FIELD OF INVENTION
The present invention in general relates to solar power conditioning
unit (PCU). The present invention in particular relates to solar PCU
with dynamic depth of discharge (DOD) control.
BACKGROUND AND PRIOR ART
The use of solar energy as a source of energy for various types of
devices is well known in the art. The solar energy is collected during
the daytime via a solar panel electrically connected to the energy
storage device. The energy stored in the energy storage device is
discharged to power the device.
While solar powered devices work well under a variety of operating
conditions, they periodically require service to replace the energy
storage device, i.e. battery. A characteristic of an energy storage
device, such as a battery, is a finite number of charge cycles.
Therefore, the energy storage device has to be periodically replaced,
and a long life cycle is more cost effective. At the same time, it may be
difficult to service the solar powered device due to the physical
location of the device. This problem is solved by power conditioning
unit integrated with solar powered device that efficiently distributes
energy to prolong the life of the battery.
In general, a power conditioner for
a solar power generation system includes an inverter unit as a main
circuit, an inverter driver unit, a controller unit, a display unit, an
operation unit, and apower supply circuit unit which provides
required power to each of these units. The display unit provides
respective indications of instantaneous output power and
integral power of the power conditioner that are detected and
calculated by the controller unit, or an indication of a
period power amount which can arbitrarily be initialized by a user.
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Now, reference may be made to the following Prior Arts:
US Patent No. 6,118,248 describes batteries having a built-in
controller to extend the battery service run time. The battery has a
built-in controller that includes a converter, which may be capable of
operating below the voltage threshold of typical electronic devices. The
controller more efficiently regulates the voltage of the electrochemical
cell and allows for a controlled discharge or an optimal discharge
depth in order to extend the service run time of the battery. This
patent does not talk about hybrid charging i.e. (charging from two
sources in this built in controller)
US Patent No. 6,163,131 provides single-cell batteries having a builtin
controller. The discharge sub-controller preferably optimizes the
service run time of the battery by controlling the discharge depth of
the cell in order to maximize number of and the efficiency of the
charge cycles, and the controller circuit may additionally include a
charge sub-controller circuit. The charge sub-controller circuit safely
and efficiently controls the charging of the electrochemical cell(s) of
the battery in which the controller circuit is integrated. This patent
does not talk about hybrid charging.
Publication No. KR20 1 100857 19 discloses apparatuses for grid
connecting a standalone solar power streetlight system to reduce
installation costs and maintenance costs by maintaining depth of
discharge and reducing necessary capacity while being charged in a
battery. In this patent also only one source of charging is there.
mtblication No. JW038130 is related to a method to elongate a
battery service life by controlling discharge depth. A battery is
determined in quantity of discharge correspondent to the quantity of
daily electric power generation of a solar cell counting the quantity of
electric power generation of it with an integrating wattmeter and the
battery is discharged to be half as much in capacity as its full capacity
when the
battery is almost overcharged, whereby the battery can be protected
against deterioration and efficiently utilized. This patent does not talk
about hybrid charging.
US Patent No. 8,350,521 is directed to systems and methods for
control of power charge/discharge from energy storage system. A
system sensor and a control computer and/or energy storage unit
may be on the customer side. After easy installation on the customer
side, a customer need not change the customer's behavior; the system
may operate automatically. Another advantage of utilizing the smart
charge system may be that the energy storage depth of discharge is
reduced resulting a longer working life of the energy storage
component. Charging is done with the single source, there is no
hybrid charging option.
US Patent No. 6,835,491 provides batteries having a built-in controller
to extend the battery service run time. The battery has a built-in
controller that includes a converter, which may be capable of
operating below the voltage threshold of typical electronic devices. The
controller more efficiently regulates the voltage of the electrochemical
cell and allows for a controlled discharge or an optimal discharge
depth in order to extend the service run time of the battery. This
patent does not talk about hybrid charging.
Publication No. W02007016661 relates to controlling operation of a
battery to assure termination of discharge of the battery before
damaging the battery. The battery operation is terminated if the extant
depth of discharge is within the first range of the maximum depth of
discharge or if the battery voltage is within the second range of the
minimum battery voltage. This patent does not talk about hybrid
charging.
