## 3 Results and Discussions
### Comparison of Harmonic Power Flow Results among CCSM, HNM and HAMM  
Based on the accuracy assessment of HAMM in Section 3.1, it can be concluded that HAMM has better performance in harmonic source representation of fluctuating-power PV systems as opposed to CCSM and HNM, due to its capability of properly considering the voltage and power dependencies of harmonic currents. In this section, the impact of harmonic source model selection on the harmonic power flow (HPF) analysis is investigated, since HPF is an important tool for assessing the power quality impact of large-scale PV integration [2]. Here, a European low voltage test feeder is simulated in OpenDSS, with the network topology illustrated in Figure 17. The basic information of the test feeder can be found in [24]; hence, it is not repeated here.  
To evaluate the harmonic impact of PV systems on the supply voltage distortion at the point of common coupling (PCC), five groups of single-phase PV systems are connected to the test feeder, with their grid integration points illustrated in Figure 17. Each group of PV systems are made up of five PV-As, with their aggregated power equaling 23 kW. As the harmonic sources in OpenDSS are modelled as harmonic currents, a co-simulation approach between MATLAB and OpenDSS is utilized in order to integrate CCSM, HNM and HAMM into the OpenDSS HPF solver, as in Figure 18. Specifically, it starts with the network model development in the OpenDSS engine, followed by activating its COM interface in MATLAB. Afterwards, a snapshot power flow is executed to initiate the grid state variables (i.e., voltage magnitudes and phase angles at all nodes), and all the harmonic current sources are initiated with their corresponding harmonic current spectrums measured under the ideal supply condition. After executing HPF, the harmonic voltage spectrums at PoCs of all the PV systems can be extracted and fed to CCSM, HNM and HAMM as their input data. By running the harmonic source models in MATLAB, their output harmonic current spectrums will be used to update the original ones allocated to all PV systems in OpenDSS. By executing the OpenDSS HPF solver, the supply voltage harmonics at all nodes are updated. The above iterative process is repeated until the ending criteria are met (e.g., the maximum number of iterations is met or the variation in voltage THD at PCC is below 1%). With the aid of the proposed co-simulation approach, the harmonic penetration analysis of PV systems with CCSM, HNM and HAMM is performed, with the simulated voltage  
Figure 17: The European low voltage test feeder with PV systems connected.  
harmonics at PCC provided in Figures 19-21. It turns out that the utilization of HAMM for PV systems generally results in lower voltage harmonics at PCC than in the cases of using CCSM and HNM, indicating that the application of CCSM for the harmonic integration analysis of PV systems can result in overestimated results.  
Figure 19: Comparison of voltage harmonics at PCC (phase A) for the application of three harmonic modelling approaches (CCSM, HNM and HAMM).  
Figure 18: The flowchart of applying a co-simulation approach for integrating customized harmonic source models into the OpenDSS HPF solver.