limited inverter input PV-voltage is ignored

[Tobias]

Dear suport,

we are working on a project for the American continent. As agreed with the customer, the DC/AC-power-Ratio shall be 125% or even higher. Losses during the daytime on sunny days are accepted.

We want to use central inverters with a maximum PV current of 1400 A. The manufacturer says, there is no void of warranty if the PV current gets higher than 1400 A because the inverter "cuts" the current to a maximum of 1400 A.

Now I have simulated the following:

- yingli 245 modules (YL245P-29b)

- SMA SC 900 CP

- 25 modules per string (warm region, so it's fine with 1000V maximum OC Voltage)

- 186 Strings per Inverter

- --> nominal power ratio of 126.6 %

To see what happens on sunny days, I have generated an output file and sorted it by the PC current. I am very concerned about the result. Apparently, PVsyst ignores completely the behavior of the inverter. In 140 hour-values during the year, the PV current exceeds the limit of 1400 A by far.

Please explain this. Is it possible to simulate the "real" behavior? The MPP tracker of the inverter should increase the voltage so that the current does not exceed the maximum input current.

Is there an option where I can "activate" the real MPP-tracking behavior of the inverter?

 

PVsyst v6,12					
File	File date	Description		
Project	XXX_Project,PRJ	09/12/13 14h33	Grid-Connected Project at xxx		
Geographical Site		09/12/13 14h33	xxx	Central America	North_America
Meteo data	XXX_MNfile_SYN,MET	06/12/13 09h55	xxx	Meteonorm file	Synthetic
Simulation variant	XXX_Project,VC1	09/12/13 15h37	New simulation variant		
				
Simulation:	Hourly values	 from 01/01/90	 to 31/12/90		
Simulation run	10.12.2013 15:18				


