Empowered by: KU Leuven, VITO, imec & UHasselt

Grid Compliance Testing of DC/AC PV InverterSolSThore – Activity 5 – PV Systems for Large Roof Surfaces and Façade IntegrationDescriptionThe general objective of the work presented is centred around grid compliance testing of single-phase & three-phase Photovoltaic (PV) inverters utilising the Real Time Digital Simulator (RTDS) and a 4-quadrant linear amplifiers environment, which is termed as a Power Hardware-in-the-Loop (PHIL) test. The RTDS and PV inverter exchange power over the PHIL interface where the electrical grid is modelled inside the RTDS. PHIL simulations are complex in nature due to the stability and accuracy issues between the device and RTDS because of non-zero time delays, limited bandwidth and non-unity gain.

Purpose• To better understand PV inverter behaviour under balanced & unbalanced AC

grid condition• To establish test procedures & templates to investigate converter interactions• To develop protocols to test new converters as proof-of-concept• To analyse interaction between the power electronic converter & protection

devices

Technical Features• Fault Ride Through (FRT) tests of PV inverters (VDE 0126-1-1 test standard)• Different disturbances like varying load conditions, transients, voltage sag &

swell• Low Voltage Ride Through (LVRT) tests of PV inverters• PV inverter grid connection requirements tests (VDE ARN-4105 test standard)

Experimental setup

PHIL Interface Algorithm• Ideal Transformer Method (ITM)

• Current injection branch modelled as an inverter in RTDS• Simple & accurate

• Transmission Line Method (TLM)• Current injection branch with an inductor modelled in RTDS• More stable but increased losses

• Damping Impedance Method (DIM)• More stable than ITM

PV inverter under test in a complete setup

Ideal Transformer Method of Interface Algorithm

Partial Circuit Duplication Method of Interface Algorithm

FRT curve LVRT test

Block diagram of Ideal Transformer Method

Damping Impedance Method of Interface Algorithm

Fault Ride Through TestAn industrial single-phase Photovoltaic (PV) inverter with a rated maximum AC power 5 kW at 230 Vac (L-G rms) and DC operating range of 125 Vdc – 600 Vdc is tested using a PHIL test platform in the laboratory. The grid compliance testing comprises of Fault Ride Through (FRT) and Low Voltage Ride Through (LVRT) tests. The grid side impedance modelled in RTDS is kept smaller than the impedance of the inverter to ensure stability of PHIL interface (Zgrid/Zinv <1).