Voltage-Based Maximum Power Point Tracking Control ofPVSystem - PDF

Document Sample
Voltage-Based Maximum Power Point Tracking Control ofPVSystem - PDF Powered By Docstoc
					                                                                     I. NOMENCLATURE

                                                                     C, Ca       Filter, array capacitance
Voltage-Based Maximum                                                d1 , d2     Duty ratios of switch S1 , S2
                                                                     DP1 , DP2   Diodes of individual boost cells
Power Point Tracking Control                                         IA          SCA current
                                                                     IAb         SCA current with boost converter
of PV System                                                         IAd         SCA current with IDB converter
                                                                     Im          SCA current at maximum power
                                                                     Iab         Average load current with boost converter
                                                                     Iaid        Average load current with IDB converter
MUMMADI VEERACHARY, Student Member, IEEE                             Iph         Insolation dependent photo current
                                                                     I0          Cell reverse saturation current
KATSUMI UEZATO                                                       L1 , L2     Inductances of individual boost cells
University of the Ryukyus
Japan                                                                Ns , Np     Number of SCA cells in series, parallel
                                                                     Pgb , Pgd   SCA power output with boost, IDB
                                                                     Pm          Maximum power of the SCA
   Photovoltaic (PV) generators exhibit nonlinear v-i                R1 , R2     Inductor series resistances
characteristics and maximum power (MP) points that vary              Rs          Cell series resistance
with solar insolation. An intermediate converter can therefore       R           Load resistance
increase efficiency by matching the PV system to the load and        S1 , S2     Switches of individual boost cells
by operating the solar cell arrays (SCAs) at their maximum           V ,V
                                                                      Ab    Ad   SCA voltage with boost, IDB converter
power point. An MP point tracking algorithm is developed using       Vm          SCA voltage at maximum power
only SCA voltage information thus leading to current sensorless                  operation
tracking control. The inadequacy of a boost converter for array      V ,V
                                                                      ab aid     Average load voltage with boost, IDB
voltage based MP point control is experimentally verified and an                 converter
improved converter system is proposed. The proposed converter
                                                                     ´b , ´id    Efficiency of the boost, IDB converter
system results in low ripple content, which improves the array
                                                                     ª           Solar insolation.
performance and hence a lower value of capacitance is sufficient
on the solar array side. Simplified mathematical expressions for     II.   INTRODUCTION
a PV source are derived. A signal flow graph is employed for
modeling the converter system. Current sensorless peak power
                                                                          The rapid trend of industrialization of nations and
                                                                     increased interest in environmental issues recently
tracking effectiveness is demonstrated through simulation results.
                                                                     led us to explore the use of renewable forms such
Experimental results are presented to validate the proposed
                                                                     as solar energy. Photovoltaic (PV) generation is
                                                                     gaining increased importance as a renewable source
                                                                     [1—2] due to its advantages like absence of fuel cost,
                                                                     little maintenance, and no noise and wear due to the
                                                                     absence of moving parts, etc. In particular, energy
                                                                     conversion from solar cell arrays (SCAs) received
                                                                     considerable attention in the last two decades. The
                                                                     PV generator exhibits a nonlinear v-i characteristic,
                                                                     and its maximum power (MP) point varies with the
                                                                     solar insolation and temperature. At a particular solar
Manuscript received March 14, 2000; revised July 3, 2001; released   insolation, there is a unique operating point of the
for publication July 26, 2001.                                       PV generator at which its power output is maximum.
IEEE Log No. T-AES/38/1/02589.
                                                                     Therefore, for maximum utilization efficiency, it is
                                                                     necessary to match the PV generator to the load such
Refereeing of this contribution was handled by I. Batarseh.          that the equilibrium operating point coincides with the
Authors’ address: Dept. of Electrical and Electronics Engineering,   MP point of the PV source. However, since the MP
Faculty of Engineering, University of the Ryukyus, 1 Senbaru,        point varies with insolation and seasons, it is difficult
Nishihara-cho, Nakagami, Okinawa 903-0213, Japan.                    to maintain MP operation at all solar insolations.
                                                                     To overcome this problem, use of an intermediate
0018-9251/02/$17.00 ° 2002 IEEE
                    c                                                dc-dc converter is proposed [3—5], which continuously

