
do not have abrupt variation of voltage or abrupt
variation of current, it has the possibility of the
Eletomagnetic Interference (EMI) reduction.
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