Method and device for recognising faults in a photovoltaic (PV) generator

Patent metadata

Field	Value
Publication number	US-11558011-B2
Application number	US-201815982412-A
Country	US
Kind code	B2
Filing date	May 17, 2018
Priority date	Nov 17, 2015
Publication date	Jan 17, 2023
Grant date	Jan 17, 2023

Abstract

A method for detecting a potential-induced degradation (PID) of PV modules of a PV installation includes operating a PV generator at a maximum power point (MPP), at a first generator voltage (U1) and first generator current (I1), and at a second generator voltage (U2) and second generator current (I2), where a first power (P1) at the first generator voltage (U1) is in a predefined first ratio V1=P1/PMPP and V1≤1, with the power (PMPP) at the maximum power point (MPP) of the PV generator, and where a second power (P2) at the second generator voltage (U2) is in a predefined second ratio V2=P2/P1 and V2<1, with the first power (P1) of the PV generator, and where a quantity Y that characterizes a progress of the potential-induced degradation (PID) is determined from the values of the voltages (U1, U2) and/or the currents (I1, I2).

First claim

The invention claimed is:

1. A method for detecting a potential-induced degradation (PID) of PV modules of a PV installation, having a measurement pass, comprising:
operating a PV generator of the PV installation at a maximum power point (MPP) with values of generator voltage (U MPP ) and generator current (I MPP ) associated with the maximum power point (MPP),
operating the PV generator of the PV installation at a first generator voltage (U 1 ) and detection of a first generator current (I 1 ) associated with the first generator voltage (U 1 ),
operating the PV generator of the PV installation additionally at a second generator voltage (U 2 ) and detection of a second generator current (I 2 ) associated with the second generator voltage (U 2 ),
operating the PV generator at a third generator voltage (U 3 ), and detecting a third generator current (I 3 ) associated with the third generator voltage (U 3 ),
wherein the first generator voltage (U 1 ) dictates that a first power (P 1 ), with P 1 =U 1 *I 1 , of the PV generator at the first generator voltage (U 1 ) is in a predefined first ratio (V 1 ), with V 1 =P 1 /P MPP and V 1 ≤1, with the power (P MPP ) at the maximum power point (MPP) of the PV generator, and
wherein the second generator voltage (U 2 ) dictates that a second power (P 2 ), with P 2 =U 2 *I 2 , of the PV generator at the second generator voltage (U 2 ) is in a predefined second ratio (V 2 ), with V 2 =P 2 /P 1 and V 2 <1, with the first power (P 1 ) of the PV generator, and
wherein the third generator voltage (U 3 ) dictates that a third power (P 3 ), with P 3 =U 3 *I 3 , of the PV generator at the third generator voltage (U 3 ) is in a predefined third ratio (V 3 ), with V 3 =P 3 /P 1 and V 3 <1, with the first power (P 1 ) of the PV generator, and a relationship in the form (U 3 <U 1 <U 2 ) or a relationship in the form (U 2 <U 1 <U 3 ) applies to the generator voltages (U 1 , U 2 , U 3 ) in accordance with their values,
wherein a characteristic quantity Y that characterizes a progress of the potential-induced degradation is determined from the values of the first, the second and the third generator voltage (U 1 , U 2 , U 3 ) and/or the first, the second and the third generator current (I 1 , I 2 , I 3 ),
wherein during a measurement pass a first approach and, with staggered timing from the first approach, a further approach are effected for one of the generator voltages (U 1 , U 2 , U 3 ),
wherein the further approach to the respective generator voltage (U 1 , U 2 , U 3 ) also results in a further generator current (I 1,2 , I 2,2 , I 3,2 ) being detected, and
wherein values of the further generator current (I 1,2 , I 2,2 , I 3,2 ) are compared with applicable values of the generator current (I 1 , I 2 , I 3 ) of the first approach to the respective generator voltage (U 1 , U 2 , U 3 ), and
wherein an applicable measurement pass is used to determine the characteristic quantity Y only when an absolute value of a difference between the generator current (I 1 , I 2 , I 3 ) and the further generator current (I 1,2 , I 2,2 , I 3,2 ) is below a predefined threshold value ΔI.

2. The method as claimed in claim 1 , wherein the third power (P 3 ) of the PV generator at the third generator voltage (U 3 ) is equal to the second power (P 2 ) of the PV generator at the second generator voltage (U 2 ).

3. The method as claimed in claim 1 , wherein the first approach to one of the generator voltages (U 1 , U 2 , U 3 ) is effected at a beginning of the measurement pass, and the further approach to the respective generator voltage (U 1 , U 2 , U 3 ) is effected at an end of the measurement pass.