262                    IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 38, NO. 1                     JANUARY 2002
adjusts the voltage, current levels and matches the PV
source to the load.
    The MP point tracking is applied to PV systems
to extract maximum available power from the
SCAs at all solar insolations. Different methods of
peak power tracking schemes have been proposed
by using different control strategies [6—9]. Boost
converter based MP point tracking using fuzzy
logic is reported [10]. These studies show that the
fuzzy control algorithm is capable of improving the
tracking performance as compared with conventional
methods. However, in fuzzy implementation several
parameters are selected on a trial and error basis,
which mainly depends on designer experience and                     Fig. 1a. Experimental setup of PV system.
intuition. To overcome some of the disadvantages
mentioned above, a fuzzy neural network based MP           stresses, fault tolerance for the system, flexibility in
point tracking is proposed [11]. All these methods         the system design, etc.
depend on the SCA power output and/or load power               This paper presents MP point tracking of SCA
detection using the instantaneous voltage and current      employing an intermediate interleaved dual boost
information, requiring voltage and current sensors.        (IDB) converter using only the array voltage
Neural network based real time MP tracking controller      information, eliminating the array current detection
for PV grid connected systems has been reported [12].      and hence achieving current sensorless peak power
The studies emphasize that the SCA operating point         tracking. This paper is organized as follows.
is shifted to its MP point by using a voltage control      In Section III, we present the development of
type inverter, which utilizes the array voltage together   mathematical models for the PV generator and power
with pilot cell voltage information. Array voltage         converters. Maximum power point tracking control
based MP point tracking using dc-dc converters is          process is discussed in Section IV. Experimental
currently under investigation by various researchers.      system description is given in Section V. Section VI
This method of MP tracking has advantages like             presents experimental results, and conclusions are
straightforward array voltage measurement (which is        provided in Section VII.
inexpensive as compared with the measurements of
solar insolation, and other environmental factors), no
need of current sensors, (which introduces losses and      III. MATHEMATICAL MODEL OF SYSTEM
complexity in the system) etc. The authors have tried         Fig. 1(a) shows the overview of the combined
to implement boost converter array voltage based MP        system, which mainly consists of SCA, IDB converter,
point control. The experimental investigations show        and data acquisition system. The analysis of the
that boost converters are not suitable for array voltage   system is carried out under the following assumptions.
based MP point tracking control as this leads to an
undesirable operation. An alternate converter scheme           1) Switching elements (MOSFET and diode) of
(interleaved dual boost (IDB) converter) is proposed       the converter are assumed to be ideal, i.e., forward
by the authors for array voltage based MP extraction,      voltage drops and ON-state resistances of the switches
by simple addition of one more boost cell in parallel      are neglected.
to the existing boost cell and controlling these two           2) The equivalent series resistance of the
boost cells in an interleaved fashion.                     capacitance and stray capacitances are neglected.
    The advantages of the present converter system             3) Passive components (R, L, C) are assumed to be
are 1) ripple cancellation both in the input and output    linear, time invariant, and frequency independent.
waveforms to the maximum extent possible, 2) lower             4) The two parallel boost cells are identical and
value of ripple amplitude, and high ripple frequency       operate in the continuous inductor current mode.
in the resulting input and output waveforms, and 3)            5) The switches (S1 , S2 ) operate in interleaved
reduced electromagnetic interference (EMI) because         fashion.
of low ripple amplitude of SCA current. Although               Mathematical models for individual components
the interleaving technique increases the number of         are developed in the following sections.
components, the actual increase of cost may not be
significant. This is because more boost cells can          A. PV Generator Model
share the current flow in the inductors and switching
devices, so lower current rating devices may be               The PV generator is formed by the combination
employed. Further, parallel connection of converters       of many PV cells connected in series and parallel to
has many desirable properties such as reduced device       provide the desired output voltage and current. This

