## 3 Experimental Results  
In order to verify and validate the effectiveness of the proposed converter and the control method, a laboratory setup is constructed and assembled (Figure 5) due to the specifications given in Table 1. In these laboratory tests, the converter is first tested under linear load and then with a non-linear load to check the performance of the provided active filter. The linear load is considered to be a balanced three-phase grounded resistive-inductive branch that makes the current flow drawn from all phases be equal. In the following, a non-linear load (diode rectifier and unequal resistive-inductive loads in each phase) is considered as the inverter output. Figure 6 shows the waveforms of the load voltage, load current, source current, and current injected by the filter. As it can be observed, the load voltage is completely sinusoidal, with an estimated total harmonic distortion (THD) as 1.3%. Figure 5: Proposed APF prototype used in laboratory tests. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Description** & **Value (SI)** & **Implemented Device** \\ \hline \(V_{AC}\) & AC grid voltage, Phase to ground & 220 V, rms & AC power source \\ \(f_{line}\) & AC line/grid frequency & 50 Hz & Function generator \\ \(f_{raw}\) & Switching frequency & 12 kHz & Function generator \\ \(V_{DC}\) & DC link voltage & 380 V & DC power supply \\ \(C_{DC}\) & DC link capacitance & 4 mF & Constant type \\ \(L_{C}\) & PPF inductance & 1.5 mH & Single coil \\ \(C_{C}\) & PPF capacitance & 220 uF & Constant type \\ MOSFET & Power switches & 600 V.. A & R6006 KNX \\ \(D_{inv}\) & Power diodes & 800 V, 2. A & VS-20 ET508 \\ DSP & Programmer & Digital Signal Processor & TMS320C6748 \\ \(R-L\) & Linear load & 60 \(\Omega+0.1\) H & Constant type \\ \(R-L-Rectifier\) & Non-linear load & 60 \(\Omega+0.1\) H & Rectifier: VS-T20 HF220 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Prototype specifications. PPF: passive power filter. Figure 6: Experimental results at normal condition; (**a**) three-phase line-to-ground load voltages [volt/div: 220 V and time/div: 10 ms], (**b**) three-phase load currents [Amp/div:. A and time/div: 10 ms], (**c**) three-phase source currents [Amp/div:. A and time/div: 10 ms], (**d**) three-phase APF current injected to the load [Amp/div:. A and time/div: 10 ms]. The current injected by the APF is completely non-linear, making the current drawn from the source totally sinusoidal. In fact, the mathematical relation \(I_{source}=I_{APF}+I_{load}\) causes the harmonic deficiencies of the load current to be compensated by the APF, so that the three-phase source does not endure high current stress and does not produce needle-shaped and pulsating currents. Figure 7 shows the THD coefficient for the source current and load current of phase \(A\). As shown in this Fourier spectrum at Figure 7a, the source current THD is equal to 1.33% and always produces a sinusoidal current, because the rest of the non-linear load current is supplied by the APF, as shown in Figure 7b. The APF current THD at phase \(A\) is approximately 23.89%, indicating practically the complete compensation of load current harmonics. The source current fundamental harmonic is a little smaller than the load current, because the non-linear part of the load current is procured by the APF. The experimental results for the three-phase average active and reactive power of the AC source in the base case (scenario 1) is presented in Figure 8. It is worth mentioning that this figure is obtained by multiplying the source voltage and current. Figure 8: Experimental results for average reactive power compensation [VA/div: 1000 VA and time/div: 10 ms]. Figure 7: Current THD; (**a**) source current, (**b**) load current. In the second scenario, the transient performance of APF is investigated. It is assumed that the hybrid APF is not connected to the grid initially. Formerly, the APF connects to the load in parallel to compensate for the non-linearity.