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Manuscript Draft
Manuscript Number: SE-D-13-00949
Title: PV based SMC Control for Negative Output Super Lift Luo Converter
Article Type: Third and Fourth generation Solar Cells
Keywords: PV system, Sliding Mode Control, Negative Output Super Lift Luo
Converter.
Corresponding Author: Mr. A ARUL ROBIN, M.E
Corresponding Author's Institution: PSG
First Author: A ROBIN, M.E
Order of Authors: A ROBIN, M.E; A RONALDMARIAN, M.E; A sivakumar, M.E; M
sasikumar, PhD
Abstract: This paper proposes a PV based SMC controller for negative
output super lift-Luo converters requiring a faster and dynamic response
over a wide range of operating conditions with low overshoot voltage. The
negative output super lift-Luo converter performs the voltage conversion
from positive input voltage from a PV system to negative load voltage. In
conventional converters the voltage increases in arithmetic progression
but in super lift converters the output voltage increases in geometric
progression. Moreover, it's easily realized with simple analog
circuitries. The SMC controller is designed by specific gain adjustment
and changing duty ratio. In order to improve the dynamic response of
converter for both static and dynamic specifications, we propose a SMC
controller. The main advantages of SMC controller over conventional
control are stability even for variations of large line and load values.
The PV module implemented design of (NOSLLC) negative output super liftLuo converter involves initialization of PV stability.
Cover Letter
Dear Editor,
We here by submit a paper entitled “PV Implemented Sliding Mode Controller for
Negative Output Super Lift Luo Converter”. I would like you to consider our paper for the
publication on solar journal for the upcoming issue. Also kindly let me know the paper’s further
consideration on any aspect of correction or modification. I would like to hear from you ASAP.
Thanking you
A..Arul Robin- SRF PSG-Institute of advanced studies, Coimbatore, India, 91-8883629363,
aarulrobin@gmail.com.
A.Ronald Marian- Dept. of Electrical and Electronics Engineering, Jeppiaar Engineering
College, Chennai, India ronald.amalraj@gmail.com,
A.Sivakumar- Dept. of Electrical and Electronics Engineering, Jeppiaar Engineering College,
Chennai, India sivaeee02@gmail.com
M. Sasikumar- Dept. of Electrical and Electronics Engineering, Jeppiaar Engineering College,
Chennai, India pmsasi77@gmail.com
*Highlights (for review)
HIGHLIGHTS:





