SIMULATION AND ANALYSIS OF
DOUBLE OUTPUT CONVERTER WITH
PI CONTROLLER
M. Indhumathi, G. Nandinini, J. Abinaya and G. Pradeepa
Department of Electrical and Electronics Engineering
A.V.C College of engineering, Mayiladuthurai.
raga_as@yahoo.co.in
ABSTRACT
PI Controller is capable of regulating the
output voltage irrespective of line and load
disturbances.
Mirror-symmetrical double-output voltages
are specially required in industrial
applications and computer periphery circuits.
Double output DC-DC converters can convert
the positive input source voltage to positive
and negative output voltages by two
conversion paths. Because of the effect of
parasitic elements, the output voltage and
power-transfer
efficiency
of
DC-DC
converters are limited. The voltage-lift
technique is a popular method that is widely
applied in electronic circuit design. This
technique gives a good way of improving
circuit characteristics, and has been
successfully applied for DC-DC converters.
As are single output (positive or negative
output). Double-output converters are a
series of new DC-DC step-up converters using
only one switch. They arc developed from
prototypes using the advanced voltage-lift
technique. These converters perform from
positive to positive and negative DC-DC
voltage-increase conversion with high power
density, high efficiency and cheap topology in
a simple structure. They are different from
any other existing DC-DC step-up converters
and possess many advantages including high
output voltage with small ripples. Therefore
these converters will be widely used in
computer
peripheral
equipment
and
industrial applications, especially for high
double-output
voltage
projects.
The
performance of the chosen converter is
evaluated using MATLAB (version 7.01)
software and the responses are obtained. The
experimental results show that the proposed
I.INTRODUCTION
Double-output DC-DC converters convert the
positive input source voltage to positive and negative
output voltages. They consist of two conversion
paths, one is positive conversion path and the other is
negative conversion path. The mirror-symmetrical
double-output voltages are especially required in
industrial applications, computer periphery circuits
such as operational amplifiers, power supplies,
differential servomotor drives and some symmetricalvoltage medical equipment. In recent years, the DCDC conversion technique has been greatly developed.
The main objective is to reach high efficiency, high
power density and cheap topology in a simple
structure. For example, in the Cuk converter and the
Class-E converter good topologies have been
developed.
in DC – DC converter due to the effect of parasitic
elements, the output voltage and power transfer
efficiency is restricted. The voltage-lift technique is a
popular method that is widely applied in electronic
circuit design. It can open a good way of improving
DC-DC converters characteristics, and has been
successfully applied for DC-DC converters. As the
positive and negative output converters, doubleoutput converters are a series of new DC-DC step-up
(boost) converters, which were developed from
prototypes using the advanced voltage- lift technique.
Only one switch S is employed to control dual
mirror-symmetrical output voltages. These converters
perform from positive to positive and negative DCDC voltage-increase conversions with high power
density, high efficiency and cheap topology in a
simple structure; they are different from any other
existing DC-DC step-up converters and possess many
advantages, including a high output voltage with
small ripples.
1
1.1 BUCK CONVERTER
In this circuit the transistor turning ON will put
voltage
on one end of the inductor. This voltage
will tend to cause the inductor current to rise. When
the transistor is OFF, the current will continue
flowing through the inductor but now flowing
through the diode. We initially assume that the
current through the inductor does not reach zero, thus
the voltage at
will now be only the voltage
across the conducting diode during the full OFF time.
The average voltage at
will depend on the average
ON time of the transistor provided the inductor
current is continuous.
which simplifies to
or
=0
=
and defining "duty ratio" as
D=
The voltage relationship becomes Vo=D Vin Since
the circuit is lossless and the input and output powers
must match on the average Vo* Io = Vin* Iin. Thus the
average input and output current must satisfy Iin =D Io
These relations are based on the assumption that the
inductor current does not reach zero.
II.INTRODUCTION
The elementary circuit can perform step-down and
step-up DC-DC conversion. The other-double output
converters are derived from this elementary circuit;
they are the self-lift circuit: re-lift circuit and multiple
lift circuits etc. Switch S in these circuits is a Pchannel power MOSFET device (PMOS). It is driven
by a pulse-width-modulated (PWM) switching signal
with 0repeating frequency f and conduction duty
cycle k. In this report, the switch repeating period is
T = l/f; so that the switch-on period is kT and the
switch-off period is (1 - k)T. For all circuits, the
loads are usually resistive, i.e
and
the normalized loads are
(where
and
for
elementary circuit) and
. In order to
keep the positive and negative output voltages
symmetrically equal to each other, we purposely
select that L=
and
.
Fig.1.1 Buck Converter
Fig.1.1.1 Voltage and Current Pulse
To analyze the voltages of this circuit let us consider
the changes in the inductor current over one cycle.