___date___________PR_______I(A)_____V(V)
		
12.03.1990 13:00	0,7479	1528	600
09.03.1990 12:00	0,7593	1527	600
13.03.1990 12:00	0,7482	1525	600
09.05.1990 12:00	0,7399	1518	600
29.05.1990 13:00	0,7296	1518	600
21.04.1990 12:00	0,7387	1517	605,1
25.03.1990 12:00	0,735	1516	605,3
17.02.1990 12:00	0,7503	1515	600
23.03.1990 12:00	0,7449	1513	600
04.04.1990 12:00	0,7383	1513	606,6
28.04.1990 12:00	0,7445	1512	600
01.05.1990 12:00	0,7282	1512	600
10.05.1990 12:00	0,7464	1511	600
24.04.1990 12:00	0,7491	1508	600
19.02.1990 12:00	0,7538	1506	600
25.03.1990 13:00	0,7406	1506	600
21.04.1990 11:00	0,7562	1505	600
11.09.1990 12:00	0,7505	1505	600
27.09.1990 12:00	0,7412	1505	600
28.02.1990 12:00	0,7471	1503	600
09.03.1990 13:00	0,7586	1503	600
04.04.1990 13:00	0,7441	1503	600
17.03.1990 12:00	0,7366	1501	600
13.04.1990 12:00	0,7399	1499	600
21.04.1990 13:00	0,7455	1499	600
22.07.1990 13:00	0,7118	1498	600
23.04.1990 12:00	0,7423	1497	600
01.05.1990 11:00	0,7439	1495	600
17.02.1990 13:00	0,75	1494	600
11.03.1990 12:00	0,7553	1494	600
04.04.1990 11:00	0,7589	1494	600
10.04.1990 12:00	0,7315	1493	600
21.10.1990 12:00	0,7302	1493	600
25.03.1990 11:00	0,7568	1492	600
09.05.1990 11:00	0,7547	1492	600
25.11.1990 12:00	0,7462	1492	600
19.09.1990 12:00	0,7337	1490	600
29.04.1990 12:00	0,7565	1485	600
23.03.1990 13:00	0,7474	1484	600
19.02.1990 13:00	0,7544	1483	600
13.03.1990 13:00	0,7516	1483	600
28.04.1990 11:00	0,7585	1483	600
09.05.1990 13:00	0,7453	1483	600
10.05.1990 11:00	0,7597	1483	600
24.05.1990 12:00	0,7377	1482	600
01.09.1990 12:00	0,7219	1482	600
10.03.1990 13:00	0,7385	1481	619,8
12.03.1990 12:00	0,7358	1481	619,5
15.09.1990 12:00	0,7302	1480	600
22.04.1990 12:00	0,747	1479	600
25.04.1990 12:00	0,745	1478	600
27.09.1990 11:00	0,7558	1476	600
25.09.1990 12:00	0,7343	1475	600
24.03.1990 12:00	0,7496	1473	600
10.05.1990 13:00	0,751	1473	600
11.03.1990 13:00	0,7545	1472	600
17.03.1990 13:00	0,7386	1471	600
28.04.1990 13:00	0,7497	1471	600
14.09.1990 12:00	0,7349	1470	600
28.02.1990 13:00	0,7502	1469	600
13.04.1990 11:00	0,7551	1469	600
01.05.1990 13:00	0,7353	1469	600
19.09.1990 11:00	0,748	1469	600
08.10.1990 12:00	0,7395	1469	600
15.04.1990 10:00	0,7457	1465	600
23.04.1990 11:00	0,7572	1464	600
26.04.1990 12:00	0,6737	1464	626,8
25.11.1990 11:00	0,7594	1464	600
14.03.1990 12:00	0,7567	1461	600
06.09.1990 12:00	0,734	1461	600
10.04.1990 11:00	0,7496	1460	600
23.04.1990 13:00	0,747	1460	600
24.04.1990 13:00	0,7556	1459	600
10.04.1990 13:00	0,7364	1458	600
24.05.1990 11:00	0,7506	1458	600
01.09.1990 11:00	0,741	1458	600
15.09.1990 11:00	0,7457	1457	600
11.09.1990 13:00	0,7572	1455	600
10.03.1990 12:00	0,7259	1454	631,1
17.03.1990 11:00	0,7555	1454	600
27.09.1990 13:00	0,7491	1454	600
02.10.1990 12:00	0,7556	1454	600
24.03.1990 13:00	0,7506	1453	600
13.04.1990 13:00	0,7463	1453	600
08.10.1990 11:00	0,7517	1453	600
07.09.1990 12:00	0,7442	1452	600
25.09.1990 11:00	0,7475	1452	600
16.03.1990 12:00	0,7565	1450	600
30.03.1990 12:00	0,75	1449	600
01.09.1990 13:00	0,7279	1448	600
08.03.1990 12:00	0,7426	1447	634,1
25.04.1990 11:00	0,7588	1447	600
03.06.1990 12:00	0,7455	1445	600
27.04.1990 12:00	0,7496	1444	600
24.05.1990 13:00	0,7438	1444	600
19.09.1990 13:00	0,7418	1444	600
14.09.1990 11:00	0,7504	1443	600
22.04.1990 13:00	0,7512	1442	600
15.08.1990 12:00	0,7395	1442	600
25.04.1990 13:00	0,75	1439	600
04.05.1990 10:00	0,7474	1438	600
08.05.1990 12:00	0,7513	1438	600
13.05.1990 10:00	0,751	1438	600
22.03.1990 12:00	0,7533	1437	600
19.08.1990 12:00	0,7335	1437	600
28.09.1990 12:00	0,7458	1437	600
06.07.1990 12:00	0,7568	1434	600
08.07.1990 12:00	0,7458	1434	600
05.10.1990 12:00	0,7477	1434	600
15.09.1990 13:00	0,7398	1430	600
25.09.1990 13:00	0,7428	1430	600
18.08.1990 12:00	0,7344	1428	600
07.10.1990 10:00	0,7445	1427	600
02.09.1990 12:00	0,7403	1426	600
06.09.1990 11:00	0,7505	1426	600
14.09.1990 13:00	0,7418	1426	600
25.10.1990 12:00	0,7532	1426	600
05.08.1990 13:00	0,7498	1425	600
07.09.1990 11:00	0,7568	1425	600
12.04.1990 10:00	0,7521	1424	600
30.06.1990 12:00	0,7579	1423	600
22.03.1990 13:00	0,7534	1422	600
05.05.1990 10:00	0,7455	1421	600
17.08.1990 12:00	0,74	1421	600
06.09.1990 13:00	0,7401	1421	600
19.11.1990 12:00	0,7507	1421	600
07.09.1990 13:00	0,7484	1419	600
19.10.1990 12:00	0,7492	1419	600
27.04.1990 13:00	0,752	1418	600
08.10.1990 13:00	0,7476	1418	600
09.08.1990 12:00	0,7527	1417	600
16.08.1990 12:00	0,744	1416	600
16.10.1990 12:00	0,7486	1416	600
03.06.1990 13:00	0,7483	1415	600
28.09.1990 11:00	0,7564	1415	600
05.10.1990 11:00	0,7583	1415	600
15.08.1990 13:00	0,7422	1414	600
19.10.1990 11:00	0,7571	1410	600
30.03.1990 13:00	0,7534	1409	600
03.06.1990 11:00	0,7589	1408	600
06.07.1990 13:00	0,7588	1407	600
19.08.1990 13:00	0,7367	1407	600
09.06.1990 12:00	0,7574	1406	600
08.07.1990 13:00	0,7478	1405	600
18.07.1990 12:00	0,7469	1405	600
18.11.1990 12:00	0,7597	1405	600
05.09.1990 12:00	0,741	1404	600
02.08.1990 12:00	0,7518	1403	600
19.08.1990 11:00	0,7493	1402	600
15.08.1990 11:00	0,756	1400	600
04.10.1990 12:00	0,756	1400	600
14.02.1990 12:00	0,7791	1399	623

[André Mermoud]

This may be a limitation of the specifications, but not an operating limitation of the inverter (i.e. the inverter will not limit the current by itself).

In this case PVsyst doesn't directly check the current at the inverter input during the simulation.

If it is an operating limitation, this will be related to the parameter "Minimum voltage for PNom".

This means that you cannot reach the nominal power if you have a voltage lower than this limit.

I.e. with lower voltages the possible output power will be reduced, just in order to match this maximum input current:

If we define Pnom(dc) = Pnom(ac) / Effic,

then Imax = Pnom(dc) / Vmpp

For your example, Pnom(dc) = 900 kWac / 0.96 = 937 kW

=> VmppMin for getting PNom = 937 kW / 1400 A = 669 V.

This should be a specification of the manufacturer in the database.

You can observe on your file that all your high current values correspond to low MPP voltage.