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    Design of Track Control System in PV

    Jun-ming Xiao Ling-yun Jiao Hai-ming Zu Rui Zang

    School of Electronic and Information EngineeringZhongyuan of Technology

    Zhengzhou, P.R. China

    [email protected](.M .Xiao) [email protected](L. Y Jiao)

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    Keywordsphotovoltaic power; automatic track control;

    controer; sun trajecto tracking; electrooptical tracking

    I.

    In the energy crisis and environmental highlight

    of today tates have adopted a series of signicant measures to

    and support the development of solar energy.

    Photovoltaic power is one of the main ways of solar energy

    utilization, has the characteristics of environmentally-iendly

    and application range is ver wide, has now

    been used in comication, transportation and other elds,

    has a place in the national economy energy system [1]. At

    present, the cost of photovoltaic power generation is too high,

    can not be compared with the traditional forms of power

    generation, the development of domestic PV power

    97814446055710$6.00 010 EEE

    517

    In order to reduce the cost of PV power, countries

    around the world are constantly exploring, at this stage the

    more approach are mainly tracking method and the

    light-gathering method. Tracking method that is using

    model, keep light vertical irradiate photovoltaicarray to improve solar panels' ability of absorb solar

    radiation. Track control system in PV using tracking

    solar power generation equipment can enhance the power

    generation efciency 35%, decrease cost by 25% [2].

    II. THE OF TRCK YTEM PV

    Fig. The block diagram of track control system in

    Solar energy as one kind of clean and non-pollution energy,has very broad prospects for development however there is

    the problem of low density, intermittent and space distribution

    changes [3], which put forward higher requirements for the

    collection and use of solar energy. At present, solar panels of

    photovoltaic power generation system are basically xed, can

    not make ll use of solar energy resources and generation

    eciency is lower. Track control system in PV can

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    automatically adjust the orientation of solar panels according

    to the altitude angle and azimuth angle of sun, make the sun

    light always perpendicular incident the surface of photo voltaic

    array to obtain the maximum power generation efciency.

    As gure I show is the block diagram of track control

    system in PV, system uses modular design, mainly composedby photovoltaic array, tracker, sensors, controller, inverter and

    other components. Sensors can accurately receive sunshine

    within a certain angle and transform it into a measurable error

    signal; tracker can handle the error signal which is measured

    by sensors, then output motor triggered signals according to

    the control algorithm; controller can control the motor's

    running and stop according to the motor triggered signals.

    III. RCKIG METHOD ND CONTROL TRTEGY DEIGN

    PRICLE

    A The calculation /sun angle

    The sun path changes as the season changes, the

    position tracking method can be divided into horizon

    coordinates tracking and equatorial coordinates tracking,

    horizon coordinate tracking method track the suns

    angle and angle, equatorial coordinate tracking

    method track the sun's declination angle and solar angle.

    Since the change range of solar declination angle is no more

    than 2327, its changes slowly so choose horizon coordinatetracing method.

    The calculation formula of sun altitude angle a and

    azimuth angle s [4]:

    a 5 + 5 Bh ( 1 )

    s = a - 5 / a

    Or, s 5 Bh / a

    Where, declination angle

    5= 23.4 sin(360x284+n )

    36

    ( 2 )

    518

    is installation site Bh is solar angle; n is the

    days of year.

    According to the geographical latitude, the declination

    Angle and observation time, using equation (1) and (2) can

    calculate the suns altitude angle and azimuth angle at anymoment, any area.

    Tracking mode

    The tracking mode that adopts at home and abroad

    is very much, it can be divided into trajectory

    tracking mode and electro-optical tracking according to the

    different forms of tracking [5], can be divided into

    tracking method and biaxial tracking method according to the

    different forms of exercise [6].

    trajector tracking mode and electro-optical

    tracking mode have some limitations, sun trajectory tracking

    mode need to positioning before running, can not

    carry on automatic when sun angle calculation has

    errors. Electro-optical tracking mode under the of

    the weather greatly, appear not to track or wrong track

    of the of the weather problem, especially in

    weather conditions may occur motor reciprocating

    motion result in the waste of energy. This paper

    selected the biaxial tracking method of trajectory trackingmode combined with electro-optical tracking mode. In the

    of strong light using light intensity detect circuit

    detect ray deviation to electro-optical tracking, In case of

    weather changes the system automatically turns into sun

    trajectory tracking mode.

    C Control mode

    In photovoltaic power tracking system, control mode can

    be divided into three types of open loop, closed loop and

    hybrid control according to whether exist feedback while thecontrol system control the quantity control. the open

    loop control mode is and easy to realize, has

    the problem of tracking when the

    overcast and rainy days, system will consume large amounts

    of power. Therefore, this article selected the closed loop

    control mode. Closed loop control mode schematic diagram is

    shown as Fig.2.

