## 5 Simulation Experiments, Verification, and Comparative Analysis  
For the proof of concept and performance validation, the proposed architecture, as presented in Figure 2, is modeled in a power simulation (PSIM) software to conduct simulation experiments. PSIM is a specialized simulation software for power electronics and renewable energy systems. From the built-in power source library of PSIM, the photovoltaic module is selected and is configured with the following specifications under the standard testing condition (STC): \(I_{sc}\) = 6.5 A, \(I_{mpp}\) = 6 A, \(V_{oc}\) = 21.7 V, and \(V_{mpp}\) = 17.2 V. A PV string is made through three series-connected PV modules, where a buck converter is used for each module. The switching frequency (\(f_{sw}\)) of each converter is set at 50 kHz, while the values of the inductor (\(L\)) and output capacitor (\(C_{o}\)) are designed at 117 uH and 1000 uF, respectively. To generate PWM pulses at the appropriate \(D\) value for each converter and On/Off control of the string switches, the control equalizer manager and its algorithm are programmed in the C block of the PSIM software (Version 9.0). The control mechanism of the equalizer manager has already been explained in the previous section. Figure 7 displays three shading cases of the PV string, which are simulated in PSIM software to assess the behavior of the proposed architecture. Figure 7a represents the moderate shading case (MS-case), where M2 receives the irradiance of 850 W/m\({}^{2}\) at 20 \({}^{\circ}\)C, while other modules M1 and M3 receive STC. On the other hand, Figure 7b represents the strong shading case (SS-case) as M2 receives a half irradiance value of 500 W/m\({}^{2}\) at 15 \({}^{\circ}\)C, as compared to the STC of modules M1 and M3. In response to these two shading cases, i.e., the MS-case and SS-case, the behavior of the proposed architecture is presented in Figures 8 and 9, respectively. Figure 6: Flowchart of the current equalizer algorithm. Five graphs are involved in each figure, where red, blue, and black curves of each graph represent modules M1, M2, and M3, respectively. Note that since the buck converter of only M2 becomes active because of different weather conditions, the output curves of M2's converter are shown in a pink color. For clarity and better understanding, the features and operation of the proposed architecture are explained for both cases together:  
* Figure 8 shows that, initially, all modules receive the STC before 30 ms. Consequently, power (\(P_{pv}\)) curves of all modules exhibit similar behavior with steady-state oscillations, as shown in Figure 8a. These oscillations occur because of the centralized inverter, which operates with the perturb and observe algorithm for MPP tracking. In this connection, the voltage tracking steps of the inverter can be observed at the DC-link voltage (\(V_{DC-link}\)), as shown in Figure 8e, where the \(V_{pv}\) of all modules are added, i.e., string voltage. The current (\(I_{pv}\)) and voltage (\(V_{pv}\)) curves of the three modules display similar characteristics, as shown in Figure 8b,c, respectively. Figure 8d shows that during this interval, the \(D\) value of all converters is '0', which implies that all PV modules are in series and the common \(I_{string}\) flows through the modules to reach the inverter. For an interval up to 30 ms, Figure 9 also displays the same behavior, as partial shading has not occurred yet. * At 30 ms, Figures 8 and 9 represent the the MS-case and SS-case, respectively. It can be noticed in the graphs of both Figures 8b and 9b that \(I_{M2}\) of M2 becomes lower than \(I_{string}\), as module M2 is under the influence of partial shading. After sensing this, the centralized current manager turns off the upper switch of module M2 and activates its buck converter by delivering the PWM pulses at an appropriate \(D\) value. It can be confirmed from Figures 8b and 9b that the output \(I_{M2\_buck}\) current of the buck converter becomes equal to \(I_{string}\), and M2 operates at its local MPP as well.