PV Microinverter Testbed for Interoperability

Jimmy E Quiroz, Sigifredo Gonzalez, Joshua S Stein Sandia National Laboratories, Albuquerque, NM, United States

This test plan is intended to provide verification for conformance of interconnection systems (ICSs) test criteria from IEEE Standard 1547-2005 , but applied to a test bed of several interconnected microinverters.  These tests also provide evaluation procedures for multi-manufacturer microinverter interoperability.  The purposes of these procedures are to develop a standard method for evaluating interconnected microinverters, and to evaluate interoperability of manufacturer supplied communication and monitoring. Utility compatibility evaluations determine the voltage and frequency operating ranges and the inverter’s response to a voltage/frequency sag or swell and the response to an interruption in utility service.  Test criteria are specified in UL 1741 and IEEE 1547-20051.  The parameters under investigation are focused on inverter loss of utility, power quality, and diagnostics monitoring and energy harvest accuracy.  The microinverter topology doesn’t allow the monitoring of the dc parameters therefore efficiency evaluations will not be performed, but monitoring the inverters reported ac parameters and comparing them to laboratory data acquisitions systems (DAS) and power analyzers will be performed. This test procedure provides verification for conformance of interconnection systems (ICSs) according to IEEE Std 15471, applied to not just a single microinverter, but a test bed of several microinverters. Virtually all modern grid-tied PV microinverters use an algorithm to extract the maximum power available from the PV array.  Without disabling this feature it is generally not straightforward either to request specific power levels from the inverter or to operate it at specific voltage levels.  The approach taken is to evaluate a number of parameters by operating the microinverters with a PV module configured to provide maximum rated power, when possible. This method maximizes the amount of useful data that can be obtained in a reasonable testing period.