# US 9,436,201 B1 · System and method for maintaining a photovoltaic power source at a maximum power point

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- Number: US 9,436,201 B1
- Document ID: US9436201B1
- Status: Granted
- Kind: B1
- Application number: 14/738,113
- Filed: 2015-06-12
- Granted: 2016-09-06
- Earliest claimed: 2015-06-12
- Assignees: KarmSolar
- Applicants: KarmSolar
- Inventors: Ahmed Teirelbar; Alia Morsi
- Web page: https://patentgrep.com/patent/US9436201B1

## CPC

- G05F 1/67: to the maximum power available from a generator, e.g. from solar cell
- H02J 3/381: {Dispersed generators}
- H02J 2101/25: {involving maximum power point tracking control for photovoltaic sources}
- Y02E 10/56: Power conversion systems, e.g. maximum power point trackers
- G05F: SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
- H02J: ELECTRIC POWER NETWORKS; CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION

## Abstract

A method is provided for setting an operating parameter for a load on a photovoltaic power source, such as an AC signal or the speed of a motor, including operating a load, using a control system, with the operating parameter set at a first value, providing a measurement of DC source voltage at the power source to the control system, and providing a measurement of DC source current at the power source to the control system, determining the logarithm of the conductance from the measurement of DC source voltage and the measurement of DC source current, and comparing a reference parameter based on the logarithm of the conductance to a reference setpoint. Based on that comparison, the operating parameter may be modified for the load if the value of the reference parameter differs from the value of the reference setpoint by more than a threshold amount.

## Claims

### Claim 1

A method for setting an operating parameter for a load on a photovoltaic power source, the method comprising:
operating a load, using a control system, with the operating parameter at a first value;
providing a measurement of DC source voltage at the power source to the control system;
providing a measurement of DC source current at the power source to the control system;
determining, at the control system, the logarithm of the conductance from the measurement of DC source voltage and the measurement of DC source current;
comparing a reference parameter based on the logarithm of the conductance to a reference setpoint; and
modifying the operating parameter for the load if the value of the reference parameter differs from the value of the reference setpoint by more than a threshold amount.

### Claim 2 (depends on 1)

The method of claim 1 further comprising repeatedly providing updated measurements of DC source voltage and DC source current at the power source to the control system, determining the logarithm of the updated conductance from the measurements, comparing an updated reference parameter to the reference setpoint, and modifying the operating parameter so long as the reference parameter differs from the reference setpoint by more than the threshold amount.

### Claim 3 (depends on 2)

The method of claim 2 further comprising tracking the reference parameter across a plurality of cycles of the method and determining a rate of change of the measurement, wherein the control system modifies the reference parameter by a first amount when the rate of change is below a threshold, and by a second amount when the rate of change is above a threshold.

### Claim 4 (depends on 2)

The method of claim 2 wherein the control system is a fuzzy control system biased towards modifying the operating parameter in a first direction.

### Claim 5 (depends on 2)

The method of claim 2 wherein the operating parameter is adjusted in a first direction if the reference parameter is larger than the setpoint and is adjusted in a second direction if the reference parameter is smaller than the setpoint.

### Claim 6 (depends on 1)

The method of claim 1 wherein the reference parameter is
M
adj
=
G
m
⁢
μ
_
voc
⁢
T
r
+
V
m
⁢
G
mr
-
V
m
⁢
Λ
⁡
(
V
mr
T
r
+
μ
_
voc
)
(
V
m
+
μ
_
voc
⁢
T
r
)
wherein G is the logarithm of the conductance;
V is the voltage;
Λ is a coefficient based on a particular photovoltaic configuration;
T is temperature
and the subscript r indicates a reference condition, m indicates the maximum power point, and mr indicates the maximum power point for a reference condition.

### Claim 7 (depends on 1)

The method of claim 1 wherein the operating parameter is an AC signal.

### Claim 8 (depends on 1)

The method of claim 1 wherein the operating parameter is a speed of a motor.

### Claim 9 (depends on 8)

The method of claim 8 wherein the control signal modifies the operating parameter by outputting an amount by which a variable speed drive will change the speed of the motor.

### Claim 10 (depends on 4)

The method of claim 4 wherein the modification in the first direction is a result of a reduced conductance.

### Claim 11

A computer based method for controlling a load on a photovoltaic power source, the method comprising:
setting an operating parameter of the load at a first value;
receiving, at a controller, a measurement of DC source voltage at the power source;
receiving, at the controller, a measurement of DC source current at the power source;
determining, at the controller, the logarithm of the conductance from the measurement of DC source voltage and the measurement of DC source current;
comparing a reference parameter based on the logarithm of the conductance to a reference setpoint; and
modifying the operating parameter for the load if the value of the reference parameter differs from the value of the reference setpoint.

### Claim 12 (depends on 11)

The method of claim 11 further comprising repeatedly receiving updated measurements of DC source voltage and DC source current at the power source, determining an updated logarithm of the conductance from the measurements, comparing an updated reference parameter to the reference setpoint, and modifying the operating parameter so long as the reference parameter differs from the reference setpoint by more than a threshold amount.

### Claim 13 (depends on 11)

The method of claim 11 wherein the operating parameter is adjusted in a first direction if the reference parameter is larger than the setpoint and is adjusted in a second direction if the reference parameter is smaller than the setpoint.

### Claim 14 (depends on 11)

The method of claim 11 wherein the reference parameter is
M
adj
=
G
m
⁢
μ
_
voc
⁢
T
r
+
V
m
⁢
G
mr
-
V
m
⁢
Λ
⁡
(
V
mr
T
r
+
μ
_
voc
)
(
V
m
+
μ
_
voc
⁢
T
r
)
.

### Claim 15 (depends on 11)

The method of claim 11 wherein the operating parameter is an AC signal.

### Claim 16 (depends on 11)

The method of claim 11 wherein the operating parameter is a speed of a motor.

### Claim 17 (depends on 16)

The method of claim 16 wherein the control signal modifies the operating parameter by outputting an amount by which a variable speed drive will change the speed of the motor.

### Claim 18

A photovoltaic power system comprising:
a photovoltaic power source;
a load driven by the photovoltaic power source;
a first sensor configured to monitor DC source voltage at the power source;
a second sensor configured to monitor DC source current at the power source; and
a controller for controlling the load, the controller configured to:
operate the load at a first value of an operating parameter;
receive, from the first sensor and the second sensor, measurements of DC source voltage and current at the power source;
determine the logarithm of the conductance from the measurement of DC source voltage and the measurement of DC source current;
compare a reference parameter based on the logarithm of the conductance to a reference setpoint; and
modify the operating parameter for the load if the value of the reference parameter differs from the value of the reference setpoint.

### Claim 19 (depends on 18)

The system of claim 18 wherein the reference parameter is
M
adj
=
G
m
⁢
μ
_
voc
⁢
T
r
+
V
m
⁢
G
mr
-
V
m
⁢
Λ
⁡
(
V
mr
T
r
+
μ
_
voc
)
(
V
m
+
μ
_
voc
⁢
T
r
)
wherein G is the logarithm of the conductance;
V is the voltage;
Λ is a coefficient based on a particular photovoltaic configuration;
T is temperature
and the subscript r indicates a reference condition, m indicates the maximum power point, and mr indicates the maximum power point for a reference condition.

### Claim 20 (depends on 18)

The system of claim 18 wherein the operating parameter is a speed of a motor.