AN IMPROVED PHOTOVOLTAIC POWER PLANT AND A METHOD OF CONTROLLING THE SAME FIELD OF THE INVENTION
The present invention in general relates to an improved photovoltaic power plai and to a method of controlling the same. In particular, the present invention relates to an improved photovoltaic power plant equipped with a central controller, which facilitates effective controlling and running of the power plant during its operation. Plant efficiency is thereby substantially improved, particularly by the efficient conversion of even very small energy, obtained from the photovoltaic modules connected at the input. BACKGROUND OF THE INVENTION
It is common knowledge that photovoltaic power plants or solar power plants as they are popularly known, work on the principle of converting solar power into electrical power. Conventional plants consist of mainly three parts, namely, photovoltaic modules for converting solar radiation into DC electrical power, inverters for converting DC power into AC power and connected load which may be grid or user defined. Photovoltaic power plants are broadly classified as grid connected system, off grid standalone system and hybrid system. Photovoltaic modules are connected in series - parallel combination to produce the required voltage and current. Such group of photovoltaic modules constitute an array. The array output is connected to electronic converters which consists of Maximum Power Point Tracker (MPPT), inverters and synchronizers. The synchronized output of the inverters is once again synchronized with grid or directly fed to the user end.
Now, a photovoltaic panel produces the power, according to the intensity of solar radiation received from the sun. The nominal output of the solar panel is measured and rated at around 1000 W/m2 solar irradiation. In accordance with the standard observation, the average radiation is more than around 200 W/m2 only, for seven to eight hours on a sunny day. The inverters efficiently convert the power only when the connected load is more than 40% of the full rating. Also inverters can be switched on only when the input power reaches the wake-

up power limit. The single high capacity systems have the wake up power limit
set at high level and efficiency at the lower radiation is less. In areas where
climate is such that cloud and rain are frequent, it leads to inefficient power
conversion by inverters. Furthermore, maintenance work of the inverter leads to
switching off, the total power plant.
Accordingly, there was a long felt need to design an improved photovoltaic power
plant and for an efficient method of controlling the power plant, whereby
maximum efficiency is ensured, by the efficient conversion of even very small
energy from the photovoltaic modules such as during lower radiation and/or
cloudy conditions.
The present invention meets the aforesaid long felt need.
All through out the specification including the claims, the words "photovoltaic", "solar",
"inverters", "converters", "synchronizers", "Maximum Power Point
Tracker"(Hereinafter referred to as MPPT) and "Mean Time Before
Failure"(Hereinafter refen-ed to as MTBF) are to be interpreted in the broadest sense
of the respective terms and includes all similar items in the field known by other
temis, as may be clear to persons skilled in the art. Restriction/limitation, if any,
referred to in the specification. Is solely by way of example and understanding the
present invention.
OBJECTS OF THE INVENTION
It is the principal object of the present invention to provide an improved photovoltaic
power plant having a central controller, whereby plant efficiency is substantially
increased, particularly by the efficient conversion of even very small energy, obtained
from the photovoltaic modules connected at the input.
It is yet another object of the present invention to provide a photovoltaic power plant
having photovoltaic modules with increased efficiency.
It is a further object of the present invention to provide a photovoltaic power plant
including inverter(s) adapted to convert very low DC power, obtained from the
photovoltaic modules, to AC power.
It is yet another object of the present invention to provide a photovoltaic power plant
adapted to operate the inverters, at its maximum efficiency.

