## 3 Experimental Results
Figure 9 represents the output waveforms of this experimental part. As it is observed, the load current is completely non-linear over the entire testing period, because the load has not been varied ever. The APF current is zero initially; however, after some time, it begins to compensate for the load current, resulting in the source current being pure sinusoidal (the purple graph). The green plot shows the DC link voltage, which is kept constant at all the experimented time intervals. These accurate results have predicated the effectiveness and applicability of the proposed control approach. The third scenario describes the non-linear load increasing from a half load to full load. In this case, the load current driven at the 50% mode, which is half the total demand at the full load, as measured in the yellow color shown in Figure 10. However, the non-linear characteristic of the load has not been changed at all, and only its amplitude has grown up. The source current and APF current have also increased substantially to supply all the load demand. A DC link voltage diagram shows that at the moment of the load increasing, a voltage drop is observed. This voltage drop will be corrected by the DC link voltage regulator loop after a certain period of time, and the voltage will return back to the value before the load variation. Figure 10: Experimental results at load variation condition; **(the orange color)** the load current wave form of phas. A [Amp/div:. A and time/div: 10 ms], **(the blue color)** the APF current wave form of phas. A [Amp/div:. A and time/div: 10 ms], **(the pink color)** the source current wave form of phas. A [Amp/div:. A and time/div: 10 ms], **(the green color)** the DC link voltage [volt/div: 500 V and time/div: 10 ms]. Figure 9: Experimental results at the transient condition; **(the orange color)** the load current wave form of phas. A [Amp/div:. A and time/div: 10 ms], **(the blue color)** the APF current wave form of phas. A [Amp/div:. A and time/div: 10 ms], **(the pink color)** the source current wave form of phas. A [Amp/div:. A and time/div: 10 ms], **(the green color)** the DC link voltage [volt/div: 500 V and time/div: 10 ms]. One of the important parameters that should be illustrated in the performance evaluation comparison of APFs is the THD in source current and load voltage. This is because the non-sinusoidal current source reduces the power source lifetime, indicating inappropriate filter performance. Figure 11 compares the THD of the source current with respect to the root mean square (_rms_) load voltage in different methods. It is noted that THD obtained from the proposed control strategy at all the voltage levels is lower than those of the existing methods, and this is proof of the proper controller performance. The comparison results shown in Figure 10 only have been conducted out in theory and simulation and the VSIs presented in [9] and [27] were not practically built in our laboratory. Their THD is calculated only in simulations and under load voltage variations in the same situations. The control methods used in [9] and [27] are \"adaptive fuzzy neural network\" and \"Kalman filter integrated with wavelet transform\", respectively. The first approach needs an extra module to adapt the membership function with a neural network, resulting in much data analysis volume and a lower response computation speed. The second one uses Kalman filter to estimate the unknown vectors of the load current FFT spectrum, and discrete wavelet transform (DWT) is used for harmonic detection. However, the proposed control approach only needs some constant SMC coefficients to insure the Lyapunov function stability with high-speed convergence. According to these explanations, much of the data analysis causes the load current not to be compensated completely, and as a result, the SMC approach is more suitable to control the APF at non-linear conditions compared with those other strategies.