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    As the gure shown, closed loop control mode is using

    sensor detect the deviation of the incident light rays of sun

    and system optical axis, when the deviation over the threshold,

    drive machine part tu to move through motor, reduce the

    deviation until the sun ray and system optical axis afresh

    parallelism, realize the tracking of the solar altitude angles

    and azimuth Angle.

    Fig.2 Closed loop control schematic diagram

    IV. EIGN OF YTEM HD

    A The basic composition ofhardwarePV tracking controller is a power plant that can make the

    solar panel track the orientation of at any time and

    the light vertical irradiates to the solar panel. It's mainly

    compose with sensor, light intensity detect

    temperature detect circuit, current/voltage detect circuit,

    stepping motor, motor driver and other the hardware

    is shown as Fig.3.

    Fig.3 Controller hardware block diagram

    Light intensi detect circuit

    The 14 parameters that PV tracking system can detect are

    the output of PV arrays, battery chargingelectric current/voltage, AC current and AC voltage of

    inverter, environment battery PV

    arrays environment light intensity, tracking light

    intensity, sun altitude angle, angle and wind velocity.

    Light intensity detect circuit schematic is shown as Fig,

    is mainly consisted by photosensitive sensor, integrated

    operational amplier, triode, resistance, capacitance and other

    519

    elements. Phototransistor and tu on aer accept

    sunshine, triode ampli the electrical signals. The voltage

    across the voltage follower is equal, avoid the mutual

    inuence of ont and back electric circuit, differential

    amplier amplify two voltage's dierence value.

    Comparator's voltage VDID2 compared with reference

    voltage Vref, if the co-rotating voltage larger than the

    reverse input voltage, the output is high-level, else is

    low-level. The motor run while the compare result VI is

    low-level.

    FigA Light intensity detect circuit schematic

    C Stepping motor driver circuit

    Stepping motor is one kind of that converts

    electric into displacement, in the tracking

    control system the controller's output signal as stepping

    motor driver's input control signal, in order to control

    stepping motor's positive inversion of longitudinal direction

    and horizontal direction. As Fig.5 shown is one of the

    stepping motor drive circuits, the system totally have

    stepping motor drive respectively drive steppingoto's postve veso o decto ad

    horizontal direction.

    Control goes into transistor after 74LS 14 reverse

    phase, the amplied by the transistor, then control

    photoelectric switch. Aer photoelectric isolation, carry on

    the voltage and amplication by power then

    drive each phase windings of stepping motor, make stepping

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    motor do forward, backward, speed up, slow down or stop

    movement. As Fig.5 shown L is one phase winding of

    stepping motor, RL is winding internal resistance, R IS

    exteal resistors, has the nction of limit current and

    improves the circuit time constant, the shunt capacitance

    across the exteal resistors can enhance the high equency

    performance of stepping motor, D is y-wheel diode, avoid

    power tuber's damage because of the back electromotive force

    that produced by motor winding.

    +25V

    Fig.S tepping motor driver circuit

    V. YTEM OFTWRE DEIGN

    0

    Fig.6 ystem operating procedures

    The soware part of PV tracking control system mainly

    include ma program, data acquisition

    monitoring subroutine, electro-optical tracking subroutine,

    trajectory tracking batter charge and

    discharge subroutine, and so on, control ow is shown as

    Fig.6. The system can detect signal acquisition,

    display, query, etc, can carry on real-time or historical data's

    graphics image processing and print for the

    information stored in the database, has the nction of

    self-calibration, self-diagnosis and self-test. At the same time,

    the system can adjust the position of PV array

    according to test in order to achieve real-time tracking

    target.

    VI.

    and of solar energy is one of the

    effective solutions of energy crisis and the effective

    means of reducing environmental pollution, solar photovoltaic

    cell array's power generation has relation with the incidence

    angle of the generation is the largest when ray

    to the PV array. PV tracking control system

    using light automatic tracking mode to make solar battery

    always perpendicular to this method can greatly

    enhance the capacity of solar array, reuce the overall cost ofPV power generation, create high economic eciency, meet

    the of setting the environmental protection

    economy energy type social, has the theory research meaning

    and application prospect of promotion.

    REFERENCES

    X.K.Li. "Photovoltaic power development and policy analysis, un

    [2] F. and P. "Design of controller for lltracking solar, Foreign electronic components, volA, pp. 4-6, 2007.

    [3] J. L. Li and . B Zhou. "Design of a new kind of solar photovoltaicpower tracking system, Electrical applications, vo.28, pp.68-71, 2009.

    [4] P and Y F hen " powe ytem aed on ntellgentsun tracking with low power cost, Measurement and controltechnology, vo.27, pp.36-39, 2008.

    [5] X. H. Wang. "Design and research of multiple plane mirrorcondensation solar tracking system, Hefei, Hefei university, 2007.

    [6] B X. Zhang. "Research of solar energy utilization tracking and gathersystem, Hefei, Hefei university, 2006.