From the relation
=L
the change of current satisfies
di =
dt +
dt
For steady state operation the current at the start and
end of a period T will not change. To get a simple
relation between voltages we assume no voltage drop
across transistor or diode while ON and a perfect
switch change. Thus during the ON time Vx=Vin and
in the OFF Vx=0. Thus
0
=
di
=
dt
+
Fig 2.1 Elementary Circuit
Each converter has two conversion paths(positive and
negative conversion path). The positive path consists
dt
2
The equivalent circuit during switch on is shown in
Fig.2.2 (a) and the equivalent circuit during switch
off in Fig 2.2(b). The relations of the average currents
and voltages are
and =
of a positive pump circuit
and a
„∏-type filter
, and a lift circuit
(except the elementary circuit). The pump
inductor , absorbs energy from the source during
switch on and transfers the stored energy to
capacitor , during switch off. The energy on
capacitor is then delivered to load R during switch
on. Therefore a high voltage
will correspondingly
cause a high output voltage
.
The negative path consists of a negative pump circuit
and ∏-type filter
and a lift circuit (except the elementary circuit). The
pump inductor
absorbs the energy from the source
during switch on and transfers the stored energy to
capacitor
during switch-off. The energy on
capacitor
is then delivered to load
during
switch on. Hence, a high voltage
will
correspondingly cause a high output voltage
.
When switch S turned off, there are existing currents
flowing though the freewheeling diodes
and
.
If the currents
and
do not fall to zero before
switch S is turned on again, we define this working
state to be a 'continuous mode'. If the currents
and
become zero before switch S is turned on
again, we define that working state to be a
'discontinuous mode'. In this paper, for any
component X, its instantaneous current and voltage
are expressed as
and
, and its average current
and voltage are expressed as
and
,The output
voltages and currents are
,
and
,
; the
input voltage and current are
and
.
Assuming that the power loss can be
ignored,
, or
,We
have the following general definitions in the
continuous mode.
The positive path input current is
=k
+ K (
+
)=k(1 +
) =
………(1)
The output current and voltage are
=
=
The voltage transfer gain in the continuous
mode is
=
=
(2)
The average voltage across capacitor
is
=
=
The variation ratios of the parameters are
=
=
=
=
=
The variation ratio of the current
=
=
is:
=
=
=
The variation ratio of
=
=
is
The variation ratio of the output voltage
is
=
If
and
=
=20 ,R=10 ,f=50kHz
find
that
=0.025
and
. Therefore the variations of ,
and
are small. The output voltage
is almost a
real DC voltage with a very small ripple. Because of
the resistive load, and the output current
(t) is
almost a real DC waveform with a very small ripple,
as well, and
= .
III.POSITIVE CONVERSION PATH
Fig 2.2 Positive Conversion Path
3
k=0.5,
we
IV. NEGATIVE CONVERSION PATH
The variation ratio of current
and
is
T
Assuming that f = 50 kHz,
=
= 0.5mH, C =
=20pF,
= 10Ω and = 0.5, we obtain
= 1,
ξ = 0.05, = 0.025,
ζ = 0.00125 and
=
0.0000156. The output voltage
is almost a real
DC voltage with a very small ripple. Since the load is
resistive, the output current
(t) is almost a real DC
waveform with a very small ripple, and it is equal to
=
V. DISCONTINUOUS MODE
The equivalent circuits of the discontinuous mode are
shown in Figs 2.2(c) and 2.3(c). In order to obtain the
mirror symmetrical double-output voltages, we
purposely
select
and
ζ=
.The free wheeling diode currents
and
become zero during switch off before the next
period switch on. The boundary between the
continuous and discontinuous modes is
ζ ≥1 or
≥1
Fig 2.3 Negative Conversion Path
The equivalent circuit during switch on is
shown in Fig. 2.3(a) and the equivalent
circuit during switch off in Fig. 2.3(b). The
relations of the average currents and
voltages are
=
and
Since
the inductor current
is defincd as:
Hence,
≤
the boundary curve has a minimum value of
that
is equal to 3.0, corresponding to k =
The filling
efficiency
is
= =
Therefore
The output current and voltage are defined
as
The voltage transfer gain in the continuous
mode is defined as
and
Therefore the positive output voltage in the
discontinuous mode is
=[2
………………………….(3)
From eqns. 2 and 3, we can define that
Because the inductor current
The variation ratios of the parameters are:
and
4
= 0 at t = so that
For the current we have
k)
= (1,
T(
and a
a
and
type filter
lift
circuit
with
and
for
the
)=(1k)
therefore the negative
output voltage in the discontinuous mode is
with
and we have
=
i.e. the output voltage will linearly increase during
increasing load resistance. A larger load resistance
may cause a higher output voltage in the
discontinuous mode.
VI. SELF LIFT
Fig 2.6 Re-Lift
The self-lift circuit shown in Fig.2.5 is derived from
the elementary circuit. The positive conversion path
consists of a pump circuit
and a
filter
and a lift circuit
The
negative conversion path consists of a pump circuit
and
a -type
filter
, and a lift circuit
.