PV system- implementation for the proposed converter
Sliding Mode Control,
Negative Output Super Lift Luo Converter
Green energy,
Economical
*Manuscript
Click here to view linked References
PV Implemented Sliding Mode Controller for Negative Output Super
Lift Luo Converter
A.Ronald Mariana, A..Arul Robinb, A.Sivakumarc, M. Sasikumard
a,c
P.G. Scholar, Dept. of Electrical and Electronics Engineering, Jeppiaar Engineering College,
Chennai, India. ronald.amalraj@gmail.com, sivaeee02@gmail.com
b
d
SRF PSG-Institute of advanced studies, Coimbatore, India, 91-8883629363,
aarulrobin@gmail.com
Professor / Head, Dept. of Electrical and Electronics Engineering, Jeppiaar Engineering
College, Chennai, India pmsasi77@gmail.com
Abstract
This paper proposes a PV based SMC controller for negative output super lift-Luo converters
requiring a faster and dynamic response over a wide range of operating conditions with low
overshoot voltage. The negative output super lift-Luo converter performs the voltage conversion
from positive input voltage from a PV system to negative load voltage. In conventional converters
the voltage increases in arithmetic progression but in super lift converters the output voltage
increases in geometric progression. Moreover, it’s easily realized with simple analog circuitries.
The SMC controller is designed by specific gain adjustment and changing duty ratio. In order to
improve the dynamic response of converter for both static and dynamic specifications, we propose
a SMC controller. The main advantages of SMC controller over conventional control are stability
even for variations of large line and load values. The PV module implemented design of
(NOSLLC) negative output super lift-Luo converter involves initialization of PV stability.
Keywords: PV system, Sliding Mode Control, Negative Output Super Lift Luo Converter.
1. Introduction
Renewable energy sources also called as non-conventional type of energy are the sources which
are continuously replenished by natural processes. Such as, solar energy, bio-energy, bio-fuels
grown sustainably, wind energy and hydropower etc., are some of the examples of renewable
energy sources [12]. Solar energy has been harnessed by humans since ancient times using a
variety of technologies. Solar powered electrical generation relies on photovoltaic system and heat
engines. Solar energy's uses are limited only by human creativity. To harvest the solar energy, the
most common way is to use photo voltaic panels which will receive photon energy from sun and
convert to electrical energy [13] as shown in figure 1. It is economic and called green energy for its
pollution free nature. Voltage lift technique has been successfully employed in design of dc/dc
converters, e.g., Luo-converters [4]. However, the output voltage increases in arithmetic
progression. Super lift technique in this system implements the output voltage increasing in
geometric progression. It effectively enhances the voltage transfer gain in power-law. The SMC
(sliding mode control) for the above system is implemented to achieve a closed loop control with
respective parametric selection. The NOSLLC (Negative Output Superlift Luo Converter)
performs the voltage conversion from positive source voltage to negative load voltage.
The simple models of power converters are usually obtained from state-space averaging and
linearization techniques, these models may then be used for classical control design. On other and
the classical PID controller [1] design procedure is well known, but it is failed to satisfactorily
perform constrained specification under large variation of system parameters and load variations,
because of the of small-signal model parameters on the converter operating point. Multi-loop
control techniques, such as current-mode control, have greatly improved power converter dynamic
behavior, but the control design remains difficult especially for high-order topologies. The solar
PV array model [9, 11] shown below is used as input source. This electricity can then be used to
power a load.
1.1 Solar PV Panel
The modeling of the Solar PV Panel [13, 14] is done based on the equivalent circuit of the PV panel.
The equivalent circuit diagram of the PV Panel is show as in figure 2. The I–V characteristic of the
ideal PV cell is mathematically described as,
I =Ip-Id
Where,
Therefore,
(1.1)


 qv 
I d  I 0,cell exp 
  1
 akt 




 qv 
I  I p ,cell exp 
  1
 akt 


(1.2)
(1.3)
Where
Ipv,cell is the current generated by the incident light (it is directly proportional to the Sun irradiation),Id
is the Shockley diode equation, I0,cell is the reverse saturation or leakage current of the diode, q is the
electron charge (1.60217646 × 10−19 C),k is the Boltzmann constant (1.3806503 × 10−23 J/K),T (in
Kelvin) is the temperature of the p–n junction, and a is the diode ideality constant. The figure 3 shows
the origination of the I – V curve for the equation. Practical arrays are composed of several connected
PV cells and the observation of the characteristics at the terminals of the PV array requires the
inclusion of additional parameters to the basic equation.
Hence,
(1.4)
Where,
V = NskT/q is the thermal voltage of the array with Ns cells connected in series. RS& RP is the
equivalent series and parallel resistance of the array. The cells connected in parallel which increases
the current and the cells connected in series provide greater output voltages. If the array is composed
of Np parallel connections of cells the PV and saturation currents may be expressed as,
Ipv = Ipv,cell* Np, and
I0 = I0,cell * Np.
This simulation is done for standard test condition (STC) when temperature is 25ᵒC and Irradiation is
1000 W/m2 [15].
2.
CONVERTER OPERATION AND MATHEMATICALMODEL OF NOESLLC
The NOSLLC is a new series of DC-DC converters possessing high-voltage transfer gain,
high power density, high efficiency, reduced ripple voltage and current. These converters are
widely used in computer peripheral equipment, industrial applications and switch mode power
supply, especially for high voltage-voltage projects. The super-lift technique considerably increases
the voltage transfer stage-by-stage gain in geometric Progression. Control for them needs to be study
for application of these good topologies. Voltage across capacitor C1 is charged to Vin. Current
flowing through inductor L1 increases with slope Vin /L1 during switching-on period DT and
decreases with slope – (Vo –Vin )/L1 during switching-off (1-D)T. The circuit diagram is shown in
figure 4.
DC-DC converters [10] that convert unregulated DC input voltage into regulated DC output
voltage. Nowadays, all the modern power electronics systems need high quality, simple,
lightweight, cheap, highly reliable and efficient power supplies. To regulate the output voltage of
DC-DC converters irrespective of load variations and line disturbances, it is necessary to operate
the converters in closed loop mode. In recent days, the use of sliding mode control (SMC) method
in variable structure control (VSC) makes this system very robust to parameter variations and
external variations. The discontinuous control action, which is often referred to as variable structure
control (VSC) is also defined in the continuous-time domain.
Thus, variation of current iL1 is,
i L1 
Vin
V  Vin
DT  o
(1  D)T
L1
L1
(2)
During mode1 the switch is closed and the supply flows through the inductor L1 and C1 charges during
this time the capacitor C2 produces a load voltage which is shown in figure 5. During mode 2 the
switch is open and the inductor L1 and capacitor C1 discharges through the load which gives the
boosted output Vo which is shown in figure 6.
2D