Patent No. 7,834,580 provides a solar powered apparatus that
includes a battery, at least one photovoltaic cell and a DC-capable AC
appliance. The controller monitors the battery and also controls the
second subsystem so as to protect the battery by limiting the depth of
discharge. In this patent also there is no grid charging or sharing of
charge.
Remote Area Power Supply provides hybrid power conditioner
designed to operate with an external AC source to enhance capacity or
operate as a standalone unit. In the event the battery capacity drops
below 50% Depth of Discharge (DOD) or the site load increases above
a preset level, the diesel generator will be automatically started and
brought on line in parallel with the inverter to supply the load and/or
charge the batteries. Once the batteries have reached a predetermined
level of charge the available solar energy will be utilized to reduce the
load on the diesel generator which will subsequently be brought off
line, stopped provided the site load is not excessive leaving the
inverter to again supply the load.
Though there are technologies in prior art to control the charge and
discharge of batteries, there still exists a need for more intelligent
power charge and discharge system particularly for grid connected
photovoltaic system which effectively utilizes the batteries in
conjunction with a variable power generator.
Therefore, the present invention proposes a power conditioning unit
(PCU) with DOD control that optimally uses the stored charge of a
rechargeable battery and optimizes the depth of discharge while
discharging the battery under variable load conditions to avoid
misuse/ overdischarge of the batteries.
OBJECTS OF THE INVENTION
The principal object of the present invention is to provide a solar PCU
with dynamic DOD control that maintains the batteries in a good state
of charge in dynamic load and variable solar power and/ or grid
power.
Another object of the present invention is to provide a solar PCU with
dynamic DOD control that maximizes the energy usage from the solar
or hybrid system.
Yet another object of the present invention is to provide a solar PCU
with dynamic DOD control that avoids any misuse/damage to the
battery while maximizing use of battery capacity.
Still another object of the present invention is to provide a solar PCU
with dynamic DOD control that increases the life of the battery.
Another object of the present invention is to provide a solar PCU with
dynamic DOD control that is capable of achieving power savings,
thereby reducing electricity costs.
Yet another object of the present invention is to provide a solar PCU
with dynamic DOD control which is capable of powering load even in
lean solar radiation months by hardly affecting battery life cycles.
SUMMARY OF THE INVENTION
According to this invention, there is provided a solar power
conditioning unit with dynamic depth of discharge control comprising
a solar panel with main control to charge battery bank through grid
power for supplying power to operate load by sharing mechanism
controlled by main controller, which automatically measures the
power from solar panel and grid and reduces the charging current
from the grid proportionally to the solar panel charging current and in
case the panel current reduces the grid charging current is
automatically increased for charging battery of battery bank.
Accordingly the present invention provides a solar PCU with dynamic
DOD control to control the charge and discharge of the battery which
maintains battery in a good state of charge in dynamic load and
variable solar power and mains availability while maximizing the
energy usage from the solar system.
In the present invention, the PCU controls the depth of discharge of
the battery depending on the user selection. To measure the depth of
discharge of battery capacity meter is used. The meter constantly
monitors the rate of charging or discharging current of the battery and
storing the data to calculate depth of discharge of the battery. This
stored data further is useful to set low battery cut off point according
to the depth of discharge of the battery. This process increases the
battery life and maintains the battery gravity. Once the set threshold
is achieved during the operation, the battery discharge is stopped and
mains recovery is enabled, if grid is available. The system is then
transferred to mains mode and charging of battery takes place using
power supplied by both grid and solar. The charging takes place in the
sharing mode that is the grid charging current is reduced
proportionally to the solar power. As the solar charging current
increases the current from grid is reduced and ultimately the battery
is charged only from solar energy and grid charging current reduces to
zero.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Further objects and advantages of this invention will be more
apparent from the ensuing description when read in conjunction with
the accompanying drawings and wherein:
Figure 1 shows: Block diagram of according to the present
invention;
Figure 2 shows: Load profile for the solar PCU according to the
present invention;
Figure 3 shows: Dynamic control of battery depth of discharge
according to the present invention;
Figure 4 shows: The flow chart of the system according to the
present invention.
DETAIL DESCRIPTION OF THE PRESENT INVENTION WITH
REFERENCE TO THE ACCOMPANYING DRAWINGS
The present invention provides a solar PCU with dynamic DOD control
to control the charge and discharge of the battery which maintains
battery in a good state of charge in dynamic load and variable solar
power and mains availability while maximizing the energy usage from
the solar system. The system comprises solar panel with control unit
to charge battery bank via grid power to supply power to the load.
