Test Case 5

5

Evangelos Rikos

1.0

ERIGrid 2.0-NA4

09/04/2021

Power efficiency characterisation of PhotoVoltaic (PV) inverters

The scope of this test case is the investigation of a PV inverter’s ability to efficiently convert the PV electric power from DC to its AC form. Under normal (steady-state) conditions on the grid’s side the inverter should always maximize its power injection to the grid so that better exploitation of the solar potential is achieved. The normal operation entails that other services or functionality, that the inverter could potentially provide, such as droop control of active/reactive power or intentional power curtailment, do not act during the test. The efficiency characterization of the PV inverter in this test comes down to two main aspects of operation: on the one hand, the power/energy efficiency of the power converter and, on the other hand, the capability of the Maximum Power Point Tracker (MPPT) to detect the actual maximum power of the PV array.

• Power conversion
• Maximum Power Point Tracker

• Photovoltaic Inverter

• Electrical
• Environment

• PoI#1: Characterisation of power converter efficiency
• PoI#2: Characterisation of MPPT accuracy

In this TC the System-under-Test is the PV inverter which is connected on one end to the PV array and on other to the AC distribution grid.

• PV conversion (Current-Voltage characteristic of the PV array)
• Droop controllers for Active/Reactive power adjustment when the inverter is equipped with this functionality

• Power/energy efficiency
• MPPT accuracy

• Ratio of output versus input power:

${\eta }_{inv.}=\frac{P_{AC}}{P_{DC}}\times 100\%$

• Ratio of input power versus maximum theoretical PV power:

${ACC}_{MPPT}=\frac{P_{PV-actual}}{P_{PV-theoretical}}\times 100\%$

Fully Controllable attributes:

• Solar irradiation (varies gradually from 0 to 1200 W/m2)
• Ambient temperature (it can vary from –20oC to +50oC)
• PV array asymmetrical operation (e.g., partial shading) (varies stepwise)
• Grid voltage and frequency (constant, e.g., 230V/50Hz)
• PV modules parameters
• PV array configuration

• Sampling time of signals (Power flows): <=1 s
• Resolution: 0.1% of maximum output (AC) power
• Points of measurement:
  • One point at the AC output of the inverter
  • One point at the DC input of the inverter
• PDC,min=5% of rated power
• PDC,max=110% of rated power
• Vmin<VDC<Vmax (the minimum and maximum voltage depends on the inverter specification provided by the manufacturer)