It is yet another object of the present invention to provide a photovoltaic power plant
adapted to generate energy at maximum efficiency, in any weather condition.
It is yet another object of the present invention to provide the synchronization of the
Inverter blocks output with gate synchronization.
It is a further object of the present invention to provide a photovoltaic power plant
adapted to easy periodic maintenance by switching off of particular inverter(s) without
the need for switching off the total power plant.
It is yet another object of the present invention to provide an improved method of
controlling a photovoltaic power plant whereby plant efficiency is substantially
enhanced, particularly by the efficient conversion of even very small energy, obtained
from the photovoltaic modules connected at the input.
It is a further object of the present invention to provide an improved method of
controlling a photovoltaic power plant whereby its easy installation is facilitated.
It is yet another object of the present invention to provide an improved method of
controlling a photovoltaic power plant, whereby the Mean Time Before Failure(MTBF)
of the inverter is increased, which also improves the availability of the plant.
How the foregoing objects are achieved and the other aspects of the present invention, will be clear from the following description which is purely by way of understanding and not by way of any sort of limitation.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides an improved photovoltaic power plant including solar array, at least one electronic controller and at least one synchronizer all operatively connected, said synchronizer being adapted to synchronize the generated output with grid or end user for its feeding to said grid or end user wherein said electronic controller is equipped with at least one means for tracking the maximum power generating point of the solar array, said means being operatively connected to at least one controlling unit and to at least one inverter bank, said controlling unit including controlling logic in connectivity with suitable hardware features for controlling the total operation of

the plant in electronic data type, whereby substantial improvement in plant
efficiency is facilitated , particularly by the efficient conversion of even very small
energy in dynamic weather condition, obtained from the photovoltaic modules,
connected at the input.
In accordance with preferred embodiments of the photo-voltaic power plant of the
present invention:
-said synchronizer comprises switches for synchronizing the generated output of
the inverter with grid or end user.
-said means for tracking the maximum power generating point of the solar array
comprises MPPT and said inverter bank includes a plurality of identical inverter
blocks.
-said controlling unit includes micro-controllers, sensors, power supplies,
analogue and digital electronic devices to control the total operation of the plant.
-total capacity of said inverter blocks are equal to capacity of the plant.
-there exists a spare block provision.
The present invention also provides an improved method of controlling a power
plant having a solar array, at least one electronic controller and at least one
synchronizer all operatively connected, said synchronizer being adapted to
synchronize the generated output with grid or end user for its feeding to said grid
or end user wherein said electronic controller is equipped with at least one MPPT
for tracking the maximum power generating point of the solar array, said MPPT
being operatively connected to at least one controlling unit and to at least one
inverter bank having a plurality of identical inverter blocks, said method including:
- measuring the maximum power drawn ,
-calculating the value in the controlling unit,
-starting power generation in the event of power generated from array being
equal to wake-up power of first inverter block,
-switching on the rest of the inverters one by one depending upon the raise in
power generation.

whereby a small power generated from an array which is equal to 1/nth time of
wake-up power of the plant is converted efficiently , where n= number of inverter
blocks.
In accordance with preferred embodiments of the method of the present
invention:
-in the event of any drop in power generation at any point of time, below the
predetermined level, the first inverter block gets switched off first, followed by the
second one and thereafter the consecutive ones, one by one in that order, with
the gradual drop in power whereby, improvement in the MTBF is achieved
-said controlling unit controls the total operation of the plant by means of a
controlling logic in connectivity with suitable hardware features in the manner
such as herein described.
- periodic maintenance of the plant is undertaken by switching off only the
particular inverter block, without switching off the total power plant thereby
resulting in improvement of plant availability.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The nature and scope of the present Invention, will be better understood from the accompanying drawings, which are by way of illustration of some preferred embodiments and not by way of any sort of limitation. In the accompanying drawings,
Figure 1 illustrates a block diagram of conventional photovoltaic power plants for conversion of solar energy into electrical energy.
Figure 2 illustrates a block diagram of a preferred embodiment of a photovoltaic power plant in accordance with the present invention
Figures 3 and 4 illustrate flow charts explaining the controlling logic in accordance with the present invention.

