Innovative RES Solutions for 100% RES System (GRIDPV100)

The Islands of Malta and Cyprus has seen an exponential growth in the uptake of Photovoltaic (PV) technology, especially at the rooftop/ low-voltage (LV) levels. The consolidated uptake, along with the direct and indirect schemes of the governments of the two Islands, is now proceeding fast towards the plan of becoming net-zero emission countries by 2050. The high number of the PV installations in the rooftop levels, however, has seen several problems in the proper operation of the grid, especially during day-time, because of the high PV power produced, and the low-loading at the distribution levels, thereby resulting in voltage rise, however this problem is encountered at a local level. The other problem that is encountered generally on the global level is the frequency regulation problem. The high penetration of PV in a weak system, such as an LV distribution network decreases the effective load, especially during the day time, and the static converters, irrespective of being a source, are essentially constant power loads, therefore, even when there is a frequency variation on the grid side, they keep generating the same amount of power which exacerbates the frequency deviation following load changes or generator events. In order for such converters to participate in the frequency regulation problem, the control loops of such converters need to be redesigned, so that they can participate whenever there is a drop in the load, or when there is an overall frequency change seen from the utility grid side.  

The droop control method is a widely used control strategy for frequency regulation within the microgrids, and the same control methodology has also been extended to active distribution networks that can seamlessly enter and exit the islanded mode with the help of a unified control. In the GRIDPV100 project-based lab access at the Austrian Institute of Technology (AIT) in Vienna, we explore the possibilities of PV providing inertial response with the help of the modification of the existing droop control philosophy, and employing a switching-based control that can provide MPPT power in the grid connected mode, and inertial response, when the network goes into the islanded mode. A real Cypriot reduced single feeder distribution network (DN) is used for the studies during this lab access period. Typhoon Hardware-In-The-Loop (HIL) based software is used for creating the simulations to be carried out under a real-time environment to achieve the following goals:

1. Emulate the virtual inertia control for the PV based sources in the distribution network of interest. 
2. Compare the performance of the grid-following and grid-forming controls of the PV based on their individual frequency responses. 

Preliminary Findings 

1. The typhoon HIL based platform gives a deep insight into the grid-forming behaviour of the PV based system. The frequency responses are similar to the droop-controlled battery-based system. 
2. The typhoon HIL 604 single arm setup provided to the lab access users did not manage to compile successfully, the simulations for the entire feeder of interest, therefore the reduced model was developed by aggregating the small PVs into a single controllable PV.  

Open threads 

1. Phasor based location of grid-forming PV in a large distribution network is to be performed 
2. Seamless (switching free) control design for the PV based grid-forming converter in the typhoon HIL environment.