Smart sensors for solar panels

• US 20090140719A1
• Filed: 11/18/2008
• Published: 06/04/2009
• Est. Priority Date: 12/03/2007
• Status: Active Grant

• Current Assignee: National Semiconductor Corporation (Texas Instruments, Inc.)
• Original Assignee: ActSolar, Inc. (Texas Instruments, Inc.)
• Inventors: Hasenfus, Gary D.
• Granted Patent: US 8,294,451 B2
• Time in Patent Office: Days
• US Class Current: 324/72
• CPC Class Codes: H02S 50/10 Testing of PV devices, e.g. of PV modules or single PV cells testing of semiconductor devices during manufacturing H01L22/00
• CPC Class Codes: H04Q 2209/84 Measuring functions
• CPC Class Codes: H04Q 2209/886 using energy harvesting, e.g. solar, wind or mechanical
• CPC Class Codes: H04Q 9/00 Arrangements in telecontrol or telemetry systems for selectively calling a substation from a main station, in which substation desired apparatus is selected for applying a control signal thereto or for obtaining measured values therefrom
• CPC Class Codes: Y02E 10/50 Photovoltaic [PV] energy

Abstract

A solar panel smart sensor system is disclosed. The sensor system permits solar power system owners and operators to monitor the voltage of individual panels in a solar array. The system uses a low wire-count bus in which the order of sensors on the bus is automatically determined. A novel technique is used to measure DC voltages of panels that may be floating hundreds of volts above ground. Bypass diodes are monitored to detect lost power generation capacity.

Claims

1. A solar panel sensor comprising:

a voltage-to-frequency converter that generates a pulse data signal; and

,

a multiplexer connected to the pulse data signal,

the multiplexer comprising;

sense-in, sense-out, ground, power, and control terminals;

wherein,

in response to signals received at the control terminal, the multiplexer connects the sense-out terminal to one of;

the pulse data signal, the sense-in terminal, the ground terminal, or the power terminal.

2. The sensor of claim 1 wherein the voltage-to-frequency converter is connected to a solar panel.

3. The sensor of claim 1 wherein the voltage-to-frequency converter has voltage inputs that are optically isolated from the pulse data output.

4. The sensor of claim 1 wherein the voltage-to-frequency converter comprises:

a precision capacitor;

a comparator that senses when the capacitor is charged to a predetermined level;

a light-emitting diode (LED) through which the capacitor is discharged when the capacitor'"'"'s voltage reaches the predetermined level; and

, a photodiode that creates an electrical pulse when the LED turns on.

5. The sensor of claim 1 further comprising an input/output device that interfaces the multiplexer to a bus.

6. The sensor of claim 5 further comprising a digital temperature sensor connected to the bus.

7. The sensor of claim 6 wherein the digital temperature sensor is placed close to a bypass diode in a solar panel such that the temperature sensor responds to changes in the diode'"'"'s temperature.

9. The method of claim 7 wherein the sensors are voltage sensors in an array of solar panels.

8. A method for ordering sensors on a bus comprising:

(a) providing a plurality of sensors on a bus, each sensor having a sense in terminal and sense out terminal;

(b) setting the sense out terminal of each sensor on the bus to logical 0;

(c) one-by-one setting each sensor'"'"'s output to logical 1 until a logical 0 to logical 1 transition is detected by a bus master;

(d) designating the last sensor to be set to logical 1 before the transition is detected by the bus master to be the “

next sensor in line”

, and setting that “

next sensor in line”

to pass mode such that its sense output is connected to its sense input; and

,

(e) repeating steps (b), (c) and (d) until the order of all sensors is determined.

10. The method of claim 8 wherein the sensors further comprise digital temperature sensors.

12. The system of claim 10 wherein each sensor is electrically isolated from earth ground.

13. The system of claim 10 wherein each sensor further comprises a digital temperature sensor.

11. A solar power generating system comprising:

a string of photovoltaic panels each connected to its own voltage sensor that transmits voltage information to a string controller via a low-wire-count bus;

wherein each voltage sensor comprises;

a voltage-to-frequency converter; and

,

a multiplexer that connects the frequency converter to the bus.