## 4 Results and Discussion  
The measurement setup is used to test all six SMPS on pure sinusoidal voltage. The measurement is performed for 1 h, and 60% of the rated load is applied to each SMPS. The THD\({}_{i}\), current harmonics magnitude, and phase angles are analyzed. Figure 4 shows the absolute percentage difference between the THD\({}_{i}\) measured when the power supplies are in the cold state and stable state. The term \"cold state\" indicates the first five minutes of the measurements, and the \"stable state\" indicates the duration when the harmonic current variation is less than 0.25%. The first two power supplies indicate only 1.2% and 0.6% difference between the THD\({}_{i}\) measurements at the cold and stable state. However, the remaining power supplies have shown a significant difference between THD\({}_{i}\) values at the cold and the stable state. The fifth power supply shows the highest variance of 21%. Both third and fifth SMPS have a variation of 18 to 19% between cold and stable state. Similarly, the fourth SMPS shows a difference of 14.8%. Hence, Figure 4 indicates that type 1 SMPS shows a minimal difference in contrast to type 2 SMPS. To estimate the stability time of power supplies, we have used the curve-fitting approach to the current harmonic amplitude and phase angle variations over time. An exponential trend curve is  
Figure 4: Histogram of total current harmonic distortion (THD\({}_{i}\)) difference between cold and stable state of all power supplies. Figure 3: Block diagram of the measurement setup. applied to the current harmonics magnitude, and phase angles up to the 19 th harmonic. Equation (4) is used to calculate the parameters of the trend line using measurement data of the current harmonic magnitude and phase angle. \[T_{L}=\triangle_{i}\times e^{(-\frac{i_{L}}{T_{C}})}+\gamma_{stable} \tag{4}\]  
\(\gamma_{stable}\) is the current magnitude or phase value in the stable state. The delta \(\triangle_{i}\) is the difference between the current harmonic magnitude or phase angle in the cold state and the stable state and calculated by Equation (5). \[\triangle_{i}=\gamma_{stable}-\gamma_{cold} \tag{5}\]  
The time constant in Equation (4) \(T_{C}\) is the time taken by the exponential trend curve to increase or decrease by the factor e. It is calculated by using Equation (6). \[T_{C}=\frac{T_{final}-T_{cold}}{1-\ln(1-\frac{1-(\gamma_{stable}-\gamma_{cold}) }{\triangle_{i}}} \tag{6}\]  
The stability time (\(T_{stable}\)) of the current harmonic magnitude and phase angle is three times of the time constant (\(T_{C}\)). Figure 5 shows the current magnitude variation of the fundamental and odd harmonics up to the 19 th for the third power supply. The green line shows the measured harmonic current, and the blue line indicates the applied trend curve. The red dot indicates the time constant, and the black dot shows the stability time. A similar approach is applied to the phase angles of odd harmonics up to the 19 th, as shown in Figure 6.  
Figure 5: Current harmonic magnitude variation over time for power supply 3. The difference between the cold and stable values of harmonic current magnitude and phase angles are more significant for type 2 power supplies. For type 1 power supplies, most of the current harmonics have less than 1% difference in the magnitude. The maximum difference observed for the fundamental and 7 th harmonic for the first power supply is 1.2%. The power supply 2 shows the maximum difference of 1.7% for the 11 th harmonic. Conversely, the type 2 power supplies exhibit a noteworthy difference, especially for the higher-order harmonics. The maximum difference was up to 194% for the 17 th harmonic of power supply 3. Table 3 shows the minimum, maximum, and average deviation of cold and stable current harmonics magnitude for type 2 power supplies. The phase angle variation between cold and stable state is also less for type 1 power supplies. The first power supply only shows more than 1-degree variation for the 3 rd, 5 th, and 7 th harmonic.