PV generator exhibits a nonlinear insolation dependent
v-i characteristic, mathematically expressed for the
SCA consisting of Ns cells in series and Np cells in
parallel [1] as
                 Ã ! µ ¶ (                          )
                    Ns     Ns           Np Iph ¡ IA
     V = ¡IA Rs
      A                 +       ln 1 +                (1)
                    Np     ¤               Np I0

where ¤ = (q=AKT), q–electric charge;
A–completion factor; K–Boltzmann’s constant;
T–absolute temperature; Rs –cell series resistance;
Iph –photo current; I0 –cell reverse saturation current;                        Fig. 1b. Equivalent circuit of system.
IA , V are the SCA current and voltage, respectively.
For given values of SCA parameters, the V ¡ IA
characteristic depends on the solar insolation and the            then the reflected equivalent load on the SCA side is
MP point varies with the solar insolation. Rewriting              given by the following equation
(1) as
                    Ã ! µ ¶                                                             Req = ´b (1 ¡ d)2 R                 (7)
                       Ns       Ns
         V = ¡IA Rs
          A                 +                                     i.e.,
                       Np       ¤                                                       V
                " µ             Ã             !#
                                                                                            = ´b (1 ¡ d)2 R:                (8)
                          ¶                                                             IAb
                     Ipha               IA
              £ ln          + ln 1 ¡                 (2)          Power extracted by the boost converter from the SCA
                       I0             Np Ipha
where Ipha = Iph + I0 . Expanding the term                                                     V2
                                                                                   Pgb =                :           (9)
ln(1 ¡ (IA =Np Ipha )) into Taylor series and neglecting                                  ´b (1 ¡ d)2 R
higher order terms [5] results in the following
                                                                      From the above expression the array power Pgb
             Ã                    ! µ ¶· µ                        depends on the load and converter duty ratio. For a
                           2Ns         Ns       Ipha              given load, the array power continuously increases
    V = ¡IA Rsg +
     A                             +         ln         :         with duty ratio, theoretically resulting in minimum
                         ¤Np Ipha      ¤         I0
                                                                  power at d = 0 and infinite power at d = 1, at which
                                                                  the SCA voltage collapses, leading to an undesirable
Simplifying the above equation for the SCA current                operation. Furthermore, the power Pgb is continuously
results in the following equation.                                increasing with duty ratio, and hence with this power
                               ·       µ      ¶     ¸             comparison method it may not be possible to reach
                     1           Ns      Ipha
       IA = Ã                !      ln          ¡VA   (4)         the MP point. To overcome this disadvantage an
                       2Ns       ¤        I0
              Rsg +                                               identical boost branch is connected in parallel to
                    ¤Np Ipha                                      the existing one and controlls these two branches in
                                                                  complementary fashion. The analytical discussion of
where Rsg = Ns Rs =Np . The equations (3) and (4) are
                                                                  this converter is given in the following section.
used in the simulation studies.

