## 4 Results and Discussion
On the other hand, power supply two shows phase angle variation of more than 1 degree for 15 th, 17 th and 19 th harmonic. The type 2 power supplies show a significant deviation of phase angles between the cold and stable state measurements. Power supply three shows less phase angle variation of between 1-2 degrees among all type 2 power supplies. The other power supplies show a variation of 2 to 35 degrees, increasing from low to higher-order harmonics. Although the IEC 61000-3-2 standards do not define any limits for phase angle variation, the harmonic cancellation depends on current harmonics phase angles. Figure 7a shows the magnitude stability time for all power supplies from fundamental to the 19 th odd harmonic. Since the variation between cold and stable state magnitude values for type 1 power supplies is less than type 2, the stability time for type 1 power supplies is also less for most of the current harmonics. The power supply 1 and 2 have maximum stability time for the fundamental and \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Harmonics**} & \multicolumn{8}{c}{**Current Harmonics Magnitude Difference**} \\ \cline{2-11}  & **F** & **H3** & **H5** & **H7** & **H9** & **H11** & **H13** & **H15** & **H17** & **H19** \\ \hline
**Minimum** & 0.4 & 0.1 & 0.8 & 2.3 & 4.5 & 7.6 & 11.8 & 17.6 & 26.2 & 11.1 \\
**Maximum** & 1.6 & 1.4 & 3.7 & 7.5 & 13.4 & 23.8 & 43.4 & 88.2 & 194.7 & 97.0 \\
**Average** & 0.8 & 0.6 & 2.0 & 5.2 & 10.0 & 17.6 & 30.0 & 54.7 & 105.4 & 39.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Difference between cold and stable state current harmonics magnitude for type 2 SMPSs (%). Figure 6: Current harmonic phase variation over time for power supply 3.  
odd harmonics up to the 7 th between 20 and 43 min. However, the 11 th and 13 th harmonic took more than 60 min to stabilize for the power supply 2. All other magnitudes of current harmonics for these two power supplies are less than the magnitude stability time of type 2 power supplies. The stability time for type 2 SMPS is in the range of 20 to 40 min, except for the 17 th harmonic of power supply 3. The stability time of power supply 3 and 6 is quite close for most of the current harmonic magnitude. Similarly, the stability time of current harmonics magnitude for power supply 4 and 5 also follows the same trend but less than the power supply 3 and 6. Figure 6(b) shows the plot for phase angle stability for the odd harmonics for all switch-mode power supplies. Power supply 2 shows the highest value of stability time. For other power supplies, most of the current harmonics achieved stable phase angles before 35 min, except for the few high order harmonics. The stability time is independent of the active power of the switch-mode power supplies. Figure 8 shows the graph of the active power of the power supplies against the stability time for all current harmonics magnitude up to the 19 th harmonic. However, it is interesting to note that power supplies with high active power have less stability time on average in comparison to the power supplies with low active power consumption. This trend is more prominent for the higher-order harmonics. The overall impact of thermal stability on harmonic current estimation could be significant in the real-time scenario. A similar study had indicated a notable difference for the harmonic current estimation for light-emitting diode (LED) lamps. The RMS current of LED lamps in a stable state was significantly different in comparison to the RMS current in a cold state [10]. Stochastic harmonic estimation models are based on the measurement results of the current harmonics of the electrical appliances. As thermal stability affects the measurement results, it may lead to a significant error in the harmonic analysis results. Figure 9 shows the percentage difference between the current RMS calculated at a cold and stable state for each power supply. Power supply 1 and 2 are type 1; therefore, it shows a small difference of about 1% between cold and stable states.