BRIEF DESCRIPTION OF THE INVENTION
The following describes some preferred embodiments of the present invention, which are purely for the sake of understanding the performance of the invention, and not by way of any sort of limitation.
As stated hereinbefore and as illustrated in the accompanying figure 1, conventional photovoltaic power plants fundamentally includes, mainly three parts, namely, photovoltaic modules for converting solar radiation into DC electrical power, inverters for converting DC power into AC power, synchronizers for synchronizing the power to grid and connected load which may be grid or end user. Photovoltaic modules are connected in series - parallel combination to produce the required voltage and current. Such group of photvoltaic modules constitute an array(1). These array output is connected to electronic converters(2) which consists of Maximum Power Point Tracker (MPPT), inverters and synchronizers(3). The synchronized output of the inverters is once again synchronized with grid (4) or directly fed to the end user(5). A photovoltaic panel produces the power, according to the intensity of solar radiation received from the sun. Furthermore, the inverters convert the power at peak efficiency only when the connected load is more than 40% of the full rating. Also, inverters can be switched on only when the input power reaches the wake-up power limit.
Conventionally operation takes place as follows:
Solar array generates the power from solar irradiation. The electronics block
MPPT & Inverter converts the power in to customer required form i.e. AC power.
The grid interactive system requires the synchronizer to synchronize the power
generated into grid.
In conventional power plant single block or two to three block of inverters are
used to obtain the total capacity of the power. The system operates at its peak
efficiently only when the radiation is more than 400w/m2. The maintenance job in
any inverter section requires total plant to be in switch off mode. Spare
maintenance is thus ©X"^"*'*'^ ^° ■'■'^'^ tntal c\/ctam ic a cinnio hlnol^

Now, high efficiency of power plant operation is must, In photovoltaic power plants. The efficiency can be defined as the product of solar efficiency MPPT efficiency and inverter efficiency. Finally the total efficiency of the power plant is power output from the plant per irradiation received from the sun. Hence, efficiency is dependent on the conversion of the radiation available and efficiency of total operation of the plant.
Extensive research is in progress, to increase the solar module efficiency. Even if inverter efficiency, is slightly increased that may not be adequate to improve total plant efficiency, which depends on the efficiency at which the lowest power is converted to AC. In the single inverter of rated power or string type inverter array applied in conventional photovoltaic power plants, separate panel arrays to individual inverter are used and the output of the inverter is paralleled. Thus, the efficiency is less in lower radiation or in cloudy conditions. Now, as stated hereinbefore, plant efficiency has to be brought to the maximum by the efficient conversion of even very small energy from the solar module. This is exactly, where the present invention contributes by providing an improved photovoltaic power plant equipped with a central controller, which facilitates effective controlling and running of the power plant during its operation. The present invention also focuses on an efficient method of controlling the power plant, particularly by the efficient conversion of even very small energy, obtained from the photovoltaic modules connected at the input.
The present invention provides an improved photovoltaic power plant which
includes solar array (1), electronic controller (8) and synchronizer (3). The above
mentioned parts are all operatively connected, as shown in the accompanying
figure 2. The power generated from this plant is fed to either grid(4) or the end
user{5). By this method the power generation of the solar power plant is more as
compared to the other plant of similar capacity in dynamically varying weather
conditions. Hence the total plant efficiency for long period is improved due to the
effective conversion of the very small power generated from solar array. The
single inverter block in the conventional solar plant is split into "n" number of
small units i.e. S1,S2,S3 Sn. to achieve high efficiency in dynamic