B. Boost Converter Model                                          C.      IDB Converter Model

    The intermediate boost converter produces a                       The intermediate IDB converter produces a
chopped output voltage and controls the average dc                chopped output dc voltage and controls the average
voltage applied to the load. Further, the converter               dc voltage applied to the load. Further, the converter
continuously matches the output characteristic of the             continuously matches the output characteristic of the
PV generator to the input characteristic of the load.             PV generator to the input characteristic of the load so
The steady-state voltage and current relations of the             that MP is extracted from the SCA. The steady-state
boost converter operating in continuous current mode              voltage and current relations of the IDB converter
are                                                               operating in continuous current mode are derived
                           VAb                                    using signal flow graph (SFG) technique [13]. The
                   V =
                    ab                                (5)
                         (1 ¡ d)                                  steady-state signal flow graph of the IDB converter is
                     Iab = ´b (1 ¡ d)IAb                    (6)   obtained as shown in Fig. 2. Voltage gain is derived
                                                                  by employing the well-known Mason’s gain formula.
where ´b is the efficiency of the boost converter,                To start with various possible forward paths and loops
V , IAb are the array voltage and current, respectively.
 Ab                                                               are identified from the steady-state SFG (Fig. 2). The
Transforming the load to the SCA side (Fig. 1(b)),                forward paths transmittances formed by the nodes

264                 IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 38, NO. 1                           JANUARY 2002
                                           Fig. 2. Steady-state SFG of IDB converter.

(V ¡ V ¡ IL1 ¡ I0 ¡ V ), (V ¡ V ¡ IL2 ¡ I0 ¡ V ) are
  g   1              0     g   2              0                  i.e.,
                            d R
                                                                                      = ´id (2d2 ¡ 2d + 1)2 R:        (19)
                        P1 = 2                           (10)                     IAd
                                                                 Substituting the IAd = IA expression (from (4)) in the
                            d R                                  above expression then
                        P2 = 1 :                         (11)
                             R2                                                                   ·      µ      ¶      ¸
                                                                           [´id (2d2 ¡ 2d + 1)2 R] Ns      Ipha
                                                                    V = Ã
                                                                     Ad                        !      ln          ¡V :
In this steady-state SFG two loops formed by the                                        2Ns         ¤       I0
nodes (V ¡ IL2 ¡ I0 ¡ V ), (V ¡ IL1 ¡ I0 ¡ V ¡ V ) exist
         2             2     1              0   1
                                                                                Rsg +
                                                                                      ¤Np Ipha
and their loop transmittances are
                      L1 =                               (12)    On simplification the array voltage equation becomes
                                                                                                        · µ       ¶¸
                             ¡Rd22                                            [´id (2d2 ¡ 2d + 1)RNs ]       Ipha
                      L2 =         :                     (13)         V =
                                                                       Ad                                ln
                              R1                                            ¤[K + ´id (2d2 ¡ 2d + 1)R]        I0
Applying Mason’s gain formula the steady-state
                                                                 where K = (Rsg + (2Ns =¤Np Ipha )). Power extracted by
voltage gain obtained as
                                                                 the IDB converter from the SCA is
             Vaid       R(R1 d1 + R2 d2 )                                                         V2
                  =               2       2
                                                         (14)                             Pgd =    Ad
                                                                                                      :               (22)
             VAd    R1 R2 + R(R1 d1 + R2 d2 )                                                     Req
where d1 , d2 are the duty ratios of the switches                Substituting (18) and (21) in (22) then the resulting
S1 , S2 , respectively. The IDB converter switching              SCA power expression is
devices (S1 , S2 ) are activated in complementary mode                                                  · µ      ¶¸
with duty ratios d1 and d2 , satisfying the relation                                 (´id RNs2 )             Ipha 2
d1 + d2 = 1. If the two parallel boost cells are identical           Pgd = 2                              ln          :
                                                                           ¤ [K + ´id (2d2 ¡ 2d + 1)R]2       I0
(R1 = R2 = r; R À r) then the above equation becomes                                                                 (23)
                              VAd                                From (23) it can be noticed that, for given values
                    V =
                     aid             :                   (15)
                           (d1    2
                              + d2 )                             of the array parameters and load, the SCA power
                                                                 (Pgd ) depends on the duty ratio of the IDB converter.
Substituting d1 = d, d2 = (1 ¡ d), the above equation            Suitable adjustment of converter duty ratio results in
can be written as                                                V = V , which in turn results in extraction of MP
                                                                  Ad     m
                                                                 from the SCA.
                 V =
                  aid                  :                 (16)
                        (2d2 ¡ 2d + 1)
Using power balance, the current expression is                   IV. MAXIMUM POWER POINT TRACKING
obtained as                                                          CONTROL PROCESS
                             2    2
                Iaid = ´id (d1 + d2 )IAd                 (17)         The control flow chart is given in Fig. 3, which
where ´id is the efficiency of the IDB converter,                controls the tracking process of the PV supplied
V , IAd are the array voltage and current, respectively.         converter system. The tracking process can be started
Transforming the load to the SCA side (Fig. 1b), then            by outputting the command signal either 0 or 5 V to
the reflected equivalent load on the SCA side is given           the pulsewidth modulation (PWM) generator, which
by the following equation                                        corresponds to duty ratio of zero or one, respectively.
                                                                 Whatever may be the duty ratio (0-1) the array power
               Req = ´id (2d2 ¡ 2d + 1)2 R               (18)    (Pg ) is computed from the (22) using the already