4. The method of claim 1 , wherein the first generator voltage (U 1 ) denotes a maximum power point of the PV generator (MPP).

5. The method of claim 1 , wherein the characteristic quantity Y is determined from a first parameter (W 1 ) that takes into consideration a relative voltage width ΔU=U 2 −U 3 around an operating point at the power P 1 within a PU graph.

6. The method of claim 1 , wherein the characteristic quantity Y is determined from a second parameter (W 2 ) that takes into consideration a discrete-point fill factor (FF) within an IU graph.

7. The method as claimed in claim 1 , wherein the characteristic quantity Y is determined from a third parameter (W 3 ) that takes into consideration a difference between the first generator current (I 1 ) and a point on an imaginary straight connecting line between the points (U 2 , I 2 ) and (U 3 , I 3 ) within an IU graph at the location of the first generator voltage (U 1 ).

8. The method as claimed in claim 1 , wherein the characteristic quantity Y is determined from a fourth parameter (W 4 ) that takes into consideration a first current difference (I 1 −I 2 ), a second current difference (I 3 −I 1 ) or a ratio of the first and second current differences between the generator currents (I 1 , I 2 , I 3 ) as per (I 1 −I 2 )/(I 3 −I 1 ) at the respective generator voltages (U 1 , U 2 , U 3 ) within an IU graph.

9. The method as claimed in claim 1 , wherein the characteristic quantity Y is determined from a fifth parameter (W 5 ) that takes into consideration a first voltage difference (U 2 −U 1 ),a second voltage difference (U 1 −U 3 ) or a ratio of the first and second voltage differences between the generator voltages (U 1 , U 2 , U 3 ) as per (U 1 −U 3 )/(U 2 −U 1 ) within an IU graph.

10. The method as claimed in claim 1 , wherein the characteristic quantity Y is determined from a combination of at least two parameters, selected from a group comprising a first (W 1 ), a second (W 2 ), a third (W 3 ), a fourth (W 4 ), a fifth (W 5 ) and a sixth (W 6 ) parameter;
wherein the first parameter (W 1 ) takes into consideration a relative voltage width ΔU=U 2 −U 3 round the operating point at the power P 1 within a PU graph; and
wherein the second parameter (W 2 ) takes into consideration a discrete-point fill factor (FF) within an IU graph; and
wherein the third parameter (W 3 ) takes into consideration a difference between the first generator current (I 1 ) and a point on an imaginary straight connecting line between the points (U 2 , I 2 ) and (U 3 , I 3 ) within the IU graph at the location of the first generator voltage (U 1 ); and
wherein the fourth parameter (W 4 ) takes into consideration a first current difference (I 1 −I 2 ), a second current difference (I 3 −I 1 ) or a ratio of the first and second current differences between the generator currents (I 1 , I 2 , I 3 ) as per (I 1 −I 2 )/(I 3 −I 1 ) at the respective generator voltages (U 1 , U 2 , U 3 ) within the IU graph; and
wherein the fifth parameter (W 5 ) takes into consideration a first voltage difference (U 2 −U 1 ), a second voltage difference (U 1 −U 3 ) or a ratio of the first and second voltage differences between the generator voltages (U 1 , U 2 , U 3 ) as per (U 1 −U 3 )/(U 2 −U 1 ) within the IU graph; and
wherein the sixth parameter (W 6 ) takes into consideration a second gradient m 2 =(I 1 −I 3 )/(U 1 −U 3 ), a first gradient m 1 =(I 2 −I 1 )/(U 2 −U 1 ) a ratio of the first and second gradients m 1 /m 2 within the IU graph.

11. The method as claimed in claim 10 , wherein the determination of the characteristic quantity Y involves the at least two parameters being weighted differently.

12. The method as claimed in claim 1 , wherein in addition to the determination of the characteristic quantity Y a check is performed to determine whether a change in a value of the characteristic quantity Y relative to values of the characteristic quantity Y from preceding measurements is attributable to a change in a parallel resistance R par that characterizes

Assignees

• Sma Solar Technology Ag

Inventors

• Bettenwort Gerd
• Merz Christopher

Classifications

• H02S50/00 Primary

  Monitoring or testing of PV systems, e.g. load balancing or fault identification · CPC title

• H02S50/10

  Testing of PV devices, e.g. of PV modules or single PV cells (testing of semiconductor devices during manufacturing {H10P74/00}) · CPC title

• Y02E10/56

  Power conversion systems, e.g. maximum power point trackers · CPC title

• H01L31/02021

  Electricity · mapped topic

• H10F77/955

  for photovoltaic devices · CPC title