weather situation. The each inverter unit will be switched ON after monitoring the
power generated at that time. The efficient and improved controlling logic is
designed as lucidly detailed in the flowcharts in the accompanying figures 3 and
4.
Apart from solar array, the various features shown in the accompanying figure 2
are as follows:
a)MPPT - This electronic unit(2) tracks the maximum power generating point of
the solar array.
b)lnverter Bank(6)-lt consists of number of inverter blocks namely S1, S2,
S3 Sn
c)Synchronizer(3)- It consists of switches to synchronize the generated output of
the inverter with grid or end user.
d)Controlling unit(7)- It comprises of number of micro-controllers, sensors, power
supplies, analogue & digital electronic devices to control the total operation of
the plant including display and communication.
e)End user(5): Customer dependent voltage and power requirement
f)Grid(4): National or private sector power supply grid
In a nutshell, the power plant in accordance with the present invention includes
solar array(1), electronic controller(8) and synchronizer(3) all operatively
connected, said electronic controller(8) being equipped with Maximum Power
Point Tracker (MPPT)(2), controlling unit(7) and inverter bank(6). The inverter
bank includes number of identical inverter blocks (S1, S2, Sn) with total
capacity of the bank being equal to capacity of the plant and also with a provision for spare block, if required by customer. The controlling unit(7) comprises the logic behind the total operation of the power plant in electronics data type. The main controller is loaded with controlling logic shown in the accompanying figures 3 and 4 and is operatively connected to suitable hardware features for its operation. As stated before, the power generated from this plant is fed to either grid or the end user.
The present invention also provides an improved method of controlling a photovoltaic power plant by operation of a central controller, thereby facilitating substantial

improvement in plant efficiency, particularly by the efficient conversion of even very small energy, obtained from the photovoltaic modules connected at the input. The total output of the solar array is fed to MPPT(2) which tracks the maximum power point(MPP) and makes the inverter to draw power from the array at MPP. The maximum power drawn from the array is then measured and the value is calculated in the controlling unit(7). If power generated from array is equal to wake-up power of the first inverter block S1 then the plant power generation starts. Hence a small power generated from array which is equal to 1/nth time of wake-up power of the plant also can be converted efficiently. Depending upon the raise in the power generation, the rest of inverter blocks are getting switched ON one by one. If any drop in the power generation at any moment of the time below prescribed power level takes place which is programmable value, the S1 will be switched OFF first. If further drop in the power takes place, the inverter blocks gets de-energized one by one. Hence the average operating time of the individual inverter block is balanced to increase MTBF.
The outputs of all the inverters are synchronized by the controlling unit, at the stage of gate signaling of the power switching device. Then this output is once again synchronized with grid or end user with the help of the controlling unit. The communication and monitoring system is also controlled and signaled by controlling unit.
The controlling logic of the total operation of solar power plant is explained with flow diagrams shown in the accompanying figures 3 and 4. The explanation of the terminologies used in the flow diagrams are:
n: number of inverter (manual feeding at the time of installation or service)
m: sequence number of individual inverter block.
x: number of ON state inverter.
y: total number of inverters switched ON in a day.
P(x): input power after (x-1) inverter is ON.
S(m): inverter of "m"th seouence.

k: ON time load share constant. (Manual programming as per environment condition)
k1: OFF time load share constant. (Manual programming as per environment condition)
P: rated power capacity of the individual inverter block. The operational flow chart can be explained as below:
Stepl: Check real time. Step2: If real time > set time, then go-to StepS or else go-to Stepl StepS: m=1, n=number of inverter, P(0) = 0, x=y=1. Step4: Measure power P(x). StepS: If P(x) ^ k*P*(x-1) + wake up power of S(m) then go-to Step6 or else go-to Step12 . Step6: Switch ON signal to S(m). Step7: m=m+1, x=x+1, y=y+1. StepS: If y ^ n then go-to Step4 or else go-to Step9. StepQ: If n=x then display "FULL OUTPUT" and go-to Step4 or else go-to Stepl 0. Stepl 0: y/n = integer number then go-to Stepl 1 or else go-to Step4. Stepl 1: Set m=1 then go¬to Step4. Stepl 2: If P(x) <. k1'P*(x-2) +wake up S(m) then go-to Stepl 3 or else go-to Step4. Stepl 3: R = Remainder{(n+m-x)/n}. Step14: If R=0 then go-to Stepl 5 or else go-to Stepl6. Stepl 5: Switch OFF signal to nth inverter and go-to Stepl7. Stepl6: Switch OFF signal to "R"th inverter and go-to Stepl 7. Stepl 7: x=x-1 and go-to Step7.
The technical advancement and economic significance achieved by the present invention was hitherto unknown and not conceived by persons skilled in the art. Some of salient advantages provided by the present invention comprises : l.lmrovement of plant efficiency through out operation. 2.Extraction of even very small energy, obtained from the photovoltaic module array connected at the input.
3. Generation of energy at maximum efficiency in any dynamically variable weather condition or at any level of radiation.
4. Easy installation and maintenance, on site provision for spare inverter block.
5. Easy periodic maintenance by switching off only particular inverter block, without switching off the total power plant.
6. Economic significance is achieved as wastage of energy is curtailed to a substantive extent.