Vo  
 1Vin
 1 D

(3)
2D
1
1 D
(4)
The voltage transfer gain is,
G1 
3.
ENERGY EQUATIONS DURING ON AND OFF STATE
Considering the modes of operation as by above figure,
Energy during ON state is given by, Won=Vin IL Ton
(5)
Energy during OFF state is given by, Woff = VL IL Toff
(6)
Therefore output voltage is given by, Vo=Vin /1-D
(7)
The variation ratio of inductor current iL1 is,  
i L1 / 2
i L1

D(1  D)TVin D(1  D) R

2 L1 I 0
G1
2 fL1
(8)
The ripple voltage of output voltage V0 is,
 
V0 / 2
(1  D )

V0
2 RfC 2
(9)
Therefore, the variation ratio of output voltage V0 is,
V 0 
I 0 (1  D)T
(1  D) V0

C2
fC 2
R
(10)
4.
STATE-SPACE AVERAGE MODEL OF NOSLLC
The state-space modeling of the equivalent circuit of NOSLLC with state variables iL1, VC1 and VC2 is
given below. According to the switching condition of circuit, i.e. In ON condition, the V1, V2, V3 are
expressed as,
diL1
V1  0 
V2 
dt
Vin
V
dVC1
I
 in  L1 
RinC1 L1
C1
dt
dV C 2
Vin
V3  

L1
dt
(11)
According to the switching condition of circuit, i.e. in OFF condition, the V1, V2, V3 are
di
V
expressed as,
V   in 
L1
1
L1
dt
dV C 1
i L1 Vin


C1
L1
dt
dV C 2
Vin
i L1
V3 


C2
L1
dt
V2  
(12)
Therefore,
1
1 
 diL1  

 dt   0  L
L 
 dV   1
 C1   
0
0 
 dt   C1

 dVC 2   1
1 
0 
 dt  

  C2
RC 2 
VC1 VC1 Vin 
     Vin 
 iL1   L1 L1 L1   L 
V     2iL1  Vin  Y   0 1 
 C1   C R C   
VC 2   1 in 1   0 
  iL1
  