                                                                 Fig. 4. Power tracking process with duty ratio.

                                                          V.   EXPERIMENTAL SYSTEM DESCRIPTION

                                                              The basic configuration of the proposed PV system
                                                          is shown in Fig. 1(a). The data acquisition system
                                                          is set up by using PC, interface AZI-3503 card,
                                                          which mainly consists of 8-channel 12-bit A/D, D/A
                                                          converters. For power measurements a digital power
                                                          meter (YOKOGAWA-WT130) is used, through which
          Fig. 3. Flow chart for MP point tracking.
                                                          a GPIB interface is connected to the PC to record the
                                                          SCA power data. The PWM modulator is a voltage
                                                          comparator made of LF311 operational amplifier.
sensed array voltage. Change (increase or decrease)       The reference signal to this comparator is the signal
the duty ratio and then measure the instantaneous         obtained from the D/A converter, generated by means
array power. This power is compared with the              of the MPPT algorithm. A synthesized YOKOGAWA
previous power and a decision on whether to increase      function generator (FG120) was used to obtain phase
or decrease the duty ratio is taken depending on the      displaced triangular carrier signals to the PWM
location of the operating point and direction of its      generator. The experimental prototype circuit was built
movement as indicated in Fig. 4. As a consequence,        with an International Rectifier IRF530N MOSFET
there are four possibilities (two if the operating        with suitable driver circuit, and the diode FML-32S.
point is left of the MP point, two if the operating       The artificial sun is realized in the laboratory by
point is right of the MP point) for the operating         means of incandescent lamp set. Further, the solar
point movement. The duty ratio control signal is          insolation level illuminated on the solar panel is
continuously adjusted to maximize the array power         adjusted by controlling the power to this incandescent
by following the equation d = d § ¢d. The sign of         lamp set.
the incremental duty ratio (¢d) is determined by
the incremental power (¢P) and operating point            VI. EXPERIMENTAL RESULTS AND DISCUSSIONS
movement as indicated in Fig. 4. If ¢P is positive
and the operating point is left of MP point, then             The simple boost converter is not able to track MP
d = (d + ¢d), otherwise d = (d ¡ ¢d). Along similar       point by sensing only the array voltage information.
lines, if the ¢P is negative and the operating point is   This is because the equivalent load impedance (in
left of the MP point, then d = (d + ¢d), otherwise d =    (7)) seen by the SCA is continuously decreasing with
(d ¡ ¢d). This tracking control process repeats           increasing the duty ratio. Further, from the (9) for a
itself until the peak power point is reached and          given load, the array power continuously increases
then oscillates within an allowable range about           with the duty ratio, resulting in minimum power at
this point. In the simulated MP point tracking            d = 0 and infinite power at d = 1, which is physically
process the instantaneous array voltage and power         an unrealizable condition. This phenomena is verified
are computed employing the models developed in            experimentally and the corresponding characteristics
preceding sections, whereas in real time computer         are shown in Fig. 5. To overcome this disadvantage
implementation the instantaneous array voltage,           and to extract MP from the SCA using only the
power information is obtained by means of                 array voltage, an identical boost cell is connected
data acquisition system. The MP point tracking            in parallel to the existing boost cell as shown in
process both in simulation and real time computer         the experimental setup (Fig. 1(a)). These two boost
implementation are same except the above mentioned        branches are controlled in an interleaved fashion using
difference.                                               phase shift between the gate signals. This converter