In the present invention, the PCU controls the depth of discharge of
the battery depending on the user selection. To measure the depth of
discharge of battery capacity measurement method is used. The
system constantly monitors the rate of charging or discharging
current of the battery and storing the data to calculate depth of
discharge of the battery. This stored data is further useful to set low
battery cut off point according to the depth of discharge of the battery.
This process increases the battery life and maintains the battery
gravity. Once the set threshold is achieved during the operation, the
battery discharge is stopped and mains recovery is enabled, if grid is
available. The system is then transferred to mains mode and charging
battery takes place using power supplied by both grid and solar. The
charging takes place in the sharing mode that is the grid charging
current is reduced proportionally to the solar power. As the solar
charging current increases the current from grid is reduced and
ultimately the battery is charged only from solar energy and grid
charging current reduces to zero.
Figure 2 shows typical load profile of a solar PCU, wherein average
load profile over a time period is maintained in the Solar PCU to
calculate the average power consumption from load in a day, based on
these and battery state of charge readings the usage of grid charging
is decided.
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Now reference may be made to fig. 1.
The complete sharing mechanism is controlled by the main controller
(1) of the system, depending on the user selection it automatically
measures the power coming from the solar panels (2) and the power
from grid (3) and reduces the charging current from the grid
proportionally to the solar panel charging current, if the panel current
reduces for some reason the grid charging current is automatically
increased so that battery of battery bank (4) can be charged properly.
The above provision is utilized to operate load (5).
The battery AH measurement is done with the help of coulomb
counting method. In this method the current signal is integrated over
time to accumulate the ampere hour. The AH measurement is also
done separately for charging from solar power and from grid charging.
The discharging current is used to calculate the AH drawn from the
battery.
The battery depth of discharge is controlled dynamically depending on
the history of the battery status.
The battery state of charge is calculated based on the Ah input from
solar and grid and Ah output from battery by load. Relying on the net
Ah available in the battery the battery state is determined.
One imperative factor for the battery health is the equalization process
in which the battery is charged to a higher boost voltage so that the
imbalance in the battery at cell level is reduced and the sulphation
from the cell plates is removed. When the periodic equalization is
given to the battery the overall health of the battery improves and it
helps in enhancing the battery life.
The PCU once powered up continuously reads the charging and
discharging profile of the battery and keeps log of all this information
in non-volatile memory, critical information such as battery voltage,
battery net AH, battery state of charge , temperature etc. which are
periodically updated in the memory. Along with this a real time clock
is maintained, so that the periodic equalization process can be
initiated.
The PCU also generates the load proftle of the system on periodic
basis; typical average load profile is stored in the memory and based
on everyday reading average daily load is calculated based on this the
battery charging is controlled. The mains power is used to charge the
battery only up to a level.
Operation
In a condition when the grid charging is disabled by user setting and
only grid bypass is allowed from PCU, the solar power remains the
source to charge the battery. Once transferred to mains the system
works on the mains bypass and the charging from solar continues.
Now the mains is cut only when the battery is fully charged (up to
absorption level) from solar power. But in case the battery is not
charged fully and the mains fail, the depth of discharge of battery is
reduced so as to compensate for the fact that the battery is not
charged completely during last charging. The depth of discharge is
reduced every time the battery is not charged to full value up to a
maximum defined level.
If these conditions repeat for defined number of time, the battery is
forced to charge from the solar panel to float level so that the battery
gravity can be maintained in which case the load is bypassed to mains
whenever mains is present and battery charging is done from solar
power. Once the battery is fully charged the battery depth of
discharge is reset at the initial set level.
The figure 3 shows one of the typical profiles of the battery depth of
discharge control, low battery condition 1 is where the system shifts to
the low battery condition and the system is transferred to the
alternate charging source and the battery charging starts taking place,
now if before full charging of battery the charging source again stops
and battery discharging starts taking place, the PCU control logic
automatically shifts the low battery point up to a higher voltage that is
the depth of discharge is reduced to protect the battery life. This
condition repeats as shown in the figure 3 low battery condition 2, 3
and 4.
Figure 4 shows flow chart according to the present invention. The
system initializes the controller, peripherals and reads the user
configuration and operation backup data measures the battery
parameters such as but not limited to the voltage, charging/
discharging current, ambient temperature, and battery temperature,
initializes the battery depth of discharge (DOD) limit, measures the
charging Ah/ discharging Ah, recalculates the battery state of charge,
enables charging from grid/ alternate source. In case the low battery
condition is repeated before full charge, recalculates the battery depth
of discharge based on the last low battery condition. When low battery
DOD reaches top limit, DOD is masked to the TOP limit.
It measures the battery voltage and chargingldischarging current,
ambient temperature, and battery temperature, calculates the load
profile and the average load profile of the system, the daily average
load requirement for system, calculates the required Ah for running
the average daily load. If the battery capacity is enough to run the
daily average load, the charging is reduced form grid to zero.
O ~ ~ ~ ~ 1N 0 JAUN L2014
When the PV power is available, the system is transferred to the
inverter mode. Battery capacity, SOC, average load profile and battery
DOD are updated in the nonvolatile memory. When the battery is fully
charged, the battery DOD is reset to the default level.
It is to be noted that the present invention is susceptible to
modifications, adaptations and changes by those skilled in the art.
Such variant embodiments employing the concepts and features of
this invention are intended to be within the scope of the present
invention, which is further set forth under the following claims:-
WE CLAIM
1. A solar power conditioning unit with dynamic depth of discharge
control comprising a solar panel with main control to charge
battery bank through grid power for supplying power to operate
load by sharing mechanism controlled by main controller, which
automatically measures the power from solar panel and grid and
reduces the charging current from the grid proportionally to the
solar panel charging current and in case the panel current reduces
the grid charging current is automatically increased for charging
battery of battery bank.
A solar power conditioning unit with dynamic depth of discharge
control as claimed in claim 1, which maintains battery in a good
state of charge in dynamic load and mains availability while
maximizing the energy usage from the solar system wherein, if the
battery is not charged fully from solar and grid fails, the depth of
discharge of battery is reduced so as to compensate for the fact
that the battery is not charged completely during last charging, the
said depth of discharge is reduced every time the battery is not
charged to full value up to a maximum defined level, in which if
these conditions are repeated for defined number of time, the
battery is forced to charge from the solar to float level so that the
battery gravity can be maintained in which case the load is
bypassed to mains whenever mains is available and battery
charging is done from solar power and once the battery is fully
charged the battery depth of discharge is reset at the initial set
level.
3. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein said
system has a metering unit to measure the depth of discharge of
battery wherein said meter constantly monitors the rate of charging
or discharging current of the battery and storing the data to
calculate depth of discharge of the battery.
4. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein once the
set threshold is achieved during the operation, the battery
discharge is stopped and mains recovery is enabled, in which if
grid is present, the system is then transferred to mains mode and
charging battery occurs from power supplied by both grid and
solar, and the charging takes place in the sharing mode that is the
grid charging current is reduced proportionally to the solar power.
5. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein once the
solar charging current increases the current from grid is reduced
and ultimately the battery is charged only from solar energy and
grid charging current reduces to zero.
6. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein during a
condition when the grid charging is disabled by user setting and
only grid bypass is allowed from power conditioning unit, the solar
power remains the source to charge the battery, in which once
transferred to mains the system works on the mains bypass and
the charging from solar continues, and the mains is cut only when
the battery is fully charged (up to absorption level) from solar
power.
7. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein in case
the battery is not charged fully and the mains fail, the depth of
discharge of battery is reduced so as to compensate for the fact
that the battery is not charged completely during last charging and
the depth of discharge is reduced every time the battery is not
charged to full value up to a maximum defined level.
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8. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein the PCU
once powered up continuously reads the charging and discharging
profile of the battery and keeps log of all this information in nonvolatile
memory and critical information such as battery voltage,
battery net AH, battery state of charge, temperature etc. which are
periodically updated in the memory, along with which a real time
clock is maintained, so that the periodic equalization process can
be initiated.
9. A solar power conditioning unit with dynamic depth of discharge
control as claimed in any of the preceding claims, wherein the PCU
also generates the load profile of the system on periodic basis;
typical average load profde is stored in the memory and based on
everyday reading average daily load is calculated based on which
the battery charging is controlled and the mains power is used to
charge the battery only up to a level.
10. A solar power conditioning unit with dynamic depth of discharge
control substantially as herein described with reference to the
accompanying drawings.