  
C2
(13)
State-space modeling of the circuit is given by,
X & x
Where above variables are the vectors of the state variables and their derivatives respectively, C is
disturbance matrix, and ω is the input.
5.
SIMULATION DIAGRAM OF NOESLLC
Simulation is carried out for the negative output elementary super-lift Luo converter with the
values, Vin =12V, f=100 KHz, L=10uH, C1, C2=30uF, R=50Ω, D=0.667. The simulation is done in
PSPICE with the calculated values and the diagram is given in figure 7.
An output voltage of -36V is shown in below diagram. This is a geometric progression of voltage
of 3 times the input voltage (12V) simulated in PSPICE. With a time period of 10us the output
voltage is depicted in figure 8.
6.
DESIGN OF SMC
In sliding mode theory, the SMC requires sensing of all state variables of NOSLLC and generation
of suitable references for each of them. According to principle of the SMC are to make the
capacitors voltage VC1 and VC2 of NOSLLC follow as faithfully as possible the capacitor voltage
references. However, the inductor current reference is difficult to evaluate since that generally
depends on load power demand, supply voltage, and load voltage. To overcome this problem in
implementation, the state variable error for the inductor current can be obtained from feedback
variable iLl by means of a high-pass filter in the assumption that their low-frequency component
is automatically adapted to actual converter operation. The high-pass filter must be suitably lower
than the switching frequency to pass the ripple at the switching frequency, but high enough to allow a
fast converter response. When good output voltage regulation of NOSLLC is required, a sliding
surface equation in the state space can be expressed by a linear combination of state-variable errors,
can be given by,
S= (iL1, VC1, VC2) =K + K + K
(14)
Where coefficients ,
and
are proper gains,
is the feedback current error,
is the
feedback voltage error and is the feedback voltage error, or
 2  VC1  VC1ref
(15)
1  iL1  iL1ref
(16)
 3  VC 2  VC 2 ref
(17)
By substituting (14) in (13) we get,
S  (iL1 ,Vc1 ,Vc2 )  K1 (iL1  iL1ref )  K 2 (Vc1  Vc1ref )  K3 (Vc2  Vc2ref )
(18)
The signal S  (iL1 ,VC1 ,VC 2 ) obtained by (10) and applied to a simple circuit (hysteresis comparator),
can generate the pulses to supply the power semiconductor drives. Status of the switch y is controlled
by hysteresis block H, which maintains the variables, S  (iL1 ,VC1 ,VC 2 ) near zero.
7.
SELECTION OF CONTROL PARAMETERS
Once the negative output superlift Luo converter parameters are selected, inductance and are
designed from specified input and output current ripples, capacitors
and
are designed so as
to limit the output voltage ripple in the case of fast and large load variations, and maximum
switching frequency is selected from the NOSLLC ratings and switch type. According to the
variable structure system theory, the converter equations must be written in the following form,
X  Ax  By  Cw
(19)
Where X represents the vector of state-variables errors, given by

V *  iLref ,VC1ref ,VC 2ref

T
(20)
Where, X  v  V  is the vector of references
By substituting (17) in (12), we obtains,
D=AV*+Cw

 0

1
D
C
 11

 C2
1
L1
0
0



0 

1 

RC 2 
1
L1
 1
 iL1ref   L 

  1
VC1ref    0  Vin
VC 2 ref   0 

 



(21)
(22)
Therefore,
V
VC 2 ref
V
 C1ref  in
 L
L
L1
1
1

iL1ref

D  
C1

i
V
L
1
ref

 C 2 ref

C2
RC 2










(23)
Substituting (17) in (15), the sliding function can be rewritten in the form,
S(x)=K1x1+K2x2+K3x3=KTx
Where,
KT= [K1+K2+K3]
and
(24)
x=[x1+x2+x3]
The existence condition of the sliding mode requires that all state trajectories near the surface be
directed toward the sliding plane. It is necessary and sufficient that
 