VIII. MULTIPLE LIFT CIRCUIT
Triple-lift circuit
The triple-lift circuit is shown in Fig. 2.7.1. The
positive conversion path consists of a pump circuit
and a filter
, and a
lift
circuit
. The negative conversion path consists of a pump
circuit
and a
type filter
,
and
a
lift
circuit
.
Fig 2.5 Self Shift
VII. RE-LIFT
The re-lift circuit shown in Fig.2.6 is derived from
the self lift circuit. The positive conversion path
consists of a pump circuit
and a
filter
and
a
lift
circuit
. The negative
conversion path consists of a pump circuit
5
in Fig. 2.4.1 the parts (
) and parts
(
) were added in the triple-lift
circuit. According to this principle, a triple-lift circuit
and a quadruple-lift circuit have been built, as shown
in Figs. 2.7.1 and 2.7.2.
SPECIFICATION OF CIRCUIT PARAMETERS
Parameters
Specification
Input voltage
12V
Output voltage
48 V
QUADRUPLE-LIFT CIRCUIT
Load resistance
100 Ohms
The quadruple-lift circuit is shown in Fig.2.7.2. The
positive conversion path consists of a pump circuit
and a filter
and a
lift
circuit
Switching
frequency
50000 HZ
Filter inductance
100 µH
. The negative conversion path consists of a pump
circuit
and a -type filter
and
a
lift
circuit
Filter
capacitance
5 µF
Fig 2.7.1 Triple Lift Circuit
Table: 2.8 Specifications of Circuit Parameters
SIMULATION OF
CONTROLLER
CONVERTER
WITH
PI
Fig 2.7.2 Quadruple Lift Circuit
Referring to Fig. 2.6, it is possible to build multiplelift circuit using only the parts
multiple times in the positive conversion path, and
using the parts (
) multiple
times in the negative conversion path. For example,
Fig 5.1 Simulink Block Diagram Of Converter with PI Controller
6
PWM GENERATION OF PI CONTROLLER
The signal output from elementary circuit is V load
and reference signal is V ref both are given to Sumer
and output of Sumer is error signal. The error signal
can be reduced by PI controller. From the PI
controller it is given to limiter. The limiter reduces
the error by linearly. And it is added with carrier
signal. The modulated signal is pulse signal and it is
given to switch of elementary circuit.
Fig 5.4.1 Startup voltage1
Startup voltage 2
Fig 5.2 PWM generation of PI Controller
SIMULINK BLOCK FOR THE LINE AND LOAD
DISTURBANCE
Fig 5.4.2 Startup voltage2
Startup current 2
Fig 5.3 Simulink block for the line and load
disturbance.
SIMULATION
CONTROLLER
RESULT
FOR
PI
The double output DC-DC converter responses
obtained by simulation using MATLAB software
with conventional control under supply and load
disturbances for continuous mode of operation of the
converter are presented in this section
OUTPUT WAVEFORMS FOR PI:
Startup voltage 1
Fig 5.4.3 Startup current2
7
Startup voltage 3
Fig 5.4.6 Line disturbance voltage1-12-15-12
Line disturbance voltage 2-12-15-12
Fig 5.44 Startup voltage3
Startup current 3
Startup voltage 2
Fig 5.4.5 Startup current3
Line disturbance voltage 1-12-15-12
Fig 7.3.2 Startup voltage2
8
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ISIC-97,
10-12
September
1997,Singapore, pp. 227-230.
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(Boost)
Conversion
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Startupcurrent2
Fig 7.3.3 Startup current 2
CONCLUSION
Since the effect of the parasitic elements of DC-DC
converters limits their output voltage and power
transfer efficiency, the conduction duty cycle k
usually should not be higher than 0.9.This report
introduced the advanced voltage lift technique to be
successfully applied in the DC-DC converters design
and feedback with PI controller. Double-output
converters, a series of new DC-DC step-up (boost)
conversion circuits, have been developed. All double
output converters implementing the advanced
voltage-lift technique, avoid taking a too high value
of the conduction duty cycle. They overcome the
effect of parasitic elements and greatly increase the
output voltage of the DC-DC converters, introducing
the characteristic of high efficiency, high power
density, cheap topology in simple structure and nearzero output voltage and current ripples. Carefully
selecting the parameters we obtain mirrorsymmetrical double output voltages from a positive
input source. These converters can be used in the
computer periphery circuits, medical equipment and
industrial applications with high output voltages.
REFERENCES
1. Luo F. L., „Negative Output Luo-Converters,
Voltage Lift Technique” IEE Proceedings on
EPA,Vol. 45, No. 6, November 1998, pp.
2. Luo F. L., “Re-Lift Converter: Design, Test,
Simulation and Stability Analysis” IEE Proceedings
on EPA, Vol. 45, No. 4, July 1998, pp. 315-325.
3. Luo F. L. „Negative Output Luo-Converters,
Voltage Lift Technique‟‟ Proceedings of the Second
World Energy Systems - WES‟98, May 19-22,
1998,Toronto, Canada, pp. 253-260.
9