       Fig. 5. Array characteristics with boost converter.          Fig. 7. Comparison of experimental SCA power tracking

                                                                                            TABLE I
                                                                                   SCA and Converter Parameters

                                                                              Np                         1
                                                                              Ns                         27
                                                                              Rs                       0.04 −
                                                                              ¤                      13.68 V¡1
                                                                              Io                     0.00045 A
                                                                              R1                      0.044 −
                                                                              R2                      0.063 −
                                                                              L1                     0.250 mH
                                                                              L2                     0.250 mH
                                                                              C                        220 ¹F
 Fig. 6. Experimental V ¡ IA characteristics of SCA module for
                  different solar insolations.                                Ca                      2200 ¹F
                                                                              fs                       25 kHz
                                                                              R                         50 −
is capable of reducing the ripple in the source current
EMI and avoids the discontinuous input current mode
even though the individual boost branches enter into             converter system (shown in Fig. 1(a)). Comprehensive
discontinuous current mode.                                      simulation studies were made to investigate the
    Prototype PV-supplied converter (SCA and                     influence of IDB converter as an intermediate
converter parameters are given in Table I) system                MP point tracker for the PV supplied system. A
was bread boarded to study the array voltage                     simulation software is developed for MP point
based maximum power point tracking. The V ¡ IA A                 tracking employing the equations derived in the
characteristics of the experimental PV generator for             preceding sections and the control flow chart given in
three different solar insolations (ª2 = 30%, ª3 =                Fig. 3. In these studies the PV array is simulated using
60%, and ª5 = 100%) are shown in Fig. 6. The 100%                (3) and (4). The simulated dynamic MP point tracking
solar insolation represents a standard intensity of              characteristics at 100% solar insolation are plotted in
1000 W/m2 . The data acquisition system measures                 Figs. 8 and 9. At this solar insolation the experimental
the instantaneous array voltage information. For a               dynamic MP tracking characteristics are also obtained
given load, the MP point control algorithm computes              and they are superimposed in Figs. 8 and 9. The
the SCA power (Pg ) from the known instantaneous                 simulation and experimental results are in close
array voltage information V . The algorithm tracks
                             g                                   agreement. Discrepancies between simulation and
the maximum power point continuously by adjusting                experimental results may be due to 1) the difficulties
the converter duty ratio such that the array power is            in realizing the identical solar insolation conditions
maximum. At solar insolation ª5 the experimental                 in the experimental setup, and 2) the fact that the
power tracking characteristic is shown in Fig. 7. For            analysis was made on the assumption that the two
verification, the output power of the SCA is measured            boost branches are identical.
by sensing the SCA voltage and current. The power                    The experimental array power tracking
characteristic so obtained is superimposed in the same           characteristics for three different solar insolations (ª2 ,
figure. These two characteristics are closely matching           ª3 and ª5 ) are also obtained as shown in Fig. 10. For
each other. Slight discrepancies may be due to errors            verification of the MP points of the SCA, experiments
in the measuring system, drops in parasitics, etc.               were conducted on the SCA by connecting a variable
    The simulation program was developed in                      load resistance. The experimental MP points obtained
the MATLAB environment for the PV-supplied                       at different solar insolations are tabulated in Table

                                                                                            TABLE II
                                                                            Experimental Maximum Power Points of SCA

                                                                             % Solar Insolation   Maximum Power (W)
                                                                                    ª1                     2.65
                                                                                    ª2                     8.17
                                                                                    ª3                    17.63
                                                                                    ª4                    21.44
                                                                                    ª5                    23.03

 Fig. 8. Comparison of experimental and simulated SCA power
                   tracking characteristics.