S ( X )  0, if S ( X )  0
 

S ( X )  0, if S ( X )  0
(25)
Sliding mode control is obtained by means of the following feedback control strategy,
which relates to the status of the switch with the value of S (x)
0 , for S ( x)  0
Y 
1, for S ( x)  0
The existence condition (18) can be expressed in the form,
S ( x)  K T Ax  K T D  0 , S ( x)  0
S ( x)  K Ax  K B  K D  0 , S ( x)  0
T
T
T
(26)
(27)
(28)
From a simulation point of view, assuming that error variables X1 are suitably smaller than
references V*, (20) and (21) can be rewritten in the form
(29)
K T D  0 , S ( x)  0
K T B  K T D  0 , S ( x)  0
(30)
By substituting matrices B and D in (26) and (27), we obtains
K 2iL1ref
K
K1
[Vc1ref  Vc2 ref  Vin ] 
 3 [ Ri L1ref  Vc2 ref ]  0
L1
C1
C2 R
(31)
K 3Vc 2 ref
K2
[Vin  Rin iL1ref ] 
0
C1 Rin
RC 2
(32)
The existence condition is satisfied if the inequalities (28) and (29) are true.
fs 
1
t1  t 2
(33)
Where
time,
conduction is time of the switch S and,
is the off time of the switch S. The conduction
is derived from (29) and it is given by,
2
(34)
t1 
K 3VC 2 ref
K2
[Vin  Rin ] 
C1 Rin
RC 2
Where,  is an arbitrary small positive quantity and
2 is the amount of hysteresis in S(X),
The off time,
is derived from (29), and it is given by,
 2
t 2 
K i
K
K1
[VC1ref  VC 2 ref  Vin ]  2 L1ref  3 Ri L1ref  VC 2 ref 
L1
C1
C2 R
8.
(35)
SIMULATION DIAGRAM OF NOESLLC WITH SMC
The simulation study of NOSLLC with SMC is presented in this section. The validation
of the system performance is done for five regions viz. transient region, line variations, load
variations, steady state region and also components variations. Simulations have been performed on
negative output elementary super lift Luo converter circuit with parameters calculated the sketch of
the model is shown in figure 9.
The static and dynamic performances of SMC for NOSLLC are evaluated in
MatLab/Simulink. The Matlab/Simulink simulation of system with control method is depicted in
Figure 10. The detailed operation of NOSLLC with SMC is discussed.
8.1 OUTPUT VOLTAGE
The output voltage is obtained to be -99V where the geometric progression of input voltage (33V)
is shown in figure 11. It can be observed that input current of NOSLLC goes up to 2.35A and output
voltage of NOSLLC travels up to -98.6V without overshoot.
8.2 GATE PULSE OF THE SWITCH
The gate pulse of the switch S (MOSFET) is given with a duty ratio of 0.66 i.e. 66% of the total
period. The adapted value of duty ratio is selected to be 0.66 for an enhanced output voltage. The gate
pulse given to the switch is shown in the figure 12.
8.3 INDUCTOR CURRENT
The inductor current waveform is shown in figure 13 which has iL1=11.2A. The inductor
energized when the supply is given with switch turned ON and during OFF condition the current
discharges through load.
8.4 RELAY ENERGISING PULSE
The relay is energized based on the summer output shown in figure 14. Also a high pass filter is
added to the current feedback, which are given to the gain amplifier and the relay is energized based
on the range of value taken. Thus the relay output is considered as input to the switch and a closed
loop will be achieved. Based on the variation parameter of load, input voltage, and change in
component values the gain parameter is chosen and converter in closed loop control is executed.
9.
EXPERIMENTAL RESULTS
In this proposed method, with the hardware setup of NOSLLC providing an input PV source
is validated experimentally [9] which have been depicted in fig: 15, fig: 16 and fig 17. Here the
prototype model includes PIC 16F877A, which is a 40-pin 8-Bit CMOS FLASH Microcontroller
from Microchip. The core architecture is high-performance RISC CPU with only 35 single word1
instructions. Since it follows the RISC architecture, all single cycle instructions take only one
instruction cycle except for program branches which take two cycles. 16F877A comes with 3
operating speeds with 4, 8, or 20 MHz clock input. Since each instruction cycle takes four operating
clock cycles, each instruction takes 0.2 μs when 20MHz oscillator is used. The core feature includes
interrupt capability up to 14 sources, power saving SLEEP mode, and single 5V In-Circuit Serial
Programming (ICSP) capability. The sink/source current, which indicates a driving power from I/O