7. High level of MTBF can be achieved by balanced operation of inverter blocks.
8. Synchronization is easy because the blocks are synchronized at the gate signalling of the Inverter power switching component.
The present invention has been described with reference to some drawings and preferred embodiments, purely for the sake of understanding and not by way of any limitation and the present invention includes all legitimate developments within the scope of what has been described hereinbefore and claimed in the appended claims.

WE CLAIM
1. An improved photovoltaic power plant including solar array, at least one electronic controller and at least one synchronizer all operatively connected said synchronizer being adapted to synchronize the generated output with grid or end user for its feeding to said grid or end user wherein said electronic controller is equipped with at least one means for tracking the maximum power generating point of the solar array, said means being operatively connected to at least one controlling unit and to at least one inverter bank, said controlling unit including controlling logic in connectivity with suitable hardware features for controlling the total operation of the plant in electronic data type, whereby substantial improvement in plant efficiency is facilitated , particularly by the efficient conversion of even very small energy in dynamic weather condition, obtained from the photovoltaic modules, connected at the input.
2. The improved photovoltaic power plant as claimed in claim 1, wherein said synchronizer comprises switches for synchronizing the generated output of the inverter with grid or end user.
3. The improved photovoltaic power plant as claimed in any of claims 1 or 2 wherein said means for tracking the maximum power generating point of the solar array comprises MPPT and said inverter bank includes a plurality of identical inverter blocks.
4. The improved photovoltaic power plant as claimed in any preceding claim, wherein said controlling unit includes micro-controllers, sensors, power supplies, analogue and digital electronic devices to control the total operation of the plant.
5. The improved photovoltaic power plant as claimed in claims 3 to 4, wherein total capacity of said inverter banks are equal to capacity of the plant.
6. The improved photovoltaic power plant as claimed in claim 5 wherein there exists a spare block provision.

7.. An improved method of controlling a power plant having a solar array, at least
one electronic controller and at least one synchronizer all operatively connected,
said synchronizer being adapted to synchronize the generated output with grid or
end user for its feeding to said grid or end user wherein said electronic controller
is equipped with at least one MPPT for tracking the maximum power generating
point of the solar array, said MPPT being operatively connected to at least one
controlling unit and to at least one inverter bank having a plurality of identical
inverter blocks, said method including :
-feeding total output of the solar array to MPPT which tracks the maximum power
point and makes the inverter to draw power from the array at MPPT,
-measuring the maximum power drawn ,
-calculating the value in the controlling unit,
-starting power generation in the event of power generated from array being
equal to wake-up power of first inverter block,
-switching on the rest of the inverters one by one depending upon the raise in
power generation,
whereby a small power generated from an array which is equal to 1/nth time of
wake-up power of the plant is converted efficiently , where n= number of inverter
blocks.
8.. The improved method of controlling a power plant as claimed in claim 7,
wherein in the event of any drop in power generation at any point of time, below
the predetermined level, the first inverter block gets switched off first, followed by
the second one and thereafter the consecutive ones, one by one in that order,
with the gradual drop in power whereby, improvement in the MTBF is achieved.
9.. The improved method of controlling a power plant as claimed in claims 7 to 8
wherein said controlling unit controls the total operation of the plant by means of
a controlling logic in connectivity with suitable hardware features in the manner
such as herein described.

10. The improved method of controlling a power plant as claimed in claims 7 to 9 wherein periodic maintenance of the plant is undertaken by switching off only the particular inverter block, without switching off the total power plant, thereby resulting in improvement of plant availability.