                                                                     Fig. 11. SCA power tracking characteristic for variable solar

  Fig. 9. Comparison of experimental and simulated duty ratio
                   tracking characteristics.

                                                                     Fig. 12. Experimental SCA power tracking characteristic for
                                                                                     partial shading conditions.

                                                                   SCA power output decreases and settles to a new MP
                                                                   point as evidenced by Fig. 12.
 Fig. 10. SCA power tracking characteristics for different solar
                                                                   VII. CONCLUSIONS
II. Comparing the tracking characteristics (Fig. 10)
with MP points, it can be noticed that the duty ratio of               Current sensorless SCA voltage based on a MP
the converter is so adjusted such that MP is extracted             point tracking algorithm is developed for an IDB
from the SCA. Experimental studies are also made to                converter supplied PV system. Analytical expressions
observe the effectiveness of the developed tracking                for the SCA, and power output expressions with
algorithm for changing solar insolations. Experimental             converters are derived. The SFG approach is used
observations (Fig. 11) show that the developed                     in modeling the IDB converter. Simulation and
algorithm is capable of tracking MP point even for                 experimental results for MP tracking are presented
variable solar insolations. The tracking capability of             for changing solar insolations and partial shading
the IDB converter system is verified under partial                 conditions. The inadequacy of the boost converter
shading conditions also. For illustration, array power             for array voltage based MP point tracking scheme
tracking characteristics when few cells (4) are shaded             is verified. The experimental results demonstrate
by 50% are shown in Fig. 12. Under this condition the              that in the array voltage based peak power tracking

268                   IEEE TRANSACTIONS ON AEROSPACE AND ELECTRONIC SYSTEMS VOL. 38, NO. 1                          JANUARY 2002
scheme the IDB converter is suitable for extracting               [6]   Kislovski, A. S. (1993)
MP from the SCA as compared with boost converter                           Power tracking methods in photovoltaic applications.
                                                                           Proceedings of Power Conversion, (1993), 513—528.
supplied PV system. Furthermore, the use of an IDB                [7]   Hua, C., Lin, J., and Shen, C. (1998)
converter avoids the discontinuous input current mode                      Implementation of a DSP controlled photovoltaic system
of operation and reduces the ripple in the array input                     with peak power tracking.
current. As a consequence the reduced ripple in the                        IEEE Transactions on Industrial Electronics, 45 (1998),
array current results in improved SCA performance.                         99—107.
                                                                  [8]   Matsui, M., Kitano, T., Xu, D.-H., and Yang, Z.-Q. (2000)
                                                                           New MPPT control scheme utilizing power balance at DC
ACKNOWLEDGMENTS                                                            link instead of array power detection.
                                                                           In Proceedings of International Power Electronics
                                                                           Conference (IPEC), 2000, 158—163.
   The first author wishes to acknowledge the
                                                                  [9]   Sharif, M. F., Alonso, C., and Martinez, A. (2000)
Government of Japan for granting MONBUSHO                                  A simple and robust maximum power point control for
scholarship and JNT University authorities for                             ground photovoltaic generators.
permission to attend these research studies.                               Proceedings of International Power Electronics Conference
                                                                           (IPEC), 2000, 164—169.
                                                                 [10]   Won, C.-Y., Kim, D.-H., and Kim, S.-C. (1994)
                                                                           A new maximum power point tracker of photovoltaic
[1]   Appelbaum, J. (1986)                                                 arrays using fuzzy controller.
        Starting and steady-state characteristics of dc motors             In Proceedings of Power Electronic Specialist Conference,
        powered by solar cell generators.                                  1994, 396—403.
        IEEE Transactions on Energy Conversion, 1 (1986),        [11]   Senjyu, T., Arashiro, Y., Uezato, K., and Hee, H. K. (1998)
        17—23.                                                             Maximum power point tracking control of photovoltaic
[2]   Fam, W. Z., and Balachander, M. K. (1988)                            array using fuzzy neural network.
        Dynamic performance of a dc shunt motor connected to               Proc. of International Conference on Power Electronics
        photovoltaic array.                                                (ICPE), 1998, 987—992.
        IEEE Transactions on Energy Conversion, 3 (1988),        [12]   Hiyama, T., Kouzuma, S., Imakubo, T., and Ortmeyer, T. H.
        613—617.                                                        (1995)
[3]   Salameh, Z., and Taylor, D. (1990)                                   Evaluation of neural network based real time maximum
        Step-up maximum power point tracker for photovoltaic               power tracking controller for PV system.
        arrays.                                                            IEEE Transactions on Energy Conversion, 10 (1995),
        Solar Energy, 44 (1990), 57—61.                                    543—548.
[4]   Alghuwainem, S. M. (1992)                                  [13]   Smedley, K., and Cuk, S. (1994)
        Steady-state performance of dc motors supplied from                Switching flow-graph nonlinear modeling technique.
        photovoltaic generators with step-up converter.                    IEEE Transactions on Power Electronics, 42 (1994),
        IEEE Transactions on Energy Conversion, 7 (1992),                  405—413.
[5]   Alghuwainem, S. M. (1997)
        A close form solution for the maximum power operating
        point of a solar cell array.
        Solar Energy Materials and Solar Cells, 46 (1997),