port, is high with 25mA. Power consumption is less than 2 mA in 5V operating condition. The table 1
shows the comparison results between hardware and software. The proposed simulated work has been
implemented in hardware using a prototype model consisting of a solar panel for the input source.
The solar input is given as source to the converter in which an output voltage of -99V is obtained.
The hardware diagram is shown below. The output voltage V0= -98.6V is measured in the
oscilloscope for an input voltage of Vin=33V. The diagram is shown below.
10.
CONCLUSION
Dc-Dc power converters are used in a variety of electric power supply systems, including
cars, ships, aircraft and computers. Power electronic converters are intrinsically periodic time-variant
structure systems due to their inherent switching operation, so the sliding mode control approach
is a strong method for the converter controller design. Application of sliding mode control in
tracking a real-time voltage profile is very critical because a switching strategy is traditionally
employed in power converters, and of the inherent robustness properties of the sliding mode. The
effect of proper selected controller parameters of sliding mode controlled NOSLLC operated
results in fast dynamic response and excellent static and transient responses. It is, therefore,
feasible for common DC-DC conversion purpose, computer power supplies and medical
equipments etc.
11.
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Authors bio-graphies
A.RonaldMarian is currently pursuing the M.E Degree from Jeppiaar Engineering
College, Anna University, Chennai, India. Earlier he received his B.E degree in Electrical
and Electronics Engineering in the same institution, India in 2011. His current research
interests include Induction Motor Drives, Renewable Energy Scorces, Multi level inverter,
smc techniques and Z-Source Converters. His e-mail ID is ronald.amalraj@gmail.com.
A.Arul Robin has completed his M.E Degree from St.Joseph’s College of Engineering,
Anna University, Chennai, India. Earlier he received his B.E Degree in Electronics and
Communication Engg., in 2010. His current area of interest includes Embedded
Controllers, Power Electronics and Drives, Special Machines and Robotics. E-mail:
aarulrobin@gmail.com.
A.sivakumar is currently pursuing the M.E Degree from Jeppiaar Engineering College,
Anna University, Chennai, India. Earlier he received his B.E degree in Electrical and
Electronics Engineering in Raja College Of Engineering and Technology, Anna University,
Chennai , India in 2012. His current research interests include Induction Motor Drives,
Renewable Energy Scorces, Multi level inverter, smc techniques and Z-Source Converters.
His e-mail ID is sivaeee02@gmail.com.
Prof. Dr. M. Sasikumarhas received the Bachelor degree in Electrical and Electronics
Engineering from K.S.RangasamyCollege of Technology, Madras University, India in
1999, and the M.Tech degree in power electronics from VIT University, in 2006. He has
obtained his Ph.d. degree from Sathyabama University, Chennai. Currently he is working
as a Professor and Head in Jeppiaar Engineering College, Chennai Tamilnadu, India. He
has published papers in National, International conferences and journals in the field of power electronics and
wind energy conversion systems. His area of interest includes in the fields of wind energy systems and power
converter with soft switching PWM schemes. He is a life member of ISTE. His email ID is:
pmsasi77@gmail.com
Figure
Tables and Figures:
Table 1:
Comparision
Simulation output
Applied
33V
voltage(Vin=33V)
PV output voltage
-99V
Table 1: Result Comparison
Experimental
output
33V
-98.6V
Figure 1. Solar cell
Figure 2: Equivalent circuit of PV panel
Figure 3. Origination of the IV Curve
Figure 4: The NOESLLC circuit
Figure 5: Mode 1 circuit diagram of NOSLLC
Figure 6: Mode 2 circuit diagram of NOSLLC.
Figure.7: Simulation Diagram of NOSLLC
Figure 8: Output Wave Form of NOSLLC
Figure.9: Sliding mode controller of NOSLLC
Figure.10: Simulated Diagram of NOSLLC
Figure.11: Output Voltage of NOESLLC
Figure.12: Gate Pulse of the Switch
Figure.13: Inductor Current
Figure.14: Relay Energizing Pulse
Figure 15. Solar Panel
Figure 16. Hardware setup
Figure 17. Output voltage measured