| Abstract |
The grid connected Photovoltaic (PV) systems are essentially constituted by arrays of PV modules
and inverters, i.e. the Power Conditioning Units (PCUs) that ensure optimum utilisation for the PV
arrays, power quality and safety for the utility. Since the PV generator supplies DC power as a
function of solar irradiance and temperature, it is advisable to track the Maximum Power Point (MPP)
of the current-voltage I(U) characteristic of PV array with the highest possible accuracy. This task,
integrated into the PCU, is performed by a properly controlled DC/DC converter (MPPT). The
inverter requirements include the highest possible efficiency for a wide range of irradiance, high
power factor and low total harmonic distortion. Since a PV system must be disconnected (islanding
prevention) whenever an utility switches off the distribution line, suitable protections shut down the
PV system within the required time limits. The paper presents a measuring procedure to determine the
PCU performance. This procedure, including new measuring methods, is carried out by a dedicated
software for automatic data acquisition. The experimental tests of the procedure determine the
following parameters: the MPPT efficiency (how close to maximum power the MPPT is operating);
the inverter efficiency, the power factor, and the total harmonic distortion of the AC current supplied
to the loads; the islanding time i.e. the time interval between the grid switching off and the automatic
disconnection of the PCU. The experimental results are reported with respect to AC modules which
consist of PV modules with integrated inverters. The described procedure can be useful for quality
control of the inverter manufacturers and for acceptance tests of the system owners. The procedure
can be also applied for on-site monitoring of any grid connected PV system. |