VEERACHARY: VOLTAGE-BASED MAXIMUM POWER POINT TRACKING CONTROL OF PV SYSTEM                                                     269
               Mummadi Veerachary was born in Survail, AP, India in 1968. He obtained
               his Bachelors degree from College of Engineering Anantapur, JNT University,
               Hyderabad, India, in 1992 and Master of Technology from Regional Engineering
               College, Warangal, India in 1994.
                   In 1994 he joined as an Assistant Professor in the Dept. of Electrical
               Engineering, JNTU College of Engineering, Anantapur, India. Presently, he
               is at the Dept. of Electrical and Electronics Engineering, University of the
               Ryukyus, Okinawa, Japan for his research studies. His fields of interest are power
               electronics, modeling and simulation of power electronics and application to
               photovoltaic solar energy utilization.
                   Mr. Veerachary was the recipient of the IEEE Industrial Electronics Society
               student travel grant award for the year 2001.

               Tomonobu Senjyu was born in Saga prefecture, Japan, in 1963. He received
               the B.S. and M.S. degrees in electrical engineering from University of the
               Ryukyus, Okinawa, Japan, in 1986 and 1988, respectively, and the Ph.D. degree
               in electrical engineering from Nagoya University, Nagoya, Japan, in 1994.
                   Since 1988, he has been with the Department of Electrical and Electronics
               Engineering, Faculty of Engineering, University of the Ryukyus, where he is
               currently a Professor. His research interests are in the areas of stability of ac
               machines, advanced control of electrical machines, and power electronics.
                   Dr. Senjyu is a member of the Institute of Electrical Engineers of Japan.

               Katsumi Uezato was born in Okinawa prefecture, Japan, in 1940. He received
               the B.S. degree in electrical engineering from the University of the Ryukyus,
               Okinawa, Japan, in 1963, the M.S. degree in electrical engineering from
               Kagoshima University, Kagoshima, Japan, in 1972, and the Ph.D. degree in
               electrical engineering from Nagoya University, Nagoya, Japan, in 1983.
                   Since 1972, he has been with the Department of Electrical and Electronics
               Engineering, Faculty of Engineering, University of the Ryukyus, where he
               is currently a Professor. He is engaged in research on stability, control of
               synchronous machines and power electronics.
                   Dr. Uezato is a member of the Institute of Electrical Engineers of Japan.


Shared By: