U.S. patent application number 14/082140 was filed with the patent office on 2014-03-13 for solar monitor for solar device.
The applicant listed for this patent is Roger L. Jungerman, Randall King. Invention is credited to Roger L. Jungerman, Randall King.
Application Number | 20140070837 14/082140 |
Document ID | / |
Family ID | 44901528 |
Filed Date | 2014-03-13 |
United States Patent
Application |
20140070837 |
Kind Code |
A1 |
Jungerman; Roger L. ; et
al. |
March 13, 2014 |
SOLAR MONITOR FOR SOLAR DEVICE
Abstract
A solar monitor measures electrical characteristics of a
designated solar device within an array of solar devices that are
coupled in series. The solar monitor includes a charge storage
element and a charger coupled to the charge storage element to
establish a positive voltage and/or a negative voltage on the
charge storage element. A switch within the solar monitor is
coupled in a shunt configuration with the designated solar device
and with a subsequent device in the array. The switch selectively
couples the charge storage element to the designated solar device
to vary an operating current that flows between the designated
solar device and the subsequent solar device. The solar monitor
includes a current detector to measure the current of the
designated solar device, and a voltage detector to measure the
voltage of the designated solar device.
Inventors: |
Jungerman; Roger L.;
(Petaluma, CA) ; King; Randall; (Santa Rosa,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jungerman; Roger L.
King; Randall |
Petaluma
Santa Rosa |
CA
CA |
US
US |
|
|
Family ID: |
44901528 |
Appl. No.: |
14/082140 |
Filed: |
November 16, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12799951 |
May 4, 2010 |
8610425 |
|
|
14082140 |
|
|
|
|
Current U.S.
Class: |
324/761.01 |
Current CPC
Class: |
H02S 50/10 20141201;
Y02E 10/50 20130101 |
Class at
Publication: |
324/761.01 |
International
Class: |
G01R 31/26 20060101
G01R031/26 |
Claims
1. A solar monitor, comprising: a switch having a first contact
coupled to a first port of a designated solar device within an
array of operating solar devices that are coupled in series,
wherein the switch is in a shunt configuration with the designated
solar device and a subsequent solar device in the array of
operating solar devices that are coupled in series, the switch
varying an operating current flowing between the designated solar
device and the subsequent solar device; a charge storage element
having a first terminal coupled to a second contact of the switch
and having a second terminal coupled to a second port of the
designated solar device; a charger coupled to the first terminal of
the charge storage element; a voltage detector coupled to a node
located between the first terminal of the charge storage element
and the first port of the designated solar device; and a current
detector configured to measure a current at the first port of the
designated solar device.
2. The solar monitor of claim 1 wherein the switch is coupled to
the first port of the designated solar device through a fuse.
3. The solar monitor of claim 1 wherein the charger establishes a
voltage on the charge storage device when the switch is open.
4. The solar monitor of claim 1 wherein the switch is open while
the charger provides a negative charge to the first terminal of the
charge storage element, wherein the switch is closed while the
voltage detector measures a voltage at the node and while the
current detector measures the current at the first port of the
designated solar device, and wherein varying the operating current
flowing between the designated solar device and the subsequent
solar device includes decreasing the operating current in response
to the negative charge when the switch is closed.
5. The solar monitor of claim 1 wherein the switch is open while
the charger provides a positive charge to the first terminal of the
charge storage element, wherein the switch is closed while the
voltage detector measures a voltage at the node and while the
current detector measures the current at the first port of the
designated solar device, and wherein varying the operating current
flowing between the designated solar device and the subsequent
solar device includes increasing the operating current in response
to the positive charge when the switch is closed.
6. The solar monitor of claim 4 wherein the switch is open while
the charger provides a positive charge to the first terminal of the
charge storage element, wherein the switch is closed while the
voltage detector measures a voltage at the node and while the
current detector measures the current at the first port of the
designated solar device, and wherein varying the operating current
flowing between the designated solar device and the subsequent
solar device includes increasing the operating current in response
to the positive charge when the switch is closed.
7. The solar monitor of claim 5 wherein the positive charge
establishes a corresponding positive voltage on the charge storage
element that exceeds an open circuit voltage of the designated
solar device.
8. The solar monitor of claim 1 wherein the current detector
includes a resistive element interposed between the first port of
the designated solar device and the subsequent solar device, a
first voltage detector coupled to a first terminal of the resistive
element, and a second voltage detector coupled to a second terminal
of the resistive element.
9. The solar monitor of claim 8 wherein the resistive element is
established by a designated length of a conductor that couples to
the first port of the designated solar device.
10. The solar monitor of claim 1 wherein the current detector is in
a shunt configuration with the first port of the designated solar
device and the subsequent solar device in the array of operating
solar devices that are coupled in series.
11. The solar monitor of claim 1 wherein the current detector is in
a series configuration with the first port of the designated solar
device and the subsequent solar device in the array of operating
solar devices that are coupled in series.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. Ser. No.
12/799,951, filed May 4, 2010, and titled "SOLAR MONITOR FOR SOLAR
DEVICE"; the contents of which are hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] Photovoltaic (PV) systems are ubiquitous contributors to
worldwide energy production. Solar panels within PV systems convert
incident sunlight into electrical energy that may be fed through an
inverter to a utility power grid, stored in battery banks or
locally consumed. The solar panels have a long specified operating
life and are typically installed on rooftops and other sites that
may be difficult to access during the operating life. Accordingly,
it is desirable to monitor the performance of the solar panels to
detect degradation due to aging, faults, or environmental
conditions, because even minor degradation in performance of one or
more solar panels can deprive the PV system of significant energy
production over the long operating life of the solar panels.
[0003] Inverters within PV systems that are coupled to the utility
power grid, or "grid-tied", typically have capability to monitor
the total operating voltage and total operating current
cumulatively provided by all of the solar panels within the PV
system. While this monitoring capability provides a useful
performance measure for the entire PV system, it does not enable
detection of subtle degradations within the solar panels.
[0004] Electrical characteristics, such as current-voltage, or
"I-V", characteristics, of the solar panels are definitive
indicators of the performance and integrity of the solar panels,
and may be used to detect even subtle degradations of the solar
panels. The I-V characteristics of individual solar panels may be
measured using traditional curve tracers in manufacturing
facilities, prior to integration into a PV system. These
measurements, disclosed for example by Warner et al. in U.S. Pat.
No. 4,456,880, titled I-V Curve Tracer Employing Parametric
Sampling, provide a baseline performance measure for the individual
solar panels in the manufacturing environment, but do not provide
for on-going monitoring of the solar panels once the solar panels
are installed and are operating in a PV system.
[0005] The I-V characteristics of one or more solar panels may also
be measured upon installation of the solar panels in a PV system to
provide a cumulative baseline performance measure for all of the
solar panels in the operating environment of the installation site.
However, this measurement typically relies on disconnecting the
solar panels from the rest of the PV system and disrupting
operation of the PV system, which makes this type of measurement
too intrusive for monitoring performance and detecting degradation
of the solar panels within an installed PV system.
[0006] In view of the above, there is a need for a solar monitor
that measures electrical characteristics of solar panels during the
operating life of an installed PV system, without significantly
disrupting the operation of the PV system.
SUMMARY OF THE INVENTION
[0007] A solar monitor according to embodiments of the present
invention measures electrical characteristics of a designated solar
device within an array of solar devices that are coupled in series.
The solar monitor includes a charge storage element and a charger
coupled to the charge storage element to establish a positive
voltage and/or a negative voltage on the charge storage element. A
switch within the solar monitor is coupled in a shunt configuration
with the designated solar device and with a subsequent device in
the array. The switch selectively couples the charge storage
element to the designated solar device to vary an operating current
that flows between the designated solar device and the subsequent
solar device. The solar monitor includes a current detector to
measure the current of the designated solar device, and a voltage
detector to measure the voltage of the designated solar device.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention can be better understood with
reference to the following Figures. The components in the Figures
are not necessarily to scale. Emphasis is instead placed upon
illustrating the principles and elements of the present
invention.
[0009] FIGS. 1-4 show examples of block diagrams of a solar monitor
according to alternative embodiments of the present invention.
[0010] FIG. 5 shows an example of a flow diagram of a solar monitor
implemented according to a method, according to alternative
embodiments of the present invention.
[0011] FIG. 6 shows an example of a current-voltage (I-V)
characteristic for a solar device, established using the solar
monitors according to embodiments of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0012] FIG. 1 shows an example of a block diagram of a solar
monitor 100, according to embodiments of the present invention,
coupled to a solar device 21 within a PV system 200. The solar
device 21 typically includes one or more solar panels, such as
photovoltaic panels, solar cells or other devices, elements or
systems that are suitable for converting incident solar radiation
RAD into electrical power.
[0013] In this example, the PV system 200 includes an array 4 of
two or more solar devices 21-2n that are coupled in series. Each of
the solar devices, in turn, may include one or more devices,
elements, or systems in a series and/or shunt arrangement. The PV
system 200 may alternatively include two or more of the arrays 4 in
a series or parallel arrangement. During operation of the PV system
200, an operating current Iop flows between the two or more solar
devices 21-2n that are coupled in series. In this example, the
operating current Iop flows between the solar device 21 and a
subsequent solar device in the array 4. The subsequent solar device
may include the solar device 22, additional solar devices in the
array 4, the inverter 6, or any of one or more elements of the PV
system 200 that are coupled in series with the solar device 21 or
with any other of the designated solar devices in the array 4. The
operating current Iop typically refers to currents that are
provided by the two or more solar devices 21-2n in response to the
incident solar radiation RAD. The operating current Iop may also
refer to substantially smaller currents, such as "dark" currents
that may be provided by the two or more solar devices 21-2n in the
absence of the incident solar radiation RAD on one or more of the
solar devices 21-2n. Alternatively, the operating current Iop may
refer to, or include, any other current that may flow between a
designated solar device and a subsequent solar device in the array
4 of two or more solar devices 21-2n, when the solar devices 21-2n
within the array 4 are coupled in series or otherwise configured
for operation or use in the PV system 200.
[0014] The output of the last solar device 2n in the array 4 is
shown coupled to an inverter 6. In a typical "grid-tied" PV system
200, the inverter 6 is coupled to a utility power grid (not shown).
In alternative examples, the PV system 200 includes a charge
controller 8 that delivers power provided by the solar devices
21-2n to a battery bank or other type of energy storage system (not
shown). While the inverter 6 and the charge controller 8 are shown
included within the PV system 200, the PV system 200 may include
neither the inverter 6 nor charge controller 8, or just one of the
inverter 6 and charge controller 8, depending on the application of
the PV system 200. The PV system 200 may include other types of
devices, elements or systems that are suitable for interfacing to
the array 4 of solar devices 21-2n that are coupled in series.
[0015] The solar monitor 100 is configured to monitor the
electrical characteristics at a first port 1 of the first solar
device 21 in the array 4. In other examples, the solar monitor 100
is configured to monitor or measure electrical characteristics of
any other of the solar devices 21-2n in the array 4 by coupling the
solar monitor 100 to another solar device 2x or subset of solar
devices in the array 4. The subscript "x" is an integer variable
that designates which solar device 2x in the array 4 of solar
devices 21-2n is monitored by the solar monitor 100, where
1<x<n and where n represents the number of solar devices in
the array 4.
[0016] The solar monitor 100 includes a switch Si that has a first
contact S1a, a second contact S1b, and a control port S1c. The
first contact S1a is coupled to the first port 1 of the solar
device 21, which couples the switch S1 in a shunt configuration
with the solar device 21 and with the subsequent solar device in
the array 4 of solar devices 21-2n that are coupled in series. In
this example, the first contact S1a of the switch S1 is coupled to
the first port 1 of the solar device 21 through an optionally
included fuse F and a current detector I1. The switch S1 may be
implemented using a high current switching transistor such as an
Insulated Gate Bipolar Transistor (IGBT) provided by MITSUBISHI
ELECTRIC, an electromechanical relay, mechanical switch, other type
of semiconductor device, or series of devices. The switch S1 is
alternatively implemented using any other type of device, element,
or system suitable for providing switching at the currents and
voltages presented at the contacts S1a, S1b. In an example wherein
the solar monitor 100 is configured to monitor a solar device 2x
that includes a single solar panel, the voltage present between the
first contact S1a and the second contact S1b of the switch S1
typically does not exceed one hundred volts and the current between
the first contact S1a and the second contact S1b of the switch S1
typically does not exceed ten amperes. However, in examples wherein
the solar monitor 100 is configured to monitor a solar device 2x
that includes multiple solar panels in a series configuration, the
voltage present between the first contact S1a and the second
contact S1b of the switch S1 may exceed several hundred volts. The
type of device, element or system that is used to implement the
switch S1 may be selected according to the configuration of the PV
system 200, or according to the coupling configuration of the solar
monitor 100 to the PV system 200.
[0017] The solar monitor 100 includes a charge storage element C
that has a first terminal 3a coupled to the second contact S1b of
the switch S1. A second terminal 3b of the charge storage element C
is coupled to the second port 2 of the solar device 21. The charge
storage element C is typically implemented using one or more
electrolytic capacitors. The capacitance of the charge storage
element C is typically larger than the capacitance that is
associated with each of the solar devices 21-2n, which enables the
charge storage element C to provide sufficiently large voltages and
corresponding currents to the solar device 21 upon activation of
the switch S1.
[0018] The solar monitor 100 includes a charger 5 having an output
O that is coupled to the first terminal 3a of the charge storage
element C. The charger 5 is typically implemented using a DC-DC
converter or other power supply that is suitable to provide
voltages and currents to the charge storage device C that are
sufficiently high to perform measurements of the electrical
characteristics of the solar device 21. The current that the
charger 5 provides to the charge storage element C is sufficiently
large to enable the solar monitor 100 to perform measurements of a
solar device 21 at a designated measurement interval. In one
example, the charger 5 provides a current at the output O of
approximately 100 mA, which enables the solar monitor 100 to
perform a measurement of the solar device 2x at least every several
seconds. Through internal switching, or by including two power
supplies of opposite polarity, the charger 5, typically under
control of the processor 9, provides either a positive charge on
the terminal 3a of the charge storage element C or a negative
charge on the terminal 3a of the charge storage element C, so that
a positive voltage or a negative voltage, respectively, may be
selectively provided between the terminals 3a, 3b of the charge
storage element C.
[0019] The solar monitor 100 includes a voltage detector V1 coupled
between a ground or other suitable voltage reference, and a node N.
The voltage detector V1 typically includes a voltage probe (not
shown) and an analog-to-digital converter, a voltmeter, a data
acquisition system, or other type of device, element or system
suitable for measuring or otherwise determining the voltage at the
node N. The node N is typically located in a signal path between
the first port 1 of the solar device 21 and the first terminal 3a
of the charge storage element C, or at any other designated
position in the solar monitor 100 or the PV system 200 that is
suitable to provide an indication of the voltage Vsd present at the
port one 1 of the solar device 21. In an example wherein the node N
is positioned between the fuse F and the switch S1, voltage
measurements acquired at the node N may be compensated for the
voltage drops that may occur across the fuse F due to inherent
resistance of the fuse F. In an example wherein the node N is
positioned at the first terminal 3a of the charge storage element
C, voltage measurements acquired at the node N may also be
compensated for voltage drops that may occur across the switch Si
due to the inherent "on" resistance associated with the switch S1
when the switch S1 is closed. Compensation is typically provided by
the processor 9, which typically interfaces with the control port
S1c of switch S1, the charger 5, the current detector I1, the
voltage detector V1, and other devices, elements, or systems
associated with the solar monitor 100 or the PV system 200. The
processor 9 typically has an associated memory (not shown).
[0020] The solar monitor 100 also includes a current detector I1
that is coupled to the first port 1 of the solar device 21 and
configured to indicate the current Isd that is present at the first
port 1 of the solar device 21. In one example, the current detector
I1 is implemented with a Hall Effect Sensor (not shown), as
disclosed for example in U.S. Pat. No. 7,164,263, issued on 16 Jan.
2007 to Yakymyshyn et al. This type of current detector I1 is
typically clamped on or otherwise disposed about one or more
conductors 11 that carry currents between solar devices 21 within
the array 4 of solar devices 21-2n within the PV system 200.
Because the Hall Effect Sensor is not interposed in the signal path
of the PV system 200, a failure of this type of current detector I1
typically will not induce a failure in the PV system 200, or
typically will not otherwise impair operation or energy production
by the PV system 200.
[0021] FIG. 2 shows another example of the solar monitor 100
wherein the current detector I1 is implemented using the voltage
detector V1, a voltage detector V2, and a resistive element Rm. The
voltage detector V2 typically includes a voltage probe (not shown)
and an analog-to-digital converter, a voltmeter, a data acquisition
system, or other type of device, element or system suitable for
measuring or otherwise determining the voltage at a terminal of the
resistive element Rm that is opposite from the terminal that is
coupled to the node N. The resistive element Rm in one example is a
temperature-stable, low value resistor. The resistance of the
resistive element Rm is typically less than one ohm or is otherwise
sufficiently low so as to not dissipate sufficient power to impair
operation of the PV system 200. The resistive element Rm is
alternatively implemented using a designated length of one or more
of the conductors 11 that connect the solar devices 21-2n within
the array 4 or that are otherwise associated with the solar device
21. In this implementation, the resistive element Rm is established
based on the cross-sectional area, the material type of the
conductor 11, and the length of a portion of the conductor 11 that
is defined by the physical separation between the voltage detectors
V1, V2. The voltage detectors V1, V2 and all of the elements of the
solar monitor 100 that are coupled in shunt with the PV system 200
typically have high input impedances, so that operation of the
solar monitor 100 or even a failure of one or more elements of the
solar monitor 100, typically will not induce a corresponding
failure in the PV system 200 or otherwise impair operation or
energy production of the PV system 200. To further isolate the
solar monitor 100 from the PV system 200, the voltage detectors V1,
V2 may each be optionally coupled to terminals of the resistive
element Rm through a corresponding series fuse (not shown). This
implementation of the current detector I1 isolates the PV system
200 from failures that may occur in the solar monitor 100 and
enables the elements of the solar monitor 100 to be located
remotely from the stringent environmental conditions of the
installation sites of the PV system 200, which typically increases
reliability of the solar monitor 100.
[0022] To acquire a first measure M1 of electrical characteristics
of the solar device 21, such as a portion of an I-V characteristic
7 (shown in the example of FIG. 6), the processor 9 activates the
control port S1c to open the switch S1, which establishes a high
impedance between the first contact S1a and the second contact S1b.
With switch S1 open, the processor 9 configures the charger 5 to
provide a negative charge, and corresponding negative voltage,
between the first terminal 3a and the second terminal 3b of the
charge storage element C. The processor 9 then decouples the
charger 5 from the charge storage element C, typically by opening
an optionally included switch SC or by otherwise providing a high
impedance at the output O of the charger 5. The processor 9 then
activates the control port S1c to close the switch S1, which
establishes a low impedance between the first contact S1a and the
second contact S1b of the switch S1. Closing the switch S1
decreases the operating current Iop between the solar device 21 and
the subsequent solar device in the array 4 in response to the
negative charge provided to the charge storage element C.
[0023] With the switch S1 closed, the voltage detector V1 monitors
the voltage Vsd at the node N and the current detector I1 monitors
the current Isd at the first port 1 of the solar device 21 by
acquiring a set {Isd, Vsd} 1 of corresponding measurements of the
current Isd and measurements of the voltage Vsd, respectively, over
a first designated time interval. While the current Isd and the
voltage Vsd are typically analog currents and voltages,
respectively, the acquired set {Isd,Vsd} 1 of corresponding
measurements of the current Isd and measurements of the voltage Vsd
includes samples of the current Isd and samples of the voltage Vsd,
acquired by the current detector I1 and the voltage detector V1,
respectively, at designated times within the first designated time
interval. The samples in the set {Isd,Vsd} 1 of corresponding
measurements of the current Isd and measurements of the voltage Vsd
are typically acquired in the direction defined by an arrow A1
shown in FIG. 6. The processor 9 typically uses the acquired set
{Isd,Vsd} 1 of corresponding measurements of the current Isd and
measurements of the voltage Vsd in this first measure M1 of the
electrical characteristics to establish a portion of an I-V
characteristic 7 for the solar device 21 that includes the short
circuit current Isc and the operating voltage Vop of the solar
device 21 as shown in FIG. 6.
[0024] Series protection diodes (not shown) within each of the
solar devices 21-2n or the inherent electrical characteristics of
the solar devices 21-2n typically prevent current from other solar
devices in the array 4 from flowing to the current detector I1,
which could otherwise influence the first measure M1 of the
electrical characteristics of the solar device 21.
[0025] To acquire a second measure M2 of electrical characteristics
of the solar device 21, such as another portion of an I-V
characteristic 7 (shown in the example of FIG. 6), the processor 9
activates the control port S1c to open the switch S1, which
establishes a high impedance between the first contact S1a and the
second contact S1b. With switch S1 open, the processor 9 configures
the charger 5 to provide a positive charge, and corresponding
positive voltage, between the first terminal 3a and the second
terminal 3b of the charge storage element C. The positive voltage
provided to the charge storage element C is sufficient to establish
a voltage at the port 1 of the solar device 21 that exceeds the
open circuit voltage Voc of the solar device 21. The processor 9
then decouples the charger 5 from the charge storage element C,
typically by opening the optionally included switch SC or by
otherwise providing a high impedance at the output O of the charger
5. The processor 9 then activates the control port S1c to close the
switch S1, which establishes a low impedance between the first
contact S1a and the second contact S1b of the switch S1. Closing
the switch S1 increases the operating current Iop between the solar
device 21 and the subsequent solar device in the array 4 in
response to the positive charge provided to the charge storage
element C.
[0026] With the switch S1 closed, the voltage detector V1 then
monitors the voltage Vsd between the reference and the node N and
the current detector I1 monitors the current Isd at the first port
1 of the solar device 21 by acquiring a set {Isd,Vsd}2 of
corresponding measurements of the current Isd and measurements of
the voltage Vsd, respectively, over a second designated time
interval. The acquired set {Isd,Vsd}2 of corresponding measurements
of the current Isd and measurements of the voltage Vsd includes
samples that are typically acquired in the direction defined by an
arrow A2 shown in FIG. 6. The processor 9 typically uses the
acquired set {Isd,Vsd}2 of corresponding measurements of the
current Isd and measurements of the voltage Vsd in this second
measure M2 of the electrical characteristics to establish a portion
of an I-V characteristic 7 for the solar device 21 that includes
the open circuit voltage Voc and the operating voltage Vop of the
solar device 21, as shown in FIG. 6. Series protection diodes
within each of the solar devices 21-2n or the inherent electrical
characteristics of the solar devices 21-2n typically prevent the
current Isd from being negative and may prevent acquisition of a
measurement of the open circuit voltage Voc of the solar device 21,
at which the current Isd is zero, the acquired set {Isd,Vsd}2 of
corresponding measurements of the current Isd and measurements of
the voltage Vsd in this second measure M2 may be used to extract
the open circuit voltage Voc and define the portion of the I-V
characteristic 7 where Isd=0, based on curve fitting or other data
processing techniques.
[0027] While the first measure M1 and the second measure M2
typically each include sets {Isd,Vsd} 1, {Isd,Vsd}2 of
corresponding measurements of the current Isd and measurements of
the voltage Vsd that are acquired at discrete times within the
first and second designated time intervals, respectively, curve
fitting techniques, interpolation techniques or extrapolation
techniques may be used to establish the I-V characteristic 7 or
other electrical characteristic for the particular solar device 2x
that is monitored using the solar monitor 100. The first measure M1
may be performed before the second measure M2 is performed, or vice
versa. Alternatively, the first measure M1 is performed in the
absence of the second measure M2, or the second measure M2 is
performed in the absence of the first measure M1.
[0028] The designated time intervals during which the measures M1,
M2 of electrical characteristics of the solar device 21 are
performed are of short duration, so that the solar monitor 100 has
negligible impact on the energy production of the PV system 200.
The short-duration time intervals of the measures M1, M2 also
provides for a low duty cycle for the solar monitor 100, which
results in low power dissipation for the elements of the solar
monitor 100. Lower power dissipation typically provides
corresponding increases in reliability of the solar monitor
100.
[0029] FIG. 3 shows an example of a block diagram of a solar
monitor 102 according to alternative embodiments of the present
invention. In this example, the current detector I1, the switch S1,
and the charge storage element C of the solar monitor 102 are all
in a shunt configuration with the solar device 21 and with the
subsequent solar device in array 4 of the solar device 21-2n that
are coupled in series and included in the PV system 200. The
coupling of all the elements of the solar monitor 102 in the shunt
configuration as shown in the example of FIG. 3, isolates failures
of the PV system 200 from failures that may occur in the solar
monitor 102. The optionally included fuse F further isolates the PV
system 200 from failures of the solar monitor 102. The shunt
configuration of the current detector I1 and the rest of the
elements of the solar monitor 102 also enables the solar monitor
102 to be located remotely from the stringent environmental
conditions of the installation sites of the PV system 200, which
typically increases reliability of the solar monitor 102.
[0030] The first measure M1 of electrical characteristics of the
solar device 21 is performed similarly when using the solar monitor
102 as when using the solar monitor 100. Using the solar monitor
102, the first measure M1 also provides the acquired set {Isd,Vsd}1
of corresponding measurements of the current Isd and measurements
of the voltage Vsd, which may be used to establish the portion of
an I-V characteristic 7, or other electrical characteristics for
the solar device 21 that includes the short circuit current Isc and
the operating voltage Vop of the solar device 21 as shown in FIG.
6. The series protection diodes within each of the solar devices
21-2n or the inherent electrical characteristics of the solar
devices 21-2n typically prevent current from other solar devices
21-2n in the array 4 from flowing to the current detector I1, which
may otherwise influence the first measure M1 of the electrical
characteristics of the solar device 21. Accordingly, the current
Isd at port 1 of the solar device 21 flows through the current
detector I1 during this first measure M1 of electrical
characteristics.
[0031] Performing the second measure M2 of the solar device 21
using the configuration shown in FIG. 3 involves additional
processing of corresponding measurements of a current Idet measured
by the current detector I1 and measurements of the voltage Vsd by
the voltage detector V1 to determine the electrical characteristics
of the solar device 21. The processor 9 activates the control port
S1c to open the switch S1, which establishes a high impedance
between the first contact S1a and the second contact S1b. With
switch S1 open, the processor 9 configures the charger 5 to provide
a positive charge, and corresponding positive voltage, on the first
terminal 3a of the charge storage element C. The positive voltage
provided to the charge storage element C is sufficient to establish
a voltage at the port 1 of the solar device 21 that exceeds the
open circuit voltage Voc of the solar device 21. The processor 9
then decouples the charger 5 from the charge storage element C,
typically by opening the optionally included switch SC or by
otherwise providing a high impedance at the output O of the
charger. The processor 9 then activates the control port S1c to
close the switch S1, which establishes a low impedance between the
first contact S1a and the second contact S1b of the switch S1. The
current detector I1 monitors current Idet and the voltage detector
V1 then monitors the voltage between the reference and the node N
by acquiring a set {Idet,Vsd} of corresponding measurements of the
current Idet and measurements of the voltage Vsd over a designated
time interval. The processor 9 typically processes the acquired set
{Idet,Vsd} of corresponding measurements of the current Idet and
measurements of the voltage Vsd in this second measure M2 of the
electrical characteristics to establish the portion of the I-V
characteristic 7 for the solar device 21 that includes the open
circuit voltage Voc and the operating voltage Vop of the solar
device 21. With the current detector I1 in the shunt configuration,
the current Isd provided by the solar device 21 is the difference
between the current Isys that is provided to the solar devices
22-2n in the array 4 and the current Idet that is measured by the
current detector I1, as shown in equation (1).
Isd=Isys-Idet (1)
[0032] In one example, the processor 9 determines the current Isys
as a function of the output voltage Vout of the array 4 based on a
measurement of the I-V characteristic 7 of the entire array 4 of
solar devices 21-2n in the PV system 200, typically acquired upon
installation of the PV system 200, as shown in equation (2).
Isys=Isys(Vout) (2)
[0033] The positive voltage provided to the charge storage element
C results in a voltage Vc equal to the sum of a voltage increment
deltaV and the operating voltage Vop of the solar device 21, which
may be measured by the voltage detector V1 at the node N. The
processor 9 then uses equation (1) and the measure of the I-V
characteristic 7 of the array 4 of solar devices 21-2n in the PV
system 200 shown in equation (2) to determine the current Isd
according to equation (3).
Isd=Isys(VoutOP-deltaV)-Idet (3)
[0034] The term VoutOP in equation (3) represents the output
voltage Vout of the array 4 of the solar devices 21-2n during
operation of the PV system 200, which may be measured with
monitoring circuitry (not shown) that is typically included in the
inverter 6. Equations (1)-(3) enable the set {Isd,Vsd}2 of
corresponding measurements of the current Isd and measurements of
the voltage Vsd to be established from the acquired set {Idet,Vsd}
of corresponding measurements of the current Idet and measurements
of the voltage Vsd. The processor 9 typically uses this resulting
set {Isd,Vsd}2 to establish the portion of the I-V characteristic 7
for the solar device 21 that includes the open circuit voltage Voc
and the operating voltage Vop of the solar device 21, as shown in
FIG. 6.
[0035] In another example, the processor 9 establishes the set
{Isd,Vsd}2 of corresponding measurements of the current Isd and
measurements of the voltage Vsd from the acquired set {Idet,Vsd} of
corresponding measurements of the current Idet and measurements of
the voltage Vsd based on a designation that estimates each of the
solar devices 21-2n in the array 4 to have equivalent electrical
characteristics. With this designation, the positive voltage
provided to the charge storage element C correspondingly reduces
the operating voltage Vop of each of the solar devices 22-2n in the
array 4 by an equal amount. The positive voltage provided to the
charge storage element C in this example does not reduce the
operating voltage Vop of the solar device 21. The reduction in
operating voltage Vop of each of the solar devices 22-2n results in
a voltage V'sd for each of the solar device 22-2n, as shown in
Equation (4).
V'sd=(Vop-deltaV/(n-1)) (4)
[0036] The current Isys of the PV system 200 may then be
established as shown in Equation (5).
Isys=Isd(Vop-deltaV/(n-1)) (5)
[0037] The current Isd is then obtained from equation (1) using the
measured current Idet and the current Isys established in equation
(5).
[0038] FIG. 4 shows another example of a solar monitor 103
according to alternative embodiments of the present invention. In
this example, the solar monitor 103 includes a multiplexer MUX in
addition to the other elements that are included in the solar
monitor 100 or the solar monitor 102. One or more switches S1-Sn-1
are included in the multiplexer MUX to provide for selective
coupling of the charge storage element C to a corresponding one or
more solar devices 21-2n in the array 4 of solar devices 21-2n that
are coupled in series. The multiplexer MUX enables each of the
solar devices 21-2n within the array 4 to be monitored through
selective activation of the switches S1-Sn-1 that are included in
the multiplexer MUX. To monitor the first solar device 21 in the
array 4, the switches S2-Sn-1 in the multiplexer MUX are opened
through activation by the processor 9. With the switches S2-Sn-1
open, the measure M1 and the measure M2 are typically performed as
in the examples of the solar monitors 100, 102, using the charger
5, the charge storage element C, the current detector I1, the
voltage detector V1, and by selectively activating the switch S1 to
establish the I-V characteristic 7, or other electrical
characteristics for the solar device 21. To monitor the second
solar device 22 in the array 4, the switch S1 and the switches
S3-Sn-1 in the multiplexer MUX are opened through activation by the
processor 9. With the switches S1 and switches S3-Sn-1 open, the
measure M1 and the measure M2 are typically performed as in the
examples shown for the solar monitors 100, 102 using the charger 5,
the charge storage element C, the current detector I1, the voltage
detector V1, and by selectively activating the switch S2 to
establish a cumulative I-V characteristic 7, or other electrical
characteristics for the series combination of the solar device 21
and the solar device 22. Based on a determination of the I-V
characteristic 7 for the solar device 21, the I-V characteristic 7
of the solar device 22 may be isolated from the cumulative I-V
characteristic 7 established for the series combination of solar
devices 21, 22. To monitor the third solar device 23 in the array
4, the switches S1, S2 and the switches S4-Sn-1 in the multiplexer
MUX are opened through activation by the processor 9. With the
switches S1, S2 and the switches S4-Sn-1 open, the measure M1 and
the measure M2 are typically performed as in the examples shown for
the solar monitors 100, 102 using the charger 5, the charge storage
element C, the current detector I1, the voltage detector V1, and by
selectively activating switch S3 to establish the cumulative I-V
characteristic, or other electrical characteristics for the series
combination of the solar device 21, the solar device 22 and solar
device 23. Based on a determination of the I-V characteristic 7 for
the solar device 21 and the solar device 22, the I-V characteristic
7 of the solar device 23 may be isolated from the cumulative I-V
characteristic 7 established for the solar devices 21-23. This
sequential activation of the switches S1-Sn-1 in the multiplexer
MUX may be continued to establish the I-V characteristic 7 for
other solar devices 21-2n in the array 4. Alternatively, the
switches S1-Sn-1 in the multiplexer MUX may be activated according
to different sequences or activated in isolation to monitor other
combinations of one or more of the solar devices 21-2n in the array
4. The output voltage Vout and current Isys, which may be measured
using the monitoring circuitry that is typically included in the
inverter 6, may provide a cumulative measure of electrical
characteristics for the solar devices 21-2n, including the solar
device 2n in the array 4.
[0039] In the example shown in FIG. 4, the current detector I1 is
shown in a shunt configuration with the solar devices 21-2n. In an
alternative example, the current detector I1 is coupled between the
solar devices 21-2n in a series configuration, positioned at the
output port 1 of the solar device 21 as shown in the solar monitor
100 of FIG. 1 and FIG. 2.
[0040] In an example wherein the PV system 200 includes multiple
arrays 4 of solar devices 21-2n, the PV system 200 may also include
one or more combiner boxes to bus or otherwise consolidate the
outputs or other connections in the multiple arrays 4 to simplify
the interface between the arrays 4 and the inverter 6. In this
example, the multiplexer MUX may be integrated or otherwise
included in the combiner boxes or other type of junction box. This
type of integration typically reduces the number of
interconnections between the multiplexer MUX and the other elements
of the solar monitor 103.
[0041] FIG. 5 shows an example of a flow diagram of a solar monitor
implemented according to a method 104, according to alternative
embodiments of the present invention. In the method 104, the
measure M1 includes coupling a negatively charged charge storage
element C in a shunt configuration with the solar device 2x and
with the subsequent solar device in the array 4, to decrease the
operating current Iop flowing between the designated solar device
2x and the subsequent solar device in the array (15), and measuring
the current and voltage of the solar device 2x over a first
designated time interval in response to the coupled negatively
charged charge storage element (17). Coupling the negatively
charged charge storage element C to the solar device 2x (15)
typically includes opening the switch S1 to establish a high
impedance between the charge storage element C and the solar device
2x (10), providing a negative charge to the charge storage element
C (12), and closing the switch S1 to establish a low impedance
between the charge storage element C and the solar device 2x (14).
Measuring the current and the voltage of the solar device 2x over
the first designated time interval in response to the coupled
negatively charged charge storage element C (17) typically includes
acquiring the set {Isd,Vsd} 1 of corresponding measurements of the
current Isd and measurements of the voltage Vsd (16) and
establishing a first portion of the I-V characteristic 7, or other
electrical characteristic for the solar device 2x (18).
[0042] In the method 104, the measure M2 includes coupling a
positively charged charge storage element C in a shunt
configuration with the solar device 2x and with the subsequent
solar device in the array 4, to increase the operating current Iop
flowing between the designated solar device 2x and the subsequent
solar device in the array 4 (25), and measuring the current and the
voltage of the solar device 2x over a second designated time
interval in response to the coupled positively charged charge
storage element C (27). Coupling the positively charged charge
storage element C to the solar device 2x (25) typically includes
opening the switch S1 to establish a high impedance between the
charge storage element C and the solar device 2x (20), providing a
positive charge to the charge storage element C (22), and closing
the switch S1 to establish a low impedance between the charge
storage element and the solar device 2x (24). Measuring the current
and the voltage of the solar device 2x over the second designated
time interval in response to the coupled positively charged charge
storage element C (27) typically includes acquiring the set
{Isd,Vsd}2 of corresponding measurements of the current Isd and
measurements of the voltage Vsd (26) and establishing a portion of
an I-V characteristic 7, or other electrical characteristic for the
solar device 2x (28).
[0043] The measure M1 and the measure M2 of electrical
characteristics of the solar device 2x are typically performed in
the operating environment of the PV system 200, during operation of
the PV system 200. During operation, the operating current Iop
flows between the solar device 2x and the subsequent solar device
in the array 4 of the solar devices 21-2n that are coupled in
series. The operating current Iop is typically provided by the two
or more solar devices 21-2n and flows in series through the solar
devices 21-2n in response to the incident solar radiation RAD.
Alternatively, the measures M1, M2 are acquired in the absence of
incident solar radiation RAD on the solar device 2x, for example by
blocking illumination to the solar device 2x to establish the"dark"
current-voltage measurement for the solar device 2x. The measures
M1, M2 may also be acquired in the absence of incident solar
radiation RAD on one or more of the solar devices 21-2n to
establish a "dark" current-voltage measurement for the one or more
of the solar devices 21-2n. Dark current-voltage measurements, as
described in "Dark Current-Voltage Measurements on Photovoltaic
Modules as a Diagnostic or Manufacturing Tool" by D. L. King et
al., presented at the 26th IEEE Photovoltaic Specialists
Conference, September 29th-October 3rd 1997, Anaheim, Calif.,
enable determination of series resistance, shunt resistance, diode
factor, diode saturation currents or other parameters that dictate
performance, establish or indicate performance, or otherwise
influence performance of the solar device 2x.
[0044] The elements of the solar monitors 100-104 are shown
separate from the PV system 200 in FIGS. 1-5. According to
alternative embodiments of the present invention, the processor 9
is implemented using a computer or other processor and associated
memory present within the inverter 6. The current detector I1, the
voltage detectors V1, V2 may also be implemented using circuitry,
or modifications of circuitry that is included within the inverter
6. One or more of the elements, or the functions of one or more
elements, of the solar monitors 100-104 may be fully integrated,
partially integrated, or otherwise included or distributed within
the inverter 6 or within other elements of the PV system 200. In
addition, coupling between the elements of the solar monitors
100-104, or coupling between elements of the solar monitors 100-104
and the PV system 200 typically refers to direct connections,
indirect connections, connections through interposed devices, or
other arrangements or configurations of elements that place the
elements that are coupled in signal communication with each other.
The I-V characteristic 7 obtained using the solar monitors 100-104
is shown as an example of an electrical characteristic that is
suitable to monitor or otherwise indicate the performance of one or
more of the solar devices 21-2n. Any other suitable electrical
characteristic acquired using the current detector I1, the voltage
detector V1, or other elements of the solar monitors 100-104 is
alternatively obtained or established according to the embodiments
of the present invention.
[0045] While the embodiments of the present invention have been
illustrated in detail, it should be apparent that modifications and
adaptations to these embodiments may occur to one skilled in the
art without departing from the scope of the present invention as
set forth in the following claims.
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